Application of 18F-FAPI PET/CT inDeep Infiltrating Endometriosis

Application of 18F-FAPI PET/CT inDeep Infiltrating Endometriosis | Authorea try { document.documentElement.classList.add('js'); } catch (e) { } var _gaq = _gaq || []; _gaq.push(['_setAccount', 'G-8VDV14Y67G']); _gaq.push(['_trackPageview']); (function() { var ga = document.createElement('script'); ga.type = 'text/javascript'; ga.async = true; ga.src = ('https:' == document.location.protocol ? 'https://ssl' : 'http://www') + '.google-analytics.com/ga.js'; var s = document.getElementsByTagName('script')[0]; s.parentNode.insertBefore(ga, s); })(); Skip to main content Preprints Collections Wiley Open Research IET Open Research Ecological Society of Japan All Collections About About Authorea FAQs Contact Us Quick Search anywhere Search for preprint articles, keywords, etc. Search Search ADVANCED SEARCH SCROLL Clinical Case Reports This is a preprint and has not been peer reviewed. Data may be preliminary. 1 December 2025 V1 Latest version Share on Application of 18F-FAPI PET/CT inDeep Infiltrating Endometriosis Authors : Haili Li 0009-0005-9672-3047 [email protected] , Tongxin Chen , Ruyu Cai , Yifan Huang , Xiangcheng Wang , Pingyue Yu , and Minge Li Authors Info & Affiliations https://doi.org/10.22541/au.176458902.27599797/v1 268 views 229 downloads Contents Information & Authors Metrics & Citations View Options References Figures Tables Media Share Application of 18F-FAPI PET/CT in Deep Infiltrating Endometriosis Ruyu Cai 11 # These authors contributed equally to this work. *Corresponding author E-mail address: [email protected] # Tongxin Chen 1# Minge S Li 1 Pingyue Yu 1 Xiangcheng Wang 2 Yifan Huang 2 Haili Li 1 * ( 1 Department of Gynecology, Shenzhen People’s Hospital, The Second Clinical Medical College of Jinan University,Shenzhen,Guangdong,China. 2 Department of Nuclear Medicine, Shenzhen People’s Hospital,The Second Clinical Medical College of Jinan University,Shenzhen,Guangdong,China.) Key clinical message： This case report demonstrates the superior imaging performance of FAPI in visualizing deep infiltrating endometriosis (DIE) lesions compared to ultrasonography and MRI, suggesting its potential as a powerful diagnostic tool in the future. Introduction： Studies over the past two decades have demonstrated that endometriosis is an estrogen-dependent chronic inflammatory process affecting pelvic tissues, the most severe phenotype is DIE, which is defined as subperitoneal lesions that penetrate tissue deeper than 5 mm under the peritoneal surface (such as the uterosacral ligaments) or as lesions that infiltrate the muscularis propria of the organs that surround the uterus, for example, the bladder, intestine with or without occlusion, and ureter with or without ureterohydronephrosis [1,2]. The predominant symptoms include dysmenorrhea, dyspareunia, and infertility. Lesions invading the bladder may cause urinary urgency and frequency, while rectal involvement may lead to anal tenesmus and constipation, severely impacting patients’ quality of life. Current clinical diagnostic strategies integrate medical history, physical examination findings, serum markers, and imaging modalities [2]. however, the gold standard remains histopathological confirmation following surgical intervention. Case Report： A 40s perimenopausal woman with a history of dysmenorrhea presented with anal tenesmus and increased bowel frequency during menstruation over the past two years. Two months prior to admission, a colonoscopy performed in the gastroenterology department revealed a raised lesion in the rectum, with postoperative histopathology confirming endometriotic involvement. She was subsequently referred to the gynecology department for hospitalization. Pre-admission transvaginal ultrasonography (TVUS) and pelvic magnetic resonance imaging (MRI) both suggested possible DIE in the anterior rectal wall. To further guide treatment planning, pelvic 18F-FDG PET/CT （18F-Fludeoxyglucose positron emission tomography / computedtomography）was performed post-admission; however, the results were suboptimal, showing no definitive 18F-FDG-avid foci in the rectovaginal septum, which was inconsistent with the preoperative MRI findings. Consequently, supplementary 18F-FAPI PET/CT was conducted, demonstrating ill-defined soft tissue density between the uterus and rectum, adjacent to mild thickening of the anterior rectal wall. The lesion exhibited intense 18F-FAPI uptake (maximum diameter: 2.0 cm, SUVmax=7.5), corresponding precisely to the MRI-identified location, thereby validating the MRI results. The patient underwent surgical resection, with postoperative histopathology