Ninth Cranial Nerve Lesions

It mediates two key reflexes:

• Gag reflex
• Baroreceptor reflex

Isolated lesions of the glossopharyngeal nerve are very rare and are usually seen in combination with lesions of other lower cranial nerves.

Anatomy

Origin and Course

• Parasympathetic fibres: Arise from the inferior salivary nucleus in the pons.
• Somatic efferents: From the nucleus ambiguus in the lateral medulla (also gives rise to fibres for CN X and XI).
• Sensory relay nuclei: Located in the nucleus solitarius, shared with CN VII and X.

The glossopharyngeal nerve exits the medulla from the posterior olivary nucleus, passes through the jugular foramen with CN X, XI, the internal jugular vein, and the inferior petrosal sinus, and enters the neck.

• Tympanic branch → Tympanic plexus → Lesser petrosal nerve → Otic ganglion → Parotid gland.
• Contains superior and inferior sensory ganglia within the jugular foramen.
• Descends in the carotid sheath, wraps around the stylopharyngeus muscle (which it innervates), then passes between the pharyngeal constrictors and divides into branches.

Major Branches and Innervation

Function	Target
Somatic motor	Stylopharyngeus muscle (all other pharyngeal muscles supplied by vagus nerve)
Somatic sensory	Posterior one-third of tongue, internal surface of tympanic membrane, pharynx, soft palate
Special sensory	Taste from posterior one-third of tongue
Parasympathetic (secretomotor)	Parotid gland
Autonomic sensory (nerve of Hering)	Carotid body and carotid sinus

Pathology

Isolated lesions are rare. More commonly, lesions occur with other lower cranial nerves.

Causes

Central

• Vascular:
  • Lateral medullary infarction (e.g. PICA or vertebral artery territory)
• Tumour
• Syringobulbia

Peripheral (Posterior Fossa Lesions)

• Aneurysm
• Tumour
• Trauma

Clinical Assessment

1. Gag Reflex

• Gently touch both sides of the posterior pharynx with a spatula.
• Glossopharyngeal nerve: Sensory limb.
• Vagus nerve: Motor limb.
• Interpretation:
  • Intact sensation but absent palate contraction → vagus nerve lesion.
  • Absent sensation and absent reflex → glossopharyngeal nerve lesion.

2. Taste Sensation

• Loss of taste in the posterior third of the tongue occurs but is rarely formally tested.

3. Bulbar and Pseudobulbar Palsies

• Pseudobulbar palsy: Bilateral UMN lesions of CN IX, X, XII.
• Bulbar palsy: Bilateral LMN lesions of the same nerves.

Investigations

Blood Tests

As indicated by clinical context:

• FBC
• U&Es / Glucose
• CRP
• ESR
• Others (e.g. blood lead levels)

Imaging

• CT / CT Angiogram: Screens for intracranial mass lesions; angiogram for suspected aneurysms.
• MRI: Useful for mass delineation and direct nerve visualization.

Management

Dependent on the underlying cause of the lesion.

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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

• Nickson C. Bulbar and pseudobulbar palsy. LITFL
• Nickson C. Pseudobulbar and bulbar palsies. LITFL
• 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