Cytodiagnosis of distant metastases from follicular thyroid carcinoma

INTRODUCTION: 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. AIMS AND OBJECTIVES: To describe the cytomorphologic features for the accurate diagnosis of distant metastases from follicular carcinoma of thyroid. MATERIALS AND METHODS: A total of 10 aspirates reported as metastatic follicular carcinoma of thyroid were reviewed for the available clinical and radiological details. RESULTS: 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. CONCLUSIONS: 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.