Intraoperative Indocyanine Green Fluorescence in Canine Meningioma: Macroscopic Visualization, Immediate MRI Verification, and Clinical Outcomes: A Case Series

Intraoperative Indocyanine Green Fluorescence in Canine Meningioma: Macroscopic Visualization, Immediate MRI Verification, and Clinical Outcomes: A Case Series | 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 Case Report Intraoperative Indocyanine Green Fluorescence in Canine Meningioma: Macroscopic Visualization, Immediate MRI Verification, and Clinical Outcomes: A Case Series Youngbeum Kim, Yongsun Kim, Hwi-Yool Kim This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-9301046/v1 This work is licensed under a CC BY 4.0 License Status: Under Revision Version 1 posted 9 You are reading this latest preprint version Abstract Background Meningioma is the most common primary intracranial neoplasm in dogs, frequently presenting with seizures and neurological deficits. While indocyanine green (ICG) near-infrared (NIR) fluorescence is increasingly used in human neurosurgery, systematic data regarding its macroscopic expression in canine meningioma remain scarce. This case series aimed to evaluate the qualitative macroscopic expression of ICG, verify intraoperative findings using exceptionally early immediate post-operative contrast-enhanced magnetic resonance imaging (MRI), and report the clinical outcomes and complication management following fluorescence-guided surgery (FGS). Case presentation: Six client-owned dogs (median age: 13 years) with histologically confirmed meningiomas were evaluated. ICG was administered intravenously (median dose: 4.46 mg/kg) 6 to 24 hours prior to surgery. FGS was performed using an ultrasonic aspirator and a dedicated fluorescence imaging system. Distinct index-margin fluorescence was observed in all 6 cases (100%), allowing for real-time differentiation between tumor tissue and normal brain parenchyma during resection. Immediate post-operative T1-weighted contrast-enhanced MRI demonstrated 100% concordance with intraoperative wound bed fluorescence assessments when thin reactive rims (≤ 1–2 mm) were appropriately excluded. No adverse reactions were associated with ICG. The median follow-up was 6.25 months (range: 1.5 to 30.0 months), with favorable neurological control. Conclusions Under a standardized delayed-window protocol with dynamic working distance control, ICG effectively demarcated macroscopic canine meningiomas in this small cohort. Immediate post-operative MRI supported the surgeon’s qualitative assessments. Ultimately, FGS may serve as a viable surgical option to help minimize damage to normal brain tissue and potentially improve surgical outcomes in canine meningioma. Canine Meningioma ICG Indocyanine green Fluorescence-guided surgery Near-infrared fluorescence Figures Figure 1 Figure 2 Background Meningioma is the most frequently diagnosed primary intracranial neoplasm in companion animals, particularly dogs, often presenting with seizures, vestibular signs, and focal neurologic deficits. The primary treatment modality is surgical resection, and the extent of resection is a well-documented prognostic factor. However, achieving gross total resection remains challenging. Meningiomas often exhibit irregular growth patterns, such as lobulated formations, en-plaque extensions, and bone invasion [ 1 , 2 ]. These features are visually difficult to distinguish from normal dura, bone, or brain parenchyma under standard white-light (WL) illumination. Furthermore, intraoperative bleeding and cerebrospinal fluid can severely degrade the surgeon's visual field, increasing the risk of inadvertent tumor retention or excessive resection of normal brain tissue. In human medicine, fluorescence-guided surgery (FGS) using indocyanine green (ICG) has been widely adopted across various surgical oncology fields, such as hepatocellular carcinoma resection, breast cancer sentinel lymph node biopsy, and colorectal tumor surgeries [ 10 , 11 ]. Specifically within human neurosurgery, ICG application via second-window indocyanine green or delayed-window indocyanine green techniques has proven highly effective [ 3 , 6 ]. ICG accumulates in tumor tissues, yielding high-contrast intraoperative visualization of the macroscopic tumor and its extensions [ 4 , 5 ]. Drawing from these human applications, the use of ICG and near-infrared (NIR) fluorescence is gradually expanding in veterinary surgical oncology, showing promise for margin assessment in various solid tumors [ 8 , 9 ]. However, compared to its well-established role in human neurosurgery, its specific translation to veterinary neuro-oncology remains limited. Systematic data regarding ICG fluorescence expression and optimal dosing parameters specifically for canine intracranial meningiomas are notably scarce. We hypothesized that intravenously administered ICG would express consistent macroscopic fluorescence in canine meningiomas, and that tumor excision based on these intraoperative fluorescent margins would result in successful marginal resection, as verified by immediate post-operative MRI. Finally, we aimed to evaluate the clinical outcomes, including survival and the management of postoperative medical and neurological complications, to demonstrate the pragmatic clinical value of FGS in veterinary neuro-oncology. Case presentation Patient Demographics and Pre-operative Management This retrospective case series included six consecutive client-owned dogs that presented to a referral animal medical center between 2023 and 2025 with an onset of cluster seizures and concurrent vestibular signs. The cohort included Maltese (n = 3), Maltipoo (n = 1), Spitz (n = 1), and Pomeranian (n = 1). The median age was 13 years (range, 9.0–14.5 years), and the median body weight was 4.2 kg (range, 2.1–9.3 kg). Inclusion criteria were defined as dogs that had a brain mass identified on pre-operative MRI, underwent surgical resection, and were definitively diagnosed with meningioma via histopathological examination. Cases were excluded if the histopathological diagnosis was not meningioma or if concurrent neurological diseases, such as meningoencephalitis, were present. Patient demographics and tumor characteristics are summarized in Table 1 . Table 1 Pre-operative Patient Demographics and Tumor Characteristics Case No. Breed Age (yr) Sex Body Weight (kg) Histopathology (WHO Grade) Tumor Location Tumor Size (L1 x L2, mm) 1 Maltipoo 9.0 FS 5.8 Transitional (Grade 1) Right frontal 22 x 18 2 Maltese 14.0 MN 5.1 Transitional (Grade 1) Left frontal 20 x 18 3 Maltese 14.0 FS 2.1 Atypical (Grade 2)* Left frontal 23 x 21 4 Maltese 14.5 MN 2.6 Transitional (Grade 1) Frontal 21 x 17 5 Spitz 12.0 MN 9.3 Atypical (Grade 2)* Right frontal 24 x 20 6 Pomeranian 9.0 FS 3.3 Transitional (Grade 1) Left frontal 19 x 16 *Atypical meningioma exhibiting meningothelial features. Upon presentation, patients exhibiting elevated intracranial pressure and seizures were medically managed with standard antiepileptic drugs, corticosteroids, and osmotic diuretics. For anesthesia, premedication was routinely performed using midazolam and fentanyl, followed by induction with propofol. Anesthesia was maintained with isoflurane combined with a fentanyl constant rate infusion for analgesia. Fluorescence-Guided Surgical Intervention Fluorescence-Guided Surgical Intervention ICG (Diagnogreen®, Daiichi Sankyo Co., Ltd., Tokyo, Japan) was administered intravenously 6 to 24 hours (median: 12 hours) prior to