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.

Discussion

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.

Glossopharyngeal and vagus nerve lesions
Cranial nerves	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.

Hypoglossal nerve lesions
Cranial nerves	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:

Abducens Nerve Palsies
Cranial nerves	Lesions
CN VI: Abducens	Expected features Failure to abduct the affected eye
	Unilateral lesion: Head injury (most common) with BOSF Raised intracranial pressure Localising lesion.... at any number of levels: Damage to the frontal eye field of the frontal lobe, which occupies some of the middle frontal gyrus Damage to the posterior hemispheres, which would be accompanied by a hemianopia Brainstem (tumour, stroke) - the paramedian prepontine reticular formation mentioned in this question, which receives information from higher cortical centres and transmits them to the abducens nucleus. Petrous portion of temporal bone (otitis media-associated osteomyelitis, mastoiditis) Clivus (intraforaminal extension of nasopharyngeal carcinoma or similar) Cavernous sinus (thrombosis) Superior orbital fissue (base of skull fracture) Any damn where (basal forms of meningitis, eg sarcoidosis, tuberculosis, cryptococcus)
	Bilateral lesion:Freakishly rare Diabetes-associated neuropathy Myasthenia gravis Generally speaking, polyneuropathies such as Guillain-Barre

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

Facial Nerve Palsy
Cranial nerves	Lesions
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.
	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.

References

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).

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Question 21.2

College Answer

Discussion

CN IX and X:

Glossopharyngeal and Vagus

CN XII: Hypoglossal

CN VI: Abducens

CN VII: Facial

References