A patient presents with inability to shrug the right shoulder and weakness turning the head to the left. Which nerve is damaged, and where is the most likely lesion causing BOTH deficits simultaneously?

• A Right spinal accessory nerve (CN XI); lesion in the jugular foramen
• B Right spinal accessory nerve (CN XI); lesion in the posterior triangle of the neck ✓
• C Right C3–C4 nerve roots; high cervical cord lesion
• D Left spinal accessory nerve; lesion in the posterior triangle

Explanation

The spinal accessory nerve (CN XI) exits the jugular foramen and traverses the posterior triangle of the neck to supply the sternocleidomastoid (SCM) and trapezius. The right SCM turns the head to the left; the trapezius elevates the shoulder (shrug). Damage to the right CN XI in the posterior triangle (e.g., lymph node biopsy, parotidectomy) denervates both the right trapezius (inability to shrug right shoulder) and right SCM (weakness turning head to left). Both deficits implicating CN XI on the right side, in the posterior triangle, is the classic presentation. A jugular foramen lesion would also involve CN IX and X causing additional symptoms.

Reference: BD Chaurasia's Human Anatomy, 8th ed.

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Written and medically reviewed by the StethoPrep medical team.