Bilateral Cystic Endosalpingiosis in Cervical Lymph Nodes Mimicking Metastatic Papillary Thyroid Carcinoma Morphologically on Cytology: A Case Report and Literature Review of Diagnostic Challenges.

The presence of cystic lymph nodes in the neck can present a challenging differential diagnosis, with considerations often including metastatic papillary thyroid carcinoma (PTC), cystic squamous cell carcinoma, and congenital cysts. The cytologic overlap between benign Müllerian inclusions and PTC features adds complexity, especially in unusual locations. A 45-year-old woman with a history of ovarian serous borderline tumor (SBT) and non-invasive Müllerian implants presented with cystic lymphadenopathy in the neck. Imaging revealed multiple suspicious, partially cystic lymph nodes. Fine-needle aspirations (FNA) from two nodes showed moderate cellularity, monolayered epithelial sheets, and nuclear features suggestive of PTC. FNA cytology, thyroglobulin level, and immunocytochemical profile revealed benign Müllerian cells within lymph nodes. Subsequent histologic evaluation of the excised lymph nodes confirmed cystic endosalpingiosis. This case emphasizes the value of comprehensive clinical-pathologic correlation and appropriate ancillary studies in the evaluation of cystic lymphadenopathy. Awareness of benign Müllerian inclusions and their mimicry of metastatic disease is essential for accurate diagnosis and optimal patient management.