the surgical incision. The median ICG dose was 4.46 mg/kg (range, 2.5–5.0 mg/kg). There were no adverse reactions associated with ICG administration. Patients were positioned in sternal recumbency, and a craniotomy was performed following a standard skin incision. Following the dural incision, an endoscope was mounted on a scope holder for continuous ICG detection. Intraoperative NIR imaging was performed using a 4K fluorescence imaging system (Solendos, Seoul, Republic of Korea). To maintain optical consistency and minimize artifacts, the working distance of the NIR camera was dynamically controlled and maintained within an optimal optical corridor of 50 to 100 mm using the scope holder. A pragmatic qualitative visual assessment was employed. The surgeon graded the index-margin fluorescence for visibility (0–3) and boundary clarity (0–2). Following biopsy, the macroscopic tumor was removed using manual dissection and an ultrasonic surgical aspirator (Sonopet®, Stryker, Kalamazoo, MI, USA) (Fig. 1 ). Distinct index-margin fluorescence was observed in all 6 cases (100%), with a median visibility grade of 3 (range: 2–3) and a median boundary clarity grade of 2 (range: 1–2). Continuous intraoperative NIR monitoring facilitated real-time identification of tumor margins, including dural-tail or small lobulated extensions that were visually indistinct under WL illumination, directly guiding the extent of resection. Based on the surgeon's discretion, a Simpson grade 3 resection (macroscopic complete resection), which is widely adapted in veterinary neuro-oncology for macroscopic evaluation of resection [ 15 ], was achieved in 4 cases, while a Simpson grade 4 resection (subtotal resection) was performed in 2 cases to protect critical structures. Intraoperative fluorescence parameters and surgical assessments are summarized in Table 2 . Histopathological analysis confirmed four cases of transitional meningioma (WHO Grade 1) and two cases (Cases 3 and 5) classified as atypical meningioma (WHO Grade 2) exhibiting meningothelial features. Table 2 Intraoperative Fluorescence Parameters and Surgical Assessments Case No. ICG Dose (mg/kg) ICG to Incision (h) Visibility Score (0–3) Clarity Score (0–2) Final Simpson Grade 1 3.91 24 3 2 Grade 4 2 5.00 16 2 2 Grade 3 3 5.00 6 2 1 Grade 3 4 2.50 12 3 2 Grade 3 5 2.50 12 3 2 Grade 4 6 5.00 12 3 2 Grade 3 Immediate Post-operative MRI Verification After resection, the wound bed was inspected under NIR mode. To strictly minimize the confounding effects of delayed reactive enhancement, immediate post-operative sagittal T1-weighted contrast-enhanced MRI was obtained exceptionally early, at a median of 21 minutes (range, 12–30 minutes) after skin closure. To prevent misinterpretation of surgically induced blood-brain barrier disruption or early hemostatic artifacts, thin linear wall enhancement of ≤ 1–2 mm along the surgical cavity was considered reactive rather than macroscopic tumor [ 12 – 14 ]. Applying this rigorous clinical criterion, there was 100% concordance between the macroscopic intraoperative wound bed fluorescence and immediate post-operative MRI findings. In the 4 cases where the surgical wound bed showed no residual fluorescence at closure, immediate T1-weighted contrast-enhanced (T1W-CE) MRI confirmed the absolute absence of any nodular or plaque-like enhancing mass (Fig. 2 ). In the 2 cases (Simpson grade 4) where fluorescent tissue was intentionally retained, residual enhancing masses were accurately verified on the immediate T1W-CE MRI. Post-operative Clinical Outcomes and Follow-up Following surgery, the median hospitalization was 5.5 days (range: 5–9 days). Postoperatively, anticonvulsants, along with a short course (2 to 4 weeks) of corticosteroids and diuretics, were prescribed. No generalized seizures were observed postoperatively in any of the patients. Postoperative medical management was required for several patients. One dog developed severe phenobarbital-induced thrombocytopenia, which was rapidly reversed upon switching to levetiracetam. Two dogs developed acute on chronic pancreatitis, requiring targeted gastrointestinal therapy. Two dogs exhibited delayed-onset ambulatory paraparesis; however, both maintained the ability to ambulate and perform daily activities. Despite their advanced age, the median follow-up was 6.25 months (range, 1.5–30.0 months). Notably, Case 1 survived over 30 months following the initial resection. Immediate post-operative MRI verification and clinical outcomes are summarized in Table 3 . Table 3 Immediate Post-operative MRI Verification and Clinical Outcomes Case No. Surgery to MRI (min) Immediate MRI Residual* Concordance with FGS Post-op Complications Status (Months) 1 24 Yes (Intentional retention) Yes None Alive (30.0) 2 30 No Yes Thrombocytopenia Alive (10.5) 3 24 No Yes Pancreatitis Alive (4.5) 4 18 No Yes Pancreatitis Alive (1.5) 5 18 Yes (Intentional retention) Yes Delayed paraparesis Alive (6.0) 6 12 No Yes Delayed paraparesis Alive (6.5) *Immediate MRI Residual distinguishes true nodular/plaque-like mass from thin reactive rims (≤ 1–2 mm). Discussion This case series demonstrates that delayed-window ICG-NIR fluorescence provides a robust and reliable "macroscopic safety net" for the resection of canine meningiomas. By utilizing a standardized delayed-window indocyanine green protocol, we achieved distinct macroscopic tumor visualization in 100% of our cohort, including complex cases with bone invasion or higher-grade pathology. Continuous NIR monitoring enabled the real-time detection and targeted resection of tumor margins that were visually indistinct under standard white light. To minimize subjective errors and optical artifacts, we utilized a scope holder to maintain the working distance within an optimal optical corridor of 50 to 100 mm. Standardizing the physical distance while fixing the wavelength (775 nm) significantly enhanced the objectivity and reliability of intraoperative fluorescence margin assessment, which holds substantial clinical significance. Furthermore, establishing an exceptionally early timeline for post-operative MRI (median 21 minutes) allowed us to validate the intraoperative visual endpoint directly against a relatively pristine radiological benchmark, separating true residual tumor from postoperative inflammation safely and effectively. In standard neuro-radiological evaluations, thin linear enhancement along the resection margin is widely recognized as a nonspecific postoperative change—often driven by localized breakdown of the blood-brain barrier and the use of intraoperative hemostatic agents—whereas nodular or plaque-like enhancement strongly suggests residual disease [ 12 – 14 ]. By applying this rigorous ≤ 1–2 mm exclusion criteria, we successfully mitigated the risk of overestimating residual tumor on our immediate MRI scans. The overall prognosis and incidence of postoperative complications in canine brain tumor surgery are closely related to the extent of resection and the preservation of adjacent normal brain tissue. Extensive resection involving normal brain parenchyma significantly increases the risk of severe complications and permanent neurological deficits. Therefore, it is critical to avoid damaging normal brain tissue at the surgical margins during tumor resection. In our study, the tumors exhibited distinct fluorescence, allowing for clear visual differentiation from the normal brain tissue. This enabled us to accurately identify and resect the tumors