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The patient has infarcted
the dorsolateral region of the rostral medulla on the right side.
This is the most commonly occurring ischemic brainstem stroke which
patients survive. The combination of signs and symptoms that he shows
is often referred to as Wallenberg's syndrome. It was once thought
that this syndrome was only produced by posterior inferior cerebellar
artery occlusion. However, more recent studies suggest that blockage
of the vertebral artery itself is responsible.
The hoarse
voice, difficulty swallowing, left palatal deviation and absent
right gag reflex all suggest damage to the 9th and 10th cranial
nerves (or nucleus ambiguus) on the right. The nystagmus (together
with the vertigo, severe nausea and vomiting that patients like
this often experience) is produced by damage to the vestibular nuclei
or vestibular connections with the cerebellum. Problems with right
limb coordination suggest involvement of the right inferior cerebellar
peduncle or the right side of the cerebellum itself.
The loss of pain and temperature sensation on the right side of
the face is caused by interruption of the descending tract of the
trigeminal (which is uncrossed). The spinothalamic tract, which
runs close to the descending tract, has already crossed in the spinal
cord so it carries information about pain and temperature in the
left (opposite) side of the body. Hint: Brainstem
lesions typically produce cranial nerve signs ipsilateral to the
lesion but sensory deficits in the trunk and limbs contralateral
to the lesion. This is because the cranial nerves are uncrossed
(except CN 4) while axons in the two major somatosensory pathways
for the body (the spinothalamic tract and medial lemniscus) have
crossed the midline at or below the caudal medulla.
Horner's syndrome (ptosis, miosis, anydrosis, enophthalmos) caused
by a lateral medullary lesion is due to interruption of reticulospinal
fibers. These fibers travel in lateral parts of the reticular formation
on their way to synapse with the preganglionic sympathetic neurons
of the intermediolateral column in the high thoracic spinal cord.
Hint: No matter where the nervous system is interrupted to
produce a Horner's syndrome (whether in the CNS or PNS), the lesion
in always on the same side as the abnormal findings.
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