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A vertebrobasilar infarct is characterized by acute onset of symptoms that may progress over hours to days.
Dr. Moster reviewed the anatomy that is involved. The vertebrobasilar circular begins off the aorta, brachiocephalic, or subclavian arteries with the right and left vertebral arteries. The vertebral arteries join to become the basilar artery. There are penetrating branches off the basilar artery and the final branch is the posterior cerebral artery. The arterial supply is to the medulla via the posterior and inferior cerebral arteries and then through the entire brainstem and cerebellum through other penetrating arteries medial and lateral to the basilar artery. The posterior cerebral artery supplies blood to the occipital lobe, explained Dr. Moster, director of neuro-ophthalmology at Albert Einstein Medical Center, professor of neurology, Thomas Jefferson University School of Medicine, and on the Neuro-Ophthalmology Service at Wills Eye Hospital, Philadelphia.
"The ophthalmic structures that are involved in the vertebrobasilar circulation and can be affected by an insult are the sympathetic pathway; the third, fourth, fifth, and sixth cranial nerves; various supranuclear pathways of motor control including the gaze centers; and the occipital cortex," he explained.
If the connection (the medial longitudinal fasciculus) between the sixth nerve and the third nerve is affected, internuclear ophthalmoplegia develops with an ipsilateral adduction deficit and contralateral abducting nystagmus. If the supranuclear pathways are involved, a supranuclear gaze disorder, skew deviation, nystagmus, and vertigo occur. If the occipital lobes are involved, a homonymous defect, quadrantanopsia, or hemianopsia can occur, and if the insult is bilateral, cerebral blindness can occur or there may be visual processing difficulties and visual hallucinations.
A vertebrobasilar infarct is characterized by acute onset of symptoms that may progress over hours to days, longer than the progression of carotid disease. In most cases, other neurologic symptoms are evident.
Crossed deficits also can occur. Dr. Moster explained that third, fourth, and sixth cranial nerve defects are typically ipsilateral. The cerebellar findings of ataxia are often ipsilateral, but because of the manner in which the fiber tracts cross the sensory loss and motor defects are contralateral.
In some patients with vertebrobasilar disease, there are only ocular manifestations of the disease.
"This can make it difficult to make the diagnosis. However, ophthalmologists can detect the subtle ocular findings better than any other specialists, including neurologists. If the patient presents with acute vertebrobasilar disease, it is extremely important to refer the patient immediately to the emergency department, because there may be interventions that can help," he said.
Vertebrobasilar disease, which is usually thrombotic or embolic, also can be associated with migraine. The ophthalmologist should be aware that patients who present with headache and ocular symptoms may have something more than a migraine, because migraines also can cause strokes.
"Ophthalmologists have to think about vertebral dissection, giant cell arteritis, and the other diseases that mimic vertebrobasilar disease such as mass lesions, encephalitis, and multiple sclerosis, especially in young patients," he advised.
Vertical gaze defects occur more often in upgaze than downgaze and often may be supranuclear. When the subnuclei of the third cranial nerve in the midbrain are affected, various syndromes can occur, the most common of which are bilateral ptosis or a unilateral third-nerve palsy with a contralateral elevation defect because of involvement of the crossed superior rectus muscle innervation. If the insult is distal to the level of the nuclei and the cerebral peduncle is involved, Weber's syndrome with a contralateral hemiparesis can occur; if the red nucleus is involved, Benedikt's syndrome can develop with a contralateral prominent cerebellar-type tremor.