Thyroid microcarcinoma: fine-needle aspiration diagnosis and histologic follow-up.

The increased sensitivity of many imaging modalities (ultrasound, computed tomography scan, magnetic resonance imaging) has resulted in the identification of thyroid nodules, measuring 1 cm or less. Usually these small lesions are regarded as incidental and are not sampled by fine-needle aspiration (FNA). However, some of these lesions undergo FNA because of suspicious radiology findings (multifocality, calcification, etc) or in patients with a history of radiation to the head and neck region. We present FNA findings and histologic follow-up of 39 thyroid nodules that measured 1.0 cm or less. All FNAs were performed under ultrasound guidance. The lesions ranged in size from 0.2 to 1.0 cm. Twenty-two lesions were diagnosed as papillary carcinoma (PTC), 4 as medullary carcinoma (MC), and 13 as suspicious for PTC on FNA. Histologic follow-up showed PTC in 35 and MC in 4 cases; 11 PTC were multifocal (31%) and lymph node metastases were present in 8 (16%) cases. Ultrasound-guided FNA is effective in the sampling of thyroid cancers that are 1.0 cm or less. The present study shows that some of these lesions can be clinically significant.