while preserving the surrounding healthy parenchyma. Additionally, as a retrospective clinical series, there was inherent variation in ICG dosage (2.5–5.0 mg/kg) and timing (6–24 hours) due to individual surgical scheduling logistics; however, all variations fell within the established temporal window for effective delayed-window fluorescence. While adverse reactions to ICG, such as anaphylaxis, are reported in a small fraction of human patients (< 0.34%) [ 7 ] and are virtually unreported in dogs [ 8 , 9 ], no ICG-related complications occurred in our cohort. This indicates that our protocol (up to 5.0 mg/kg) was well-tolerated even in geriatric dogs. Our results highlight the necessity of rigorous postoperative medical management in geriatric patients. While FGS facilitates macroscopic tumor removal, managing secondary medical complications, such as drug-induced thrombocytopenia or pancreatitis, is essential for maximizing long-term survival. There are inherent limitations to this study, including its retrospective nature and small sample size. While ICG-NIR fluorescence carries a known risk of false-positives at resection margins due to the 'blooming effect' or non-specific accumulation in peritumoral edema, we employed dynamic distance control and careful clearance of the surgical field to mitigate these optical artifacts and ensure optimal fluorescence contrast. Furthermore, distinguishing a thin surgically induced reactive rim from microscopic residual tumor on immediate post-operative MRI remains challenging. Future prospective studies incorporating quantitative fluorescence analysis and long-term volumetric MRI are warranted. Conclusions In conclusion, under a standardized delayed-window protocol with dynamic distance control, ICG effectively demarcated macroscopic canine meningiomas in our small cohort. Immediate post-operative MRI supported the intraoperative visual assessments. Ultimately, FGS may serve as a viable surgical option for canine meningiomas, potentially minimizing inadvertent damage to normal brain parenchyma and improving overall surgical outcomes when combined with meticulous postoperative medical management. Abbreviations FGS Fluorescence-guided surgery ICG Indocyanine green MRI Magnetic resonance imaging NIR Near-infrared T1W-CE T1-weighted contrast-enhanced WHO World Health Organization WL White-light Declarations Ethics approval and consent to participate As this is a case report involving client-owned animal, formal ethical approval was not required by the Institutional Animal Care and Use Committee (IACUC). The owner provided informed consent for all diagnostic procedures, surgical interventions, and the use of clinical data for publication purposes. Consent for publication Not applicable. Competing interests The authors declare no competing interests. Funding None declared. Author Contribution Y.K. (Yongsun Kim), Y.K. (Youngbeum Kim), and H-Y.K. conceptualized the study. Y.K. (Yongsun Kim) performed the surgeries and clinical management. Y.K. (Youngbeum Kim) analyzed the patient data and drafted the manuscript. H-Y.K. critically revised the manuscript for important intellectual content. Y.K. (Yongsun Kim) and H-Y.K. contributed to supervising the procedures. All authors read and approved the final manuscript. Acknowledgements Not applicable. Data Availability The datasets analyzed during the current study are available from the corresponding author on reasonable request. References Boudreau CE, Freeman AC, Powell C, et al. Clinical presentation, diagnostic findings and outcome of dogs undergoing surgical resection for intracranial meningioma: 101 dogs. BMC Vet Res. 2024;20(1):45. Sturges BK, Dickinson PJ, Bollen AW, Koblik PD, Kass PH, Kortz GD, et al. Magnetic resonance imaging and histological classification of intracranial meningiomas in 112 dogs. Vet Radiol Ultrasound. 2008;49(6):519–40. Muto J, Murayama K, Ideguchi M, et al. Delayed-window indocyanine green highlights meningioma and dural tail. Front Neurosci. 2022;16:855421. Cho SS, Salinas R, Lee JYK. Near-infrared imaging with indocyanine green in glioma and meningioma surgery. Front Oncol. 2019;9:742. Lee ZK, Chen L, Mallela AN, et al. Second-window ICG for meningioma resection: A systematic review. J Neurosurg. 2018;131(1):12–20. Karsalia R, Teng C, Ahmed U, et al. Dose optimization of second-window indocyanine green in neurosurgery. Clin Neurol Neurosurg. 2024;236:108076. Hope-Ross M, Yannuzzi LA, Gragoudas CG, Guyer DR, Slakter JS, Sorenson JA, et al. Adverse reactions to indocyanine green. Ophthalmology. 1994;101(4):529–33. Lapsley J, Selmic LE. Near-infrared fluorescence imaging in veterinary surgical oncology. Vet Comp Oncol. 2022;20(1):1–14. Newton AL, Liptak JM, Brisson BA, et al. Use of indocyanine green for sentinel lymph node mapping in dogs. Vet Surg. 2020;49(1):124–33. Boni L, David G, Mangano A, Dionigi G, Rausei S, Spampatti S, et al. Clinical applications of indocyanine green (ICG) enhanced fluorescence in laparoscopic surgery. Surg Endosc. 2015;29(7):2046–55. Vahrmeijer AL, Hutteman M, van der Vorst JR, van de Velde CJ, Frangioni JV. Image-guided cancer surgery using near-infrared fluorescence. Nat Rev Clin Oncol. 2013;10(9):507–18. Chow K, Vite CH, Sharma D, et al. Magnetic resonance imaging features of the early postoperative brain after cranial surgery in dogs. Vet Radiol Ultrasound. 2015;56(5):500–9. Bendszus M, Klein R, Burger R, Warmuth-Metz M, Hofmann E, Solymosi L. MRI of normal brain after uncomplicated surgery. Neuroradiology. 2001;43(11):940–5. Ginat DT, Meyers SP. Postoperative Imaging of the Cranial Vault and Brain. Neuroimaging Clin N Am. 2014;24(4):717–40. Rossmeisl JH, Parker RL, et al. Prognostic value of magnetic resonance imaging defined extent of surgical resection in dogs with intracranial meningiomas. Vet Comp Oncol. 2026. 10.1111/vco.70044 . Epub ahead of print. Additional Declarations No competing interests reported. Cite Share Download PDF Status: Under Revision Version 1 posted Editorial decision: Revision requested 06 May, 2026 Reviews received at journal 04 May, 2026 Reviewers agreed at journal 15 Apr, 2026 Reviews received at journal 09 Apr, 2026 Reviewers agreed at journal 07 Apr, 2026 Reviewers invited by journal 07 Apr, 2026 Editor assigned by journal 06 Apr, 2026 Submission checks completed at journal 05 Apr, 2026 First submitted to journal 02 Apr, 2026 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. We do this by developing innovative software and high quality services for the global research community. 