A Case Report of a Giant Mucinous Cystadenoma Suspected to Be Associated with Ovarian Remnant Syndrome After Bilateral Adnexectomy: Diagnostic Pitfalls and Implications for Clinical Management

The patient, a 65-year-old woman with a history of two vaginal deliveries and regular menstruation, underwent total abdominal hysterectomy in 2011 due to adenomyosis at a different hospital. In 2013, she had laparoscopic bilateral adnexectomy performed elsewhere for “bilateral hydrosalpinx”. Intraoperative findings revealed that the bilateral adnexectomy was adherent to the pelvic wall and wrapped into a mass. After dissecting the adhesions, the fallopian tubes were discovered to be flexed, resulting in bilateral fimbrial blind ends. Partial residual tissue remained in the left ovary, while the right ovary was atrophic. Postoperative pathology confirmed bilateral chronic salpingitis and corpora albicantia in both ovaries. The patient reported a 23-year history of hypertension treated with amlodipine besylate tablets at a dosage of 5mg daily. A history of smoking was denied, and there was no reported family history of hereditary conditions. Table 1 summarized the patient’s clinical and auxiliary examination characteristics. Table 1 Clinical and Para-Clinical Features of the Patient Category Data Age/Sex 65 years, female Obstetric history G2P2, 2 spontaneous vaginal deliveries Past gynecological surgical history 2011: total hysterectomy for uterine adenomyosis; 2013: bilateral adnexectomy for hydrosalpinx; menopause at age 50 Comorbidities Hypertension for 23 years Chief complaint Lower abdominal distension and difficult defecation for 1 month Physical examination (abdomen) An abdominopelvic mass of approx. 20×20 cm palpable, medium consistency, well-defined borders, limited mobility, no tenderness Tumor markers CEA 5.20 ng/mL; AFP, CA125, CA19-9, HE4, CA724 all within normal range Ultrasound Cystic mass 230×152×110 mm, dense spot-like echoes, band-like septations, no blood flow CT Cystic low-density mass 204×136×185 mm, septal and wall enhancement, no mural nodules; bilateral hydroureteronephrosis MRI Multilocular cystic mass 206×167×145 mm, mixed T1 signal, T2 hyperintense, diffuse DWI restriction; septal enhancement, no mural nodules Intraoperative findings Large abdominopelvic mass adherent to bowel and bladder; appendix grossly unremarkable Surgical procedure Tumor resection + adhesiolysis + ureteroscopy + ureteral stent placement Pathology and ascites cytology Ovarian mucinous cystadenoma; no atypical cells on ascites smear Clinical and Para-Clinical Features of the Patient By the end of March 2026, a 65-year-old female patient was admitted to the hospital with symptoms of lower abdominal distension and difficult defecation lasting over a month. Dyschezia began one month prior, with bowel movements occurring every 3–4 days, accompanied by significant abdominal distension, loss of appetite, and no weight loss. A palpable mass, measuring approximately 20 by 20 cm, was noted; it was of medium consistency, well-circumscribed, poorly mobile, and non-tender. Gynecological ultrasound revealed a cystic structure in the pelvic cavity measuring approximately 230 × 152 × 110 mm, exhibiting dense punctate echoes with band-like septa and no detectable blood flow. Contrast-enhanced computed tomography (CT) results ( Figure 1A and B ) indicated a large cystic low-density shadow in the abdomen and pelvis, approximately 204 × 136 × 185 mm in size, characterized by a smooth boundary, multiple septations, and wall enhancement. No significant enhancement was observed within the cyst, and no distinct wall nodules were identified. Surrounding structures appeared compressed and displaced, leading to consideration of a mucinous cystadenoma of adnexal origin. The uterus was not visualized, and mild hydronephrosis was noted in the bilateral renal pelvis and upper ureters. Figure 1 Computed tomography (ct) imaging of the tumor. Two CT pelvis images show bones and a central soft-tissue area; image has a red arrow. Notes : The computed tomography (CT) scan ( A ) showed a large low-density shadow in the abdominal and pelvic cavities. The largest dimension was approximately 204mm × 136mm × 185mm. The boundary was smooth, with multiple partitions inside (( A ) red arrow). The enhanced scan ( B ) revealed local linear high-density partitions with enhancement within the lesion, while the cystic part showed no enhancement. Computed tomography (ct) imaging of the tumor. Magnetic resonance imaging (MRI) findings ( Figure 2A–D ) further corroborated that the uterus was not visible, revealing a large polycystic mass in the abdominal and pelvic cavities. This mass exhibited mixed signals on T1-weighted imaging (T1WI), high signals on T2-weighted imaging (T2WI), and no diffusion restriction on diffusion-weighted imaging (DWI). The mass measured approximately 206 × 167 x 145 mm, with defined borders and visible septations. Enhanced MRI showed that the septations were enhanced with no internal enhancement within the cyst, and there was no significant thickening of the wall or nodular formations. No markedly enlarged lymph nodes were present in the pelvic cavity. Carcinoembryonic antigen (CEA) levels were recorded at 5.20 ng/mL, while alpha-fetoprotein (AFP), cancer antigen 125 (CA125), cancer antigen 199 (CA199), human epididymis protein 4 (HE-4), and cancer antigen 724 (CA724) remained within normal ranges. Blood routine, liver function, and kidney function tests also yielded normal results. Urinalysis showed occult blood (+), a white blood cell count of 150.0/μL, and a red blood cell count of 20.0/μL. Figure 2 Magnetic resonance imaging (MRI) imaging of the tumor. Five