Anatomy of adipose compartments and fascial structures in the posterolateral region of the kidney with special focus on the thin adipose compartment

Anatomy of adipose compartments and fascial structures in the posterolateral region of the kidney with special focus on the thin adipose compartment | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Anatomy of adipose compartments and fascial structures in the posterolateral region of the kidney with special focus on the thin adipose compartment Atsuhiko Ochi, Satoru Muro, Sho Mitsumaru, Akimoto Nimura, Keiichi Akita This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7324278/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Objectives To anatomically and histologically define adipose and fascial structures posterior and lateral to the kidney and propose a compartment-based anatomical model aligned with intraoperative observations. Methods Seven cadavers were used for macroscopic and histological analyses. In the macroscopic analysis, the spatial relationships between the perirenal fat, pararenal fat, posterior renal fascia, and extraperitoneal fascia were examined. Histological observations focused on the distribution and continuity of adipose compartments and the organization of the surrounding dense fibrous connective tissues. Results Macroscopically, the extraperitoneal fascia covered the anteromedial pararenal fat and extended posteriorly to the kidney. Upon incision, a small amount of adipose tissue was observed directly beneath it. Removing this thin adipose layer exposes the peritoneum and posterior renal fascia, with a clear demarcation between them. Histological analysis confirmed that the posterior renal and extraperitoneal fascia were distinct, with dense connective tissue structures enclosing a separate, thin adipose compartment. This compartment extended anteriorly between the perirenal fat and peritoneum, and laterally between the peritoneum and extraperitoneal fascia. These extensions converge near the peritoneal reflection in the lateral renal region, forming the characteristic triradiate configuration of the adipose tissue. Conclusions Our findings challenge the classical notion that the renal fascia is a single continuous layer supporting a compartment-centered anatomical model. The posterior and lateral regions of the kidney contain a distinct third adipose compartment bordered by the posterior renal and extraperitoneal fasciae. This model offers improved anatomical clarity and may aid understanding during laparoscopic, retroperitoneoscopic, and robot-assisted surgeries. Urology & Nephrology laparoscopic surgery lateroconal fascia pararenal fat renal fascia retroperitoneal space Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 INTRODUCTION The renal fascia is a fibrous membranous structure located in the retroperitoneal region that envelops the kidneys, adrenal glands, ureters, gonadal vessels, and perirenal fat (PeRF) from both the anterior and posterior aspects. Zuckerkandl first described the posterior renal fascia (PRF), followed by Gerota identifying the anterior renal fascia (ARF). 1 – 3 These fasciae converge laterally to form the lateroconal fascia (LCF). 4 Collectively, they function as mechanical barriers that protect retroperitoneal organs from external forces and the spread of inflammation or infection as well as critical anatomical landmarks that influence radiological interpretation, intraoperative visualization, and the selection of dissection planes during surgical procedures. Traditionally, the fascia of the retroperitoneal region is regarded as a single, continuous, membranous structure, 5 as reflected in current anatomical textbooks. 6 However, since the advent of computed tomography (CT) in the 1980s, radiologists have proposed the concept of the interfascial plane, suggesting that the ARF, PRF, and LCF each consist of multilayered, thin fibrous membranes. 7 , 8 These layers contain potential spaces that may serve as pathways for fluid components such as inflammatory exudates or hemorrhages. Based on CT imaging and cadaveric studies, Marks et al. reported that the PRF could be divided into two distinct membranous structures: one connected to the LCF and the other connected to the ARF. 9 During retroperitoneal surgery, the outermost membranous structure within the pararenal fat (flank pad) on the posterior aspect of the kidney is sometimes referred to as the LCF to distinguish it from the PRF, 10 – 12 although this usage deviates from the original anatomical definition. These observations challenge the conventional model of a single PRF, suggesting its insufficiency to fully represent the complex tissue organization in the posterior and lateral regions of the kidney. This study aimed to anatomically and histologically investigate the configuration of adipose tissue compartments and surrounding dense connective tissue structures in the posterior and lateral regions of the kidney from a perspective distinct from the conventional renal fascia theory. Ochi et al. 13 previously reexamined the internal architecture of the renal fascia through a novel framework of adipose tissue compartmentalization (zoning) based on the anatomical continuity of fat tissue. In the present study, we applied this concept to investigate the distribution and spatial relationships of adipose tissue in the retroperitoneal region, lateral and posterior to the kidney, and interpreted the dense fibrous connective tissue membranes that delineate fat compartments as fasciae. This fat-based approach may provide a more accurate anatomical model of the retroperitoneum and enhance the interpretation of findings during laparoscopic, retroperitoneoscopic, and robot-assisted surgeries. MATERIALS AND METHODS Preparation of Cadaveric Specimens Seven adult male cadavers (mean age at death, 81.7 [range, 73–92] years) were donated to our department in accordance with Japanese law entitled The Act on Body Donation for Medical and Dental Education (Act No. 56 of 1983). All donors voluntarily agreed that their remains would be used for educational and research purposes before their death. Written informed consent was obtained from the bereaved families, and no objections were raised. All cadavers were fixed in 8% formalin via arterial perfusion and preserved in 30% alcohol to maintain tissue integrity and prevent fungal growth. Cadavers with histories of major abdominal or pelvic surgery were excluded. Macroscopic Anatomy Among the seven cadavers, three were used for macroscopic analysis. Following sample retrieval, two specimens were used for macroscopic cross-sectional observations, and the remaining specimens were used for layer-by-layer anatomical dissection. For macroscopic observation, each specimen was sectioned horizontally using a diamond band saw to obtain cross-sectional images of the kidneys. During the anatomical dissection of the layered structures, a midline laparotomy was performed, and the right abdominal wall was laterally reflected. Subsequently, the peritoneum and extraperitoneal fascia (EPF) were carefully separated en bloc from the underlying adipose tissue and reflected medially, thereby exposing the fascial structures that enclosed the kidney and PeRF. Histological Analysis Histological analyses were performed on the remaining four cadavers. A single transverse section at the level intersecting the kidney was prepared using a diamond band saw (EXAKT 312; EXAKT Technologies, Inc., Germany), following previously described methodology. 14 , 15 Representative tissue blocks containing the lateral and posterior regions of the kidneys were excised for histological examination. All tissue blocks were fixed in 10% neutral-buffered formalin for 24 h, dehydrated using a graded ethanol series (70%, 80%, 90%, and 100%), cleared in xylene, and embedded in paraffin under negative pressure. The paraffin was replaced three times over a period of 5 days to ensure complete infiltration. Paraffin sections (5-µm thick) were prepared using a rotary microtome (RM2235; Leica Biosystems Nussloch GmbH, Wetzlar, Germany) and stained with Elastica van Gieson staining. RESULTS Macroscopic Findings The peritoneum lining the abdominal cavity was identified in a transverse abdominal section through the kidneys (Fig. 1 ). The peritoneum covered the posterior abdominal wall, including the ascending colon and its mesocolonic fat, and was then reflected laterally along the inner surface of the lateral abdominal wall. The abdominal wall musculature extended from the lateral wall toward the posterior side, anteromedial to these muscles, and the fat compartment corresponding to the pararenal fat (PaRF) was observed. PeRF surrounding the kidney was visible medially and anteriorly to the PaRF. The boundary between the PaRF and PeRF was clearly demarcated in the cross section. The peritoneal reflection was located between PaRF and PeRF. The peritoneum lining the right abdominal wall extended seamlessly from the anterior to the lateral and posterior abdominal walls (Fig. 2 A). When the peritoneum and EPF were dissected together from the abdominal wall and reflected medially, the transversalis fascia covering the muscular layer of the abdominal wall and adipose tissue attached to its anterior surface became clearly visible (Fig. 2 B). The adipose tissue extended from the posterior aspect of the kidney to the abdominal wall and was identified as the PaRF. A thin layer of adipose tissue was observed between the peritoneum and EPF (Fig. 2 B). The EPF continued posteriorly and covered the dorsal aspects of the perirenal structures (Fig. 2 C). Upon