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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-9301046","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Case Report","associatedPublications":[],"authors":[{"id":620522350,"identity":"831f7e3a-4e09-4cca-831c-9b22b44ec7bc","order_by":0,"name":"Youngbeum Kim","email":"","orcid":"","institution":"Bon Animal Medical Center","correspondingAuthor":false,"prefix":"","firstName":"Youngbeum","middleName":"","lastName":"Kim","suffix":""},{"id":620522351,"identity":"00f72475-6449-4ca0-bc8f-1a94df6d96c0","order_by":1,"name":"Yongsun Kim","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA9UlEQVRIiWNgGAWjYDACHsYGBOcDELOxk6KFcQZICzNBLUhsZjCHkBaDM4dbNzD8OZwv7977TNrm1zZ5PmYGxg8fc/BoOdvYdoOx7bDlxjPHzaRz+24btjEzMEvO3IZHy3lGoJaGwwaGM9LYpHN7bjMCtbAx8xLSAnSYgeH8Z2zSlj237QlrATmMge2wgbwEG5s0w4/biQS1SJ452HYjsS3dwIAnjdmyt+F2chszYzNev/CdSX9248MfawP59mOMN378uW07v7354IePeLQoHAASCSAXHmBgkWBsA4khpwcsQL4BwWD+wPAHr+JRMApGwSgYoQAAWkxS8LhSI5QAAAAASUVORK5CYII=","orcid":"","institution":"Bon Animal Medical Center","correspondingAuthor":true,"prefix":"","firstName":"Yongsun","middleName":"","lastName":"Kim","suffix":""},{"id":620522352,"identity":"0e0c548b-f36a-4657-811f-eaed41a40c50","order_by":2,"name":"Hwi-Yool Kim","email":"","orcid":"","institution":"Konkuk University","correspondingAuthor":false,"prefix":"","firstName":"Hwi-Yool","middleName":"","lastName":"Kim","suffix":""}],"badges":[],"createdAt":"2026-04-02 09:25:25","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-9301046/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-9301046/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":106871033,"identity":"5d73bfdc-8e9e-401f-8c2a-d40f35cef6f4","added_by":"auto","created_at":"2026-04-14 09:44:15","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":1025722,"visible":true,"origin":"","legend":"\u003cp\u003eIntraoperative visualization and fluorescence-guided resection of canine meningioma. \u003cstrong\u003eA\u003c/strong\u003ePre-resection view. Near-infrared imaging demonstrates strong indocyanine green fluorescence, clearly distinguishing the tumor mass from the adjacent normal brain parenchyma. \u003cstrong\u003eB\u003c/strong\u003e Targeted resection of the fluorescent tumor tissue using an ultrasonic aspirator. \u003cstrong\u003eC\u003c/strong\u003e Post-resection inspection of the surgical wound bed. The NIR imaging confirms the macroscopic completeness of the resection with no residual fluorescence detected.\u003c/p\u003e","description":"","filename":"floatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-9301046/v1/9c5c842574ab05b6c1f34961.png"},{"id":106871137,"identity":"155dc742-91f0-44bb-879a-bb38513bf09c","added_by":"auto","created_at":"2026-04-14 09:44:28","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":568426,"visible":true,"origin":"","legend":"\u003cp\u003eImmediate post-operative MRI verification\u003cstrong\u003e. A\u003c/strong\u003e Pre-operative transverse T1-weighted contrast-enhanced (T1W-CE) MRI revealing a strongly enhancing extra-axial mass (white arrow). \u003cstrong\u003eB\u003c/strong\u003e Immediate post-operative transverse T1W-CE MRI confirming the complete removal of the enhancing tumor mass. The surgical cavity (arrowhead) demonstrates no residual nodular enhancement, and the surrounding normal brain parenchyma is well-preserved without inadvertent damage.\u003c/p\u003e","description":"","filename":"floatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-9301046/v1/65bd3c60d2a0f2a1ce6d885c.png"},{"id":106871177,"identity":"7b917abb-c5d8-4584-b46d-4b4a71cb9c54","added_by":"auto","created_at":"2026-04-14 09:44:44","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2714382,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-9301046/v1/ec5fe08d-699d-427f-99c2-8b24df4e23ac.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Intraoperative Indocyanine Green Fluorescence in Canine Meningioma: Macroscopic Visualization, Immediate MRI Verification, and Clinical Outcomes: A Case Series","fulltext":[{"header":"Background","content":"\u003cp\u003eMeningioma is the most frequently diagnosed primary intracranial neoplasm in companion animals, particularly dogs, often presenting with seizures, vestibular signs, and focal neurologic deficits. The primary treatment modality is surgical resection, and the extent of resection is a well-documented prognostic factor. However, achieving gross total resection remains challenging. Meningiomas often exhibit irregular growth patterns, such as lobulated formations, en-plaque extensions, and bone invasion [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. These features are visually difficult to distinguish from normal dura, bone, or brain parenchyma under standard white-light (WL) illumination. Furthermore, intraoperative bleeding and cerebrospinal fluid can severely degrade the surgeon's visual field, increasing the risk of inadvertent tumor retention or excessive resection of normal brain tissue.\u003c/p\u003e \u003cp\u003eIn human medicine, fluorescence-guided surgery (FGS) using indocyanine green (ICG) has been widely adopted across various surgical oncology fields, such as hepatocellular carcinoma resection, breast cancer sentinel lymph node biopsy, and colorectal tumor surgeries [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e, \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]. Specifically within human neurosurgery, ICG application via second-window indocyanine green or delayed-window indocyanine green techniques has proven highly effective [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e, \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]. ICG accumulates in tumor tissues, yielding high-contrast intraoperative visualization of the macroscopic tumor and its extensions [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e, \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eDrawing from these human applications, the use of ICG and near-infrared (NIR) fluorescence is gradually expanding in veterinary surgical oncology, showing promise for margin assessment in various solid tumors [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e, \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]. However, compared to its well-established role in human neurosurgery, its specific translation to veterinary neuro-oncology remains limited. Systematic data regarding ICG fluorescence expression and optimal dosing parameters specifically for canine intracranial meningiomas are notably scarce.\u003c/p\u003e \u003cp\u003eWe hypothesized that intravenously administered ICG would express consistent macroscopic fluorescence in canine meningiomas, and that tumor excision based on these intraoperative fluorescent margins would result in successful marginal resection, as verified by immediate post-operative MRI. Finally, we aimed to evaluate the clinical outcomes, including survival and the management of postoperative medical and neurological complications, to demonstrate the pragmatic clinical value of FGS in veterinary neuro-oncology.\u003c/p\u003e"},{"header":"Case presentation","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003ePatient Demographics and Pre-operative Management\u003c/h2\u003e \u003cp\u003eThis retrospective case series included six consecutive client-owned dogs that presented to a referral animal medical center between 2023 and 2025 with an onset of cluster seizures and concurrent vestibular signs. The cohort included Maltese (n\u0026thinsp;=\u0026thinsp;3), Maltipoo (n\u0026thinsp;=\u0026thinsp;1), Spitz (n\u0026thinsp;=\u0026thinsp;1), and Pomeranian (n\u0026thinsp;=\u0026thinsp;1). The median age was 13 years (range, 9.0\u0026ndash;14.5 years), and the median body weight was 4.2 kg (range, 2.1\u0026ndash;9.3 kg). Inclusion criteria were defined as dogs that had a brain mass identified on pre-operative MRI, underwent surgical resection, and were definitively diagnosed with meningioma via histopathological examination. Cases were excluded if the histopathological diagnosis was not meningioma or if concurrent neurological diseases, such as meningoencephalitis, were present. Patient demographics and tumor characteristics are summarized in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003ePre-operative Patient Demographics and Tumor Characteristics\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"8\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCase No.