MRI images show a large polycystic mass in abdomen and pelvis with mixed signals, defined borders. Notes : The magnetic resonance imaging (MRI) scan revealed multiple compartments within the tumor, with dimensions approximately 206 × 167 × 145 mm ( A ). The cyst wall and septa were relatively thin (red arrow); the contents within the cyst showed mixed high and low signals on T1-weighted Imaging (T1WI) ( A ), high signal on DWI, and no signal drop on ADC maps, indicating the absence of restricted diffusion ( B and C ). Enhanced scan showed the cyst wall with a separated-like enhancement, while no significant enhancement was observed within the cyst ( D and E ). Magnetic resonance imaging (MRI) imaging of the tumor. In April 2026, the patient underwent pelvic tumor resection, intestinal adhesion lysis, ureteroscopy, and ureteral stent implantation. The results of intraoperative exploration revealed a massive tumoral mass in the pelvis and abdomen, covered with intestinal loops, and adherent at the lower end to the bladder. Gradual blunt dissection was performed to separate the bowel and bladder adhesions, allowing for downward retraction of the bladder to expose the tumor’s surface. Following meticulous identification of blood vessels, a 9-gauge needle was inserted to decompress the mass, resulting in the slow release of approximately 2000 mL of dark brown gelatinous viscous fluid. During this procedure, the intestinal loops were progressively separated, revealing a cystic mass measuring 8 × 6 x 6 cm located in the right lateral wall of the pelvic cavity, which was compressing the right ureter. The right ureter was carefully dissociated and retracted, facilitating further separation of the intestinal and bladder adhesions along the lateral wall. Additionally, cystic masses measuring 10 × 8 x 8 cm, 6 × 5 × 5 cm, and 4 × 4 × 3 cm were identified on the surfaces of the left pelvic wall peritoneum and pelvic floor peritoneum, closely adhering to the left ureter, which was subsequently separated and dissociated. Complete dissection of both sides of the pelvic wall was performed, and the pelvic floor peritoneum was dissected from the sacrococcygeal region to the top of the vagina. Ultimately, the entire pelvic mass was resected in a carpet-like manner. The appendix appeared normal upon intraoperative examination. Rapid intraoperative pathology and routine postoperative pathology confirmed the diagnosis of ovarian mucinous cystadenoma ( Figure 3A–D ). No atypical cells were detected in the ascitic fluid smear. One week postoperatively, CEA levels returned to normal. Figure 3 Histological examination of the tumor. Micrograph of four H&E stained sections (A-D) showing folded glandular mucosa with pink stroma and pale spaces. Notes : ( A and B ) (Hematoxylin and eosin stain, ×100): Multiple cystic spaces were identified within ovarian stroma, lined by mucinous epithelial cells. ( C ) (Hematoxylin and eosin stain, ×200): The cysts were lined by a single layer of mucinous epithelium resembling gastric foveolar epithelium or goblet cell-containing intestinal epithelium. The nuclei were basally located with bland cytomorphology and no significant atypia. The red arrow indicated papillary structures. ( D ) (Hematoxylin and eosin stain, ×400): High-power view demonstrated the detailed features of the single-layered mucinous epithelium lining the cyst wall. Histological examination of the tumor.

Ovarian mucinous cystadenoma is among the most common benign ovarian tumors, with a peak incidence occurring between the ages of 30 and 50, accounting for 20–25% of benign ovarian tumors, second only to serous cystadenoma. 1 It typically presents with slow growth and a favorable prognosis. Unlike conventional cases, de novo giant ovarian mucinous cystadenoma arising in the pelvic cavity following bilateral adnexectomy is rare. There remains controversy regarding its lesion origin, differential diagnosis and clinical management, and it is highly susceptible to clinical misdiagnosis. Ovarian remnant syndrome (ORS) comprises syndromes characterized by the presence of functional ovarian tissue in the pelvic cavity following bilateral oophorectomy, leading to clinical manifestations such as pelvic pain or mass. 2 This syndrome has a low clinical incidence and is not a common complication of ovarian surgery; it mostly occurs secondary to technically demanding pelvic procedures. Previous studies have reported that pelvic adhesions, pelvic endometriosis, chronic pelvic inflammatory disease, and a history of multiple pelvic surgeries constitute the major high-risk factors predisposing to ORS. 3 Notably, residual ovarian tissue is not always histologically stable. Under persistent hormonal stimulation and alterations in the pelvic microenvironment, these residual tissues carry a rare but clinically significant risk of neoplastic transformation, which may lead to secondary benign or even malignant ovarian neoplasms. Compared with conventional primary ovarian mucinous cystadenomas, ORS-associated pelvic mucinous lesions pose substantial diagnostic challenges and entail a more complicated differential diagnosis. On the one hand, the origin of giant pelvic mucinous masses is difficult to define, requiring differentiation between mucinous neoplasms derived from residual ovarian tissue and metastatic mucinous lesions of gastrointestinal or appendiceal origin. Given the distinct therapeutic strategies and long-term prognoses among these entities, misdiagnosis may adversely affect clinical decision-making. On the other hand, such pelvic masses should also be differentiated from giant mature ovarian cystic teratomas. Although typically benign, mature teratomas exhibit overlapping imaging features with giant ovarian mucinous cystadenomas. Both present as large, well-circumscribed, multiloculated pelvic or abdominal cystic lesions with fibrous septa and high-protein cystic fluid, showing higher CT attenuation than simple water-filled cysts and homogeneous hyperintense signals on T1WI and T2WI, with visible cyst walls and septa. 