Eleventh Cranial Nerve Lesions

Anatomy

Course and Components

The accessory nerve has two roots: spinal and cranial (the latter generally considered part of the vagus nerve).

• Spinal root: Arises from C3–C4, ascends through the vertebral canal, and enters the skull via the foramen magnum.
• Cranial root: Arises from the nucleus ambiguus in the medulla, emerges as multiple fine rootlets, and joins the spinal root. The combined nerve exits the skull via the jugular foramen (with CN IX and X).
• The cranial root then separates to join the vagus nerve below its inferior ganglion and contributes to pharyngeal and recurrent laryngeal branches.

The spinal root:

• Passes behind the sternomastoid muscle.
• Emerges into the posterior triangle, running across levator scapulae and prevertebral fascia.
• Passes deep to the trapezius muscle and innervates it.

Innervation

Muscle	Function
Sternomastoid	Turns head to opposite side
Trapezius	Elevates shoulder (shrug)

Pathology

Isolated lesions are uncommon.

Causes include:

1. Penetrating trauma
   • Especially to the posterior triangle of the neck.
2. Space-occupying lesions
   • Tumours
   • Aneurysms
   • Abscesses

Other causes are rare.

Clinical Assessment

Trapezius

• Ask patient to shrug shoulders against downward pressure.
• Weakness indicates trapezius dysfunction.

Sternomastoid

• Ask patient to turn head against resistance applied to the mandible.
• Note: The right sternomastoid turns the head to the left.

Investigations

Blood Tests

• FBC
• CRP
• ESR
• U&Es / Glucose

Imaging

• CT / CT Angiogram: For mass lesion screening or suspected aneurysm.
• MRI: Most sensitive for detecting head and neck lesions.

Management

Management depends on the underlying cause of the lesion.

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Appendix 1

Anatomy of the Eleventh cranial nerve

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Appendix 2

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References

Publications

• Brazis PW, Masdeu JC, Biller J. Localization in Clinical Neurology. 8e 2021
• Fuller G. Neurological Examination Made Easy. 6e 2019
• O’Brien M. Aids to the Examination of the Peripheral Nervous System. 6e 2023

FOAMed

• Coni R. Neuro 101: Cranial Nerves. LITFL
• Nickson C. The Brainstem Rules of Four. LITFL
• Ercleve T. The rule of 4 of the brainstem. LITFL
• Nickson C. Cranial nerve lesions DDx. LITFL