Hybrid Peripheral Nerve Sheath Tumours - A Review

Hybrid peripheral nerve sheath tumours (PNSTs) are mainly benign, which represent combined areas of neurofibroma, schwannoma, and perineurioma in various combinations and pose challenges to the surgeon and the pathologist. They are relatively new in pathology and were first published in the fourth edition of World Health Organization Classification of Tumors of Soft tissue and Bone in 2013. They are mainly dermal or subcutaneous, and the most common variant of hybrid nerve sheath tumour is perineurioma-schwannoma. The combination of neurofibroma/schwannoma usually has an increased frequency with neurofibromatosis (NF) type 1 or 2 and schwannomatosis. In contrast, neurofibroma/perineurioma, mainly associated with NF1, are rare. Diagnosis is established by histopathology and immunohistochemistry. Hence, they embark diagnostic challenge and demand extreme vigilance and caution. However, the molecular pathogenesis, recurrence rates, and risk of malignant transformation of hybrid PNST remain poorly understood. A novel fusion gene in a hybrid schwannoma-perineurioma and recurrent mutations in a subset of hybrid neurofibroma/schwannomas were identified. We have tried, via this article, to represent a brief update on hybrid nerve sheath tumours.