Primary intra-osseous Hybrid Schwannoma-Perineurioma in the mandible.

Benign nerve sheath tumours include perineuriomas, schwannomas and neurofibromas. Hybrid schwannoma-perineurioma represents a cutaneous, subcutaneous or occasionally intra-osseous tumour with schwannian cytomorphology and perineurioma-like architecture consisting of a mixture of both types of cells. These tumours can develop at any age and there is no gender-predilection. Tongue is the most frequently affected site, followed by palate, mouth floor, jugal mucosa, lips and, more rarely, mandible. We present a case of hybrid tumour with schwannoma-perineurioma morphology located on the right mandibular body (intra-osseous) of a 54-year-old female patient. The tumour was symptomatic and evolving for six months. Microscopically, it was encapsulated and highly cellularised, presenting fascicular aspect and exhibiting scant mitotic activity. The tumour consisted of distinct cellular populations involving fusiform cells, cells with wavy and hyperchromatic nucleus or even epithelioid cells. Positive immunostaining for S-100 and epithelial membrane antigen (EMA) was observed. The lesion was completely removed under general anaesthesia, with the patient showing no clinical or radiographic sign of relapse after two-year follow-up. Despite the limited knowledge on the pathogenesis of Hybrid Schwannoma-Perineurioma, these tumours seem to present a non-aggressive biological behaviour. Conservative surgery provides adequate solution without recurrence, even after a long-term follow-up. Nerve sheath tumours, Schwannoma, Perineurioma, Immunohistochemistry.