For each of the following three clinical photographs, name the side of the lesion and the cranial nerve/s involved.
(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 | |
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
Subtle features
and, via the vagus...
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Unilateral loss of the obvious features
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Bilateral loss of the obvious features
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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 | |
CN XII: Hypoglossal |
Expected features
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. |
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Supranuclear lesions
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Nuclear and peripheral lesions
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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:
Cranial nerves | Lesions | |
CN VI: Abducens |
Expected features
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Unilateral lesion:
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Bilateral lesion:Freakishly rare
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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 | |
CN VII: Facial |
Obvious features
Subtle features
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Unilateral lesion:
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Central (forehead-sparing) lesions:
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Bilateral lesion:Freakishly rare in isolation
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).