longitudinal incision and careful bilateral reflection of the EPF, a thin adipose layer was observed immediately beneath it (Fig. 2 D, asterisk). After the removal of the adipose layer, the deep surface of the peritoneum was exposed anteriorly. Subsequently, a membranous structure enclosing the kidney and PeRF was exposed and identified as the PRF (Fig. 2 E). The PRF extended anteriorly and formed a boundary with the peritoneum at the point where it passed in front of the PeRF. Histological Findings In cross-sectional observations of the retroperitoneal region, the PeRF was located adjacent to the kidney, whereas a distinct adipose compartment identified as the PaRF was found posterolateral to the PeRF (Fig. 3 A). The PeRF was distributed around the anterior, lateral, and posterior aspects of the kidney and was restricted to the perirenal region without extending into the adjacent extrarenal areas. Conversely, the PaRF was located posterior and lateral to the PeRF and extended anteriorly toward the lateral abdominal wall. Lateral to the PaRF, the abdominal wall musculature was observed. Histological examination clearly demonstrated the adipose compartments of PeRF and PaRF, including peritoneal reflections and dense connective tissue structures that enclosed these fat compartments (Fig. 3 B, C). Higher magnification views revealed a thin adipose layer (asterisks in Fig. 3 D, E) interposed between the peritoneum and PeRF, and between the peritoneum and EPF. This thin adipose compartment (TAC) was located between the peritoneum and EPF in the lateral abdominal wall and between the peritoneum and PeRF in the posterior abdominal wall. These adipose layers converge at the inflection point of the peritoneal reflection, forming a triradiate configuration of the fat compartments. From this junction, the tissue extended posteriorly into the dorsal region to the PeRF (Fig. 3 D, E). The interface between this thin adipose layer and PeRF and that between the thin adipose layer and PaRF were demarcated by distinct dense connective tissue membranous structures. The former was identified as the PRF and the latter as the EPF. DISCUSSION This investigation clarified the structure of adipose tissue compartments located posterior and lateral to the kidney, as well as the arrangement of their surrounding membranous structures. Two principal findings were obtained (Fig. 4 ). First, the EPF was observed as an independent membranous structure along the posterior surface of the kidney, clearly distinct from the PRF. Second, a TAC interposed between the PaRF and PeRF was continuous with TACs situated between the peritoneum and EPF, as well as between the peritoneum and PeRF. These three extensions converge in the lateral region of the kidney to form a triradiate configuration of adipose tissue. These findings indicate that the classical single-layer model of the renal and LCF is insufficient to account for the actual anatomical complexity of the retroperitoneal region, necessitating a reevaluation of the current structural interpretations. The PRF was first described by Zuckerkandl in 1883 as a fibrous membrane along the dorsal aspect of the kidneys. Subsequently, Gerota identified an analogous fibrous structure on the anterior side of the kidney called the ARF; 3 both layers are now commonly referred to collectively as the Gerota fascia. 2 , 3 , 16 , 17 Tobin 5 further defined the retroperitoneum as the region between the parietal peritoneum and the transversalis fascia. According to this framework, the renal fascia is a condensation of the retroperitoneal connective tissue that envelops the kidneys, surrounding fat, adrenal glands, gonadal vessels, and major vasculature. Both Gerota and Tobin believed that the anterior and posterior renal fasciae fuse laterally in a region referred to as the subperitoneal fascia. This structure was later termed the LCF based on anatomical dissections. 4 . With the advent of CT, the PRF was recognized as thicker than its anterior counterpart. Marks et al. 9 demonstrated that the PRF could be divided into two distinct layers: one continuous with the ARF and the other with the LCF. These findings laid the foundation for the concept of the “interfascial plane,” wherein the fascial structures—anterior, posterior, and LCF—are viewed as multilayered membranes containing potential spaces that serve as conduits for fluid, inflammation, or hemorrhage. 7 , 8 , 18 . In modern urologic surgery, particularly with retroperitoneal approaches, the fibrous membrane covering the medial surface of the PaRF and the lateral border of the PeRF is often identified as the LCF and distinguished from the renal fascia. 10 – 12 Notably, all these models remain fundamentally fascia-centered, offering limited insight into the spatial configuration and continuity of the surrounding adipose tissues. Our study introduces a novel structural model that places adipose tissue compartments, not fasciae, at the core of the anatomical delineation. By shifting the focus to the organization and continuity of the fat compartments, this model enables a more accurate representation of the structures encountered intraoperatively. Table 1 summarizes the correspondence between the traditional renal fascia model used in urology, the interfascial plane model adopted in radiology, and the anatomical configuration demonstrated in this study (adipose compartment model). By identifying TAC in the posterior, lateral, and anterior regions of the kidney, the surrounding dense connective tissue structures (PRF, EPF, and ARF) can be interpreted as continuous and coherent anatomical entities within the adipose compartment model. In the conventional renal fascia model, the lack of TAC recognition of has led to inconsistent interpretations of the fascial structures in the posterior region of the kidney. Similarly, the interfascial plane model did not anatomically define the TAC, but rather inferred the existence of potential spaces. Thus, recognizing the TAC in all three regions—posterior, lateral, and anterior—provides a unified framework that accommodates previously disparate fascia-based models. The presence of PRF and EPF in the posterior region of the kidney supports the long-recognized possibility that the renal fascia is composed of multiple layers rather than a single continuous sheet. This finding aligns with those described by Marks et al., 9 who reported that the PRF comprises inner and outer layers; the inner layer was continuous with the ARF, whereas the outer layer extended laterally and merged with the LCF. However, Marks et al. 9 ’s study involved mechanical dissection, which may have compromised the preservation of interfascial relationships and continuity of adipose tissue compartments. In contrast, we examined intact cadaveric specimens without prior dissection, enabling the histological visualization of a clearly delineated and continuous thin adipose layer enclosed between the PRF and EPF. Furthermore, per recent histological studies, the Gerota fascia exhibits a “sandwich” structure, consisting of a central dense collagenous core flanked by looser connective tissue layers on both sides. 19 If such a layered configuration applies to both the anterior and posterior renal fasciae, the EPF may share a similar architecture. Accordingly, we observed the EPF as an independent fascial structure, supporting the notion that compartmental boundaries in the retroperitoneal space are formed through a gradual and continuous transition from adipose tissue to loose fibrous connective tissue and finally to dense fibrous connective tissue. Our findings offer valuable insights into clarifying anatomical landmarks during laparoscopic and robot-assisted urological procedures. Traditionally, surgical dissection around the kidney relies on the anterior and posterior layers of the renal fascia as key landmarks. However, in actual surgical fields, the fascial structures on the lateral and posterior sides of the kidney are often not perceived as a single continuous layer but rather as multilayered and complex tissue planes. This study identified a TAC between PaRF and PeRF, bounded by the EPF posterolaterally and PRF anteromedially. The EPF, which extends to the posterior aspect of the kidney, is sometimes referred to as the LCF in the field of urology. 18 Our observations are consistent with the multilaminar fascial appearance frequently encountered intraoperatively (Fig. 5 ). Figure 5 shows intraoperative photographs of laparoscopic radical nephrectomy. Surgery was performed via a transperitoneal approach (Fig. 5 A), and the renal artery and vein were transected from the anteromedial side of the kidney, followed by identification and incision of the peritoneal reflection at the lateral aspect of the kidney (Fig. 5 B). Subsequent dissection between the kidney and lateral abdominal wall revealed the EPF enveloping the PaRF, and medially revealed the PRF enclosing the PeRF (Fig. 5 C). This dissectible plane extended posteriorly, allowing the kidney and surrounding PeRF to be mobilized en bloc, while preserving the PRF (Fig. 5 D). Entry into the PeRF compartment requires deliberate incision of the PRF. By contrast, during retroperitoneal approaches, both the EPF and PRF must be incised to access the PeRF from the PaRF side, highlighting the importance of structural understanding in such approaches. Notably, in patients with reduced visceral fat, the TAC between the EPF and PRF may appear diminished, and the two fascial layers may be closely apposed, mimicking a single fascial membrane. Thus, the number of fascial layers per se is not a critical issue; rather, recognizing the existence of the TAC as a distinct space is the key to accurately identifying the fascial boundaries that define it. These fascial structures should be understood not as primary anatomical entities themselves but as boundary-forming elements of the adipose compartments they enclose. Clear identification of the interposed adipose compartment and its surrounding fascial layers provides a practical framework for safe and anatomically precise dissection during minimally invasive renal surgery. This study has some limitations. First, the analysis was limited to the posterior and lateral regions of the kidney, and the anatomical relationships between adipose compartments and fascial structures in the anterior perirenal region should be investigated in future studies. Second, as no systematic assessment of individual variability was conducted, the potential influence of factors such as sex, age, and body habitus on compartmental architecture remains to be elucidated. Third, the study was based on static observations of formalin-fixed cadavers, which may not fully reflect the dynamic behavior of tissues or morphological changes that occur intraoperatively under varying pressure conditions. Accordingly, further validation of the anatomical findings in this study through correlation with intraoperative observations and radiological imaging is warranted. In conclusion, our macroscopic and histological analysis findings demonstrated that the EPF and PRF exist as two distinct layers of dense fibrous connective tissue with a thin interposed adipose compartment between them. This adipose tissue compartment, which has not been fully recognized in previous anatomical literature, exhibits a distribution distinct from that of both PaRF and PeRF. This structure was recognized as the TAC. These results suggest that understanding the retroperitoneal anatomy in terms of adipose compartment configuration, rather than relying solely on the classical concept of Gerota’s fascia as a single continuous membrane, may offer a more intuitive and practical framework for anatomical orientation. Future studies examining the anterior renal region and assessing interindividual variability are important to refine this model and explore its broader clinical relevance. Abbreviations Computed tomography (CT) Extraperitoneal fascia (EPF) Lateroconal fascia (LCF) Posterior renal fascia (PRF) Anterior renal fascia (ARF) Perirenal fat (PeRF) Pararenal fat (PaRF) Thin adipose compartment (TAC) Declarations Acknowledgment The authors sincerely thank the volunteers who aided in anatomical research so that it could be performed. The results of this research can potentially increase the overall knowledge of humankind and improve patient care. Therefore, the donors and their families are greatly appreciated. During the preparation for this study, ChatGPT was used to improve the clarity and grammatical usage of the English. After using these services, the authors reviewed and edited the content as required and take full responsibility for the content of the published article. No funding was received for this study. Conflict of Interest The authors declare no conflict of interest. Ethical Approval The Human Subjects Research Ethics Review Committee of the Institute of Science, Tokyo, Japan (approval number: M2019-075). All procedures were conducted in accordance with relevant guidelines and regulations. Informed Consent Written informed consent was obtained from the bereaved families, and no objections were raised. Registry Not applicable. Data availability statement Data supporting the findings of this study are available from the corresponding author upon request. Author contributions Conceptualization: Atsuhiko Ochi and Satoru Muro. Methodology: Atsuhiko Ochi and Satoru Muro. Investigation: Atsuhiko Ochi, Satoru Muro, and Sho Mitsumaru. Writing – Original Draft Preparation: Satoru Muro and Atsuhiko Ochi. Visualization: Atsuhiko Ochi, Satoru Muro, Akimoto Nimura, and Keiichi Akita. Supervision: Keiichi Akita. All authors reviewed the manuscript critically for important intellectual content and approved the final version of the manuscript. Atsuhiko Ochi and Satoru Muro contributed equally to this work and share first authorship. References Gerota D Der ano-rectale Lymphapparat. Harvard University, Massachusetts. 1895 Amin M, Blandford AT, Polk HC Jr (1976) Ren fascia Gerota Urol 7:1–3 Chesbrough RM, Burkhard TK, Martinez AJ, Burks DD (1989) Gerota versus Zuckerkandl: the renal fascia revisited. Radiology 173:845–846 Congdon ED, Edson JN (1941) The cone of renal fascia in the adult white male. Anat Rec (Hoboken) 80:289–313 Tobin CE (1944) The renal fascia and its relation to the transversalis fascia. Anat Rec (Hoboken) 89:295–311 Standring S (ed) (2020) Gray's Anatomy, 42nd Edition. The Anatomical Basis of Clinical Practice. Elsevier, Amsterdam Molmenti EP, Balfe DM, Kanterman RY, Bennett HF (1996) Anatomy of the retroperitoneum: observations of the distribution of pathologic fluid collections. Radiology 200:95–103 Aizenstein RI, Wilbur AC, O’Neil HK (1997) Interfascial and perinephric pathways in the spread of retroperitoneal disease: refined concepts based on CT observations. AJR Am J Roentgenol 168:639–643 Marks SC Jr, Raptopoulos V, Kleinman P, Snyder M (1986) The anatomical basis for retrorenal extensions of pancreatic effusions: the role of the renal fasciae. Surg Radiol Anat 8:89–97 Yin X, Cui L, Li F, Qi S, Yin Z, Gao J (2016) Lateroconal fascia suspension for management of peritoneal tear and curtain effect during retroperitoneal laparoscopic operations. Int Urol Nephrol 48:201–206 Alimu P, Dai J, Huang X, Zhao J (2022) Lateroconal fascia suspension facilitates retroperitoneal partial nephrectomy. Transl Cancer Res 11:1141–1145 Takahashi R, Furubayashi N, Nakamura M, Hasegawa Y (2012) Surgical considerations of the renal fascia and the retroperitoneal space around the kidney. J Bodyw Mov Ther 16:392–396 Ochi A, Muro S, Adachi T, Akita K (2020) Zoning inside the renal fascia: The anatomical relationship between the urinary system and perirenal fat. Int J Urol 27:625–633 Muro S, Nimura A, Ibara T, Chikazawa K, Nakazawa M, Akita K (2023) Anatomical basis for contribution of hip joint motion by the obturator internus to defaecation/urinary functions by the levator ani via the obturator fascia. J Anat 242:657–665 Muro S, Tharnmanularp S, Tsukada Y, Ito M, Nimura A, Akita K (2025) Three-dimensional heterogeneity of smooth muscle fiber density anterior to the rectum in males: quantitative analysis with implications for transanal total mesorectal excision. Int J Colorectal Dis 40:95 Mitchell GAG (1950) The renal fascia. Br J Surg 37:257–266 MacLennan GT (ed) (2012) Hinman's Atlas of UroSurgical Anatomy, Second Edition. Elsevier, Amsterdam Huang J, Zhang T, Mo J et al (2024) Interfascial planes as surgical landmarks for laparoscopic upper retroperitoneal surgery: a cadaveric and retrospectively clinical study. Transl Androl Urol 13:720–735 Kobayashi Y, Edamura K, Sadahira T et al (2025) What is the identity of Gerota fascia? Histological study with cadavers. Int J Urol 32:62–68 Tables Table 1. Comparison of anatomical interpretations of the perirenal region Posterior region of the kidney Lateral region of the kidney Anterior region of the kidney Tissue composition and distribution Dense connective tissue covering the PeRF TAC Dense connective tissue covering the PaRF Basal lamina of the peritoneum TAC Dense connective tissue covering the PaRF Basal lamina of the peritoneum TAC Dense connective tissue covering the PeRF Renal fascia model (Anatomy) PRF ? (Unrecognized) PRF Peritoneum Subperitoneal fat LCF Peritoneum Subperitoneal fat ARF Renal fascia model (Urology) PRF ? (Unrecognized) LCF Peritoneum Subperitoneal fat LCF Peritoneum Subperitoneal fat ARF Interfascial plane model (Radiology) PRF (Plane) LCF (Plane) ARF (Plane) Adipose compartment model (The present study) PRF Posterior TAC EPF Peritoneum Lateral TAC EPF Peritoneum Anterior TAC ARF ARF, anterior renal fascia; EPF, extraperitoneal fascia; LCF, lateroconal fascia; PaRF, pararenal fat; PeRF, perirenal fat; PRF, posterior renal fascia; TAC, Thin adipose compartment. Additional Declarations The authors declare no competing interests. Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-7324278","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":497532006,"identity":"166bf630-b8d4-435d-aa5d-0efd4c354932","order_by":0,"name":"Atsuhiko Ochi","email":"","orcid":"","institution":"Kameda Medical Center","correspondingAuthor":false,"prefix":"","firstName":"Atsuhiko","middleName":"","lastName":"Ochi","suffix":""},{"id":497532007,"identity":"80a1a6c9-f19c-4d7b-acf8-ac26b25b94b2","order_by":1,"name":"Satoru Muro","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAzUlEQVRIiWNgGAWjYNACGyBmb2Bg4AHzDhCjJQ2IeQ6TrEUiGaaFANCdkfvwAUOCXR7/zPdHN7xhsJNnYDyL3xqzG+nGBgwJycUSt5PZbs5hSDZsYDiXQEBLGpsE4w/mxAaglts8DMxA5WcMCGthSKhPnH/zMEhLPdFaDiduuMEM0nKYCC1nnjEbJCQcT9x4Jtns5hyD44ZtBP1yPI3xwYeE6sR5xw8+u/GmolqeX4JAiIEBwlSgk9gkzhDWgQb4e0jWMgpGwSgYBcMbAABod0WBISj6QgAAAABJRU5ErkJggg==","orcid":"","institution":"Institute of Science","correspondingAuthor":true,"prefix":"","firstName":"Satoru","middleName":"","lastName":"Muro","suffix":""},{"id":497532008,"identity":"dc06510a-d6c5-4373-8a0c-d61c56bfa24b","order_by":2,"name":"Sho Mitsumaru","email":"","orcid":"","institution":"Institute of Science","correspondingAuthor":false,"prefix":"","firstName":"Sho","middleName":"","lastName":"Mitsumaru","suffix":""},{"id":497532009,"identity":"2b378058-9f7f-4204-8e04-246fcefe4d64","order_by":3,"name":"Akimoto Nimura","email":"","orcid":"","institution":"Institute of Science","correspondingAuthor":false,"prefix":"","firstName":"Akimoto","middleName":"","lastName":"Nimura","suffix":""},{"id":497532010,"identity":"185b6210-a166-4239-b49c-119019264565","order_by":4,"name":"Keiichi Akita","email":"","orcid":"","institution":"Institute of Science","correspondingAuthor":false,"prefix":"","firstName":"Keiichi","middleName":"","lastName":"Akita","suffix":""}],"badges":[],"createdAt":"2025-08-08 06:53:29","currentVersionCode":1,"declarations":{"humanSubjects":true,"vertebrateSubjects":false,"conflictsOfInterestStatement":false,"humanSubjectEthicalGuidelines":true,"humanSubjectConsent":true,"humanSubjectClinicalTrial":false,"humanSubjectCaseReport":false,"vertebrateSubjectEthicalGuidelines":false},"doi":"10.21203/rs.3.rs-7324278/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-7324278/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":88777969,"identity":"4745f120-3421-4697-86ce-fc4ee9a82e26","added_by":"auto","created_at":"2025-08-11 10:20:01","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":2280742,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003ePeritoneal reflection and fat compartments around the kidney.