Paraganglioma-like medullary thyroid carcinoma: fine needle aspiration cytology features with histological correlation

Objectives:  Two cases of an extremely rare paraganglioma-like variant of medullary thyroid carcinoma (MTC) are reported.
Methods:  The patients were a 65-year-old male (case 1) and a 14-year-old female (case 2). Unilateral thyroid nodule and homolateral cervical lymphadenopathy was present in case 1; bilateral thyroid nodules were seen in case 2. Fine needle aspiration cytology (FNAC) was performed from thyroid nodules (in both cases) and from a cervical lymph node (in case 1).
Results:  The cytological smears contained predominantly ovoid to spindled epithelial cells arranged in cohesive three-dimensional clusters with sharp margins; isolated individual cells were seen only rarely. No colloid or other material was present in the background. The tumour cells showed significant nuclear atypia with occasional bizarre and/or binucleated cells. The nuclear chromatin was coarse and granular, sometimes with grooves and intranuclear inclusions. The cytoplasm was inconspicuous. Polygonal or triangular cells, amyloid and azurophillic cytoplasmic granules were absent in both cases. Calcitonin expression was demonstrated in case 2. Histological examination confirmed the paraganglioma variant of MTC in both cases.
Mutation of RET proto-oncogene in exon 16 (Met918Thr) – germline in case 2 and somatic in case 1 was detected by sequencing of DNA in both cases.
Conclusions:  This is the first description of cytological findings in the paraganglioma-like variant of MTC. Despite its rarity, it can be reliably diagnosed by FNAC if material for immunocytochemistry is obtained.