Neurological Examination, clinical cases and neuropsychological ...

23/07/54
This 48‐year‐old woman had the sudden onset and rapid progression of her symptoms,
which is the temporal profile of an acute vascular event or a stroke. Risk factors for stroke
include hypertension, cardiac disease, diabetes mellitus, smoking as well as coagulation and
autoimmune disorders. This patient had none of these risk factors.
One of the first steps in localizing the occluded vessel in a stroke is to decide if the vessel is
in the anterior or posterior arterial circulation of the brain. Most strokes occur in the
anterior or carotid circulation because most of the brain’s blood supply is supplied by the
carotids. Although strokes in the posterior or vertebrobasilar circulation are less common,
this patient’s cranial nerve findings suggest an infarct in the brainstem and not the carotid
territory.
By history and examination there are 3 findings that indicate possible cranial nerve
involvement. Her history of diplopia indicates a right 6th (abducens) cranial nerve deficit
(remember the most peripheral image is the false image and covering the right eye
eliminated this image) and by examination she has a right 7th (facial) cranial nerve deficit. To
explain these two deficits one has to localize the lesion in the caudal pons in the area of the
6th and 7th cranial nerve nuclei or the pathway of the nerves at this level.
To explain the sensory findings on the left side of her face, we could postulate either a left
spinal trigeminal tract lesion or it could be from a lesion affecting the axons of the 2nd order
neurons which have crossed over to the right side of the pons and are ascending in the
ventral trigeminothalamic tract. The left spinal trigeminal tract lesion hypothesis is
unattractive, because it would mean a second lesion. In the pons, the ascending ventral
trigeminothalamic tract is near the facial nucleus, so a lesion affecting this tract is the likely
explanation.
The last finding that we have to account for anatomically is the sensory deficit on
the left side of the body. We first have to decide if the deficit is from a lesion in the
DC‐ML system or the spinothalamic (ALS) system. For this patient, pain and
temperature are affected while vibratory, position sense, and discriminatory
sensation are preserved, which indicates that the spinothalamic tract is involved
but the DC‐ML system is spared. Recall that the axons from the second order
neurons that form the spinothalamic tract cross immediately in the spinal cord and
ascend in the anterolateral spinal cord and the lateral part of the brainstem. In the
pons, the spinothalamic tract, carrying pain and temperature for the left side of the
body, is adjacent to the facial motor nucleus.
So we could explain all the clinical findings for this case by a lesion in the
mediolateral part of the right lower pons most likely caused by occlusion of one of
the short circumferential branches of the basilar artery. It is not a paramedian
lesion because the patient has no findings referable to the corticospinal tracts and
the medial lemniscus. It is also not a far lateral lesion because there are no rightsided
spinal trigeminal tract, vestibular, or cerebellar findings.
An MRI scan of the patient done 6 months after her stroke shows a small residual
lesion in the area of the right abducens nucleus. This imaging finding doesn’t cover
the entire anatomical area where we know there has to be disease, but it does
support the hypothesis that there has been a small stroke in the area where we
localized her lesion based on her clinical findings
Review and Summary:
6