\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eTransverse abdominal sections through the kidneys. The peritoneum covers the posterior abdominal wall, including the ascending colon and mesocolonic fat, and reflects the lateral abdominal wall. The pararenal fat (PaRF) lies anteromedial to the abdominal wall muscles, whereas the perirenal fat (PeRF) surrounds the kidney. The boundary between the PaRF and PeRF is distinct, with a peritoneal reflection positioned between them.\u003c/p\u003e","description":"","filename":"figure1.png","url":"https://assets-eu.researchsquare.com/files/rs-7324278/v1/993fda0074eea9937e79b14f.png"},{"id":88777414,"identity":"0006f863-e089-45df-a629-d4f23684ced7","added_by":"auto","created_at":"2025-08-11 10:12:01","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":2134000,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eMacroscopic anatomy of the posterior and lateral retroperitoneal region.\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e(A) Anterior aspect of the right half of the abdomen. The peritoneum lining the right abdominal wall continues from the anterior to the lateral and posterior abdominal walls.\u003c/p\u003e\n\u003cp\u003e(B) After the peritoneum and EPF are dissected and reflected medially, PaRF are observed on the TF covering AWM.\u003c/p\u003e\n\u003cp\u003e(C) Enlarged view of the dashed square in B. The EPF extends posteriorly to cover the posterior aspect of the perirenal region.\u003c/p\u003e\n\u003cp\u003e(D) The EPF is cut along the dashed line in C. Following longitudinal incision and reflection of the EPF, a thin adipose compartment (asterisk) is observed immediately beneath the EPF. The arrowhead indicates the edge of the EPF incision.\u003c/p\u003e\n\u003cp\u003e(E) After removal of the adipose layer, PRF enclosing PeRF is clearly exposed. The arrow indicates the border between the peritoneum and the PRF.\u003c/p\u003e\n\u003cp\u003eAC, ascending colon; AWM, abdominal wall musculature; EPF, extraperitoneal fascia; GB, gallbladder; L, liver; PaRF, pararenal fat; PeRF, perirenal fat; Pn, peritoneum; PRF, posterior renal fascia; TC, transverse colon; TF, transversalis fascia.\u003c/p\u003e","description":"","filename":"figure2.png","url":"https://assets-eu.researchsquare.com/files/rs-7324278/v1/831859718b91521c0db2e2dd.png"},{"id":88779102,"identity":"7068826a-c1b0-4185-b1df-a10811294933","added_by":"auto","created_at":"2025-08-11 10:28:01","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":841878,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eHistological examination of the posterior and lateral adipose compartments and fasciae.\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e(A) Cross-sectional overview showing PeRF surrounding the kidney, PaRF located posterolaterally, and the abdominal wall muscles with the TF.\u003c/p\u003e\n\u003cp\u003e(B) Low-magnification histological image showing the spatial distribution of the PeRF and PaRF, the peritoneal reflection, and surrounding fascial structures.\u003c/p\u003e\n\u003cp\u003e(C) Schematic illustration corresponding to panel B.\u003c/p\u003e\n\u003cp\u003e(D, E) D is an enlarged view of the dashed square d in Figure 3B, and E is an enlarged view of the dashed square e in Figure 3B. Higher-magnification images demonstrate a thin adipose compartment (asterisks) interposed between the peritoneum and EPF laterally, between the peritoneum and PeRF anteriorly, and between the PRF and EPF posteriorly. These three extensions converge at the peritoneal reflection, forming a triradiate adipose tissue configuration. In the posterior region of the kidney, this thin adipose compartment is bordered by dense connective tissue structures: EPF posterolaterally and PRF anteromedially.\u003c/p\u003e\n\u003cp\u003eAWM, abdominal wall musculature; EPF, extraperitoneal fascia; PaRF, pararenal fat; PeRF, perirenal fat; Pn, peritoneum; PRF, posterior renal fascia; QL, quadratus lumborum muscle; TF, transversalis fascia.\u003c/p\u003e","description":"","filename":"figure3.png","url":"https://assets-eu.researchsquare.com/files/rs-7324278/v1/91b2fd62831144b37ea7257f.png"},{"id":88777971,"identity":"cb306aab-0712-44fc-bb36-4bb1323a9eda","added_by":"auto","created_at":"2025-08-11 10:20:01","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":173082,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eSchematic representation of the adipose tissue compartments and surrounding fascial structures in the posterolateral retroperitoneal region.\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis diagram illustrates the spatial configuration of the three distinct adipose tissue compartments (asterisks): perirenal fat (PeRF), pararenal fat (PaRF), and an interposed thin adipose layer. The thin adipose compartment is bordered anteromedially by the posterior renal fascia (PRF) and posterolaterally by the extraperitoneal fascia (EPF), both of which are dense fibrous connective tissue layers. This thin adipose compartment continues anteromedially between the PeRF and peritoneum and anterolaterally between the EPF and peritoneum. These three extensions converged at the lateral margin of the kidney, forming a triradiate configuration. This arrangement challenges the classical unilaminar concept of the Gerota fascia and supports a compartment-based anatomical model.\u003c/p\u003e","description":"","filename":"figure4.png","url":"https://assets-eu.researchsquare.com/files/rs-7324278/v1/97ce6882b22a3dc3358dadaa.png"},{"id":88777973,"identity":"8989b63d-3cc7-4dec-88ac-75eab8b6e0ba","added_by":"auto","created_at":"2025-08-11 10:20:01","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":1246529,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eIntraoperative observations during laparoscopic right nephrectomy.\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eIntraoperative photographsof laparoscopic radical nephrectomy performed for T1a right cystic renal cell carcinoma in a 49-year-old female patient undergoing hemodialysis.\u003c/p\u003e\n\u003cp\u003e(A) Overview of the operative field from a transperitoneal approach, illustrating a horizontal cross-sectional perspective of the right retroperitoneal region. The red line indicates the dissection plane.\u003c/p\u003e\n\u003cp\u003e(B) Identification and incision of the peritoneal reflection at the lateral aspect of the kidney (white arrowheads). Arrowheads indicate the margins of the incised peritoneum.\u003c/p\u003e\n\u003cp\u003e(C) After dissection between the kidney and the lateral abdominal wall, two distinct fascial layers became clearly visible: laterally, the extraperitoneal fascia (EPF) enclosing the pararenal fat (PaRF); and medially, the posterior renal fascia (PRF) surrounding the perirenal fat (PeRF). (D) A dissectible plane—corresponding to the thin adipose compartment—extended posteriorly between these fascial layers, enabling mobilization of the kidney and PeRF while preserving the PRF. These intraoperative findings correspond closely to the compartmental anatomy elucidated in this study.\u003c/p\u003e","description":"","filename":"figure5.png","url":"https://assets-eu.researchsquare.com/files/rs-7324278/v1/6c1cff8c8a6d3cb2c8911b4d.png"},{"id":88779104,"identity":"e6ad46ea-e28c-49d7-bc20-0fe0ccf403f2","added_by":"auto","created_at":"2025-08-11 10:28:09","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":8902211,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7324278/v1/5ca14465-6726-4df4-84ca-aa858e8f9524.pdf"}],"financialInterests":"The authors declare no competing interests.","formattedTitle":"\u003cp\u003eAnatomy of adipose compartments and fascial structures in the posterolateral region of the kidney with special focus on the thin adipose compartment\u003c/p\u003e","fulltext":[{"header":"INTRODUCTION","content":"\u003cp\u003eThe renal fascia is a fibrous membranous structure located in the retroperitoneal region that envelops the kidneys, adrenal glands, ureters, gonadal vessels, and perirenal fat (PeRF) from both the anterior and posterior aspects. Zuckerkandl first described the posterior renal fascia (PRF), followed by Gerota identifying the anterior renal fascia (ARF).\u003csup\u003e\u003cspan additionalcitationids=\"CR2\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e\u003c/sup\u003e These fasciae converge laterally to form the lateroconal fascia (LCF).