Paratracheal Cervical Mass in a Dog

Abstract

A 14-year-old female Welsh Terrier was presented for evaluation of multiple skin masses. Two of them were diagnosed as a follicular (epidermal) cyst and a sebaceous epithelioma by cytology and histopathology. The third mass was located in the subcutis adjacent to the cervical trachea. Clinical findings, thoracic radiography, and laboratory results were otherwise unremarkable. Cytologically, the cervical mass was characterized by the presence of round to polygonal cells with distinct cell borders, mild to moderate anisocytosis, round to oval eccentric nuclei with prominent nucleoli, and a variable amount of finely granular, eosinophilic cytoplasm. Differential diagnoses included endocrine/neuroendocrine tumors such as thyroid adenocarcinoma, medullary thyroid carcinoma, carotid body chemodectoma, and parathyroid carcinoma. The mass was removed surgically and submitted for histopathologic and immunohistochemical examination. Histologically, the mass was composed of rows and nests of densely packed cells separated by thin fibrovascular stroma. Neoplastic cells had moderate to large amounts of pale eosinophilic dusty or finely vacuolated cytoplasm and round to oval nuclei with finely dispersed chromatin and 1 or 2 small nucleoli. On immunohistochemistry, neoplastic cells were positive for chromogranin A, calcitonin, and neuronspecific enolase, and were negative for cytokeratin and thyroglobulin. The final diagnosis was medullary thyroid carcinoma, an uncommon endocrine tumor of dogs that has cytologic and histopathologic features similar to other endocrine and neuroendocrine tumors. Immunohistochemistry or immunocytochemistry should be performed to differentiate medullary thyroid carcinoma from other endocrine/neuroendocrine tumors of dogs.

Endocrine/Neuroendocrine System

“…No sex predilection has been established; however, a breed predilection has been suggested for Boxers, Beagles, and Golden Retrievers (Harari et al, 1986). Approximately 50% to 70% of the thyroid tumors identified clinically in the dog are carcinomas (Bailey and Page, 2007), including thyroid follicular carcinoma arising from the follicular epithelium, and less commonly medullary carcinoma from parafollicular or C-cell origin (Barber, 2007;Bertazzolo et al, 2003). The biologic behavior of canine thyroid tumors is well characterized.…”

“…Most thyroid tumors, even adenocarcinomas, are composed of a fairly uniform population of cells, displaying few, if any, criteria of malignancy (Figs. Definitive diagnosis as medullary carcinoma requires histopathology and immunohistochemistry (Bertazzolo et al, 2003). There may be mild to moderate anisokaryosis ( Fig.…”

Computed Tomographic Features of Basihyoid Ectopic Thyroid Carcinoma in Dogs

“…In small animals, thyroid ectopic tissue has been reported in the cranial mediastinum, at the heart base, very rarely at different intracardiac locations, in the subcutis adjacent to the cervical trachea, and at the base of the tongue/hyoid apparatus . Other unusual locations such as along the esophagus or in the abdomen are described in people …”