4 , 5 Furthermore, a subset of mature cystic teratomas may be associated with mucinous neoplasms. 6 These teratoma-associated mucinous tumors share morphological and immunohistochemical similarities with lower gastrointestinal-type mucinous neoplasms, necessitating careful discrimination from metastatic mucinous lesions. 6 At present, case reports of giant mucinous cystadenoma associated with ovarian remnant syndrome following bilateral adnexectomy are scarce globally, and there are no systematic clinical summaries or unified diagnostic and therapeutic consensus. In this article, we present a case of ORS-related giant mucinous cystadenoma after total hysterectomy combined with bilateral adnexectomy, perform a systematic review of relevant domestic and international literature, and summarize the clinical features, pathological mechanisms, key differential points and comprehensive therapeutic strategies of this disease. This study aims to supplement clinical data of such rare cases and provide references for standardized diagnosis and management of similar difficult cases.

This case reported the diagnosis and management of a giant pelvic mucinous cystadenoma in a patient who had previously undergone total hysterectomy combined with bilateral adnexectomy. Our findings emphasized that ovarian remnant syndrome (ORS) should be included in the differential diagnosis of pelvic masses occurring after bilateral oophorectomy. For patients who underwent technically challenging primary pelvic surgery, review of prior operative records was critical for determining the origin of newly developed postoperative pelvic masses. Once a pelvic mucinous lesion was identified, gastrointestinal and appendiceal tumors should be meticulously excluded before a definitive diagnosis was established, and thorough pathological evaluation was mandatory rather than arbitrarily attributing the lesion to an ovarian origin. Although microscopic examination identified ovarian stroma and confirmed the presence of residual ovarian tissue in this case, the origin of the mucinous epithelium remained indeterminate, and occult appendiceal mucinous lesions could not be completely ruled out. This study provides two important clinical implications. First, complete resection of ovarian tissue should be performed during bilateral adnexectomy to minimize the long-term risk of ORS and secondary neoplasms. Second, targeted clinical evaluation is warranted for patients with new symptoms or newly detected pelvic masses after adnexectomy to screen for lesions associated with residual ovarian tissue.

Ovarian mucinous cystadenoma is a benign ovarian epithelial neoplasm lined by mucin-secreting epithelium, 7 which may differentiate into endocervical-type or gastrointestinal-type mucinous epithelium. This tumor has substantial growth potential and often presents as a giant multilocular cystic mass, resulting in abdominal distension and compressive symptoms of adjacent tissues. 8 The uniqueness of the present case lies in the patient’s history of total hysterectomy combined with bilateral adnexectomy. A giant pelvic mucinous cystic mass developed years after the surgery, posing substantial diagnostic challenges for this condition. Combined with the patient’s surgical history, pathological type of the lesion and clinical features, the lesion in this case is highly suspected to be an ovarian mucinous cystadenoma associated with ovarian remnant syndrome, which is considered to arise from ovarian tissue left behind during bilateral adnexectomy. The pathological basis of ORS is that pelvic adhesions secondary to endometriosis, pelvic inflammatory disease or multiple pelvic surgeries hinder surgical dissection during bilateral oophorectomy, leaving fragments of ovarian cortex on the pelvic peritoneal surface. These detached tissues, lacking a primary blood supply, can undergo necrosis, cystic transformation, or neoplastic changes while potentially retaining functional activity. Shemwell and Weed established in 1970, through animal models, that remaining ovarian tissue could remain viable even with interrupted blood supply. 9 The most frequent clinical manifestation of ORS includes lower abdominal pain associated with pelvic masses. 2 Diagnostic criteria 10 consist of: (1) a history of bilateral ovarian resection; (2) absence of estrogen replacement therapy, with serum estradiol (E2) and follicle-stimulating hormone (FSH) levels at pre-menopausal ranges; (3) confirmation of ovarian tissue presence in the pelvic cavity through surgical exploration and histological examination. It is important to highlight that although this case can be clinically considered an ovarian mucinous cystadenoma associated with ovarian remnant syndrome, there are inherent limitations in distinguishing the tissue origin of the lesion, and a definitive conclusion cannot be drawn solely based on clinical and imaging findings. Although the appendix showed no abnormalities on preoperative CT and intraoperative gross examination, radiological and macroscopic evaluation could not rule out the possibility of an occult appendiceal mucinous lesion. Meanwhile, appendectomy and histopathological examination of the appendix were not performed intraoperatively, and no origin-determining immunohistochemical markers were assessed. Therefore, an appendiceal mucinous neoplasm could not be completely excluded, which constitutes the key limitation precluding definitive confirmation of the lesion’s origin. In terms of auxiliary examinations, the imaging manifestations of ovarian mucinous cystadenoma secondary to ovarian remnant syndrome (ORS) are similar to those of primary ovarian mucinous cystadenoma. CT and MRI can demonstrate multilocular cystic lesions, enhancement of the cyst wall and septa, and variable density or signal intensity of cystic fluid. However, these imaging features lack tissue-specificity and cannot effectively differentiate lesions arising from residual ovarian tissue from those of gastrointestinal or appendiceal origin. Histopathology constitutes the core basis for diagnosing ovarian mucinous neoplasms. 