The knowledge of the functions and disorders of some very important arteries of the Brain can give us a very clear picture of Neurovascular syndromes. Such arteries are the Anterior and Posterior Cerebra arteries, Vertibral artery and the Basilar artery.
Anterior cerebral artery
This supplies the medial surface of the anterior ¾ of the cerebral hemisphere, anterior 4/5 of the corpus callosum and the anterior limb of the internal capsule. There is no serious disturbance in occlusion of the ACA proximal to the anterior communicating artery since adequate collateral flow develops from the opposite ACA. However, if the occlusion is distal to the anterior communicating artery, it results in weakness of the contralateral lower limb and slight weakness of the upper limb. The face is spared, sometimes both the anterior cerebrals arise from a common stem. In such instances, occlusion produces paraplegia, incontinence of Urine, abulia (in which there is slowness of reaction and reduction of all activity).
Posterior cerebral artery (PCA)
The anterior branches of the PCA supply the sensory nuclei of the thalamus through the thalamogeniculate branches and parts of the basal ganglia through the thalamoperforate branches. Occlusion of these branches result in characteristic syndromes. Infarction of the thalamus causes severe sensory loss and mild hemiparesis contralaterally. After sometime, sensations begin to return and patient complains of pain and hyperpathia. The term hyperpathia indicates an increased threshold to induce pain, but once pain is produced it is severe (thalamic syndrome of Dejerine and Roussy).
Infarction of the midbrain results in ipsilateral third nerve palsy and contralateral hemiparesis (Weber’s syndrome). Sometimes ataxic tremors on the side of hemiparesis appear (ataxic hemiparesis). Hemiballismus, hemichoreoathetosis or tremors result due to occlusion of the thalamoperforate branches.
The cortical branches supply the calcarine cortex as well as the inferomedial portion of the temporal lobe. Bilateral occipital infarctions cause total blindness of the cortical types. Here, the papillary reflexes are preserved and the fundus is normal. Many a time the patient is unaware of his blindness. This type of blindness has to be distinguished from hysterical blindness. Infarctions involving the infero-medial portions of the temporal lobe cause impairment of memory, especially for recent events (Korsakoff’s amnesic state).
The two vertebral arteries supply the medulla. It is not uncommon for one of the arteries to be hypoplastic. In such instances, occlusion of the sole arterial supply for the medulla may produce significant bilateral disturbances. Sometimes, in occlusion of the subclavian arery, proximal to the origin of the vertebral, exercise of the upper limb results in siphoning of blood from the vertebral to the distal part of the subclavian. This retrograde flow of blood from the vertebral artery renders the brainstem ischemic and symptoms of basilar insufficiency develop (subclavian steal syndrome).
In occlusions of branches of the vertebral artery supplying the lateral aspect of the medulla s characteristic syndrome called the lateral medullary syndrome occurs (Wallenberg’s syndrome). This is perhaps the commonest mode of presentation of vertebral artery occlusion. The resultant neurological features consists of sensory impairment over the face, Horner’s syndrome and ataxia on the ipsilateral side, and impaired pain and temperature sensations on the contralateral side. In addition, vertigo, nausea, vomiting, dysphagia, hoarseness of voice, and hiccups also occur in many cases.
In the medial medullary syndrome, there is paralysis of the ipsilateral half of the tongue with contralateral hemiparesis. The face is spared. In addition, there is impaired proprioceptive sensations contralaterally. In total, unilateral vertebral occlusions, a combination of both medial and lateral medullary syndromes result.
The basilar artery supplies essentially the pons, the middle and superior cerebellar peduncles and through the cerebellar arteries, the cerebellar hemispheres, Basillar occlusion due to thrombosis involves either the basilar stem or both vertebral arteries. Emboli usually lodge in the basilar bifurcation or in one of the posterior communicating arteries. Total occlusion of the basilar artery is rare, but it is more common to find occlusion of its branches. Often the deficit includes bilateral long tract signs with variable abnormalities of the cranial nerves and cerebellum. The patient is usually comatose.