Adult Neuromuscular Choristoma of the Mental Nerve: Diagnostic Pitfalls and Surgical Considerations

Neuromuscular choristoma (NMC) is an extremely rare, benign nerve tumor composed of intermingled mature skeletal muscle fibers and nerve bundles. Most cases arise in childhood from major nerves such as the sciatic or brachial plexus. Surgical manipulation, including biopsy or partial excision, has been reported to induce desmoid-type fibromatosis (DTF); therefore, invasive procedures should be avoided. Here, the authors report a case of NMC arising from the mental nerve in a 24-year-old man who presented with a gradually enlarging, soft, and poorly mobile subcutaneous mass with indistinct borders. Magnetic resonance imaging (MRI) revealed findings characteristic of NMC, and en bloc resection, including the overlying skin, was performed. Histopathologic examination revealed mature skeletal muscle fibers intermingled with nerve fascicles, confirming the diagnosis of NMC. No neurological deficits or recurrences occurred during a several-month follow-up. This is the first reported case of adult-onset NMC arising from a peripheral branch and the only second peripheral nerve case worldwide. NMC may mimic lipoma or schwannoma in the craniofacial region, and a biopsy can trigger DTF formation; therefore, noninvasive MRI-based diagnosis and cautious surgical planning are essential.