Encapsulated Papillary Oncocytic Neoplasm: A Newly Recognized Hurthle Cell Neoplasm With Unique Morphology.

Diagnosis of oncocytic neoplasm of the thyroid gland can be challenging especially on fine needle aspiration biopsy (FNAB), given the wide differential diagnoses. In this report, we present the case of a 66-year-old male with an incidental thyroid nodule identified on imaging. In this case, identification of the distinctive cytologic features leads to the diagnosis of papillary oncocytic neoplasm on FNAB and helped to decide the appropriate surgical management. To date, the cytomorphologic features of this lesion are not well studied and established, with only a single case report in the literature. Herein, we describe the characteristic cytomorphologic and immunophenotypic features of this neoplasm. The recognition of the unique cytomorphologic features and awareness of the non-classic expression of the thyroid lineage markers will help in accurate diagnosis and management of this entity.