Brainstem

Brainstem signs are sometimes complicated and can be difficult to accurately classify. They include features such as cranial nerve palsies, cerebellar signs (ataxia) and locked-in syndrome.

Cerebellar signs should be reasonably easy to identify; the typical feature are dysarthria, nystagmus, intention tremor, past pointing and a broad based staggering gait– ‘drunken sailor'.

Locked-in syndrome is where the patient is unable to move or speak, but may be able to make limited communication by eye gestures. It can be mistaken for coma.

The cranial nerve lesions arise because of a stroke in the brainstem. The signs will vary according to which part of the brainstem is affected. One way of thinking about brainstem signs is of ‘crossed signs'. An example would be Weber syndrome, in which there is an ipsilateral IIIrd nerve lesion and a contralateral hemiplegia. These signs are difficult to interpret, so doesn't worry if you are not confident – the table below describes the brainstem syndrome in detail but you do not need to learn these!!

The brainstem is not well seen on CT scans and so an MRI scan may be required to support your clinical diagnosis.

You may find it easy to think about this classification by separating out POCS from TACS/LACS/PACS. Think about three signs initially, hemiparesis, hemianopia and higher cortical dysfunction (dysphasia if dominant lobe lesion, parietal signs if non dominant hemisphere). If the patient has 3/3, they have a TACS; 2/3 PACS, 1/3 LACS. Crossed signs, isolated hemianopia or cerebellar signs are likely to be POCS.

This system is not perfect, but it will be correct on most occasions. A more precise classification system is shown below. You should discuss classification further with you tutors.

Level

 

Ipsilateral

Contralateral

Eponym

Midbrain

Dorsolateral

Horner's/cerebellar

Total sensory loss

 

 

Paramedian

III

Cerebellar, hemichorea

Benedikt

 

Basal

III

Hemiplegia

Weber

Pons

Dorsolateral

Horner's, cerebellar
+/- VII, Vs, gaze palsy

Spinothalamic sensory loss

 

 

Paramedian

VI, gaze palsy

+/- Spinothalamic sensory loss

 

 

Basal

VI, LMN VII

hemiplegia
+/- UMN VII

Millard-Gubler

 

Bilateral ventral

Locked in syndrome

 

 

Medulla

Lateral

Horner's, VII ST loss, cerebellar, LMN VII, VIII, IX, X

Corporal ST loss

Wallenberg

 

Central

XII

Hemiplegia, dorsal column sensory loss

 

The table outlines the different brainstem syndromes. They can be confusing and it is best not to focus too much on the detail, but remember that cerebellar signs, ‘crossed signs' (cranial nerve lesion on one side and contralateral hemiparesis), eye signs and locked in syndrome should all make you think of posterior circulation stroke.

Video:

Testing understanding video

This lady has features suggestive of a partial left third nerve lesion. The eye movements appear to be normal, but there is a dilated left pupil and a suggestion of a partial left ptosis.

This site allows you to test eye movements and is well worth trying (opens in a new browser)

Questions: