An Unsuspected Intraneural Perineurioma in a Pediatric Patient: A Case Report.

Perineuriomas are rare tumors arising from perineurial cells that form the protective layer surrounding peripheral nerve fascicles. Four types of perineuriomas have been described: (i) intraneural, (ii) soft tissue (extraneural), (iii) sclerosing, and (iv) mucosal. Intraneural perineuriomas are rarely reported nerve sheath tumors that primarily affect the peripheral nerves of the upper and lower extremities. In this report, we present a pediatric case in which the diagnosis of perineurioma was not suspected until lesional tissue was obtained, and the final pathologic diagnosis was made. The patient is a 17-year-old girl who presented with a three-year history of symptoms involving the left upper extremity, including weakness and cramping, which became progressively worse over time. Diagnostic workup included magnetic resonance imaging (MRI), which showed enlargement and contrast enhancement of two of the left brachial plexus nerve trunks, suggestive of an inflammatory or infectious etiology, with schwannoma or neurofibroma also listed as less likely possibilities. An electromyogram (EMG) showed findings concerning for an anterior horn cell process, including amyotrophic lateral sclerosis (ALS). Nerve conduction studies (NCS) demonstrated axonal findings only in motor nerves, and needle EMG demonstrated denervation and fasciculations in multiple muscles. An initial biopsy of the brachial plexus was performed but was non-diagnostic. Ultimately, resection of the involved nerve trunks was performed. The diagnosis of intraneural perineurioma was not suspected preoperatively and was made only after histologic and immunohistochemical examination.