Granular cell tumour of the thyroid gland: a case report and review of the literature.

Granular cell tumours of the thyroid gland are rare, with only six previously reported cases in the English literature. Current histological, immunohistochemical and electron microscopic evidence favours a neural/Schwannian relationship. A case of a granular cell tumour of the thyroid gland in a healthy 36-year-old woman is described. The tumour was found incidentally following a right thyroid lobectomy for symptoms from an asymmetric multinodular goitre. Macroscopically, the lesion resembled a papillary microcarcinoma. Microscopically, the tumour was composed of nests of epithelioid cells with abundant granular, eosinophilic cytoplasm. The nests were divided by fibrous septa and peripherally interdigitated with surrounding thyroid follicles. Immunohistochemistry helped to distinguish the lesion from other neoplasms such as Hurthle cell tumour, medullary carcinoma or metastasis, and also from a histiocytic reaction to previous fine needle aspiration. On the basis of this diagnosis, no further intervention was required, and the patient was discharged following post-operative review.