Dilated pore of Winer in a dog

A 9-year-old male neutered Goldendoodle was presented to the Animal Medical Center of Seattle with a history of a firm, hairless, cystic mass on the dorsal aspect of the neck. The mass had been present for 2 years and would periodically rupture and discharge moderate quantities of yellow-green, soft, semi-solid, keratinaceous material. As rupture of the mass was reported to cause the patient significant pain and discomfort, it was surgically excised. Histopathology of the mass revealed a bulbous keratin-filled cyst that communicated with the external environment via a small ostium. At the base of the cyst, the cyst lining was characterized by a markedly irregular and hyperplastic stratified squamous epithelium with an overt stratum granulosum and prominent, irregularly sized, shaped and spaced rete ridges. At the superficial aspect of the cyst near the ostium, the cystic lining was characterized by a relatively thinner stratified squamous epithelium with an overt stratum granulosum and regular basal contour. Based on the histomorphological appearance of the mass, a diagnosis of a dilated pore of Winer was made. Dilated pores of Winer are follicular cysts arising from the infundibulum of the hair follicle. They are relatively common in humans and uncommon in cats, and single case reports have been described in a horse and a woodchuck (Marmota monax). To the best of the authors' knowledge, this is the first description of a dilated pore of Winer in a dog.