8 Microscopically, ovarian stroma was identified, containing multiple cysts lined by a single layer of mucinous epithelium. The epithelium resembled gastric foveolar epithelium or intestinal epithelium with goblet cells, featuring basally situated nuclei, bland cytomorphology, absence of cellular atypia and mitotic figures, and focal simple papillary structures. These morphological features were consistent with ovarian mucinous cystadenoma. Detection of ovarian stroma surrounding the lesion indicated a close relationship with residual ovarian tissue following bilateral adnexectomy, providing morphological support for an ORS-associated lesion. Nevertheless, gastrointestinal and intestinal-type mucinous epithelium are not specific markers of ovarian origin; low-grade appendiceal mucinous neoplasms, for instance, may display similar morphology. Routine HE staining alone cannot reliably determine tissue origin, and origin-tracing immunohistochemical markers are required for differential diagnosis. Immunohistochemistry was not performed in this case, and the appendix was only examined grossly without resection and histologic submission. Therefore, the lesion is only highly suspected to be an ORS-related ovarian mucinous cystadenoma. Occult appendiceal mucinous lesions cannot be completely excluded, and an ovarian primary origin cannot be definitively confirmed. The differential diagnosis in this case is complicated by the absence of clear ovarian structures within the pelvic cystic mass, necessitating clarification of the tumor’s origin—whether from residual ovarian tissue, the primary peritoneum, or gastrointestinal metastasis. During the patient’s bilateral salpingo-oophorectomy in 2013, significant pelvic adhesions and partial residual left ovarian tissue were documented, providing key clinical indicators regarding the primary origin of the tumor. However, intraoperative exploration involved only appendiceal inspection without appendectomy, and postoperative immunohistochemical staining was not performed. Accordingly, the origin of the lesion can only be prudently differentiated based on imaging manifestations, intraoperative findings, and routine morphological features. Occult mucinous lesions of gastrointestinal or appendiceal origin cannot be entirely excluded. Firstly, low-grade appendiceal mucinous neoplasm (LAMN) and pseudomyxoma peritonei (PMP) need to be excluded. Low-grade appendiceal mucinous neoplasms (LAMN) typically lack infiltrative invasion, but may be complicated by appendiceal rupture, extraappendiceal mucin, and cellular dissemination, and represent one of the common sources of PMP. 11 PMP is characterized by the accumulation of substantial amounts of jelly-like mucus within the abdominal cavity, leading to peritoneal implantation. PMP is not classified as a true tumor; rather, it is a progressive space-occupying lesion that forms as a result of the implantation of mucin-secreting cells within the peritoneal cavity. 12 The appendix is the most common primary site for PMP (due to epithelial perforation), while occurrences originating from the ovaries are considered extremely rare. 12 Immunohistochemistry plays a vital role in determining the primary origin; typical appendiceal tumors express cytokeratin 20 (+), caudal type homeobox 2 (+), with cytokeratin 7 (−) and paired box gene 8 (−). In contrast, most primary ovarian tumors show cytokeratin 7 (+) and paired box gene 8 (+). 13 Preoperative contrast-enhanced CT in this case displayed multilocular cystic lesions in the pelvis, with thin-slice reconstruction of the appendix showing no abnormalities such as luminal dilation, cyst wall calcification, or soft tissue thickening. Intraoperative thorough abdominal exploration identified a grossly normal appendix and a pelvic cystic lesion with an intact capsule. No gelatinous mucinous accumulation or peritoneal mucinous implantation, the hallmark features of PMP, was detected. Postoperative pathological examination showed that the cyst wall was lined by a single layer of benign mucinous columnar epithelium with adenomatous expansile growth. No malignant invasive findings, such as pushing-border invasion or cellular budding, were observed. Furthermore, no mucinous epithelial cells were found in the peritoneal lavage fluid. Collectively, these clinical, radiological, and morphological results rendered the diagnoses of LAMN and PMP highly unlikely. Notably, neither complete appendectomy with full-length histological evaluation nor specific immunohistochemical staining (CK7, PAX8, CK20, CDX2) was performed in the present case. Accordingly, tiny, early-stage occult appendiceal mucinous lesions cannot be completely ruled out. This diagnostic uncertainty remains throughout the differential diagnosis and represents one of the major limitations of this study. Furthermore, benign polycystic peritoneal mesothelioma (BMPM) can be distinctly differentiated based on the characteristics of the cystic fluid and microscopic morphology. BMPM typically presents as multiple “grape bunch-like” thin-walled cysts filled with clear serous fluid within the pelvic peritoneum. Microscopic examination reveals numerous small cystic cavities lined by a single layer of cuboidal or flat mesothelial cells. Immunohistochemistry for BMPM typically shows positivity for calretinin, aiding in differentiation from vascular or enterogenous cysts. 