Benign triton tumors (BTT) are very rare lesions composed of mature skeletal muscle and neural tissue. We report a case of a 14-year-old boy who presented with asymptomatic swelling of the chin over an 18-month duration which increased gradually to involve the left side of the lower lip. Clinically, a diagnosis of neurofibroma was made. Excisional biopsy confirmed the diagnosis of a BTT. Having an affinity for large nerve trunks like the brachial and sciatic, these tumors rarely occur in the head and neck region. When they do, they may involve the large central cranial nerve trunk and present as intracranial masses or involve the smaller peripheral nerve twigs and present as asymptomatic skin nodules, of which only four cases involving peripheral nerves are reported in the English literature. Here, we report the fifth documented case of a BTT involving the mental branch of the trigeminal nerve. A brief review of the literature is also provided.
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Perineuriomas are composed of differentiated perineurial cells. Perineuriomas have been recently recognized by the immunoreactivity for epithelial membrane antigen (EMA). Microscopically, perineuriomas show proliferation of spindle cells with wavy nuclei and delicate elongated bipolar cytoplasmic processes. The tumor cells are usually negative for the S-100 protein. Ultrastructurally, perineurial cells reveal slender, nontapered processes containing pinocytic vesicles and discontinuous basal lamina. Interestingly, hybrid tumors of benign peripheral nerve sheath tumor (PNST) have been recently reported by using immunohistochemical and ultrastructural investigations. Herein, we report a case of soft tissue perineurioma arising in the skin of a 56-year-old female; another case of a hybrid tumor of perineurioma and schwannoma in the posterior mediastinum occurred in a 53-year-old male, which is the first case of the hybrid PNST tumor reported in Korea.
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