Spontaneous spinal plexiform perineurioma in a juvenile chicken ( Gallus domesticus).

A 2-mo-old pet chicken ( Gallus domesticus) was presented because of lameness and a hind limb mass of 1 mo duration. Radiographs revealed a soft tissue mass extending from the mid-femur into the body wall. Cytology of a sample obtained from a fine-needle aspirate was unremarkable. The bird was prepared for surgical investigation of the mass but died acutely at the time of pre-medication. Autopsy revealed an extradural mesenchymal neoplasm that focally compressed the lumbar spinal cord, extended into and along the adjacent nerve structures, and displaced the kidneys, skeletal muscle, and body wall. Histopathology was consistent with a perineurioma, which was positive for alcian blue and negative for S100, GLUT1, and neurofilament proteins on immunohistochemistry. PCR testing of tumor tissue was negative for gallid herpesvirus 2 (Marek's disease virus) and avian leukosis virus. Although the etiology of the mass was not determined, our case highlights a severe manifestation of an uncommonly diagnosed tumor in the chicken. Though uncommon, perineurioma should be considered a differential diagnosis for lameness in the chicken.