Cytodiagnosis of distant metastases from follicular thyroid carcinoma

Follicular carcinoma of the thyroid is second most common primary malignancy of the thyroid gland after papillary carcinoma and metastasis is uncommonly seen in these patients.

To describe the cytomorphologic features for the accurate diagnosis of distant metastases from follicular carcinoma of thyroid.

A total of 10 aspirates reported as metastatic follicular carcinoma of thyroid were reviewed for the available clinical and radiological details.

All the patients were females. Six of these patients presented with subcutaneous and soft tissue swellings, one presented with a lung mass, one with right breast swelling, one with lumbar vertebral lesion and one with left iliac bone involvement. The cytology smears revealed tumour cells predominantly arranged in a repetitive microfollicular pattern with some scattered individually and in sheets. The tumour cells were small, had mild nuclear pleomorphism, round nuclei, low nuclear-cytoplasmic ratio, fine chromatin, inconspicuous nucleoli, and scanty to moderate amount of cytoplasm with some showing marginal vacuoles with "fire-flare" appearance. Occasional microfollicles showed scanty eosinophilic colloid in the center.

Identification and establishment of a correct clinical diagnosis of a distant metastasis from a follicular thyroid carcinoma is a challenging task. We believe that with prior knowledge of characteristic cytologic features, such metastases can be rapidly and accurately diagnosed by fine needle aspiration cytology.