14 However, the cyst fluid in our case was thick and gelatinous. Microscopically, the cyst wall was lined by a single layer of mucinous epithelium resembling gastric foveolar epithelium or goblet cell-containing intestinal epithelium, with no evidence of mesothelial differentiation, rendering BMPM unlikely. In addition, occult metastatic mucinous adenocarcinoma arising from the appendix, colorectum, stomach or pancreas requires exclusion. Metastatic carcinoma was considered unlikely for the following three reasons: (1) Preoperative thin-slice CT reconstruction of the appendix revealed no abnormalities; (2) Comprehensive intraoperative exploration of the liver, gallbladder, pancreas, stomach and colorectum identified no serosal implants or parenchymal masses; (3) Postoperative microscopic examination showed the cyst wall lined by a single layer of benign mucinous columnar epithelium lacking cellular atypia, with simple adenomatous expansile growth instead of destructive invasion. Meanwhile, the absence of urinary symptoms including renal colic and hematuria, together with preserved ureteral architecture on imaging, ruled out a ureteral lesion. Intraoperative exploration confirmed no anatomical continuity between the lesion and the mesentery; furthermore, the cyst content was mucinous rather than serous, excluding a mesenteric cyst. Following this multi-faceted differential diagnosis, together with intraoperative gross observations and postoperative routine morphological features, the lesion is highly suspected to represent an ovarian mucinous cystadenoma secondary to ORS. Objectively, however, supportive ovarian-specific immunohistochemical markers such as CK7 and PAX8 were not available, and no molecular immunophenotypic data could definitively assign the tissue origin. This diagnosis is inferred exclusively from clinical, radiological and routine pathological findings and fails to satisfy criteria for histologic confirmation; definitive proof of ovarian origin cannot be obtained. Moreover, the coexistence of ovarian neoplasms and autoimmune encephalitis deserves attention. Pham et al reported a 39-year-old female patient with anti-N-methyl-D-aspartate receptor (anti-NMDAR) encephalitis associated with an ovarian tumour. After excluding alternative aetiologies, laparoscopic resection of the pelvic mass was undertaken, and histopathology confirmed ovarian teratoma. 15 The patient made a full neurological recovery two months after treatment. 15 That report noted that anti-NMDAR encephalitis is a rare subtype of autoimmune encephalitis and is frequently associated with ovarian teratoma. Nonetheless, Cho et al published the first case of anti-NMDAR encephalitis associated with ovarian mucinous cystadenoma in 2019. 16 The patient achieved complete resolution of neurological symptoms after laparoscopic lesion resection plus immunotherapy, broadening the spectrum of ovarian neoplasms implicated in this paraneoplastic syndrome. 16 Clinically, prompt anti-NMDAR antibody screening should be performed in patients with pelvic masses and unexplained neuropsychiatric manifestations to facilitate early intervention and improve prognosis. Adhering to the principles of standardized treatment for ovarian tumors, surgery combined with rapid intraoperative pathological assessment remains the gold standard for diagnosing and managing tumors associated with ORS. 17 For large-volume tumors with a high suspicion of malignancy, open laparotomy is often the preferred method in clinical practice. However, laparoscopic surgery offers advantages, including faster postoperative recovery and a lower incidence of complications, which has led to its increased use in the resection of substantial ovarian tumors. Notably, incomplete surgical resection, tumor rupture, or cyst fluid leakage during the procedure significantly heightens the risk of tumor recurrence and peritoneal implantation metastasis. 5 , 18 Therefore, regardless of the surgical approach taken, ensuring complete removal of the lesion and preventing cyst fluid leakage is critical. 5 , 18 Such surgeries frequently present considerable challenges and often necessitate extensive dissections, including ureteral release and peritoneal resection, as well as combined organ resections involving partial bladder, vaginal, or intestinal resections. As such, meticulous preoperative planning is essential, and collaboration with relevant departments such as colorectal surgery and urology is advisable. In this particular case, cysts were multicentrically distributed at the pelvic floor peritoneum and sacrococcygeal level, accompanied by severe pelvic adhesions. To achieve complete resection, a “carpet-rolling” peritonectomy was performed. Dissection extended from the sacrococcygeal level along the pelvic floor peritoneum to the vaginal apex for en bloc stripping. This anatomical space was notably narrow, bordered posteriorly by the rectum and ureters and anteriorly by the urinary bladder; thus, even minor deviations during the operation could lead to iatrogenic injuries to adjacent viscera. Throughout the dissection, moderate tissue tension was maintained, advancing closely along the extraperitoneal space to ensure negative surgical margins while safeguarding surrounding organs. Ultimately, the multiloculated cysts and the involved peritoneum were removed en bloc. Moreover, Casarin et al 19 demonstrated that for adnexal masses with diameters of ≥10 cm, the cyst fluid overflow rate during laparoscopic surgery exceeded 50%, with the risk of cyst rupture approximately four times higher than during open laparotomy. This disparity may stem from the controlled cyst puncture and aspiration utilized to enhance surgical visibility. Therefore, for laparoscopic resection of large tumors, standardized cyst puncture and drainage to prevent uncontrolled rupture and cyst fluid leakage are critically important. 