\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eBreed\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eAge (yr)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eSex\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eBody Weight (kg)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eHistopathology (WHO Grade)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003eTumor Location\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c8\"\u003e \u003cp\u003eTumor Size (L1 x L2, mm)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eMaltipoo\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e9.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eFS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e5.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eTransitional (Grade 1)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003eRight frontal\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e22 x 18\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eMaltese\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e14.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eMN\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e5.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eTransitional (Grade 1)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003eLeft frontal\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e20 x 18\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eMaltese\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e14.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eFS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e2.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eAtypical (Grade 2)*\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003eLeft frontal\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e23 x 21\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eMaltese\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e14.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eMN\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e2.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eTransitional (Grade 1)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003eFrontal\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e21 x 17\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSpitz\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e12.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eMN\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e9.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eAtypical (Grade 2)*\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003eRight frontal\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e24 x 20\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003ePomeranian\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e9.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eFS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e3.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eTransitional (Grade 1)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003eLeft frontal\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e19 x 16\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003ctfoot\u003e \u003ctr\u003e\u003ctd colspan=\"8\"\u003e\u003cem\u003e*Atypical meningioma exhibiting meningothelial features.\u003c/em\u003e\u003c/td\u003e\u003c/tr\u003e \u003c/tfoot\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eUpon presentation, patients exhibiting elevated intracranial pressure and seizures were medically managed with standard antiepileptic drugs, corticosteroids, and osmotic diuretics. For anesthesia, premedication was routinely performed using midazolam and fentanyl, followed by induction with propofol. Anesthesia was maintained with isoflurane combined with a fentanyl constant rate infusion for analgesia.\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eFluorescence-Guided Surgical Intervention\u003c/h3\u003e\n\u003cdiv class=\"Heading\"\u003eFluorescence-Guided Surgical Intervention\u003c/div\u003e \u003cp\u003eICG (Diagnogreen\u0026reg;, Daiichi Sankyo Co., Ltd., Tokyo, Japan) was administered intravenously 6 to 24 hours (median: 12 hours) prior to the surgical incision. The median ICG dose was 4.46 mg/kg (range, 2.5\u0026ndash;5.0 mg/kg). There were no adverse reactions associated with ICG administration. Patients were positioned in sternal recumbency, and a craniotomy was performed following a standard skin incision. Following the dural incision, an endoscope was mounted on a scope holder for continuous ICG detection. Intraoperative NIR imaging was performed using a 4K fluorescence imaging system (Solendos, Seoul, Republic of Korea). To maintain optical consistency and minimize artifacts, the working distance of the NIR camera was dynamically controlled and maintained within an optimal optical corridor of 50 to 100 mm using the scope holder.\u003c/p\u003e \u003cp\u003eA pragmatic qualitative visual assessment was employed. The surgeon graded the index-margin fluorescence for visibility (0\u0026ndash;3) and boundary clarity (0\u0026ndash;2). Following biopsy, the macroscopic tumor was removed using manual dissection and an ultrasonic surgical aspirator (Sonopet\u0026reg;, Stryker, Kalamazoo, MI, USA) (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). Distinct index-margin fluorescence was observed in all 6 cases (100%), with a median visibility grade of 3 (range: 2\u0026ndash;3) and a median boundary clarity grade of 2 (range: 1\u0026ndash;2). Continuous intraoperative NIR monitoring facilitated real-time identification of tumor margins, including dural-tail or small lobulated extensions that were visually indistinct under WL illumination, directly guiding the extent of resection. Based on the surgeon's discretion, a Simpson grade 3 resection (macroscopic complete resection), which is widely adapted in veterinary neuro-oncology for macroscopic evaluation of resection [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e], was achieved in 4 cases, while a Simpson grade 4 resection (subtotal resection) was performed in 2 cases to protect critical structures. Intraoperative fluorescence parameters and surgical assessments are summarized in Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e. Histopathological analysis confirmed four cases of transitional meningioma (WHO Grade 1) and two cases (Cases 3 and 5) classified as atypical meningioma (WHO Grade 2) exhibiting meningothelial features.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eIntraoperative Fluorescence Parameters and Surgical Assessments\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"6\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCase No.