During radical neck dissection, the surgeon identifies the accessory nerve (CN XI) coursing through the posterior triangle. Which fascial compartment must be opened to identify and preserve it, and at which landmark does it enter the sternocleidomastoid muscle?

• A Prevertebral fascia; at Erb's point
• B Investing layer of deep cervical fascia; Erb's point is 1 cm above CN XI crossing
• C Carotid sheath fascia; at the posterior belly of digastric
• D Investing layer of deep cervical fascia; junction of upper and middle thirds of SCM ✓

Explanation

The accessory nerve (CN XI) exits the posterior border of the SCM at the junction of its upper and middle thirds, then crosses the posterior triangle to enter the trapezius. It lies within the investing layer of the deep cervical fascia in the posterior triangle. During neck dissection, this fascial layer must be opened and the nerve identified before proceeding with dissection. Erb's point is the confluence of superficial cervical nerves at the posterior SCM border, approximately 1 cm inferior to where CN XI exits the muscle.

Reference: Dhingra Diseases of Ear, Nose and Throat, 7th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.