\u003csup\u003e\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e\u003c/sup\u003e Collectively, they function as mechanical barriers that protect retroperitoneal organs from external forces and the spread of inflammation or infection as well as critical anatomical landmarks that influence radiological interpretation, intraoperative visualization, and the selection of dissection planes during surgical procedures.\u003c/p\u003e\u003cp\u003eTraditionally, the fascia of the retroperitoneal region is regarded as a single, continuous, membranous structure,\u003csup\u003e\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e\u003c/sup\u003e as reflected in current anatomical textbooks.\u003csup\u003e\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e\u003c/sup\u003e However, since the advent of computed tomography (CT) in the 1980s, radiologists have proposed the concept of the interfascial plane, suggesting that the ARF, PRF, and LCF each consist of multilayered, thin fibrous membranes.\u003csup\u003e\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e,\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e\u003c/sup\u003e These layers contain potential spaces that may serve as pathways for fluid components such as inflammatory exudates or hemorrhages. Based on CT imaging and cadaveric studies, Marks et al. reported that the PRF could be divided into two distinct membranous structures: one connected to the LCF and the other connected to the ARF.\u003csup\u003e\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e\u003c/sup\u003e During retroperitoneal surgery, the outermost membranous structure within the pararenal fat (flank pad) on the posterior aspect of the kidney is sometimes referred to as the LCF to distinguish it from the PRF,\u003csup\u003e\u003cspan additionalcitationids=\"CR11\" citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e\u003c/sup\u003e although this usage deviates from the original anatomical definition. These observations challenge the conventional model of a single PRF, suggesting its insufficiency to fully represent the complex tissue organization in the posterior and lateral regions of the kidney.\u003c/p\u003e\u003cp\u003eThis study aimed to anatomically and histologically investigate the configuration of adipose tissue compartments and surrounding dense connective tissue structures in the posterior and lateral regions of the kidney from a perspective distinct from the conventional renal fascia theory. Ochi et al.\u003csup\u003e\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u003c/sup\u003e previously reexamined the internal architecture of the renal fascia through a novel framework of adipose tissue compartmentalization (zoning) based on the anatomical continuity of fat tissue. In the present study, we applied this concept to investigate the distribution and spatial relationships of adipose tissue in the retroperitoneal region, lateral and posterior to the kidney, and interpreted the dense fibrous connective tissue membranes that delineate fat compartments as fasciae. This fat-based approach may provide a more accurate anatomical model of the retroperitoneum and enhance the interpretation of findings during laparoscopic, retroperitoneoscopic, and robot-assisted surgeries.\u003c/p\u003e"},{"header":"MATERIALS AND METHODS","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\u003ch2\u003ePreparation of Cadaveric Specimens\u003c/h2\u003e\u003cp\u003eSeven adult male cadavers (mean age at death, 81.7 [range, 73\u0026ndash;92] years) were donated to our department in accordance with Japanese law entitled The Act on Body Donation for Medical and Dental Education (Act No. 56 of 1983). All donors voluntarily agreed that their remains would be used for educational and research purposes before their death. Written informed consent was obtained from the bereaved families, and no objections were raised. All cadavers were fixed in 8% formalin via arterial perfusion and preserved in 30% alcohol to maintain tissue integrity and prevent fungal growth. Cadavers with histories of major abdominal or pelvic surgery were excluded.\u003c/p\u003e\u003c/div\u003e\n\u003ch3\u003eMacroscopic Anatomy\u003c/h3\u003e\n\u003cp\u003eAmong the seven cadavers, three were used for macroscopic analysis. Following sample retrieval, two specimens were used for macroscopic cross-sectional observations, and the remaining specimens were used for layer-by-layer anatomical dissection. For macroscopic observation, each specimen was sectioned horizontally using a diamond band saw to obtain cross-sectional images of the kidneys. During the anatomical dissection of the layered structures, a midline laparotomy was performed, and the right abdominal wall was laterally reflected. Subsequently, the peritoneum and extraperitoneal fascia (EPF) were carefully separated en bloc from the underlying adipose tissue and reflected medially, thereby exposing the fascial structures that enclosed the kidney and PeRF.\u003c/p\u003e\n\u003ch3\u003eHistological Analysis\u003c/h3\u003e\n\u003cp\u003eHistological analyses were performed on the remaining four cadavers. A single transverse section at the level intersecting the kidney was prepared using a diamond band saw (EXAKT 312; EXAKT Technologies, Inc., Germany), following previously described methodology.\u003csup\u003e\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e,\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e\u003c/sup\u003e Representative tissue blocks containing the lateral and posterior regions of the kidneys were excised for histological examination. All tissue blocks were fixed in 10% neutral-buffered formalin for 24 h, dehydrated using a graded ethanol series (70%, 80%, 90%, and 100%), cleared in xylene, and embedded in paraffin under negative pressure. The paraffin was replaced three times over a period of 5 days to ensure complete infiltration. Paraffin sections (5-\u0026micro;m thick) were prepared using a rotary microtome (RM2235; Leica Biosystems Nussloch GmbH, Wetzlar, Germany) and stained with Elastica van Gieson staining.\u003c/p\u003e"},{"header":"RESULTS","content":"\u003cdiv id=\"Sec7\" class=\"Section2\"\u003e\u003ch2\u003eMacroscopic Findings\u003c/h2\u003e\u003cp\u003eThe peritoneum lining the abdominal cavity was identified in a transverse abdominal section through the kidneys (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). The peritoneum covered the posterior abdominal wall, including the ascending colon and its mesocolonic fat, and was then reflected laterally along the inner surface of the lateral abdominal wall. The abdominal wall musculature extended from the lateral wall toward the posterior side, anteromedial to these muscles, and the fat compartment corresponding to the pararenal fat (PaRF) was observed. PeRF surrounding the kidney was visible medially and anteriorly to the PaRF. The boundary between the PaRF and PeRF was clearly demarcated in the cross section. The peritoneal reflection was located between PaRF and PeRF.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eThe peritoneum lining the right abdominal wall extended seamlessly from the anterior to the lateral and posterior abdominal walls (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eA). When the peritoneum and EPF were dissected together from the abdominal wall and reflected medially, the transversalis fascia covering the muscular layer of the abdominal wall and adipose tissue attached to its anterior surface became clearly visible (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eB). The adipose tissue extended from the posterior aspect of the kidney to the abdominal wall and was identified as the PaRF. A thin layer of adipose tissue was observed between the peritoneum and EPF (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eB). The EPF continued posteriorly and covered the dorsal aspects of the perirenal structures (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eC). Upon longitudinal incision and careful bilateral reflection of the EPF, a thin adipose layer was observed immediately beneath it (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eD, asterisk). After the removal of the adipose layer, the deep surface of the peritoneum was exposed anteriorly. Subsequently, a membranous structure enclosing the kidney and PeRF was exposed and identified as the PRF (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eE). The PRF extended anteriorly and formed a boundary with the peritoneum at the point where it passed in front of the PeRF.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec8\" class=\"Section2\"\u003e\u003ch2\u003eHistological Findings\u003c/h2\u003e\u003cp\u003eIn cross-sectional observations of the retroperitoneal region, the PeRF was located adjacent to the kidney, whereas a distinct adipose compartment identified as the PaRF was found posterolateral to the PeRF (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eA). The PeRF was distributed around the anterior, lateral, and posterior aspects of the kidney and was restricted to the perirenal region without extending into the adjacent extrarenal areas. Conversely, the PaRF was located posterior and lateral to the PeRF and extended anteriorly toward the lateral abdominal wall. Lateral to the PaRF, the abdominal wall musculature was observed.