A 9-year-old spayed female domestic shorthair cat was evaluated for a right-sided head tilt and circling of 24 hours' duration. The cat had a 6-year history of intermittent otitis externa, which had been treated with prednisone and antimicrobials. Results of serologic testing for infection with FeLV and FIV were negative, and the cat's vaccination status was adequate. On physical examination, the cat was quiet but responsive. Decreased conscious proprioception was detected in the right forelimb; conscious proprioception in the other limbs and spinal reflexes in all limbs were considered normal. Radiographs of the thorax were obtained to evaluate for evidence of neoplasia (Figure 1).
Radiographic Findings and Interpretation
On the lateral radiographic view, a round soft tissue opacity can be seen in the ventral aspect of the cranial mediastinum. On the ventrodorsal radiographic view, the cranial mediastinum appears wide and has round, convex margins (Figure 2). Radiographic findings were compatible with a cranial mediastinal soft tissue mass. Differential diagnoses for a cranial mediastinal mass in cats include mediastinal lymphoma, thymoma, ectopic thyroid tumor, lymphadenopathy, granuloma, abscess, hematoma, and mediastinal cyst.1
Ultrasonography of the thorax revealed a discrete, thin-walled, anechoic mass with regular margins in the cranial mediastinum (Figure 3). Analysis of an ultrasonographically guided, fine-needle aspirate of the mass revealed fluid with low cellularity, low protein concentration, rare nucleated cells, and erythrocytes; infectious agents and neoplastic cells were not detected. The cytologic character of the fluid was consistent with cystic fluid. In the cat of this report, these findings were compatible with a diagnosis of mediastinal cyst.
Mediastinal cysts are not common in cats.1 Often congenital, mediastinal cysts tend to develop in the cranial mediastinum. Histologic examination is necessary to differentiate the cellular origin of the cyst; however, this invasive step is seldom necessary as mediastinal cysts are often incidental findings with few associated clinical signs. In the cat of this report, no further diagnostic or therapeutic procedures were performed because of the lack of clinical signs attributable to the cyst.
Otoscopic and cytologic examinations of both ears were performed to rule out peripheral vestibular disease as the cause of the neurologic signs in the cat. The cause of the right-sided head tilt, circling, and central proprioceptive deficits was localized to a right-sided central vestibular lesion. Neurologic signs in the cat resolved within 24 hours; therefore, the owners chose not to pursue further diagnostic testing. Because of the acute onset and resolution of neurologic signs, feline ischemic encephalopathy and feline idiopathic vestibular disease were considered as possible differential diagnoses2,3; however, other differential diagnoses such as otitis media, encephalitis, meningitis, neoplasia, or abscess or granuloma of the brainstem could not be ruled out without further diagnostic testing.2,3 Five months after the initial evaluation, the owner reported that the cat appeared to be normal.