20 In the present case, the huge pelvic and abdominal mass was densely adherent to the bowel and urinary bladder. It occupied the entire surgical field, leaving no sufficient operative space for direct complete enucleation. Forcible blunt dissection carries a high risk of spontaneous irregular rupture of the mass, injury to adjacent viscera and massive hemorrhage, which may further result in uncontrolled dissemination of cyst fluid. Given that preoperative imaging and tumor marker workup revealed no definitive malignant features, occult malignancy could not be entirely excluded. Standardized controlled puncture decompression was performed in the present case. Intraoperatively, a 9-gauge fine needle was used to puncture precisely an avascular, protruding safe region of the mass. The whole maneuver was carried out within a sealed operative view. Sterile gauze was tightly packed around the puncture site to establish a confined drainage compartment. Following puncture, approximately 2000 mL of dark brown gelatinous cyst fluid was aspirated gently and released at a constant rate. There was no abrupt rapid evacuation of fluid, laceration of the puncture tract, cyst fluid extravasation, or intraperitoneal dissemination during the procedure. This standardized controlled puncture technique, featuring targeted puncture, barrier protection and gradual decompression, aids in avoiding intraoperative visceral injury and improving surgical exposure while lowering the risks of cyst fluid leakage and intraperitoneal tumor cell implantation. Clinical studies have also confirmed that purse-string sutures, Kelly clamps, or surgical clamps can effectively mitigate puncture-related cyst fluid extravasation in large adnexal masses. 21 For massively adherent, voluminous adnexal masses not amenable to primary enucleation and with preoperative uncertainty regarding malignancy, selective, standardized, controlled intraoperative puncture decompression constitutes a safe and necessary strategy. It substantially lowers the likelihood of spontaneous rupture and enables subsequent complete mass resection; this approach aligns better with the safety principles of minimally invasive surgery than blind dissection. 20 Meanwhile, slow decompression and gentle tumor resection are recommended intraoperatively, with continuous vital sign monitoring and individualized fluid management to prevent rare complications including hemodynamic instability and reexpansion pulmonary edema triggered by an abrupt decrease in intra-abdominal pressure. 22 , 23 The separation of severe dense pelvic adhesions represented a key technical challenge during this operation. Intraoperative exploration revealed that the mass was obscured by intestinal loops, with its inferior portion adhering tightly to the urinary bladder due to significant tissue fibrosis, making anatomical planes difficult to identify. To navigate this, this study employed a meticulous approach, patiently searching for relatively avascular planes between the intestinal serosa and the cyst wall. We progressed stepwise using a combination of blunt and sharp dissection, balancing the efficiency of adhesiolysis with the need to preserve intestinal integrity. Strict precautions were taken to prevent seromuscular laceration of the bowel, which could lead to postoperative enterocutaneous fistula formation. For the adhesions related to the bladder, dissection was performed close to the cyst wall to avoid inadvertent penetration into the bladder muscularis. The bladder was mobilized downward until sufficient free margins were identified to facilitate the en bloc resection of the mass. Identifying, mobilizing, and protecting the bilateral ureters posed another significant challenge. Preoperative imaging indicated compression of the right ureter, accompanied by hydronephrosis. This was confirmed intraoperatively, showing that the right ureter was compressed by the cyst, while the left ureter was stretched and closely adherent to the cyst wall. Dense adhesive scar tissue further complicated the situation, obscuring the normal peristalsis and color of the ureters and making gross visual identification exceedingly difficult. To address these challenges, ureteroscopy and ureteral stent placement were included in the preoperative plan. The stents provided structural support, which allowed for clearer palpation and identification of the ureteral course during surgery. This individualized, multidisciplinary collaborative strategy not only facilitated the safe mobilization of the ureters but also demonstrated the importance of prospective planning aimed at preserving adjacent organ function and avoiding iatrogenic injuries when managing complex pelvic masses. The case provided significant clinical insights into effective patient management strategies. This case presents a giant mucinous cystadenoma associated with ORS that developed years after bilateral adnexectomy, a remarkably rare clinical entity. The clinical significance of reporting this case lies in three main aspects. First, it increases awareness among