An Unusual Femoral Nerve Lesion

Perelman School of Medicine University of Pennsylvania Philadelphia, PA

Zarina Ali, MD, Stephen Miranda, MD, Paul Zhang, Antje Greenfield, MD, Ronald Wolf, MD, Giorgos Karakousis, MD

A healthy 22-year-old woman presented with a 7 year history of slowly progressive right proximal leg weakness and atrophy. She denied a history of trauma or pain, and there were no sensory symptoms. There was no family history of nerve tumors, and she had no stigmata of neurofibromatosis. She had been evaluated by a local neurosurgeon, and she was found to have weakness of right hip flexion and knee extension. She was still able to walk well and even played sports, with some difficulty. MR imaging of the spine was unrevealing. An MRI of the abdomen and pelvis showed an elongated, enhancing mass extending obliquely through the posterior aspect of the right psoas muscle, measuring 1.1 cm in transverse diameter and 5.5 cm in length. This was diagnosed as a probable nerve sheath tumor, and it was followed with annual MRI scans. She was first seen at our institution in February 2023, and at that visit she had worsened to 4/5 hip flexion and 2/5 knee extension, with no sensory loss. The right patellar reflex was absent, the left normal. An EMG study showed denervational changes in the right quadriceps and iliopsoas with isolated long duration, polyphasic motor units suggesting reinnervation. We recommended a femoral nerve biopsy for diagnosis and suspected a perineurioma. The first surgical intervention involved co-surgery with Surgical Oncology: a retroperitoneal exposure of the femoral nerve revealed an enlarged segment of the femoral nerve. Using internal neurolysis and fascicular stimulation, a single nerve fascicle was harvested and sent for pathology. There were no clinical changes in her symptoms or exam following the open biopsy. Pathology showed a perineurial cell predominant nerve sheath tumor with mature ganglion cells, most consistent with a ganglioneuroma. She continued to deteriorate gradually to 1/5 quadriceps weakness, and 3/5 hip flexion. Following discussion with the patient, we performed a distal fascicular nerve transfer from the anterior branch of the obturator nerve to the rectus femoris branch of the femoral nerve, without complication or a new deficit. There was no tumor present in the thigh segment of the femoral nerve, on fascicular biopsy. We are awaiting the clinical and EMG results of surgery.