Thyroid follicular adenoma with numerous intracytoplasmic lumina mimicking yellow bodies: a case report

Intracytoplasmic lumina (ICL) are distinct, intracytoplasmic spherical structures enclosed by a cell membrane. ICL are usually solitary and are 5–10 lm in diameter. Ultrastructural studies have shown that they are composed of an epithelial membrane bearing apical microvilli. ICL sometimes contain inspissated secreted material, have been observed in adenocarcinomas, particularly of the breast, and their presence is a cytological clue to indicate carcinoma. In the thyroid, their presence has not always indicated malignancy as ICL have been observed in both benign and malignant thyroid lesions including non-neoplastic H€ urthle cell lesions (NNHCLs), H€ urthle cell tumours (HCTs), and medullary carcinomas (MCs). Recently, we encountered a case of follicular adenoma (FA) with numerous ICL. To the best of our knowledge, such a case has never been reported. At the time of cytological diagnosis, we confused ICL with yellow bodies (YBs) that are characteristic of hyalinising trabecular tumours (HTTs). Herein, we report our rare case and discuss the distinction between ICL and YBs.