Nerve sheath myxoma masqueraded as intramuscular myxoma: an extremely rare tumor with unusual location - a case report and literature review.

Nerve sheath myxoma (NSM) is a very rare benign nerve sheath tumor that mostly affects young adults, with a peak incidence in the 30s. Patients usually present with an asymptomatic swelling commonly affecting the dermis and subcutaneous tissues of the head, neck, and upper extremities. Lower extremities are a much rarer location, and when this occurs, the knee/pretibial region is the most common location. NSM has not been reported within the anterior tibialis muscle. Case Presentation: The authors present the first reported case of NSM in the anterior tibialis muscle in a 39-year-old man presented as deep swelling in the left leg. Discussion: NSM is difficult to diagnose clinically or using standard imaging techniques; MRI and ultrasonography cannot differentiate it from other anomalies. Histopathology alone is not enough to distinguish NSM from neurothekeomas, which were considered synonymous in the past. They can be distinguished by using immunohistochemical markers. Conclusion: Soft tissue tumors in lower extremity muscles are somewhat difficult to diagnose. Excision of the tumor by a specialized orthopedic surgeon and histopathological/immunohistochemical analysis were the only avenues to correctly diagnose the NSM.