Case 170825-2

17-year-old, 4.6 kg, female, North American river otter (Lontra canadensis)

This individual was hospitalized two days prior to necropsy for treatment of hindlimb paraparesis. She was started on tramadol and gabapentin. She has a previous history of hemiparesis five months ago, which improved with medical management. A suspect diagnosis of intervertebral disc disease (IVDD) was made, but further diagnostics were not performed. The patient also has a prior history of osteoarthritis, dental disease, and suspect renal calculi. For the past 1.5 months, she had intermittent vomiting (once approximately every two weeks). During hospitalization, the animal started to show other neurologic signs besides paraparesis, including a left turn and intermittent rolling. The morning of necropsy, the patient was quiet - she was observed turning to the left and a grand mal seizure was observed, which was stopped with intramuscular administration of midazolam. Due to the increased suspicion of intracranial disease, and the patient’s clinical progression, humane euthanasia was elected. Clinically, her signs were localized as most likely intracranial disease, particularly right forebrain, with the possibility as well of multifocal neurologic disease.

The animal examined is a 4.6 kg, approximately 17-year-old female North American river otter (Lontra canadensis). The necropsy is performed at 1300 on 12/22/16. Postmortem interval is approximately 3 hours, and postmortem condition is good. Nutritional condition is good based on adequate muscling and moderate subcutaneous and intracavitary fat stores. The fur is shaved over the right lateral saphenous vein. The muzzle, right thoracic paw, and left pelvic paw are stained with green ink. There are 2- to 4-mm-diameter foci of thinned or lost fur over the ventral aspects of the first five caudal vertebrae. All claws are worn short, most prominently on the thoracic limbs. There is marked, generalized accumulation of plaque and calculus on essentially all teeth, and the gingival margins are multifocally bright red. The kidneys are externally lobulated. The right kidney is 8.5 x 3 x 1.5 cm and 29.6 g. The left kidney is markedly smaller (atrophied), 7.2 x 2.5 x 1.5 cm and 12.9 g, and approximately 50% of its reniculi, clustered at the caudal pole, are smaller and slightly firmer than the left cranial reniculi and right renal reniculi. A reniculus at the medial aspect of the center of the left kidney has a 2-mm-diameter cyst containing transparent, watery fluid. The liver is 193.8 g (4.2% of body weight) and mottled dark red to brown, with a slightly granular texture and multifocal, hazy, gray-white, poorly demarcated foci covering 20% of its capsular surface. The lungs are mottled pink to dark red. There are hundreds of evenly-spaced, 2- to 3-mm-diameter, white, soft, slightly raised foci scattered over the pleural surfaces of all lobes. These do not correspond with changes in the underlying parenchyma. The heart is 33.8g (0.7% of body weight). The right ventricular free wall, interventricular septum, and left ventricular free wall are 3 mm, 6 mm, and 8 mm thick, respectively. A mesenteric lymph node is 4 x 1.5 x 1.5 cm and has a 1 x 1 x 1.3 cm, pale tan to white, soft, nodular focus that protrudes slightly from cut surfaces. The articular surface of the right femoral head is flattened, broadly eburnated, and surrounded by a rim of osteophytic proliferation on the femoral neck. The corresponding acetabulum is shallow.

This slide has a section of brain at the level of the thalamus in which there are lesions of multifocal vessels with occasional parenchymal malacia. Nearly all small vessels have some degree of change to the vessels walls ranging from minimal to severe intimal and intimomedial expansion or proliferation. Vessel walls are asymmetrically expanded by a smudgy, amorphous, eosinophilc to amphophilic material admixed with few numbers of transmigrating lymphocytes and plasma cells, which also occasionally form small cuffs or clusters in the perivascular space. Other vessels have mild to moderate, intimal, perpendicular proliferation, which encroaches into the luminal space. Lastly, many vessels have intimomedial vacuolation with aggregates of foamy macrophages, rare mineralization and occasional clusters of cholesterol clefts. Occasional parenchymal vessels are variably obscured by hemorrhage, which extends into the surrounding neuropil and studded by brown, globular pigment, which is both intra- and extracellular and intermixed with mats of fibrin. Adjacent to one of these hemorrhagic foci is a cluster of large cavitations surrounded by rarefied neuropil and similarly infiltrated by pigment-laden macrophages. The pia meninges are multifocally infiltrated by few to moderate numbers of lymphocytes and plasma cells.

N/A

Brain (arteries, arterioles): mild to marked, multifocal, hyaline arteriolosclerosis with hemorrhage and multifocal atherosclerosis Brain: Severe, acute to chronic (polyphasic), multifocal hemorrhage with malacia, cavitation and reactive gliosis (consistent with multifocal infarctions)

This case had extensive vascular changes to the central nervous system and, interestingly, rare vessels with mild arteriosclerosis in other tissues. This was a captive river otter with presumably diet-induced vascular changes. The large parenchymal cavitations are likely secondary to previous infarctions, particularly given the evidence of chronic hemorrhage associated with these malacic regions. The patient’s neurologic signs are attributed to the described vascular changes in the CNS. The discussion revolved around the distribution, being primarily restricted to the CNS, and lacking arteriosclerotic changes to other typical vessels such as in the heart and kidneys (retinas not evaluated).

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