Infected oral squamous cell carcinoma associated with purulent otitis media in an adult pet rat <i>(Rattus norvegicus)</i>.

A 15-month-old intact female rat was presented with worsening lethargy and dysorexia present for 1 wk and bruxism present for 3 d. The diet was fruits, vegetables, and granola. On presentation, the rat was mildly dehydrated and had marked incisor malocclusion with enamel hypoplasia. On oral examination, the left mandibular molars were not visible and the gum line was prominent. Black punctate enamel discoloration was observed multifocally on molars, but no mucosal lesions were observed. The incisors were trimmed and the rat was discharged with analgesics, supportive care, and dietary recommendations. The rat's condition continued to deteriorate and, 1 wk later, a left mandibular mass appeared that the owner perceived as painful. Computed tomography of the head showed lysis of the body of the left mandible, absence of left mandibular molar teeth, and abnormal soft-tissue attenuation in the left tympanic bulla. On the last visit (Day 31), purulent discharge was visible in the left external ear canal and along the left mandibular gingiva. Fine-needle aspiration and cytology of the mandibular mass suggested a keratinizing epithelial tumor of benign appearance. Euthanasia was elected, based on the poor prognosis. Histopathological examination revealed a well-differentiated oral squamous cell carcinoma of the left mandibular region with ipsilateral subacute purulent otitis media. Key clinical message: Squamous cell carcinoma should be included in the differential diagnosis of an infected, non-ulcerated oral mass in a rat.