Postoperative Brachial Plexus Injury following Retrosigmoid Excision of a Vestibular Schwannoma: Review of Institutional Case Series

Background: Injury to the brachial plexus (BP) remains a rare but potentially devastating complication of skull-base surgery and anesthesia.^1,2 Functional limitation and recovery is determined but the grade of injury, and while most cases demonstrate good outcome², some may be prolonged or permanent. We report a case of proximal BP injury in a healthy young male undergoing retrosigmoid excision of a right vestibular schwannoma in the park-bench position in the context of our unit’s experience with this procedure since 1990.

Case Presentation: A 28-year-old healthy male patient presented with several month history of unilateral hearing loss and episodic vertigo. MRI imaging confirmed a right vestibular schwannoma. He underwent sub-total (~90%) retrosigmoid resection in the right park-bench position in Mayfield pins. There is a protocol for patient positioning for these procedures in our institution to optimize access to the skull base. The dependent axilla is padded and the arm slung below the patient. The head is turned to contralateral side and the top arm is pulled inferiorly; this improves surgical access by opening up the space between head and shoulder but also exposes the ipsilateral BP to stretch and compressive forces. Immediately after waking from an 8-hour anesthetic, the patient complained of right upper limb weakness. Clinically the patient demonstrated proximal upper limb muscle weakness of the shoulder and elbow, with relative sparing of the wrist and hand. Physiotherapy review day 1 postoperatively showed 0/5 power with elbow flexion/extension and 0–1/5 power with shoulder abduction, improving to 1/5 and 3/5 by day 3. There was slow improvement over his inpatient stay to muscle power of 3–4^-/5 across all groups. He also complained of neuropathic-type upper limb/shoulder pain. Serial nerve conduction studies and MRI (Fig. 1) confirmed a right BP pan-plexopathy consistent with neuropraxia/axonotmesis, and edema of the shoulder girdle muscles. The posterior cord (or posterior division arising from the upper trunk) was most severely affected, with severely reduced brachioradialis function (elbow flexion).One year post-operatively the patient demonstrated significant improvement but experienced mild continued shoulder instability, elbow weakness and decreased median nerve sensation.

Discussion: Since 1990, our institution has managed over 1,200 patients with vestibular schwannoma; performing 680 surgical procedures including 341 retrosigmoid excisions. This is the second peripheral nerve injury in this case series, the other being a transient C8 nerve root injury in 1990, giving our overall rate for this procedure of 1:340 (0.4%).

Conclusion: This is only the second documented nerve injury in a large single-unit case series of vestibular schwannoma treatment. Despite this position being high-risk for peripheral nerve injury, we report an overall rate of 1:340 (0.29%).

Fig. 1 MRI Shoulder & Brachial Plexus.