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eHistological examination clearly demonstrated the adipose compartments of PeRF and PaRF, including peritoneal reflections and dense connective tissue structures that enclosed these fat compartments (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eB, C). Higher magnification views revealed a thin adipose layer (asterisks in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eD, E) interposed between the peritoneum and PeRF, and between the peritoneum and EPF. This thin adipose compartment (TAC) was located between the peritoneum and EPF in the lateral abdominal wall and between the peritoneum and PeRF in the posterior abdominal wall. These adipose layers converge at the inflection point of the peritoneal reflection, forming a triradiate configuration of the fat compartments. From this junction, the tissue extended posteriorly into the dorsal region to the PeRF (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eD, E). The interface between this thin adipose layer and PeRF and that between the thin adipose layer and PaRF were demarcated by distinct dense connective tissue membranous structures. The former was identified as the PRF and the latter as the EPF.\u003c/p\u003e\u003c/div\u003e"},{"header":"DISCUSSION","content":"\u003cp\u003eThis investigation clarified the structure of adipose tissue compartments located posterior and lateral to the kidney, as well as the arrangement of their surrounding membranous structures. Two principal findings were obtained (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e). First, the EPF was observed as an independent membranous structure along the posterior surface of the kidney, clearly distinct from the PRF. Second, a TAC interposed between the PaRF and PeRF was continuous with TACs situated between the peritoneum and EPF, as well as between the peritoneum and PeRF. These three extensions converge in the lateral region of the kidney to form a triradiate configuration of adipose tissue. These findings indicate that the classical single-layer model of the renal and LCF is insufficient to account for the actual anatomical complexity of the retroperitoneal region, necessitating a reevaluation of the current structural interpretations.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eThe PRF was first described by Zuckerkandl in 1883 as a fibrous membrane along the dorsal aspect of the kidneys. Subsequently, Gerota identified an analogous fibrous structure on the anterior side of the kidney called the ARF;\u003csup\u003e\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e\u003c/sup\u003e both layers are now commonly referred to collectively as the Gerota fascia.\u003csup\u003e\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e,\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e,\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e,\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e\u003c/sup\u003e Tobin\u003csup\u003e\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e\u003c/sup\u003e further defined the retroperitoneum as the region between the parietal peritoneum and the transversalis fascia. According to this framework, the renal fascia is a condensation of the retroperitoneal connective tissue that envelops the kidneys, surrounding fat, adrenal glands, gonadal vessels, and major vasculature. Both Gerota and Tobin believed that the anterior and posterior renal fasciae fuse laterally in a region referred to as the subperitoneal fascia. This structure was later termed the LCF based on anatomical dissections.\u003csup\u003e\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e\u003c/sup\u003e. With the advent of CT, the PRF was recognized as thicker than its anterior counterpart. Marks et al.\u003csup\u003e\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e\u003c/sup\u003e demonstrated that the PRF could be divided into two distinct layers: one continuous with the ARF and the other with the LCF. These findings laid the foundation for the concept of the \u0026ldquo;interfascial plane,\u0026rdquo; wherein the fascial structures\u0026mdash;anterior, posterior, and LCF\u0026mdash;are viewed as multilayered membranes containing potential spaces that serve as conduits for fluid, inflammation, or hemorrhage.\u003csup\u003e\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e,\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e,\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e\u003c/sup\u003e. In modern urologic surgery, particularly with retroperitoneal approaches, the fibrous membrane covering the medial surface of the PaRF and the lateral border of the PeRF is often identified as the LCF and distinguished from the renal fascia.\u003csup\u003e\u003cspan additionalcitationids=\"CR11\" citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e\u003c/sup\u003e\u003c/p\u003e\u003cp\u003eNotably, all these models remain fundamentally fascia-centered, offering limited insight into the spatial configuration and continuity of the surrounding adipose tissues. Our study introduces a novel structural model that places adipose tissue compartments, not fasciae, at the core of the anatomical delineation. By shifting the focus to the organization and continuity of the fat compartments, this model enables a more accurate representation of the structures encountered intraoperatively. Table\u0026nbsp;1 summarizes the correspondence between the traditional renal fascia model used in urology, the interfascial plane model adopted in radiology, and the anatomical configuration demonstrated in this study (adipose compartment model). By identifying TAC in the posterior, lateral, and anterior regions of the kidney, the surrounding dense connective tissue structures (PRF, EPF, and ARF) can be interpreted as continuous and coherent anatomical entities within the adipose compartment model. In the conventional renal fascia model, the lack of TAC recognition of has led to inconsistent interpretations of the fascial structures in the posterior region of the kidney. Similarly, the interfascial plane model did not anatomically define the TAC, but rather inferred the existence of potential spaces. Thus, recognizing the TAC in all three regions\u0026mdash;posterior, lateral, and anterior\u0026mdash;provides a unified framework that accommodates previously disparate fascia-based models.\u003c/p\u003e\u003cp\u003eThe presence of PRF and EPF in the posterior region of the kidney supports the long-recognized possibility that the renal fascia is composed of multiple layers rather than a single continuous sheet. This finding aligns with those described by Marks et al.,\u003csup\u003e\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e\u003c/sup\u003e who reported that the PRF comprises inner and outer layers; the inner layer was continuous with the ARF, whereas the outer layer extended laterally and merged with the LCF. However, Marks et al.\u003csup\u003e\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e\u003c/sup\u003e\u0026rsquo;s study involved mechanical dissection, which may have compromised the preservation of interfascial relationships and continuity of adipose tissue compartments. In contrast, we examined intact cadaveric specimens without prior dissection, enabling the histological visualization of a clearly delineated and continuous thin adipose layer enclosed between the PRF and EPF. Furthermore, per recent histological studies, the Gerota fascia exhibits a \u0026ldquo;sandwich\u0026rdquo; structure, consisting of a central dense collagenous core flanked by looser connective tissue layers on both sides.\u003csup\u003e\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e\u003c/sup\u003e If such a layered configuration applies to both the anterior and posterior renal fasciae, the EPF may share a similar architecture. Accordingly, we observed the EPF as an independent fascial structure, supporting the notion that compartmental boundaries in the retroperitoneal space are formed through a gradual and continuous transition from adipose tissue to loose fibrous connective tissue and finally to dense fibrous connective tissue.\u003c/p\u003e\u003cp\u003eOur findings offer valuable insights into clarifying anatomical landmarks during laparoscopic and robot-assisted urological procedures. Traditionally, surgical dissection around the kidney relies on the anterior and posterior layers of the renal fascia as key landmarks. However, in actual surgical fields, the fascial structures on the lateral and posterior sides of the kidney are often not perceived as a single continuous layer but rather as multilayered and complex tissue planes. This study identified a TAC between PaRF and PeRF, bounded by the EPF posterolaterally and PRF anteromedially. The EPF, which extends to the posterior aspect of the kidney, is sometimes referred to as the LCF in the field of urology.\u003csup\u003e\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e\u003c/sup\u003e Our observations are consistent with the multilaminar fascial appearance frequently encountered intraoperatively (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e). Figure\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e shows intraoperative photographs of laparoscopic radical nephrectomy. Surgery was performed via a transperitoneal approach (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eA), and the renal artery and vein were transected from the anteromedial side of the kidney, followed by identification and incision of the peritoneal reflection at the lateral aspect of the kidney (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eB). Subsequent dissection between the kidney and lateral abdominal wall revealed the EPF enveloping the PaRF, and medially revealed the PRF enclosing the PeRF (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eC). This dissectible plane extended posteriorly, allowing the kidney and surrounding PeRF to be mobilized en bloc, while preserving the PRF (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eD). Entry into the PeRF compartment requires deliberate incision of the PRF. By contrast, during retroperitoneal approaches, both the EPF and PRF must be incised to access the PeRF from the PaRF side, highlighting the importance of structural understanding in such approaches.