Atypical angiomatous meningioma with E-cadherin-positive inclusion bodies in a dog.

An 11-year-old toy poodle presented with abnormal gait. Magnetic resonance imaging revealed a demarcated intradural extramedullary mass at the dorsal medulla oblongata, which was surgically removed. Histopathologically, a well-demarcated tumor was composed of small nests of meningothelial neoplastic cells separated by abundant fibrovascular tissue. The nuclei of neoplastic cells were often eccentric due to eosinophilic cytoplasmic inclusion bodies. Immunohistochemically, the neoplastic cells were positive for E-cadherin and vimentin, and endothelial cells were positive for CD31, von Willebrand factor, and vimentin. The cytoplasmic inclusion bodies of the neoplastic cells were E-cadherin-positive and, by electron microscopy, composed of folded membrane-like structures. The tumor was diagnosed as an angiomatous meningioma with cytoplasmic inclusion bodies, which were likely cell membranes containing E-cadherin.