Fine needle aspiration cytology of primary thyroid paraganglioma. Report of a case with cytologic, histologic and immunohistochemical features and differential diagnostic considerations.

BACKGROUND: Thyroid paraganglioma is a rare tumor and can cause diagnostic difficulties when using fine needle aspiration cytology (FNAC), especially when associated with some cytologic atypia. This case report appears to be the first on FNAC of primary thyroid paraganglioma.

CASE: FNAC of a thyroid nodule situated in the right lobe was performed on a 46-year-old female. FNAC showed single cells and loose clusters of large, oval cells with round to oval nuclei, evenly dispersed chromatin, focally discrete nucleoli, moderate anisocytosis and anisonucleosis. A few larger cells showing irregular nuclei and coarser chromatin. The tumorous appearance of the lesion and some cytologic atypia led to a right lobe thyroidectomy, revealing a primary thyroid paraganglioma associated with capsular invasion; slight, focal cytologic atypia; and no vascular invasion.

CONCLUSION: The atypia probably originated in the area of capsular invasion. To avoid misdiagnosing these tumors as malignancies, paraganglioma should be added to the differential diagnosis list when dealing with thyroid FNAC showing some atypia.