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eNotably, in patients with reduced visceral fat, the TAC between the EPF and PRF may appear diminished, and the two fascial layers may be closely apposed, mimicking a single fascial membrane. Thus, the number of fascial layers per se is not a critical issue; rather, recognizing the existence of the TAC as a distinct space is the key to accurately identifying the fascial boundaries that define it. These fascial structures should be understood not as primary anatomical entities themselves but as boundary-forming elements of the adipose compartments they enclose. Clear identification of the interposed adipose compartment and its surrounding fascial layers provides a practical framework for safe and anatomically precise dissection during minimally invasive renal surgery.\u003c/p\u003e\u003cp\u003eThis study has some limitations. First, the analysis was limited to the posterior and lateral regions of the kidney, and the anatomical relationships between adipose compartments and fascial structures in the anterior perirenal region should be investigated in future studies. Second, as no systematic assessment of individual variability was conducted, the potential influence of factors such as sex, age, and body habitus on compartmental architecture remains to be elucidated. Third, the study was based on static observations of formalin-fixed cadavers, which may not fully reflect the dynamic behavior of tissues or morphological changes that occur intraoperatively under varying pressure conditions. Accordingly, further validation of the anatomical findings in this study through correlation with intraoperative observations and radiological imaging is warranted.\u003c/p\u003e\u003cp\u003eIn conclusion, our macroscopic and histological analysis findings demonstrated that the EPF and PRF exist as two distinct layers of dense fibrous connective tissue with a thin interposed adipose compartment between them. This adipose tissue compartment, which has not been fully recognized in previous anatomical literature, exhibits a distribution distinct from that of both PaRF and PeRF. This structure was recognized as the TAC. These results suggest that understanding the retroperitoneal anatomy in terms of adipose compartment configuration, rather than relying solely on the classical concept of Gerota\u0026rsquo;s fascia as a single continuous membrane, may offer a more intuitive and practical framework for anatomical orientation. Future studies examining the anterior renal region and assessing interindividual variability are important to refine this model and explore its broader clinical relevance.\u003c/p\u003e"},{"header":"Abbreviations","content":"\u003cp\u003eComputed tomography (CT)\u003c/p\u003e\n\u003cp\u003eExtraperitoneal fascia (EPF)\u003c/p\u003e\n\u003cp\u003eLateroconal fascia (LCF)\u003c/p\u003e\n\u003cp\u003ePosterior renal fascia (PRF)\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eAnterior renal fascia (ARF)\u0026nbsp;\u003c/p\u003e\n\u003cp\u003ePerirenal fat (PeRF)\u003c/p\u003e\n\u003cp\u003ePararenal fat (PaRF)\u003c/p\u003e\n\u003cp\u003eThin adipose compartment (TAC)\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgment\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors sincerely thank the volunteers who aided in anatomical research so that it could be performed. The results of this research can potentially increase the overall knowledge of humankind and improve patient care. Therefore, the donors and their families are greatly appreciated. During the preparation for this study, ChatGPT was used to improve the clarity and grammatical usage of the English. After using these services, the authors reviewed and edited the content as required and take full responsibility for the content of the published article. No funding was received for this study.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConflict of Interest\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare no conflict of interest.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEthical Approval\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe Human Subjects Research Ethics Review Committee of the Institute of Science, Tokyo, Japan (approval number: M2019-075). All procedures were conducted in accordance with relevant guidelines and regulations.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eInformed Consent\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eWritten informed consent was obtained from the bereaved families, and no objections were raised.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eRegistry\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNot applicable.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData availability statement\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eData supporting the findings of this study are available from the corresponding author upon request.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor contributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eConceptualization: Atsuhiko Ochi and Satoru Muro. Methodology: Atsuhiko Ochi and Satoru Muro. Investigation: Atsuhiko Ochi, Satoru Muro, and Sho Mitsumaru. Writing \u0026ndash; Original Draft Preparation: Satoru Muro and Atsuhiko Ochi. Visualization: Atsuhiko Ochi, Satoru Muro, Akimoto Nimura, and Keiichi Akita. Supervision: Keiichi Akita. All authors reviewed the manuscript critically for important intellectual content and approved the final version of the manuscript. Atsuhiko Ochi and Satoru Muro contributed equally to this work and share first authorship.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eGerota D Der ano-rectale Lymphapparat. Harvard University, Massachusetts. 1895\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eAmin M, Blandford AT, Polk HC Jr (1976) Ren fascia Gerota Urol 7:1\u0026ndash;3\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eChesbrough RM, Burkhard TK, Martinez AJ, Burks DD (1989) Gerota versus Zuckerkandl: the renal fascia revisited. Radiology 173:845\u0026ndash;846\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eCongdon ED, Edson JN (1941) The cone of renal fascia in the adult white male. Anat Rec (Hoboken) 80:289\u0026ndash;313\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eTobin CE (1944) The renal fascia and its relation to the transversalis fascia. Anat Rec (Hoboken) 89:295\u0026ndash;311\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eStandring S (ed) (2020) Gray's Anatomy, 42nd Edition. The Anatomical Basis of Clinical Practice. Elsevier, Amsterdam\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eMolmenti EP, Balfe DM, Kanterman RY, Bennett HF (1996) Anatomy of the retroperitoneum: observations of the distribution of pathologic fluid collections. Radiology 200:95\u0026ndash;103\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eAizenstein RI, Wilbur AC, O\u0026rsquo;Neil HK (1997) Interfascial and perinephric pathways in the spread of retroperitoneal disease: refined concepts based on CT observations. AJR Am J Roentgenol 168:639\u0026ndash;643\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eMarks SC Jr, Raptopoulos V, Kleinman P, Snyder M (1986) The anatomical basis for retrorenal extensions of pancreatic effusions: the role of the renal fasciae. Surg Radiol Anat 8:89\u0026ndash;97\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eYin X, Cui L, Li F, Qi S, Yin Z, Gao J (2016) Lateroconal fascia suspension for management of peritoneal tear and curtain effect during retroperitoneal laparoscopic operations. Int Urol Nephrol 48:201\u0026ndash;206\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eAlimu P, Dai J, Huang X, Zhao J (2022) Lateroconal fascia suspension facilitates retroperitoneal partial nephrectomy. Transl Cancer Res 11:1141\u0026ndash;1145\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eTakahashi R, Furubayashi N, Nakamura M, Hasegawa Y (2012) Surgical considerations of the renal fascia and the retroperitoneal space around the kidney. J Bodyw Mov Ther 16:392\u0026ndash;396\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eOchi A, Muro S, Adachi T, Akita K (2020) Zoning inside the renal fascia: The anatomical relationship between the urinary system and perirenal fat. Int J Urol 27:625\u0026ndash;633\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eMuro S, Nimura A, Ibara T, Chikazawa K, Nakazawa M, Akita K (2023) Anatomical basis for contribution of hip joint motion by the obturator internus to defaecation/urinary functions by the levator ani via the obturator fascia. J Anat 242:657\u0026ndash;665\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eMuro S, Tharnmanularp S, Tsukada Y, Ito M, Nimura A, Akita K (2025) Three-dimensional heterogeneity of smooth muscle fiber density anterior to the rectum in males: quantitative analysis with implications for transanal total mesorectal excision. Int J Colorectal Dis 40:95\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eMitchell GAG (1950) The renal fascia. Br J Surg 37:257\u0026ndash;266\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eMacLennan GT (ed) (2012) Hinman's Atlas of UroSurgical Anatomy, Second Edition. Elsevier, Amsterdam\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eHuang J, Zhang T, Mo J et al (2024) Interfascial planes as surgical landmarks for laparoscopic upper retroperitoneal surgery: a cadaveric and retrospectively clinical study. Transl Androl Urol 13:720\u0026ndash;735\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eKobayashi Y, Edamura K, Sadahira T et al (2025) What is the identity of Gerota fascia? Histological study with cadavers. Int J Urol 32:62\u0026ndash;68\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"},{"header":"Tables","content":"\u003cp\u003e\u003cstrong\u003eTable 1.