Nasal carcinoma with leptomeningeal carcinomatosis in a dog.

A 7-y-old, castrated male Standard Poodle was presented to the North Carolina State University Small Animal Neurology Service (Raleigh, NC, USA) with a 2-wk history of progressive neurologic signs, including inappropriate mentation, ataxia, seizures, hyporexia, and nasal discharge. Neurologic examination indicated a forebrain lesion, and MRI revealed a large, contrast-enhancing mass centered at the right cribriform plate, extending into the cranial vault and causing brain compression. CSF analysis showed neutrophilic pleocytosis with neoplastic epithelial cells. Because of further clinical deterioration, the patient was euthanized. Postmortem examination revealed a large nasal mass extending into the brain and right orbit, with infiltration into the right olfactory lobe. Histologically, the mass was identified as an undifferentiated carcinoma with metastases along the leptomeninges as far caudal as the L3-L4 segment of the spinal cord. Nasal origin was supported by strong pan-cytokeratin and E-cadherin positivity and negative staining to synaptophysin, neural-specific enolase, S100, and CD18; partial positivity to vimentin suggested epithelial-to-mesenchymal transition in portions of the neoplasm. These findings confirmed leptomeningeal carcinomatosis secondary to the primary nasal carcinoma.