confirming all imaging-suspected lesions as endometriotic foci. A B C D Figure 1.A (18F-FAPI PET/CT) demonstrates a high uptake (SUVmax=7.5) in the rectouterine pouch (pouch of Douglas), whereas B (18F-FDG PET/CT) exhibits diffuse uterine uptake with no significant tracer accumulation in the same region.C and D display coronal and sagittal views of 18F-FAPI and 18F-FDG PET/CT, respectively. Consistent with the axial images, only C (18F-FAPI PET/CT) reveals a well-defined high uptake lesion (diameter: ~2.0 cm, SUVmax=7.5) in the rectouterine pouch, while D (18F-FDG PET/CT) shows nonspecific background activity. Figure 2. Gross specimen photograph of the deep infiltrating endometriosis (DIE) lesion in the rectouterine pouch (pouch of Douglas) from this patient. Discussion： The most common subtypes of pelvic endometriosis include superficial peritoneal lesions, DIE, and ovarian endometriotic cysts. Primary symptoms encompass dysmenorrhea, dyspareunia, infertility, urinary urgency during menstruation, and anal tenesmus. In this case, the patient had a history of dysmenorrhea and was admitted due to anal tenesmus. Although definitive diagnosis of endometriosis is confirmed histologically, preoperative imaging remains critical in clinical practice; however, visualization can be challenging due to the heterogeneous nature of lesions and their highly variable imaging appearances [3] . TVUS and MRI are currently the most widely used imaging modalities with the highest specificity for endometriosis. However, their sensitivity remains limited and highly operator-dependent. In a systematic review, Guerriero et al. [4] reported that for rectosigmoid DIE, both MRI and TVUS demonstrated sensitivities of 85%, with specificities of 95% and 96%, respectively. Conversely, for uterosacral ligament DIE, the sensitivities dropped to 70% for MRI and 67% for TVUS. In the present case, while TVUS indicated an anterior rectal lesion, it failed to delineate its boundaries with adjacent tissues, whereas MRI demonstrated excellent performance, revealing lesions that closely matched intraoperative findings. Recent advances in imaging technology have highlighted the potential of PET as an attractive diagnostic tool, leveraging novel PET tracers combined with superior soft tissue contrast and detailed abdominopelvic anatomical resolution [5] . A 2016 study found that 18F-FES PET/CT （18-Ffluoro-17β-estradiol positron emission tomography / computedtomography）outperformed MRI in diagnostic accuracy, achieving a true positive rate of 100% (9/9 suspected lesions confirmed by histopathology) compared to MRI’s false-positive rate of 66.6% [6] . However, the efficacy demonstrated by different PET probes varies significantly. For instance, a study by Balogova et al. [7] found that 18F-FDG PET/CT showed a positive rate of 72% in 18 patients, with 9 patients exhibiting 13 non-endometriosis-related lesions showing positivity on imaging, where SUVmax ranged between 2.7 and 23. These results were deemed unsatisfactory. Consequently, a novel PET probe has emerged 18F-Fibroblast Activation Protein Inhibitor (18F-FAPI), a PET tracer with high selectivity for fibroblast activation protein. Yangmeihui Song et al. have completed a clinical trial and suggested that FAPI PET has demonstrated significant potential in preclinical experiments and preliminary clinical trials for non-invasive visualization and dynamic monitoring of hepatic fibrosis, particularly outperforming other common clinical indicators in early stages [8] . As varying degrees of fibrosis have been confirmed in endometriosis lesions, 18F-FAPI may serve as an effective PET radiotracers for endometriosis detection. Currently, only three cases of 18F-FAPI application in endometriosis diagnosis have been reported, ¹⁸F-FAPI PET/CT accurately diagnosed DIE lesions in all cases. [9-11] . The imaging findings of TVUS and MRI in this case were consistent, both suggesting suspected DIE in the anterior rectal wall. Additionally, MRI indicated potential lesions in the bilateral uterosacral ligaments, which were later confirmed by postoperative pathology. However, 18F-FDG PET/CT showed no increased uptake in these corresponding lesions. Subsequent 18F-FAPI PET/CT only detected lesions in the rectouterine pouch but failed to visualize the bilateral uterosacral ligament lesions. This discrepancy might be attributed to CT’s inherent limitations in resolving inter-tissue relationships compared to MRI, which demonstrates superior soft tissue differentiation capabilities. Certainly, given that ¹⁸F-FAPI PET/CT also exhibits high uptake in most malignancies—notably ovarian cancer—its use for DIE lesion visualization carries a risk of potential false positives. This necessitates validation through extensive clinical trial data in future studies. Acknowledgments This study was supported by the Sanming Project of Medicine in Shenzhen(NO.SZSM202311011). We gratefully acknowledge the substantial assistance provided by the SanMing Project and the technical support from Director Wang of the Department of Nuclear Medicine in imaging processing. The authors declare no competing interests. References 1. Bulun, S. E., Yilmaz, B. D., Sison, C., Miyazaki, K., et al.Endometriosis. Endocrine reviews, 2019;40(4), 1048–1079. 