\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eICG Dose (mg/kg)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eICG to Incision (h)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eVisibility Score (0\u0026ndash;3)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eClarity Score (0\u0026ndash;2)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eFinal Simpson Grade\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e3.91\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e24\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eGrade 4\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e5.00\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e16\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eGrade 3\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e5.00\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eGrade 3\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e2.50\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e12\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eGrade 3\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e2.50\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e12\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eGrade 4\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e5.00\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e12\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eGrade 3\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e\n\u003ch3\u003eImmediate Post-operative MRI Verification\u003c/h3\u003e\n\u003cp\u003eAfter resection, the wound bed was inspected under NIR mode. To strictly minimize the confounding effects of delayed reactive enhancement, immediate post-operative sagittal T1-weighted contrast-enhanced MRI was obtained exceptionally early, at a median of 21 minutes (range, 12\u0026ndash;30 minutes) after skin closure. To prevent misinterpretation of surgically induced blood-brain barrier disruption or early hemostatic artifacts, thin linear wall enhancement of \u0026le;\u0026thinsp;1\u0026ndash;2 mm along the surgical cavity was considered reactive rather than macroscopic tumor [\u003cspan additionalcitationids=\"CR13\" citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e]. Applying this rigorous clinical criterion, there was 100% concordance between the macroscopic intraoperative wound bed fluorescence and immediate post-operative MRI findings. In the 4 cases where the surgical wound bed showed no residual fluorescence at closure, immediate T1-weighted contrast-enhanced (T1W-CE) MRI confirmed the absolute absence of any nodular or plaque-like enhancing mass (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). In the 2 cases (Simpson grade 4) where fluorescent tissue was intentionally retained, residual enhancing masses were accurately verified on the immediate T1W-CE MRI.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e\n\u003ch3\u003ePost-operative Clinical Outcomes and Follow-up\u003c/h3\u003e\n\u003cp\u003eFollowing surgery, the median hospitalization was 5.5 days (range: 5\u0026ndash;9 days). Postoperatively, anticonvulsants, along with a short course (2 to 4 weeks) of corticosteroids and diuretics, were prescribed. No generalized seizures were observed postoperatively in any of the patients. Postoperative medical management was required for several patients. One dog developed severe phenobarbital-induced thrombocytopenia, which was rapidly reversed upon switching to levetiracetam. Two dogs developed acute on chronic pancreatitis, requiring targeted gastrointestinal therapy. Two dogs exhibited delayed-onset ambulatory paraparesis; however, both maintained the ability to ambulate and perform daily activities. Despite their advanced age, the median follow-up was 6.25 months (range, 1.5\u0026ndash;30.0 months). Notably, Case 1 survived over 30 months following the initial resection. Immediate post-operative MRI verification and clinical outcomes are summarized in Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab3\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eImmediate Post-operative MRI Verification and Clinical Outcomes\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"6\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCase No.\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSurgery to MRI (min)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eImmediate MRI Residual*\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eConcordance with FGS\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003ePost-op Complications\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eStatus (Months)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e24\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eYes (Intentional retention)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eYes\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eNone\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eAlive (30.0)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e30\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eNo\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eYes\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eThrombocytopenia\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eAlive (10.5)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e24\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eNo\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eYes\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003ePancreatitis\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eAlive (4.5)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e18\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eNo\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eYes\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003ePancreatitis\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eAlive (1.5)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e18\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eYes (Intentional retention)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eYes\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eDelayed paraparesis\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eAlive (6.0)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e12\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eNo\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eYes\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eDelayed paraparesis\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eAlive (6.5)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003ctfoot\u003e \u003ctr\u003e\u003ctd colspan=\"6\"\u003e\u003cem\u003e*Immediate MRI Residual distinguishes true nodular/plaque-like mass from thin reactive rims (\u0026le;\u0026thinsp;1\u0026ndash;2 mm).\u003c/em\u003e\u003c/td\u003e\u003c/tr\u003e \u003c/tfoot\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e"},{"header":"Discussion","content":"\u003cp\u003eThis case series demonstrates that delayed-window ICG-NIR fluorescence provides a robust and reliable \"macroscopic safety net\" for the resection of canine meningiomas. By utilizing a standardized delayed-window indocyanine green protocol, we achieved distinct macroscopic tumor visualization in 100% of our cohort, including complex cases with bone invasion or higher-grade pathology. Continuous NIR monitoring enabled the real-time detection and targeted resection of tumor margins that were visually indistinct under standard white light.\u003c/p\u003e \u003cp\u003eTo minimize subjective errors and optical artifacts, we utilized a scope holder to maintain the working distance within an optimal optical corridor of 50 to 100 mm. Standardizing the physical distance while fixing the wavelength (775 nm) significantly enhanced the objectivity and reliability of intraoperative fluorescence margin assessment, which holds substantial clinical significance. Furthermore, establishing an exceptionally early timeline for post-operative MRI (median 21 minutes) allowed us to validate the intraoperative visual endpoint directly against a relatively pristine radiological benchmark, separating true residual tumor from postoperative inflammation safely and effectively.