Posterior interosseous nerve syndrome caused by a ganglion cyst and its surgical release with intraoperative neurophysiological monitoring A case report

Rationale: Intraoperative neurophysiological monitoring (IONM) has been utilized not only for the rapid detection of neural insults during surgeries, but also to verify the neurophysiological integrity of nerve lesions in the surgical field. Patient concerns: A 32-year-old woman presented with a wrist and finger drop that had lasted about 3 months. Diagnoses: The result of the initial electrodiagnostic test was consistent with posterior interosseous nerve (PIN) syndrome. Ultrasonography and magnetic resonance imaging of the proximal forearm showed a cystic mass at the anterolateral aspect of the radial head, which was diagnosed as a ganglion cyst. Interventions: Surgical release of the ganglion cyst with IONM was performed. During the surgery, we induced nerve action potentials and compound motor action potentials across the ganglion cyst, which demonstrated neural continuity. Outcomes: Three months after the surgery, the patient showed partial recovery of wrist and finger extensor muscle power. An electrodiagnostic test conducted 3 months after the surgery showed reinnervation potentials in PIN-innervated muscles. Lessons: IONM during peripheral nerve surgeries can support surgical decisions and confirm the location and degree of nerve damage.