A 4-year-old 11.4-kg (25.1-lb) sexually intact female Shetland Sheepdog was referred to the University of Wisconsin Veterinary Care neurology service because of sudden-onset ataxia of 12 hours' duration. At the initial evaluation, the dog's abnormalities were limited to the neurologic system.
Etiologic diagnosis—The primary differential diagnoses for this dog included meningoencephalitis (infectious or inflammatory), neoplasia (meningioma, lymphoma, glioma, ependymoma, or choroid plexus neoplasm), acute vascular event, or cyst. The diagnostic plan included a CBC, serum biochemical analysis, urinalysis, thoracic radiography, and abdominal ultrasonography (to evaluate for evidence of compressive, inflammatory, or infectious disease), brain MRI (with and without gadolinium contrast administration), and CSF analysis (to evaluate for inflammatory, infectious, or neoplastic disease).
Diagnostic test findings—Results of the CBC, serum biochemical analysis, thoracic radiography, and abdominal ultrasonography were within reference limits. The dog was anesthetized, and MRI of the brain was performed with and without IV administration of gadolinium contrast agent.a Transverse T1-weighted images (before and after contrast agent administration), T2-weighted gradient echo and fluid attenuated inversion recovery (FLAIR) images, and sagittal T2-weighted and sagittal and dorsal plane T1-weighted images after contrast administration were obtained. Within the fourth ventricle, a well-marginated, round, ring-enhancing mass was identified. The lesion measured 9 × 8.5 × 10 mm and was hyperintense on T2-weighted images and hypointense on T1-weighted images (compared with the appearance of gray matter) with heterogeneous signal intensity on FLAIR images (Figure 1). The mass displaced the cerebellum dorsally. The lateral ventricles, third ventricle, and mesencephalic aqueduct were moderately distended, consistent with obstructive hydrocephalus. Analysis of a CSF sample (collected at the cerebellomedullary cistern) revealed high total protein concentration (107 mg/dL; reference interval, < 20 mg/dL) and high total nucleated cell count (375 cells/μL; reference interval, < 5 cells/μL). Cytologic interpretation of these findings was neutrophilic pleocytosis. The dog was discharged from the hospital and treated orally every 12 hours with prednisone (0.2 mg/kg [0.09 mg/1b]), ciprofloxacin (10 mg/kg [4.5 mg/1b]), clindamycin (6.5 mg/kg [3 mg/lb]), and fluconazole (4.3 mg/kg [2 mg/lb]). A urine sample was negative for Blastomyces antigen; Cryptococcus antigen was not detected in a serum sample. Anti-Neospora caninum IgG was not present in the CSF sample. Therefore, administration of all medications except prednisone was discontinued. On the basis of the diagnostic imaging findings, signs of inflammatory processes in the CSF, and the lack of positive results following infectious disease testing, a presumptive diagnosis of a cyst with secondary inflammation and obstructive hydrocephalus was made 7 days following presentation.
Sagittal plane T1-weighted image (obtained after contrast agent administration) of the brain of a 4-year-old Shetland Sheepdog that had sudden-onset ataxia of 12 hours' duration. Notice the round lesion in the fourth ventricle with mild rim enhancement (white arrow) and mild dilation of the ventricular system rostral to the lesion (black arrow).
Citation: Journal of the American Veterinary Medical Association 249, 1; 10.2460/javma.249.1.55
Sagittal plane T1-weighted image (obtained after contrast agent administration) of the brain of a 4-year-old Shetland Sheepdog that had sudden-onset ataxia of 12 hours' duration. Notice the round lesion in the fourth ventricle with mild rim enhancement (white arrow) and mild dilation of the ventricular system rostral to the lesion (black arrow).
Citation: Journal of the American Veterinary Medical Association 249, 1; 10.2460/javma.249.1.55
Sagittal plane T1-weighted image (obtained after contrast agent administration) of the brain of a 4-year-old Shetland Sheepdog that had sudden-onset ataxia of 12 hours' duration. Notice the round lesion in the fourth ventricle with mild rim enhancement (white arrow) and mild dilation of the ventricular system rostral to the lesion (black arrow).
Citation: Journal of the American Veterinary Medical Association 249, 1; 10.2460/javma.249.1.55
Comments
The dog of the present report underwent repeated CSF analysis 5 weeks after the initial diagnosis. At that time, marked improvement in the dog's condition was noted; therefore, the prednisone dosage was gradually tapered and administration was discontinued 10 months after the initial diagnosis. An examination at 16 months after the initial diagnosis revealed abnormalities similar to those identified initially, with the presence of hypermetria of the right thoracic limb suggesting cerebellar involvement. Prednisone had been intermittently administered by the owner but treatment was restarted at a higher dosage (0.4 mg/kg [0.18 mg/lb], PO, q 12 h). Thirty-two months after the initial diagnosis, the dog was found laterally recumbent and was euthanized.
At necropsy, abnormalities were limited to the CNS and liver. Hepatic histopathologic findings were consistent with previous corticosteroid administration. Gross examination of the CNS revealed a gelatinous substance to the right of the cerebellum, consistent with fluid from a ruptured cyst, and a mass lesion on the ventral left aspect of the cerebellar vermis. Histologic evaluation of the mass revealed a central cavity surrounded by a single layer of tall ciliated columnar epithelial cells. These cells were positive for S-100 and cytokeratin and negative for glial fibrillary acidic protein. There were several areas of mild papilliferous epithelium folds, surrounded by vascularized dense collagenous connective tissue attached to the leptomeninges. Large numbers of lymphocytes and neutrophils were present in the folds. The external side of the cyst had papilliferous proliferations of a single layer of cuboidal cells consistent with choroid plexus. The cerebellum was moderately displaced dorsally with a localized area of necrosis and a moderate number of gitter cells within the neuropil. Findings were consistent with an ependymal cyst in the fourth ventricle and cerebellar necrosis.
Ependymal cysts are reported rarely in the veterinary and human medical literature.1,2 In people, ependymal cysts arise most commonly from the lateral ventricle3 but have been reported in the fourth ventricle and cerebellopontine angle.4–8 In humans, ependymal cysts often have no associated clinical signs; however, when patients are affected clinically, the signs reflect supratentorial disease (eg, seizures or motor deficits) or infratentorial disease (eg, cranial nerve VII, VIII, or IX dysfunction).9 The dog of the present report had central vestibular (cranial nerve VIII) dysfunction initially, with cerebellar signs developing later. As for this dog, CSF abnormalities have been noted previously for a dog with an intracranial cyst and were considered to be secondary to leakage of cystic fluid or compression of surrounding tissues.10 The dog of the present report had a fair to good prognosis as evidenced by an almost 3-year survival period following diagnosis and intermittent administration of prednisone. Ependymal cysts are rare in dogs; however, an ependymal cyst should be considered a differential diagnosis for dogs with a cystic lesion at the level of the fourth ventricle.
Footnotes
Signa Advantage (1.0 T), GE Healthcare, Milwaukee, Wis.
References
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