Cutaneous Schwannomas in 22 Horses

B A Summers,S Schöniger,C J Fernandez,B A Valentine

doi:10.1177/0300985810377072

B A Summers, S Schöniger + Show 2 more

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https://doi.org/10.1177/0300985810377072

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Abstract

Schwannomas are uncommonly recognized in horses. This study describes cutaneous schwannomas in 22 horses aged 8 to 25 years: 12 male, 7 female, and 3 of unknown sex. The horses had solitary cutaneous masses: 9 on the head, 3 on the neck, and the others on the shoulder, hip, thorax, abdomen, rump, extremities, or tail. The location of 1 tumor was unknown. The dermal tumors were well demarcated and expansile. Twelve had a multinodular pattern, whereas 10 formed a single nodule. Antoni A areas were observed in all tumors, and 10 tumors contained Antoni B areas. In Antoni A areas, the densely packed spindle-shaped neoplastic cells were arranged in short fascicles with nuclear palisading. In the hypocellular Antoni B areas, neoplastic cells were separated by abundant myxomatous stroma. Tumors commonly had hyalinization of stroma and vessel walls and ancient change. Cellular vacuolation was observed in 18 tumors. In all 22 cases, neoplastic cells were immunopositive for S100 protein. Expression of laminin and glial fibrillary acidic protein was observed in all 6 tumors evaluated by immunohistochemistry for these markers. One tumor was examined ultrastructurally: Neoplastic cells had branched cytoplasmic processes and were surrounded by an external lamina. Follow-up information was available 8 months to 10 years postexcision for 9 horses, for which surgical excision of the tumor was curative. The equine cutaneous schwannomas in this study had microscopic features like those of human schwannoma and had benign clinical behavior. Correct classification of equine cutaneous schwannoma will facilitate accurate prognosis and appropriate treatment.

Highlights

peripheral nerve sheath tumors (PNSTs) have characteristic diagnostic features, and their distinction is important for prognosis and treatment
The identification of patients with multiple neurofibromas may lead to the diagnosis of von Recklinghausen disease, which has implications for family members.[3,41]
The terms benign PNST, schwannoma, and neurofibroma are often used interchangeably,[7,15,31] whereas ganglioneuroma is classified as a separate entity.[15,16]

Summary

Introduction

This study describes cutaneous schwannomas in 22 horses aged 8 to 25 years: 12 male, 7 female, and 3 of unknown sex. Benign peripheral nerve sheath tumors (PNSTs) are a diverse group of neoplasms that includes 4 main types: schwannoma (synonym: neurilemmoma), neurofibroma, perineurioma, and ganglioneuroma. The identification of patients with multiple neurofibromas may lead to the diagnosis of von Recklinghausen disease (neurofibromatosis I), which has implications for family members.[3,41] In the veterinary literature, the terms benign PNST, schwannoma, and neurofibroma are often used interchangeably,[7,15,31] whereas ganglioneuroma is classified as a separate entity.[15,16]. Instead of schwannoma and neurofibroma has been recommended in the veterinary literature because the criteria to distinguish between these two are not well established for animals.[7,15] In contrast, we believe that benign PNSTs can be subclassified in veterinary medicine; variants of neurofibroma have been recently described in several species.[30]

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