Encapsulated Follicular Variant of Papillary Thyroid Carcinoma Arising in a Follicular Adenoma: a Diagnostic Dilemma.

Papillary thyroid carcinoma (PTC) arising within follicular adenoma is a rare histological subset of papillary carcinoma. A 24-year-old female (euthyroid and asymptomatic) presented with a solitary mass in the right lobe of thyroid for 2 years. Fine-needle aspiration cytology (FNAC) suggested features of hyperplasia of thyroid. Hemithyroidectomy was performed. Histopathological examination revealed two distinct areas and was reported as encapsulated variant of papillary carcinoma along with follicular adenoma. Papillary carcinoma was confirmed by positive immunohistochemistry for HBME-1. CT head and neck region ruled out metastasis and the patient was kept on follow-up. There have been reports of medullary and papillary carcinomas occurring together; however, there is a paucity of literature on co-existing follicular neoplasm and papillary carcinoma. We hereby report a rare case of follicular variant of papillary carcinoma arising within follicular adenoma of the thyroid.