Localized, plexiform, diffuse, and other variants of neurofibroma in 12 dogs, 2 horses, and a chicken.

In humans, neurofibroma and schwannoma are distinct entities within the group of benign peripheral nerve sheath tumors. In the veterinary literature, these tumors are often classified together simply as benign peripheral nerve sheath tumors, and diagnostic criteria for their subclassification are not well established. We describe peripheral nerve sheath tumors with microscopic, immunohistologic, and ultrastructural features similar to those in subtypes of human neurofibroma in 12 dogs, 2 horses, and 1 chicken. Dogs were of different breeds and were aged 2 months to 15 years. The canine tumors were located in the skin, peripheral nerve, tongue, and large intestine. The 2 horses were 11 and 12 years old. The equine tumors were located in the subcutis of the neck and axilla. The chicken was a mature white Leghorn chicken with an ocular neoplasm. Neurofibromas of this study had localized, plexiform, diffuse and combined plexiform and diffuse growth patterns, and microscopic features similar to those in classic, collagenous, cellular, myxoid, and pigmented neurofibromas of humans. One diffuse neurofibroma contained areas of schwannian differentiation (hybrid neurofibroma-schwannoma). Two plexiform neurofibromas occurred together with diffuse ganglioneuromatosis in the large intestine of young dogs, as has also been reported in humans. This investigation shows the existence of identical subtypes of neurofibroma in animals and humans and identifies similarities in tumor location and patient age between animals and humans. This report will allow a more discriminating classification of benign peripheral nerve sheath tumors and probably has a bearing on epidemiology, pathogenesis and prognosis.