Aetiology of CN XI Palsy

The eleventh nerve has two parts. The smaller cranial part arises from cells in the nucleus ambiguus and ultimately is distributed with the vagus nerve. This portion innervates the pharyngeal muscles. The main part, the spinal portion, arises from a long column of nuclei situated in the ventral part of the medulla and extending to the fifth cervical segment or lower. Supranuclear innervation is not well known.¹

The accessory spinal nerve or XI cranial nerve is essential for neck and shoulder movement, the intrinsic musculature of the larynx, and the sensitive afferences of the trapezius and sternocleidomastoid musculature.²

The sternocleidomastoid and trapezius muscles perform the following functions:

1. Rotation of head away from the side of the contracting sternocleidomastoid muscle.
2. Tilting of the head toward the contracting sternocleidomastoid muscle.
3. Flexion of the neck by both sternocleidomastoid muscles.
4. Elevation of the shoulder by the trapezius.
5. Drawing the head back so the face is upward by the trapezius muscles.

When the CN XI lesion is nuclear or infranuclear, there is associated muscle atrophy and fasciculations.¹

Unilateral

• trauma – neck / base of skull
• poliomyelitis
• syringomyelia
• tumour (near jugular foramen)

Bilateral

• Motor Neurone Disease
• Poliomyelitis
• Guillain Barre Syndrome (GBS)

Differential diagnosis:

• muscular dystrophy e.g. dystrophia myotonica.

The [lower cranial nerves] LCNs can be affected individually or in combination, since the cranial nerves at this level share their courses through the jugular foramen and hypoglossal canal and the extracranial spaces. … Symptoms and signs that have localization value for LCN lesions include impaired speech, deglutition, sensory functions, alterations in taste, autonomic dysfunction, neuralgic pain, dysphagia, head or neck pain, cardiac or gastrointestinal compromise, and weakness of the tongue, trapezius, or sternocleidomastoid muscles.³

The accessory or spinal nerve has a double origin but always comes out of the jugular foramen. … Its spinal portion comes from a series of roots starting at C6-C7 and traveling cranially to enter in the foramen magnum. It then runs superolaterally along the floor of the posterior cranial fossa to enter in the dural canal of the jugular foramen, joining the small roots coming out of the medulla elongated caudally to the region of the ambiguous nucleus. From the jugular foramen, it comes out as nerve XI, together with X and IX, sigmoid sinus and the inferior petrosal sinus, while entering into jugular foramen the occipital and pharyngeal meningeal arteries.

Nerves IX, X, and XI travel together in the jugular foramen, where they may be compressed by tumors and aneurysms (Vernet’s syndrome).¹

Exiting the jugular foramen, the spinal accessory nerve is wrapped by the meningeal dura, attached to the periosteum. Once released, it separates into an internal and external branch: the internal branch is composed of fibers of the cranial part, giving an anastomosis with the vagus at the level of the upper edge of the transverse process of C1 and contributing to the vagal function of the pharyngeal and laryngeal area, transporting parasympathetic fibers; the outer branch mainly creates the fibers that will innervate the trapezius and sternocleidomastoid muscles, which receive innervation also from C1-C4, that derive from the spinal portion and travel downwards.¹

In the anterior triangle, the spinal accessory nerve usually passes anterior to the internal jugular vein (See Medscape):

Relationship of internal jugular vein to the spinal accessory nerve (SAN) [Medscape]

Spinal accessory nerve (SAN) posterior to the internal jugular vein [Medscape]

It crosses the posterior triangle lying on levator scapulae, were it remains vulnerable to surgical trauma. Otherwise, isolated lesions of the spinal accessory nerve are rare.¹

References

1. Walker HK. Cranial Nerve XI: The Spinal Accessory Nerve. In: Walker HK, Hall WD, Hurst JW, editors. Clinical Methods: The History, Physical, and Laboratory Examinations. 3rd edition. Boston: Butterworths; 1990. Chapter 64. Available from: https://www.ncbi.nlm.nih.gov/books/NBK387/
2. Bordoni B, Reed RR, Tadi P, et al. Neuroanatomy, Cranial Nerve 11 (Accessory) [Updated 2020 Jul 31]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2020 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK507722/.
3. Gutierrez, S., Warner, T., McCormack, E. et al. Lower cranial nerve syndromes: a review. Neurosurg Rev (2020). https://doi.org/10.1007/s10143-020-01344-w
4. Johal, J., Iwanaga, J., Tubbs, K., Loukas, M., Oskouian, R.J. and Tubbs, R.S. (2019), The Accessory Nerve: A Comprehensive Review of its Anatomy, Development, Variations, Landmarks and Clinical Considerations. Anat. Rec., 302: 620-629. doi:10.1002/ar.23823.