Cytohistology of morule in cribriform-morular variant of papillary thyroid carcinoma.

Cribriform-morular variant (CMV) is a rare variant of papillary thyroid carcinoma. It frequently occurs in association with familial adenomatous polyposis (FAP), although some cases are sporadic. Herein, we report a case of CMV and analyse morule cytohistology. The patient was a 47-year-old woman with no familial history of FAP. A 3.0-cm unifocal mass was identified in the left thyroidal lobe. Fine-needle aspiration cytology revealed papillary clusters of atypical cells with nuclear grooves, which was suspected to be conventional papillary thyroid carcinoma. Histologically, the tumour comprised a papillary and cribriform growth of atypical cells with cytoplasmic accumulation and nuclear translocation of b-catenin. In addition, frequent morule formation was identified. In this case, we performed morule analysis through correlative light and electron microscopy (CLEM), and revealed its ultrastructure. Although CMV is a rare form of thyroid carcinoma, it should be considered along with its distinct clinicopathological characteristics.