Plexiform nerve root tumour of perineurial origin in a dog

A nine year old, male Mittelschnauzer dog was transferred to neuropathologi cal necropsy because of an intraspinal tumour of intradural-extramedullary location. Histological and ultrastructural inspection gave rise to the diag nosis of an intraneural perineurioma which has not been described in this s pecies so far. Analogously to human cases extensive onion bulb formation su rrounding preexisting endoneurial axon/Schwann cell complexes, as well as c ertain blood vessels are the histological hallmark of this neoplasia. Elect ron microscopically tumour cells exhibited a fibroblast-like phenotype with marked rough endoplasmatic reticulum. Moreover, many cellular interdigitat ions could be detected. The submicroscopical detection of remnants of a bas al lamina is consistent with immunohistochemical features of a marked lamin in- and collagen IV-expression bordering both flattened sites of the bipola r spindle cells. While vimentin-expression could be detected in some anapla stic regions in a patchy manner, the restricted S-100-positivity of onion b ulb-centers clearly rules out a tumour of Schwann cell origin. Unfortunatel y, use of human specific antisera against epithelial membrane antigen did n ot work in canine tissues. Considering both, benign growth patterns and ana plastic properties, a low degree of malignancy is to be stated.