Strokes: MCA

Diagrams

Strokes in Middle Cerebral Artery Territory  

Infarctions in the distribution of the MCA are by far the most common strokes that are seen in clinical practice. Unlike the situation with the extracranial internal carotid, there are limited ways to establish anastamotic blood flow that can "rescue" ischemic tissue if the MCA or its branches are blocked.

Occlusion of the MCA stem is most often caused by embolism from a cardiac source or artery-to-artery embolism from the extracranial ICA. In a complete occlusion, blood flow is blocked both to the 10-15 deep penetrating lenticulostriate branches, which supply the internal capsule and basal ganglia, and to the more lateral superior and inferior MCA branches, which supply most of the lateral cerebral cortex. As a result, much of the hemisphere is infarcted.

After such a large stroke, the resulting brain swelling may cause sufficient side-to-side and downward herniation of the brain that the resulting midbrain compression kills the patient. Those who survive the initial period will have a contralateral hemiplegia affecting the lower face, arm and (to a lesser extent) leg. Damage to the frontal lobe motor cortex and its projections results in brisk reflexes and a dorsiflexor Babinski response. There is also contralateral hemianesthesia produced by damage to the anterior parietal lobe somatosensory cortex, and a complete contralateral homonymous hemianopsia resulting from damage to the visual radiations as they travel from the lateral geniculate nucleus to the primary visual cortex in the white matter of the posterior temporal and parietal lobes.

In addition, damage to frontal, parietal and temporal lobes near the sylvian fissure in the language-dominant hemisphere (almost always the left one) produces global aphasia. Although fully conscious, these patients understand nothing that is said and are unable to utter more than a few stereotyped words. 

Damage to the posterior parietal and temporal lobes (and, most likely, the frontal lobes as well) in the non-language, right hemisphere produces a severe defect in visuospatial conceptualization. These patients neglect the left side of their own body and of their world. They may deny that their left limbs are paralyzed or even deny that their left arm and leg belong to them. They may shave only the right side of their face or draw only the right side of a symmetrical object such as a clock.  They may have major problems in putting on clothes, an activity that requires understanding 3-D visuospatial relationships. They often appear emotionally blunted, dull, inattentive, apathetic or confused.