Histopathological and immunohistochemical characteristics of a thyroglossal duct cyst in a budgerigar (Melopsittacus undulatus).

A thyroglossal duct cyst is a developmental disorder that occurs in the neck, widely described in humans and rarely reported in animals. This paper describes the microscopic and immunohistochemical characteristics of a thyroglossal duct cyst in a 7-year-old budgerigar (Melopsittacus undulatus) that presented with dyspnoea and lethargy and a radiopaque tissue mass in the ventral region of the neck that did not involve vertebrae or muscles. At necropsy, a fluid-filled cystic structure (3.2 × 2.9 cm) was identified. Microscopically, the cyst was lined by stratified squamous epithelium and had a thick wall composed of cuboidal epithelial cells that formed follicles, occasionally occupied by homogeneous eosinophilic colloid. These cells were immunopositive for thyroglobulin and thyroid transcription factor 1. This is the first report of a thyroglossal duct cyst, which is a mass on the neck that develops from cells and tissues remaining after the formation of the thyroid gland, in companion birds. Thyroglossal duct cysts in humans and animals have a good prognosis and can be successfully removed surgically, hence the importance of considering them as a differential diagnosis in birds that develop masses in the neck region.