1608 - Spinal Accessory Mononeuropathy Following Carotid Endarterectomy

Friday, February 20, 2026

5:00 PM - 6:30 PM AST

Presenting Author(s)

SA

Sameer Allahabadi, MD

Resident Physician
Baylor University Medical Center
Dallas, Texas, United States
PC

Pranavi Chamarti, BA

Medical Student
TCOM
Fort Worth, Texas, United States

Corresponding Author(s)

JM

Jit Mookerjee, DO

Physician
Baylor Scott & White
Dallas, Texas, United States

Co-Author(s)

JO

Justin Owens, DO

Physician
PMR Fort Worth
Dallas, Texas, United States

Submitter(s)

SA

Sameer Allahabadi, MD

Resident Physician
Baylor University Medical Center
Dallas, Texas, United States

Case Diagnosis: R CN XI chronic/partial incomplete mononeuropathy

Case Description: An 80-year-old right-handed female presented with significant right shoulder weakness that was interfering with her daily activities. After undergoing a right anteromedial carotid endarterectomy for carotid artery stenosis, she developed increasing difficulty using her right arm. Specifically, she was unable to lift her arm overhead or perform tasks requiring forward flexion or abduction. She denied any trauma or sensory symptoms such as numbness or tingling. However, she did report localized pain near the right trapezius muscle, which was aggravated by activity. She denied any constitutional symptoms.

Discussions:
Carotid endarterectomy (CEA) is performed via two main approaches: anteromedial and retrojugular. The anteromedial (standard) approach passes anterior and medial to the internal jugular vein, often requiring facial nerve exposure. The retrojugular approach avoids this by passing behind the vein. In the European Carotid Surgery Trial, Cunningham et al. reported 88 cranial nerve injuries among 1,739 patients, with only one involving CN XI, making such injuries rare but potentially causing shoulder weakness. Electrodiagnostic studies in our case revealed a chronic, partial right CN XI mononeuropathy, with decreased insertional activity, 3+ PSW, 3+ Polys, increased duration, decreased recruitment, and CRDs in the right trapezius. EMG of the deltoid, teres minor, supraspinatus, and infraspinatus was normal. Given the patient's right shoulder weakness in abduction and forward flexion, along with her history of CEA, the findings are most consistent with a rare injury to CN XI.

Conclusions: This case highlights the importance of understanding anatomical relationships and considering cranial nerve injuries, particularly in the differential diagnosis of shoulder weakness during EMG/NCS studies. It also emphasizes the value of incorporating clinical history into the interpretation of these tests. Injury to the spinal accessory nerve (CN XI) is uncommon, making this case a rare and significant finding.