Abstract
An 8-year resident, mature, female, beluga whale originating from the Sea of Okhotsk in Russia, with a nursing 16-month-old calf by her side, presented with acute cessation of eating. Within one hour of refusal to eat, she began to swim aimlessly. By that evening she had a slight head/body tilt to the right, she refused to nurse her calf, and ignored all signals for trained behaviours. The next morning, she was manually moved into the medical pool, placed in a sling, and treatment was begun with broad-spectrum antibiotics, corticosteroids, fluids and electrolytes. Besides listlessness and weakness, bilateral haemorrhaging into the skin of the lower eyelids was noted. All blood work and other diagnostics were normal.
In spite of aggressive therapy, the beluga died 28 hours after onset of clinical signs. A soft, friable, hemorrhagic mass of softball size and elongated yet coral-like shape protruded grossly from the right rostral-dorsal aspect of the cerebellum. Careful dissection showed the tumour protruded from the fourth ventricle.1 The lateral ventricles of the brain were dilated. All other organs appeared normal grossly.
Microscopic examination identified the mass to be a choroid plexus papilloma (CPP). Only three tumours have been documented in the brain of cetaceans, two of which--a neurofibroma and a lipoma--were found in baleen whales and only one, an undifferentiated carcinoma, was observed in toothed whales.2 This third tumour affected a beluga as well. It originated from the brain stem, and (by definition) also had an epithelial origin. That beluga, housed in Hawaii and later in San Diego, originated from Churchill, Manitoba.3
The choroid plexus is a richly vascularized infolding of the lining of the ventricular surface and is involved in the production of most of the cerebrospinal fluid. In human oncology, these tumours account for one to three percent of paediatric brain tumours, are hallmarked by severe hydrocephalus due to the obstruction of CSF flow, and are most common in children under 2 years of age.4 In domestic animals, CPPs are most commonly found in male dogs over 6 years of age, but have been documented in mice, cows and horses.5,6 A case has been reported in a mature dogfish shark (Squalus acanthias).7 In dogs, CPPs are often found in the fourth ventricle, and can cause spastic tetraparesis, positional nystagmus, head tilt and vomiting over a course of many weeks to months. Except for a slight head tilt 24 hours before death, this beluga had none of these clinical signs and also died peracutely. This is the first choroid plexus papilloma documented in marine mammals and it is only the second tumour to be documented in the brain of toothed whales.
References
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