Embolic occlusion limited to one of the distal branches of the superior division, perhaps the most common stroke seen in clinical practice, produces a more circumscribed infarct that further fractionates the above-described syndrome. With occlusion of the ascending frontal branch, the motor deficit is limited to the face and arm with little or no weakness of the leg, and the latter, if weakened at all, soon improves. With left-sided lesions, there is dysfluent and agrammatic speech and normal comprehension (Broca aphasia). Embolic occlusion of the left rolandic branch alone results in sensorimotor paresis with severe dysarthria but little evidence of aphasia. A cortical– subcortical branch occlusion may give rise solely to a brachial monoplegia or hand weakness that simulates a problem in the peripheral nervous system. Embolic occlusion of ascending parietal and other posterior branches of the superior division may cause no sensorimotor deficit but only a conduction aphasia (see Chap. 22) and ideomotor apraxia.
There are many other limited stroke syndromes or combinations of the aforementioned deficits relating to small regions of damage in the frontal, parietal, or temporal lobes. Among these are the Gerstmann syndrome and various forms of agnosia (in some patients, these may be in the territory of the inferior division of the MCA discussed below). Most of these are discussed in Chap. 21, which details the result of lesions in particular parts of the cerebrum. As indicated earlier, the distal territory of the middle cerebral artery may also be rendered ischemic by failure of the systemic circulation, especially if the carotid artery is stenotic; this situation may simulate embolic branch occlusions.
Inferior division Occlusion of the inferior division of the MCA is slightly less frequent than occlusion of the superior one, but again is nearly always the result of embolism. The usual result in left-sided lesions is a
Wernicke aphasia, which generally remains static for days or weeks after which some improvement can be expected. In less-extensive infarcts that are the result of selective distal branch occlusions (superior parietal, angular, or posterior temporal), the deficit in comprehension of spoken and written language may be especially severe. As with superior division stroke, there may be mutism at the outset but the two are differentiated by a severe receptive language deficit with inferior division infarction. After a few months, the deficits usually improve, often to the point where they are evident only in self-generated efforts to read and copy visually presented words or phrases. With either rightor left-hemispheric lesions, there is usually a superior quadrantanopia or homonymous hemianopia and, with right-sided ones, a left visual neglect and other signs of amorphosynthesis may be apparent (Chap. 21). Rarely, an agitated confusional state may be a prominent feature of nondominant hemispheral lesions and sometimes of dominant ones. Some of the syndromes applicable to the angular gyrus and the supramarginal gyrus may occur in strokes within this division, depending on the distributions of the vessels in an individual.
This artery, through its cortical branches, supplies the anterior three-quarters of the medial surface of the frontal lobe, including its medial-orbital surface, the frontal pole, a strip of the lateral surface of the cerebral hemisphere along its superior border, and the anterior four-fifths of the corpus callosum. Most strokes are of the embolic variety, far less often atherosclerotic, and occasionally due to other processes such as vasospasm or vasculitis. Deep branches, arising near the circle of Willis (proximal and distal to the anterior communicating artery) supply the anterior limb of the internal capsule, the inferior part of the head of the caudate nucleus, and the anterior part of the globus pallidus (Figs. 33-6 and 33-7).