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.
Signa Advantage (1.0 T), GE Healthcare, Milwaukee, Wis.
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