Clinical-Anatomical Syndromes of Ischemic Infarction

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Chapter 2 Clinical-Anatomical Syndromes of Ischemic Infarction

Ischemic stroke can be defined as a sudden focal neurological deficit corresponding to a vascular distribution. Brain imaging techniques allow us to visualize lesions with great anatomical precision. However, optimal interpretation of the information provided by neuroimaging requires having detailed knowledge of the arterial anatomy (Figures 2-1 through 2-4) and the vascular territories of the brain (Figure 2-5).

Brain imaging has also enhanced our understanding of clinical-anatomical correlations in patients with ischemic infarctions. Before the development of modern neuroimaging modalities, these correlations could only be established by necropsy studies. In fact, clinical research using radiological data has shown that localization based on classical semiological syndromes may often be incorrect. Similar clinical presentations may occur in patients with strokes in different territories and, conversely, infarctions in the same territory may produce dissimilar manifestations in different patients. Nonetheless, accurate diagnosis relies on the recognition of the brain lesion in a defined vascular territory.

This chapter provides illustrations of ischemic infarctions in all major vascular territories and presents the most common clinical correlations. It is conceived as a practical and concise guide to the correct interpretation of brain imaging and not as a comprehensive anatomical or semiological monograph on this important topic. The reader should keep in mind that the variety of distribution of infarctions encountered in practice is enormous. The boundaries of arterial territories are far from invariable across patients, and anatomical variations in the constitution of the cerebral circulation and its interconnections are relatively common.

CAROTID BIFURCATION OCCLUSION

Case Vignette

A 61-year-old man with history of coronary artery disease, previous myocardial infarction, and multiple vascular risk factors presented to the emergency department with global aphasia and right hemiplegia for more than 6 hours. On examination, he was drowsy and exhibited forced left gaze deviation, right hemianopia, right flaccid hemiplegia involving the arm and the leg to similar degree, and absent response to pain on the right side. Diffusion-weighted imagery (DWI) of the brain revealed a large area of ischemia in the left hemisphere, including the territories of the anterior and middle cerebral arteries (Figure 2-6). Fluid-attenuated inversion recovery (FLAIR) sequence showed no parenchymal hyperintensity but disclosed extensive hyperintense signal in the left middle cerebral artery consistent with fresh thrombus (Figure 2-7). Magnetic resonance angiography (MRA) of the intracranial circulation confirmed the presence of a left carotid terminus occlusion (Figure 2-7). The patient was subsequently diagnosed with acute myocardial infarction and a left ventricular mural thrombus. His neurological condition deteriorated over the following 48 hours, and he expired after care was restricted to palliative measures.

An intravascular hyperdensity at the level of the carotid bifurcation may often be seen on CT scan. Thin-section computed tomography (CT) scans1 and T2* gradient echo magnetic resonance (MR) sequence2 may reveal intra-arterial thrombus with greater sensitivity.

MIDDLE CEREBRAL ARTERY OCCLUSION

The MCA is divided in four segments (see Figures 2-1 and 2-2). The M1 or horizontal segment is a single stem that give rise to the penetrating lenticulostriate branches. It branches into two (or occasionally three) M2 or insular segments as it enters the Sylvian fissure. The M3 or opercular segments ascend following the curvature of the operculum. The M4 or cortical segments travel along the sulci and gyri of the cerebral convexity.

Territorial MCA Infarction

Hyperdense MCA sign may be seen on the initial CT scan. Its presence is associated with less chances of recanalization after thrombolysis5,6 and worse likelihood of favorable recovery.57 Still, intravenous thrombolysis remains the standard of care for patients with MCA stroke presenting within 3 hours of symptom onset regardless of the presence of this radiological sign.6 Although preferential use of intra-arterial interventions has been advocated by some groups, the benefits of this approach are thus far unproved.8

Deep Middle Cerebral Artery Infarction

Superficial Divisional Middle Cerebral Artery Infarction

Acute confusional state, often associated with agitated delirium, may predominate in right-sided infarctions of the inferior M2 division.16 It is important to keep this diagnosis in mind when evaluating any patient presenting with acute confusion and agitation, because detailed neurological examination may be difficult in these cases, and sensory, visual, and perceptual deficits may be easily missed.
Infarctions of the inferior division of the MCA are predominantly caused by cardiac embolism.15,16 Carotid artery disease is rarely a cause of infarctions in this vascular distribution.

Superficial Cortical Infarctions

Left20 and right-sided18,19 infarctions have been associated with worse cardiac outcomes in different studies. Hence, the degree of lateralization in the control of autonomic cardiac function in humans remains to be fully elucidated.
Other cortical branch infarctions may be caused by occlusion of M3 branches (Figure 2-12) and may present with distinctive clinical syndromes. Some common examples of localizing clinical features encountered in practice are shown in Table 2-1.

Hemispheric Border-Zone Infarctions