Fine Needle Aspiration Cytology of Langerhans Cell Histiocytosis of the Thyroid

BACKGROUND: Langerhans cell histiocytosis (LCH) of the thyroid is a rare condition, and fine needle aspiration cytology (FNAC) of this entity has rarely been described. CASE: FNAC was done on a 3-cm-diameter thyroid swelling in the left lower lobe of the thyroid gland. Smears showed a large number of lymphocytes, eosinophils, thyroid follicular cells and discrete, large cells with prominent nuclear grooves. Mitotic activity was frequent. A cytologic diagnosis of LCH was offered. Subtotal thyroidectomy was performed, and the cytologic diagnosis was confirmed by histology. CONCLUSION: LCH of the thyroid has certain salient diagnostic features. The presence of histiocytes with prominent nuclear grooves, reactive lymphoid cells and eosinophils along with benign thyroid follicular cells should raise the suspicion of this rare entity on FNAC smears of the thyroid.