\u003c/strong\u003e\u003cstrong\u003e\u0026nbsp;Comparison of anatomical interpretations of the perirenal region\u003c/strong\u003e\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\" width=\"932\" class=\"fr-table-selection-hover\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 99px;\"\u003e\n \u003cp\u003e \u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"3\" valign=\"top\" style=\"width: 282px;\"\u003e\n \u003cp\u003ePosterior region of the kidney\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"3\" valign=\"top\" style=\"width: 275px;\"\u003e\n \u003cp\u003eLateral region of the kidney\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"3\" valign=\"top\" style=\"width: 275px;\"\u003e\n \u003cp\u003eAnterior region of the kidney\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 99px;\"\u003e\n \u003cp\u003eTissue composition and distribution\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 84px;\"\u003e\n \u003cp\u003eDense connective tissue covering the PeRF\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 115px;\"\u003e\n \u003cp\u003eTAC\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 84px;\"\u003e\n \u003cp\u003eDense connective tissue covering the PaRF\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 88px;\"\u003e\n \u003cp\u003eBasal lamina of the peritoneum\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 103px;\"\u003e\n \u003cp\u003eTAC\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 84px;\"\u003e\n \u003cp\u003eDense connective tissue covering the PaRF\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 88px;\"\u003e\n \u003cp\u003eBasal lamina of the peritoneum\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 103px;\"\u003e\n \u003cp\u003eTAC\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 84px;\"\u003e\n \u003cp\u003eDense connective tissue covering the PeRF\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 99px;\"\u003e\n \u003cp\u003eRenal fascia model\u003c/p\u003e\n \u003cp\u003e(Anatomy)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 84px;\"\u003e\n \u003cp\u003ePRF\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 115px;\"\u003e\n \u003cp\u003e?\u003c/p\u003e\n \u003cp\u003e(Unrecognized)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 84px;\"\u003e\n \u003cp\u003ePRF\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 88px;\"\u003e\n \u003cp\u003ePeritoneum\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 103px;\"\u003e\n \u003cp\u003eSubperitoneal fat\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 84px;\"\u003e\n \u003cp\u003eLCF\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 88px;\"\u003e\n \u003cp\u003ePeritoneum\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 103px;\"\u003e\n \u003cp\u003eSubperitoneal fat\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 84px;\"\u003e\n \u003cp\u003eARF\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 99px;\"\u003e\n \u003cp\u003eRenal fascia model\u003c/p\u003e\n \u003cp\u003e(Urology)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 84px;\"\u003e\n \u003cp\u003ePRF\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 115px;\"\u003e\n \u003cp\u003e?\u003c/p\u003e\n \u003cp\u003e(Unrecognized)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 84px;\"\u003e\n \u003cp\u003eLCF\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 88px;\"\u003e\n \u003cp\u003ePeritoneum\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 103px;\"\u003e\n \u003cp\u003eSubperitoneal fat\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 84px;\"\u003e\n \u003cp\u003eLCF\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 88px;\"\u003e\n \u003cp\u003ePeritoneum\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 103px;\"\u003e\n \u003cp\u003eSubperitoneal fat\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 84px;\"\u003e\n \u003cp\u003eARF\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 99px;\"\u003e\n \u003cp\u003eInterfascial plane model\u003c/p\u003e\n \u003cp\u003e(Radiology)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"3\" valign=\"top\" style=\"width: 282px;\"\u003e\n \u003cp\u003ePRF (Plane)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"3\" valign=\"top\" style=\"width: 275px;\"\u003e\n \u003cp\u003eLCF (Plane)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"3\" valign=\"top\" style=\"width: 275px;\"\u003e\n \u003cp\u003eARF (Plane)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 99px;\"\u003e\n \u003cp\u003eAdipose compartment model\u003c/p\u003e\n \u003cp\u003e(The present study)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 84px;\"\u003e\n \u003cp\u003ePRF\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 115px;\"\u003e\n \u003cp\u003ePosterior TAC\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 84px;\"\u003e\n \u003cp\u003eEPF\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 88px;\"\u003e\n \u003cp\u003ePeritoneum\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 103px;\"\u003e\n \u003cp\u003eLateral TAC\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 84px;\"\u003e\n \u003cp\u003eEPF\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 88px;\"\u003e\n \u003cp\u003ePeritoneum\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 103px;\"\u003e\n \u003cp\u003eAnterior TAC\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 84px;\"\u003e\n \u003cp\u003eARF\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003eARF, anterior renal fascia; EPF, extraperitoneal fascia; LCF, lateroconal fascia; PaRF, pararenal fat; PeRF, perirenal fat; PRF, posterior renal fascia; TAC, Thin adipose compartment.\u003c/p\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"hideJournal":true,"highlight":"","institution":"Institute of Science Tokyo","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"laparoscopic surgery, lateroconal fascia, pararenal fat, renal fascia, retroperitoneal space","lastPublishedDoi":"10.21203/rs.3.rs-7324278/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7324278/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003ch2\u003eObjectives\u003c/h2\u003e\u003cp\u003eTo anatomically and histologically define adipose and fascial structures posterior and lateral to the kidney and propose a compartment-based anatomical model aligned with intraoperative observations.\u003c/p\u003e\u003ch2\u003eMethods\u003c/h2\u003e\u003cp\u003eSeven cadavers were used for macroscopic and histological analyses. In the macroscopic analysis, the spatial relationships between the perirenal fat, pararenal fat, posterior renal fascia, and extraperitoneal fascia were examined. Histological observations focused on the distribution and continuity of adipose compartments and the organization of the surrounding dense fibrous connective tissues.\u003c/p\u003e\u003ch2\u003eResults\u003c/h2\u003e\u003cp\u003eMacroscopically, the extraperitoneal fascia covered the anteromedial pararenal fat and extended posteriorly to the kidney. Upon incision, a small amount of adipose tissue was observed directly beneath it. Removing this thin adipose layer exposes the peritoneum and posterior renal fascia, with a clear demarcation between them. Histological analysis confirmed that the posterior renal and extraperitoneal fascia were distinct, with dense connective tissue structures enclosing a separate, thin adipose compartment. This compartment extended anteriorly between the perirenal fat and peritoneum, and laterally between the peritoneum and extraperitoneal fascia. These extensions converge near the peritoneal reflection in the lateral renal region, forming the characteristic triradiate configuration of the adipose tissue.\u003c/p\u003e\u003ch2\u003eConclusions\u003c/h2\u003e\u003cp\u003eOur findings challenge the classical notion that the renal fascia is a single continuous layer supporting a compartment-centered anatomical model. The posterior and lateral regions of the kidney contain a distinct third adipose compartment bordered by the posterior renal and extraperitoneal fasciae. This model offers improved anatomical clarity and may aid understanding during laparoscopic, retroperitoneoscopic, and robot-assisted surgeries.\u003c/p\u003e","manuscriptTitle":"Anatomy of adipose compartments and fascial structures in the posterolateral region of the kidney with special focus on the thin adipose compartment","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-08-11 10:11:56","doi":"10.21203/rs.3.rs-7324278/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"a6b2f1ad-5d20-417a-8e8a-cf1a47eeb553","owner":[],"postedDate":"August 11th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[{"id":52853148,"name":"Urology \u0026 Nephrology"}],"tags":[],"updatedAt":"2025-08-11T10:11:56+00:00","versionOfRecord":[],"versionCreatedAt":"2025-08-11 10:11:56","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-7324278","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7324278","identity":"rs-7324278","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}