Vertebral-Basilar Case 2: Veering Right
The patient presented with a hoarse voice and coughed every time he attempted to swallow. Examination revealed deviation of the palate to the left and an absent gag reflex on the right. Attempts to follow the examiner's finger with his eyes elicited nystagmus especially when he looked to the left. The patient fell or veered to the right when attempting to walk. The finger-to-nose and heel-to-shin tests demonstrated dysmetria of arm and leg movements on the right. He had lost pain and temperature sensation on theright side of the forehead and mouth but also on the left leg, trunk and arm. He had a partial Horner's syndrome (his right pupil was smaller than the left but reactive, and his right lid drooped slightly).
Diagrams
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Expert Note Case 2.
Veering Right
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.