\u003c/p\u003e \u003cp\u003eIn standard neuro-radiological evaluations, thin linear enhancement along the resection margin is widely recognized as a nonspecific postoperative change\u0026mdash;often driven by localized breakdown of the blood-brain barrier and the use of intraoperative hemostatic agents\u0026mdash;whereas nodular or plaque-like enhancement strongly suggests residual disease [\u003cspan additionalcitationids=\"CR13\" citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e]. By applying this rigorous\u0026thinsp;\u0026le;\u0026thinsp;1\u0026ndash;2 mm exclusion criteria, we successfully mitigated the risk of overestimating residual tumor on our immediate MRI scans. The overall prognosis and incidence of postoperative complications in canine brain tumor surgery are closely related to the extent of resection and the preservation of adjacent normal brain tissue. Extensive resection involving normal brain parenchyma significantly increases the risk of severe complications and permanent neurological deficits. Therefore, it is critical to avoid damaging normal brain tissue at the surgical margins during tumor resection. In our study, the tumors exhibited distinct fluorescence, allowing for clear visual differentiation from the normal brain tissue. This enabled us to accurately identify and resect the tumors while preserving the surrounding healthy parenchyma.\u003c/p\u003e \u003cp\u003eAdditionally, as a retrospective clinical series, there was inherent variation in ICG dosage (2.5\u0026ndash;5.0 mg/kg) and timing (6\u0026ndash;24 hours) due to individual surgical scheduling logistics; however, all variations fell within the established temporal window for effective delayed-window fluorescence. While adverse reactions to ICG, such as anaphylaxis, are reported in a small fraction of human patients (\u0026lt;\u0026thinsp;0.34%) [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e] and are virtually unreported in dogs [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e, \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e], no ICG-related complications occurred in our cohort. This indicates that our protocol (up to 5.0 mg/kg) was well-tolerated even in geriatric dogs. Our results highlight the necessity of rigorous postoperative medical management in geriatric patients. While FGS facilitates macroscopic tumor removal, managing secondary medical complications, such as drug-induced thrombocytopenia or pancreatitis, is essential for maximizing long-term survival.\u003c/p\u003e \u003cp\u003eThere are inherent limitations to this study, including its retrospective nature and small sample size. While ICG-NIR fluorescence carries a known risk of false-positives at resection margins due to the 'blooming effect' or non-specific accumulation in peritumoral edema, we employed dynamic distance control and careful clearance of the surgical field to mitigate these optical artifacts and ensure optimal fluorescence contrast. Furthermore, distinguishing a thin surgically induced reactive rim from microscopic residual tumor on immediate post-operative MRI remains challenging. Future prospective studies incorporating quantitative fluorescence analysis and long-term volumetric MRI are warranted.\u003c/p\u003e"},{"header":"Conclusions","content":"\u003cp\u003eIn conclusion, under a standardized delayed-window protocol with dynamic distance control, ICG effectively demarcated macroscopic canine meningiomas in our small cohort. Immediate post-operative MRI supported the intraoperative visual assessments. Ultimately, FGS may serve as a viable surgical option for canine meningiomas, potentially minimizing inadvertent damage to normal brain parenchyma and improving overall surgical outcomes when combined with meticulous postoperative medical management.\u003c/p\u003e"},{"header":"Abbreviations","content":"\u003cdiv class=\"DefinitionList\"\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eFGS\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eFluorescence-guided surgery\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eICG\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eIndocyanine green\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eMRI\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eMagnetic resonance imaging\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eNIR\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eNear-infrared\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eT1W-CE\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eT1-weighted contrast-enhanced\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eWHO\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eWorld Health Organization\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eWL\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eWhite-light\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003c/div\u003e"},{"header":"Declarations","content":"\u003cp\u003e \u003cstrong\u003eEthics approval and consent to participate\u003c/strong\u003e \u003cp\u003eAs this is a case report involving client-owned animal, formal ethical approval was not required by the Institutional Animal Care and Use Committee (IACUC). The owner provided informed consent for all diagnostic procedures, surgical interventions, and the use of clinical data for publication purposes.\u003c/p\u003e \u003c/p\u003e \u003cp\u003e \u003cstrong\u003eConsent for publication\u003c/strong\u003e \u003cp\u003eNot applicable.\u003c/p\u003e \u003c/p\u003e\u003cp\u003e \u003ch2\u003eCompeting interests\u003c/h2\u003e \u003cp\u003eThe authors declare no competing interests.\u003c/p\u003e \u003c/p\u003e\u003ch2\u003eFunding\u003c/h2\u003e \u003cp\u003eNone declared.\u003c/p\u003e\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eY.K. (Yongsun Kim), Y.K. (Youngbeum Kim), and H-Y.K. conceptualized the study. Y.K. (Yongsun Kim) performed the surgeries and clinical management. Y.K. (Youngbeum Kim) analyzed the patient data and drafted the manuscript. H-Y.K. critically revised the manuscript for important intellectual content. Y.K. (Yongsun Kim) and H-Y.K. contributed to supervising the procedures. All authors read and approved the final manuscript.\u003c/p\u003e\u003ch2\u003eAcknowledgements\u003c/h2\u003e \u003cp\u003eNot applicable.\u003c/p\u003e\u003ch2\u003eData Availability\u003c/h2\u003e\u003cp\u003eThe datasets analyzed during the current study are available from the corresponding author on reasonable request.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eBoudreau CE, Freeman AC, Powell C, et al. Clinical presentation, diagnostic findings and outcome of dogs undergoing surgical resection for intracranial meningioma: 101 dogs. BMC Vet Res. 2024;20(1):45.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSturges BK, Dickinson PJ, Bollen AW, Koblik PD, Kass PH, Kortz GD, et al. Magnetic resonance imaging and histological classification of intracranial meningiomas in 112 dogs. Vet Radiol Ultrasound. 2008;49(6):519\u0026ndash;40.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMuto J, Murayama K, Ideguchi M, et al. Delayed-window indocyanine green highlights meningioma and dural tail. Front Neurosci. 2022;16:855421.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eCho SS, Salinas R, Lee JYK. Near-infrared imaging with indocyanine green in glioma and meningioma surgery. Front Oncol. 2019;9:742.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLee ZK, Chen L, Mallela AN, et al. Second-window ICG for meningioma resection: A systematic review. J Neurosurg. 2018;131(1):12\u0026ndash;20.