clinicians regarding ORS and its potential long-term complications, including the risk of neoplastic development. It serves as a reminder that practitioners should not dismiss the possibility of tumors originating from adnexal tissues simply because of a prior history of adnexal resection. Second, this case underscores the importance of thoroughly reviewing previous surgical records, combined with precise preoperative evaluation through imaging modalities—especially MRI—and appropriate tumor markers for patients with complex pelvic surgical histories. Detailed assessments can help identify potential issues that may arise due to retained ovarian tissue. Third, surgeons should aim for en bloc resection of all ovarian tissues while meticulously preventing cyst fluid spillage to reduce recurrence risks. Care must be taken to avoid adjacent visceral injuries during the procedure. Complete removal of ovarian tissue, along with clear operative documentation during the initial adnexectomy, is particularly critical. A study by Fennimore et al demonstrated that ovarian stroma could microscopically extend into the infundibulopelvic ligament by 0.2–1.4 cm beyond the grossly visible margin. 24 Based on this anatomical finding, some scholars have proposed ligation of the infundibulopelvic ligament at least 2 cm proximal to the gross ovarian margin. 24 This technical strategy can be considered to reduce the risk of ovarian remnant syndrome and secondary tumor formation. 24 Therefore, the treatment and prevention of ORS should adhere to fundamental surgical principles, which include high ligation of the infundibulopelvic ligament, dissection of the retroperitoneal space, and complete excision of all peritoneal and ovarian adhesive tissues. 25 Additionally, it is noteworthy that the 2024 position statement from the International Federation of Gynecology and Obstetrics (FIGO) recommends concurrent opportunistic salpingectomy for women who have completed childbearing, have no further fertility requirements, and undergo abdominopelvic surgery for other benign conditions (eg, hysterectomy, cesarean delivery, cholecystectomy), as a primary preventive measure for tubal-origin high-grade serous ovarian carcinoma. 26 In the present case, the patient was a 50-year-old perimenopausal woman who had undergone total hysterectomy for adenomyosis at an outside hospital. From an oncologic prevention perspective, concurrent opportunistic salpingectomy could have been considered at that time to reduce the subsequent risk of tubal-origin high-grade serous carcinoma. However, ovarian remnant syndrome results from residual ovarian tissue. Reducing the risk of ORS requires complete resection of ovarian tissue rather than salpingectomy alone. This report has certain limitations. On one hand, molecular genetic or immunohistochemical tracing of residual ovarian tissue from the initial surgery and the current tumor was not performed, preventing absolute confirmation of homology. On the other hand, despite the normal appearance of the appendix during the operation, it was not removed for histological examination, which means the possibility of an occult appendiceal mucinous tumor could not be ruled out. Such factors somewhat limit the strength of the evidence presented. Finally, to systematically delineate the disease spectrum of ORS, we searched for ORS-related case reports following bilateral adnexectomy published over the past decade (from 2016 to present). We comprehensively summarized the clinical data of the enrolled cases, including surgical background, disease interval, lesion characteristics, pathological types, diagnostic basis, and follow-up information, as detailed in Table 2 . The literature review revealed diverse pathological types of secondary tumors arising from ORS, including endometriosis, serous cystadenoma, clear cell carcinoma, borderline ovarian endometrioid cystic fibroma, and ovarian endometrioid carcinoma. Notably, cases of pure ORS complicated with mucinous cystadenoma are extremely rare. All of the documented cases were characterized by a history of pelvic adhesions and difficult initial pelvic surgery, with lesions developing several years after bilateral adnexectomy. Consistent with most previously reported cases, the present case shared the diagnostic challenge of tissue origin tracing. Although microscopic examination confirmed the presence of residual ovarian stroma, HE staining alone was insufficient to definitively distinguish whether the mucinous epithelium was of ovarian or appendiceal origin. This finding reflects the common diagnostic dilemma encountered in cases of ORS combined with mucinous cystic lesions. Table 2 Summary of Published Neoplastic Cases Associated with Ovarian Remnant Syndrome (ORS), 2016–2026 No. First Author, Year Age (Years) Initial Surgery and Indication Interval from Initial Surgery to ORS Diagnosis Clinical Manifestations Imaging/Tumor Markers Lesion Size Pathological Findings Management Follow-Up/Outcome 1 Gupta Ret al, 2016 3 56 Bilateral salpingo-oophorectomy (BSO); indication not specified Not described Persistent nausea, vomiting, abdominal pain, presentation of acute intestinal obstruction CT: abdominal distension, irregular soft-tissue mass near the sharp angle of small bowel stricture Not described Ovarian tissue identified in small mesenteric nodules (non-neoplastic) Exploratory laparotomy; adhesiolysis for ascites, small bowel distension and near-complete intestinal obstruction; resection of small bowel mesenteric nodules Postoperative relief of intestinal obstruction, good recovery 2 Chan TL et al, 2017 27 44 Total hysterectomy + BSO (for endometriosis); previous adhesiolysis and attempted resection of residual left ovarian tissue Not described (after multiple reoperations) Chronic, persistent left pelvic pain CT: soft-tissue mass at the site of previous left oophorectomy, volume approx. 