2. Chapron, C., Marcellin, L., Borghese, B., & Santulli, P. Rethinking mechanisms, diagnosis and management of endometriosis. Nature reviews. Endocrinology ,2019; 15 (11), 666–682. 3. Taylor, H. S., Kotlyar, A. M., & Flores, V. A. Endometriosis is a chronic systemic disease: clinical challenges and novel innovations. Lancet (London, England),2021;397 (10276), 839–852. 4. Guerriero, S., Saba, L., Pascual, M. A., Ajossa, S., et al. Transvaginal ultrasound vs magnetic resonance imaging for diagnosing deep infiltrating endometriosis: systematic review and meta-analysis. Ultrasound in obstetrics & gynecology : the official journal of the International Society of Ultrasound in Obstetrics and Gynecology , 2018; 51 (5), 586–595. 5. Galgano, S. J., Calderone, C. E., Xie, C., et al. Applications of PET/MRI in Abdominopelvic Oncology. Radiographics : a review publication of the Radiological Society of North America, Inc , 2021; 41 (6), 1750–1765. 6. Cosma, S., Salgarello, M., Ceccaroni, M., et al.Accuracy of a new diagnostic tool in deep infiltrating endometriosis: Positron emission tomography-computed tomography with 16α-[18F]fluoro-17β-estradiol. The journal of obstetrics and gynaecology research ,2016; 42 (12), 1724–1733. 7. Balogova, S., Daraï, E., Noskovicova, L., et al.Interference of Known or Suspected Endometriosis in Reporting FDG PET/CT Performed in Another Indication. Clinical nuclear medicine , 2022; 47 (4), 305–313. 8. Song, Y., Qin, C., Chen, Y., et.al.Non-invasive visualization of liver fibrosis with [68Ga]Ga-DOTA-FAPI-04 PET from preclinical insights to clinical translation. European journal of nuclear medicine and molecular imaging , 2024; 51 (12), 3572–3584. 9. Zou, Y., Hu, H., Tian, R., & Wang, R. (2025). Focal 68Ga-FAPI-04 Uptake in Endometriosis at the Rectouterine Pouch. Clinical nuclear medicine , 2025;Advance online publication. 10. Burgard, C., Rosar, F., Ezziddin, S., Hamoud, B. H., Solomayer, E. F., et al.[68Ga]Ga-FAPI-04 PET/CT in a patient with endometriosis: a potential game changer?. European journal of nuclear medicine and molecular imaging , 2025;10.1007/s00259-025-07252-9. Advance online publication. 11. Kellers, F., Lützen, U., Verburg, F., Lebenatus, A., et al. FAP+ activated fibroblasts are detectable in the microenvironment of endometriosis and correlate with stroma composition and infiltrating CD8+ and CD68+ cells. Human reproduction open , 2025 (1), hoaf003. Statements and Declarations –Funding: the Sanming Project of Medicine in Shenzhen(NO.SZSM202311011) –Competing Interests: All authors disclosed no relevant relationships. –Consent to Publish declaration：not applicable –Author Contributions: Tongxin Chen: Original Draft and Translation. Ruyu Cai: Data Curation and Original Draft. Minge S Li: Review & Editing. Pingyue Yu: Translation. Yifan Huang:Formal analysis and Visualization. Haili Li:Review & Editing. Xiangcheng Wang:Formal analysis and Editing. –Data Availability: The data that support the findings of this study are available from the corresponding author, [author initials], upon reasonable request. Information & Authors Information Version history V1 Version 1 01 December 2025 Copyright This work is licensed under a Non Exclusive No Reuse License. Collection Clinical Case Reports Keyword obstetrics/gynecology Authors Affiliations Haili Li 0009-0005-9672-3047 [email protected] Shenzhen People's Hospital View all articles by this author Tongxin Chen Shenzhen People's Hospital View all articles by this author Ruyu Cai Shenzhen People's Hospital View all articles by this author Yifan Huang Shenzhen People's Hospital View all articles by this author Xiangcheng Wang Shenzhen People's Hospital View all articles by this author Pingyue Yu Shenzhen People's Hospital View all articles by this author Minge Li Shenzhen People's Hospital View all articles by this author Metrics & Citations Metrics Article Usage 268 views 229 downloads .FvxKWukQNSOunydq8rnd { width: 100px; } Citations Download citation Haili Li, Tongxin Chen, Ruyu Cai, et al. 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