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKarsalia R, Teng C, Ahmed U, et al. Dose optimization of second-window indocyanine green in neurosurgery. Clin Neurol Neurosurg. 2024;236:108076.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eHope-Ross M, Yannuzzi LA, Gragoudas CG, Guyer DR, Slakter JS, Sorenson JA, et al. Adverse reactions to indocyanine green. Ophthalmology. 1994;101(4):529\u0026ndash;33.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLapsley J, Selmic LE. Near-infrared fluorescence imaging in veterinary surgical oncology. Vet Comp Oncol. 2022;20(1):1\u0026ndash;14.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eNewton AL, Liptak JM, Brisson BA, et al. Use of indocyanine green for sentinel lymph node mapping in dogs. Vet Surg. 2020;49(1):124\u0026ndash;33.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBoni L, David G, Mangano A, Dionigi G, Rausei S, Spampatti S, et al. Clinical applications of indocyanine green (ICG) enhanced fluorescence in laparoscopic surgery. Surg Endosc. 2015;29(7):2046\u0026ndash;55.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eVahrmeijer AL, Hutteman M, van der Vorst JR, van de Velde CJ, Frangioni JV. Image-guided cancer surgery using near-infrared fluorescence. Nat Rev Clin Oncol. 2013;10(9):507\u0026ndash;18.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eChow K, Vite CH, Sharma D, et al. Magnetic resonance imaging features of the early postoperative brain after cranial surgery in dogs. Vet Radiol Ultrasound. 2015;56(5):500\u0026ndash;9.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBendszus M, Klein R, Burger R, Warmuth-Metz M, Hofmann E, Solymosi L. MRI of normal brain after uncomplicated surgery. Neuroradiology. 2001;43(11):940\u0026ndash;5.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eGinat DT, Meyers SP. Postoperative Imaging of the Cranial Vault and Brain. Neuroimaging Clin N Am. 2014;24(4):717\u0026ndash;40.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eRossmeisl JH, Parker RL, et al. Prognostic value of magnetic resonance imaging defined extent of surgical resection in dogs with intracranial meningiomas. Vet Comp Oncol. 2026. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1111/vco.70044\u003c/span\u003e\u003cspan address=\"10.1111/vco.70044\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e. Epub ahead of print.\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"bmc-veterinary-research","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"","sideBox":"Learn more about [BMC Veterinary Research](http://bmcvetres.biomedcentral.com/)","snPcode":"12917","submissionUrl":"https://submission.nature.com/new-submission/12917/3?","title":"BMC Veterinary Research","twitterHandle":"@BMC_series","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"BMC Series","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"Canine, Meningioma, ICG, Indocyanine green, Fluorescence-guided surgery, Near-infrared fluorescence","lastPublishedDoi":"10.21203/rs.3.rs-9301046/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-9301046/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003ch2\u003eBackground\u003c/h2\u003e \u003cp\u003eMeningioma is the most common primary intracranial neoplasm in dogs, frequently presenting with seizures and neurological deficits. While indocyanine green (ICG) near-infrared (NIR) fluorescence is increasingly used in human neurosurgery, systematic data regarding its macroscopic expression in canine meningioma remain scarce. This case series aimed to evaluate the qualitative macroscopic expression of ICG, verify intraoperative findings using exceptionally early immediate post-operative contrast-enhanced magnetic resonance imaging (MRI), and report the clinical outcomes and complication management following fluorescence-guided surgery (FGS).\u003c/p\u003e\u003ch2\u003eCase presentation:\u003c/h2\u003e \u003cp\u003eSix client-owned dogs (median age: 13 years) with histologically confirmed meningiomas were evaluated. ICG was administered intravenously (median dose: 4.46 mg/kg) 6 to 24 hours prior to surgery. FGS was performed using an ultrasonic aspirator and a dedicated fluorescence imaging system. Distinct index-margin fluorescence was observed in all 6 cases (100%), allowing for real-time differentiation between tumor tissue and normal brain parenchyma during resection. Immediate post-operative T1-weighted contrast-enhanced MRI demonstrated 100% concordance with intraoperative wound bed fluorescence assessments when thin reactive rims (\u0026le;\u0026thinsp;1\u0026ndash;2 mm) were appropriately excluded. No adverse reactions were associated with ICG. The median follow-up was 6.25 months (range: 1.5 to 30.0 months), with favorable neurological control.\u003c/p\u003e\u003ch2\u003eConclusions\u003c/h2\u003e \u003cp\u003eUnder a standardized delayed-window protocol with dynamic working distance control, ICG effectively demarcated macroscopic canine meningiomas in this small cohort. Immediate post-operative MRI supported the surgeon\u0026rsquo;s qualitative assessments. Ultimately, FGS may serve as a viable surgical option to help minimize damage to normal brain tissue and potentially improve surgical outcomes in canine meningioma.\u003c/p\u003e","manuscriptTitle":"Intraoperative Indocyanine Green Fluorescence in Canine Meningioma: Macroscopic Visualization, Immediate MRI Verification, and Clinical Outcomes: A Case Series","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-04-14 09:42:40","doi":"10.21203/rs.3.rs-9301046/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2026-05-06T08:32:22+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-05-05T01:06:06+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"77928059282756290212716156701979713332","date":"2026-04-15T15:01:59+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-04-09T18:41:49+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"124014951294829415935076587343309236298","date":"2026-04-07T15:13:13+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2026-04-07T07:17:13+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2026-04-06T04:00:33+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2026-04-06T03:59:49+00:00","index":"","fulltext":""},{"type":"submitted","content":"BMC Veterinary Research","date":"2026-04-02T09:19:06+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"bmc-veterinary-research","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"","sideBox":"Learn more about [BMC Veterinary Research](http://bmcvetres.biomedcentral.com/)","snPcode":"12917","submissionUrl":"https://submission.nature.com/new-submission/12917/3?","title":"BMC Veterinary Research","twitterHandle":"@BMC_series","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"BMC Series","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"61a2028c-f3b6-47c1-bfe1-e4d04620a87c","owner":[],"postedDate":"April 14th, 2026","published":true,"recentEditorialEvents":[{"type":"decision","content":"Revision requested","date":"2026-05-06T08:32:22+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-05-05T01:06:06+00:00","index":23,"fulltext":""}],"rejectedJournal":[],"revision":"","amendment":"","status":"in-revision","subjectAreas":[],"tags":[],"updatedAt":"2026-05-06T08:41:14+00:00","versionOfRecord":[],"versionCreatedAt":"2026-04-14 09:42:40","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-9301046","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-9301046","identity":"rs-9301046","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}