Isolated femoral nerve neurofibroma with vastus medialis muscle atrophy as the initial symptom: a case report and literature review.

Background: Neurofibromas are benign tumors that originate in the peripheral nerve sheath. Most patients initially present with a palpable mass on the body. In this patient, no body surface mass was detected, and the initial symptoms were muscle pain and atrophy. Isolated femoral neurofibromas have been reported less frequently. Case presentation: In June 2024, a 38-year-old man was admitted to the hospital due to pain in his left knee and the inner side of his thigh for 2-3 months, accompanied by muscle atrophy for half a month. After electromyography, ultrasound examination of the thigh muscles, and enhanced MR scan of the femur, and through a multidisciplinary case discussion, a high suspicion of femoral nerve fibroma was formed. At another hospital, the "left femoral nerve tumor resection + nerve transplantation + pedicled composite tissue flap formation + gastrocnemius nerve resection" surgery was performed, and the postoperative pathology confirmed it to be a neurofibroma. Conclusion: Most neurofibromas initially present as visible masses on the body. However, there are also cases in which no body surface mass is detectable, and the initial symptoms may be muscle pain and muscle atrophy. Because these tumors are prone to recurrence, thorough clinical and imaging examinations, as well as long-term follow-up, are necessary.