Ultrasonographic and Computed Tomographic Features of Dermoid Cyst of the Neck in a Dog: A Case Report

Abstract

A 13-year-old castrated male mixed-breed dog presented for a health screening with a small nodule on the left hindlimb, which was revealed to be a mast cell tumor. A CT scan was performed to evaluate the mast cell tumor, and it incidentally revealed a well-marginated, fluid-attenuating, non-contrast enhanced mass in the deep ventral region of the left lower neck. Ultrasonography confirmed a well-capsulated mass with a cranio-ventrally protruding lesion extending into sternohyoid muscles. The outer layer of the mass had a hypoechoic thick wall and the internal parenchyma contained hyperechoic foci and multiple hyperechoic parallel lines. The mass was surgically resected. Histopathological examination confirmed a dermoid cyst characterized by cornifying squamous epithelial cells, keratinaceous debris, and hair shaft fragments. The dog showed no signs of recurrence or additional abnormalities three months post-surgery. This report highlights the importance of considering dermoid cysts in the differential diagnosis of neck masses on imaging examinations using CT or ultrasonography. © The Korean Society of Veterinary Clinics.