Diagnosis of medullary carcinoma of the thyroid by fine needle aspiration biopsy.

Fine needle aspiration biopsy has been evaluated as a diagnostic method for medullary carcinoma of the thyroid (MCT) in 18 patients with verified hereditary or sporadic MCT. The typical MCT cell was asymmetrical, sometimes triangular and often with a characteristic red granulation in May-Grünwald-Giemsa staining. Eccentrically positioned, multiple nuclei were common. Amyloid was seen both intra- and extracellularly, staining blue-grey or violet with May-Grünwald-Giemsa and with green birefringence in polarized light after staining with alkaline Congo. The method was simple and quick to perform, causing negligible discomfort to the patient. No complications were seen. An adequate bioptic yield was obtained in 15 patients. In 13 of them (87 percent), including one patient with a normal thyroid at clinical examination, a correct diagnosis was reached.