Question 21.2

For each of the following three clinical photographs, name the side of the lesion and the cranial nerve/s involved.

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College Answer

(a) Left Glossopharyngeal (IX) cranial nerve.

(b) Right Hypoglossal (XII) cranial nerve.

(c) Left Facial (VII) and Left Abducens (VI) nerves.


The college loves gaze palsies. And cranial nerve lesions in general.

a) demonstrates a deviated uvula. This results from palatine paralysis: the pharyngeal muscles on the affected side are weaker, and the tonic contraction of the muscles on the healthy side effects an unopposed pull on the uvula, causing it to deviate away from the lesion.The college has described this as a glossopharyngeal nerve palsy. However, as one of the more clever readers has pointed out, the motor innervation of the the palate muscles is in fact mainly supplied by the pharyngeal branches of the vagus nerve, specifically the branchial motor fibres (so called because their corresponding relatives in fish innervate the gill arches). These are the main muscles which elevate the palate when the patient says "Aaah". The only palatine muscle innervated by the glossopharyngeal nerve is the stylopharyngeus, which stretches between the styloid process and the pharynx and therefore may not have much of a role in moving the uvula. This correction of the college answer is offered with the caveat that even highly detailed explorations of these cranial nerves (eg. Clinical Anatomy of the Cranial Nerves by Paul Rea, p. 105-116) allow that both vagus and glossopharyngeal nerves are being tested by the "Aah" deviated uvula test, and that isolated lesions of one nerve without the other are virtually unknown. As such, here and elsewhere descriptions of CN IX and X lesions are grouped together.

Cranial nerves Lesions
Glossopharyngeal and vagus nerve lesions

CN IX and X:

Glossopharyngeal and Vagus

These two are usually tested (and described) together because isolated lesions of one but not the other are essentially unknown.

Obvious features

  • Absent gag reflex
  • Deviated uvula (away from the lesion)
  • Laryngeal paralysis (unilateral or bilateral)

Subtle features

  • Difficulty swallowing
  • Impairment of taste over the posterior one-third of the tongue and palate
  • Loss of sensation over the posterior one-third of the tongue, palate, and pharynx
  • Dysfunction of the parotid gland

and, via the vagus...

  • Decreased oesophageal motility
  • Dysregulation of heart rate

Unilateral loss of the obvious features

  • Tumour (cerebellopontine angle, acoustic neuroma)
  • Trouble in the jugular foramen (eg. base of skull fracture)
  • Medullary infarct
  • Carotid artery aneurysm
  • Recurrent laryngeal nerve paralysis due to a neoplastic mass or surgery along its course

Bilateral loss of the obvious features

  • Pseudobulbar palsy
  • Medullary infarct
  • Bihemispheric infarct (supranuclear

b) demonstrates a tongue the right side of which has been affected by chronic muscle wasting, as occurs with denervation. Only a hypoglossal nerve lesion can give this appearance.

Cranial nerves Lesions
Hypoglossal nerve lesions

CN XII: Hypoglossal

Expected features

  • Paralysis, atrophy and fasciculations of the tongue on the ipsilateral side (with nuclear or infranuclear lesions)
  • Mild weakness of the tongue on the contralateral side (with supranuclear lesions)

The "central" supranuclear lesions tend to cause mild and transient weakness, because the hypoglossal nerve nuclei receive bilateral cortical input. Hemispheric lesions rarely cause a clinically important CN XII palsy.

Nuclear lesions are frequently bilateral: there is little space in the medulla, and the nucli are close together.

Supranuclear lesions

  • Hemispheric lesions, eg. stroke

Nuclear and peripheral lesions

  • Stroke
  • Syringobulbia
  • Basilar meningitis
  • Intraspinal tumours
  • Epidural abscess

c) demonstrates an eye which cannot abduct past midline (an abducens nerve palsy). This is weird, because Question 21.3 (the very next question) goes on to ask about this in greater detail. To simplify revision, the abducens nerve table is reproduced below:

Finally, the last picture presents a mouth apparently smiling with only the right side. This is characteristic of a seventh nerve palsy.

Cranial nerves Lesions
Facial Nerve Palsy

CN VII: Facial

Obvious features

  • Facial paralysis:
    • Supranuclear "central" lesions spare the forehead and brow
    • Peripheral lesions take out the whole hemiface

Subtle features

  • Failure of lacrimation
  • Failure of salivation
  • Loss of taste in the anterior 2/3rds of the tongue
  • Loss of sensation from tympanic membrane, part of external auditory canal, lateral surface of ear, and area behind the ear.
facial nerve lesion

Unilateral lesion:

  • Peripheral (complete) lesions: ipsilateral paralysis
    • Trauma
    • Tumour (cerebellopontine angle)
    • Otitis media
    • Parotidectomy
    • Meningitis
    • Diabetic neuropathy
    • Bell's Palsy

Central (forehead-sparing) lesions:

  • Traumatic brain injury
  • Tumour
  • Stroke

Bilateral lesion:Freakishly rare in isolation

  • Guillain-Barre Syndrome
  • Lyme disease
  • Meningitis
  • Melkersson-Rosenthal syndrome (a rare neurological disorder characterized by facial palsy, granulomatous cheilitis, and fissured tongue)
  • Diabetic neuropathy
  • Bilateral neurofibromas.

Obviously, the facial nerve forms the efferent component of the corneal reflex, and a bilateral absence of the corneal reflex is to be expected in the context of braindeath.


The LITFL summary of cranial nerve lesions is without peer in terms of useful information density.

Lapresle, J., and P. Lasjaunias. "CRANIAL NERVE ISCHAEMIC ARTERIAL SYNDROMES A REVIEW." Brain 109.1 (1986): 207-215.

Walker, H. Kenneth, W. Dallas Hall, and J. Willis Hurst. "Clinical methods." (1990).