12.5 cc Approx. 12.5 cc No surgical resection; pathology not available (NA) Ovarian artery embolization (after failure of medical and gynecological treatment) Residual tissue volume decreased markedly to 3.2 cc at 4 months post-procedure; symptoms nearly resolved 3 Wei M et al, 2019 28 32 Laparoscopic assisted vaginal hysterectomy + BSO (prophylactic resection for BRCA2 pathogenic variant and stage IIIc positive invasive ductal breast cancer) Not described Menopausal symptoms; elevated serum estradiol (226 pg/mL) MRI: complex mass 2.5×3.1×3.8 cm in right adnexa; cyst 1.4×1.3 cm in left adnexa Maximum 3.8 cm on the right Ovarian parenchymal tissue in the right ovarian remnant; simple cyst on the left Laparoscopic excision of ovarian remnant tissue Uneventful postoperative recovery, hormone levels normalized 4 Tien CT et al, 2022 29 73 Transabdominal total hysterectomy + BSO (for uterine fibroids) 30 years Chronic lower abdominal pain for 3 years Transabdominal ultrasound: cystic lesion 5.3×3.3 cm in lower abdomen; CT: multiple cystic masses in mesentery; CA125 70.4 U/mL, CEA 3.5 ng/mL (mild elevation) 5×3 cm Ovarian serous cystadenofibroma Laparoscopic single-port surgery + adhesiolysis + tumor resection (repair of small bowel serosal laceration); a smooth serosal cyst measuring approx. 5×3 cm adherent to anterior abdominal wall was noted intraoperatively Discharged 2 days after surgery, uncomplicated and smooth recovery 5 Wills E et al, 2022 30 68 Total hysterectomy + BSO; indication unknown Not described Abdominal pain CT: multiple pelvic masses, maximum 16.1×15.1×12.1 cm Maximum 16.1 cm Serous cystadenomas, multiple, consistent with ovarian origin Exploratory laparotomy + mass resection (5 pelvic masses and multiple mesenteric masses identified intraoperatively) Good postoperative recovery 6 Xiao P et al, 2023 31 69 Prophylactic hysterectomy and bilateral salpingo-oophorectomy (history of ovarian endometriotic cyst and breast cancer) 2 years Asymptomatic; distal vaginal mass detected on routine surveillance TVS: septated cystic mass 3.7×3.3×3.9 cm at distal vagina, with mildly enhanced wall echo; CA125, CA199 and CEA within normal limits 3.7 cm Borderline endometrioid cystic fibroma Exploratory laparoscopy + mass resection + omentectomy; a bulging lesion at the left vaginal stump filled with thick yellowish-brown fluid; papillary protrusions about 2 cm attached to the cyst wall Chemotherapy commenced 3 weeks postoperatively with regular surveillance 7 Yao TT et al, 2023 32 47 Unilateral salpingo-oophorectomy; indication not specified; note: non-classic BSO, unilateral resection before ORS 19 years Chronic lower abdominal pain for 6 months CT: round soft-tissue mass 46×40 mm within uterine wall; CA125 181.4 U/mL, SCC 1.5 ng/mL 50×40×30 mm (specimen) Clear cell carcinoma Re-do total hysterectomy + left adnexectomy + omentectomy + appendectomy + pelvic and para-aortic lymphadenectomy; pale yellow nodular mass approx. 50×40×30 mm identified in the right parametrium intraoperatively Six cycles of postoperative chemotherapy; normal findings at 3-year follow-up 8 Colombi I et al, 2025 2 65 Laparoscopic BSO (for left serous cystadenoma 7 cm; dense adhesions between colon and left adnexa noted intraoperatively, uterus deviated leftward) 6 years (diagnosed malignant in 2021 after initial surgery in 2015) Pelvic discomfort starting in 2017; progressive enlargement of pelvic mass thereafter Serial TVS: 71×49×62 mm solid tumor in left Douglas pouch in 2017; multi-loculated cystic lesion 80×62 mm posterior to uterus in 2020 with rich blood flow on color Doppler (color score 2–3) Final size 80×62 mm Final diagnosis: endometrioid ovarian carcinoma; misdiagnosed as endometriotic cyst with hemosiderin deposition at an intermediate stage Radical total hysterectomy + omentectomy + pelvic lymphadenectomy + segmental bowel resection (discoid resection) + ureteral reimplantation No ovarian carcinoma recurrence after surgery, no adjuvant chemotherapy 9 Colombi I et al, 2025 2 67 Open left oophorectomy (for dermoid cyst in 1989); note: unilateral oophorectomy, non-BSO 35 years Left iliac fossa pain, lower abdominal distension, rectal compressive symptoms MRI: multi-loculated cystic lesion 6.5 cm in rectouterine pouch with mild heterogeneous enhancement after contrast; solid component 42×63 mm with arterial blood supply (color score 2); spontaneous shrinkage to 2 cm on follow-up TVS in 2024 6.5 cm (spontaneously decreased to 2 cm) Right ovary: serous cystadenoma; rectouterine pouch: ovarian parenchymal fragments with recent hemorrhage and simple cyst (functional, non-neoplastic) Laparoscopic right oophorectomy + resection of rectouterine pouch mass + pelvic irrigation Normal adnexal ultrasound postoperatively, no further intervention required, regular follow-up 10 Colombi I et al, 2025 2 52 Laparoscopic right adnexectomy + left salpingectomy (for 8 cm right ovarian cyst; dense adhesions between right ovary and uterosacral ligaments and anterior rectum noted intraoperatively) Approx. 6 months Asymptomatic; detected on routine surveillance Postoperative TVS at 6 months: residual ovarian tissue in right adnexa with viable ovarian tissue; additional deep rectouterine endometriotic lesions Residual tissue approx. 2 cm Ovarian tissue with focal endometriosis (non-neoplastic) Close ultrasound surveillance; no surgery while asymptomatic Asymptomatic, under surveillance Summary of Published Neoplastic Cases Associated with Ovarian Remnant Syndrome (ORS), 2016–2026