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

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.