Fallopian fimbriae entrapped in an ovarian endometriotic cyst mimicking malignancy: a case report

Ovarian endometriotic cysts are associated with an increased risk of clear cell and endometrioid carcinomas, as well as borderline neoplasms. Although contrast-enhancing nodules on magnetic resonance imaging (MRI) suggest malignancy, benign endometriotic cysts can also present with such features, complicating differentiation from malignancy. When malignancy is suspected, minimally invasive procedures, such as laparoscopic cystectomy, are typically avoided. However, preserving fertility and ovarian function warrants careful consideration when selecting invasive surgical procedures. From the perspective of selecting appropriate surgical approaches, accurate preoperative differentiation between benign and malignant ovarian tumors is essential. We present the first case of MRI showing fallopian fimbriae entrapped in an endometriotic cyst mimicking malignancy. A 49-year-old female presented with atypical genital bleeding. MRI revealed a right ovarian endometriotic cyst with a contrast-enhancing mural nodule (10 mm), suggestive of malignancy. The nodule demonstrated T2-weighted hypointensity equivalent to the cyst fluid without diffusion restriction. Laparotomy revealed the nodule as entrapped fallopian fimbriae within the endometriotic cyst, with no malignancy detected. In this case, the fallopian fimbriae entrapped in the endometriotic cyst appeared as an enhancing nodule because of their vascularity, mimicking malignancy. Fallopian fimbriae are inconspicuous structures that can produce false findings suggestive of malignancy, similar to other benign enhancing nodules, such as polypoid endometriosis and decidualization. However, their lack of diffusion restriction and low T2-weighted signal intensity may help distinguish them from malignancy. This knowledge is crucial for accurate diagnosis and avoiding unnecessary interventions. Graphical abstract Similar content being viewed by others Data availability No datasets were generated or analysed during the current study.

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We would like to thank Editage (www.editage.jp) for the English language editing. Author information Authors and Affiliations Contributions All authors contributed to the conception and design of this study. Material preparation, data collection, and analyses were performed by A.Y. and S.K. The first draft of the manuscript was written by A.Y., and all authors commented on previous versions of the manuscript. All the authors have read and approved the final version of the manuscript. Corresponding authors Ethics declarations Competing interests The authors declare no competing interests. Additional information Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. Rights and permissions Springer Nature or its licensor (e.g. a society or other partner) holds exclusive rights to this article under a publishing agreement with the author(s) or other rightsholder(s); author self-archiving of the accepted manuscript version of this article is solely governed by the terms of such publishing agreement and applicable law. About this article Cite this article Yoshida, A., Kohno, S., Oka, S. et al. Fallopian fimbriae entrapped in an ovarian endometriotic cyst mimicking malignancy: a case report. Abdom Radiol 50, 4374–4379 (2025). https://doi.org/10.1007/s00261-025-04882-3 Received: Revised: Accepted: Published: Version of record: Issue date: DOI: https://doi.org/10.1007/s00261-025-04882-3