[Agenesis of the thyroid lobe associated with Hashimoto's thyroiditis]

A thyroid hemiagenesis in association with Hashimoto's thyroiditis and mild hypofunction in a 40 years woman, is described. It is an unusual association. The clinical, hormonal, immunological, instrumental and cytological diagnosis has been established. The importance of the scintigraphic pattern and the differential diagnosis with other pathological situations, such as Plummer's disease and several destroying processes, is emphasized. It is suggested that thyroid hemiagenesis has not to be regarded as clinically insignificant, in consideration of a possible association with pathologies of the normally developed lobe (Graves' disease, myxoedema, goiter, Hashimoto's thyroiditis, and especially neoplastic degeneration) or with nonthyroid diseases (hyperparathyroidism).