[Ultimobranchial cysts in goitrous thyroids of sheep at high altitude]

Histomorphology of ultimobranchial cysts of thyroid glands of sheep is presented. The average incidence of cysts in sheep was 17.3%. The cysts have some characteristic features indicating their ultimobranchial origin: the presence of inhomogeneous "foamy" colloid staining positively for glycosaminoglycans, heteromorphism of the cells lining the internal surface of the cysts, and the presence of ciliary cells among them. The detection of ultimobranchial cysts in sheep with strumous thyroid glands not only extends the concept of the species appurtenance of these formations but also indicates the possibility of frequent occurrence of ultimobranchial cysts in hyperplastic processes of strumous and neoplastic nature which is of great diagnostic and prognostic significance.