Diagnostic dilemma on cytology - spindle cell variant of anaplastic carcinoma and medullary carcinoma of thyroid.

Abstract

Anaplastic thyroid carcinoma (ATC) is most aggressive malignancy with an incidence of 1 - 2%. It is common in sixth decade of life with female predominance. Fine needle aspiration (FNA) is an important tool and provides correct diagnosis of ATC in upto 90% of cases. On cytology, ATC shows high cellularity smears composed of pleomorphic population of cells in a necrotic background.The three main patterns of ATC are spindle cell, giant cell, and squamoid. Spindle cell variant should be differentiated mainly from medullary carcinoma of thyroid( MCT) & Malignant fibrous histiocytoma The presence of amyloid in the smear is one of the distinguishing feature from MCT to ATC, but amyloid is not identified in all cases. Spindle cell variant of ATC may be indistinguishable from MCT when scant necrosis is present, but differentiation of the two lesions is important for further management.