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Epidermoid cysts (EC) are benign lesions of ectodermal origin lined by a stratified squamous epithelium that resembles normal epidermis, but lacks the skin appendage present in dermoid cysts (Hagr and others 2001). While ECs are one of the most common type of cutaneous cysts (Withrow and Vail 2007), their occurrence in the abdomen (ie, spleen (Chen and others 2013), caecum (Demir and others 2012), etc) and retroperitoneum (Fdili Alaoui and others 2012)) has been rarely reported in human medicine. We describe the first case report, to our knowledge, of retroperitoneal pelvic EC in a dog.
An 11-year-old intact male Alaskan malamute was investigated for recently developed abdominal pain, low appetite and intermittent constipation and dysuria. A large mass compressing the rectum was felt on rectal inspection. Complete blood count, serum biochemical analyses and urinalysis were performed and unremarkable. The dog was then examined via abdominal radiography, ultrasound and CT. Radiography detected a retroperitoneal lumbar large radiopaque area with ventral and lateral displacement of the large intestine. Abdominal ultrasound was performed and revealed a large hypoechoic mass in the dorsal portion of the abdomen, compressing the surrounding organs. A CT scan showed a 50 mm×47 mm×72 mm cystic mass filled with homogeneous material (25 Hounsfield units; HU), with smooth boundaries and no contrast medium enhancement. The lesion was located in the pelvic cavity, dorsal to the rectum between the iliac internal veins and arteries ( Fig 1 ). While the dog was anesthetised, a trans-rectal fine-needle aspiration of the mass was performed. Abundant lamellar keratin debris was found on cytology, and a diagnosis of retroperitoneal pelvic dermoid/epidemoid cyst was hypothesised. The patient underwent surgery: the laparotomy showed a large retroperitoneal thin-walled cyst with no evident connection with surrounding organs ( Fig 2...