Cerebellar Herniation in Captive Lions (Panthera Leo)

head tilt to the left. Cerebrospinal fluid and electromyogram were within normal limits. At necropsy, the osseous tentorium cerebelli was markedly thickened with a central 4- 3 3.5- 3 3-cm irregular hard knob continuous with the markedly thickened occipital bone. The protuberance was located between the posterior aspect of the cerebrum and the cerebellum and compressed the cerebellum and reduced the size of the cerebellar fossa. There was mild dorso-ventral flattening of the cerebral hemispheres. The ventral third of the cerebellar vermis was flattened, with a lip-like projection extruding from the vermis and resting on the medulla (Fig. 1). The fourth ventricle and medulla were elongated and extended beyond the foramen magnum. Lion 2 was a weak, month-old female cub that had poor weight gain and developed a head tilt at 3 weeks of age. Skull radiographs, retinal examination, and otic examinations were conducted at VMTH and were found to be within normal limits. The cub died, and at necropsy, removal of the tentorium cerebelli was difficult. Gross changes at necropsy were similar to those of lion 1. Lions 3, 4, and 5 were littermates with neurologic signs consisting of progressive ataxia, head tilt, and loss of orientation of variable severity. Toxoplasma, FIV, and FeLV tests were negative, and CBC and serum chemistry were within normal limits. The cubs were euthanized and necropsies were performed at the VMTH. Similar lesions were present in the 3 cubs, with a thick, nodular osseous tentorium cerebelli (Fig. 2) and reduction in posterior fossae with dorso-ventral compression of the cerebellum. A portion of the caudal cerebellar vermis was markedly flattened, with a peglike projection that extended beyond the foramen magnum (Fig. 3). In addition, cubs 4 and 5 had elongation of the fourth ventricle and displacement of the choroid plexus. Sagittal section of the cerebral hemispheres revealed mildly dilated lateral ventricles. Archival reports from the VMTH revealed 3 other lions, lions 6, 7, and 8 from the same collection, that showed neurologic signs. These lions were euthanized and necropsied by the referring veterinarian, and tissues were submitted to the VMTH. No gross lesions were noted. Lion 6 was a 1.2year-old female that had recurring problems with orientation, rolling with its head up, bellowing, and progressive difficulties in swallowing and defecating. Keepers noted that the lioness had never behaved completely normally since birth. Lion 7 was a 1.2-year-old male with incoordination and opisthotonus for approximately 2‐3 months. Skull radiographs, serum chemistries, and CBC were within normal limits. Lion 8 was a 1.5-year-old female with recurring equilibrium problems, and often the animal would lose its balance when it became excited and would run blindly into objects and fall. The brains and spinal cords of all the lions except lion 8 were examined in detail. Histologic lesions of the central