Acute Radial Nerve Palsy From a Spiral-Groove Pseudoneuroma Mimicking a Nerve Sheath Tumor

Radial nerve palsy may result from various pathologies, including trauma, nerve sheath tumor, neuritis, or compression neuropathy. In most instances, the underlying cause is apparent preoperatively and an appropriate operative plan can be formulated. Here, we present a case where the preoperative diagnosis was inaccurate and intraoperative decision-making required deviation from the planned procedure. The patient's history, physical examination, and imaging were consistent with a radial nerve tumor; however, surgical exploration revealed a compression neuropathy with pseudoneuroma formation. This case reinforces the importance of including compression neuropathy and pseudoneuroma in the differential diagnosis of a mass-associated motor nerve palsy, even at sites where nerve compression is relatively uncommon. Surgeons should be prepared to abort a planned biopsy and instead perform complete nerve decompression at the time of exploration when intraoperative findings are inconsistent with a neoplasm.