Boundary and vulnerability estimation of the internal borderzone using ischemic stroke lesion mapping

Distinction between deep and superficial middle cerebral artery (MCA) territories and their junctional vascular area (the internal borderzone or IBZ) constitutes a predictor of stroke patient outcome. However, the IBZ boundaries are not well-defined because of substantial anatomical variance. Here, we built a statistical estimate of the IBZ and tested its vulnerability to ischemia using an independent sample. First, we used delineated lesions of 122 patients suffering of chronic ischemic stroke grouped in deep, superficial and territorial topographies and statistical comparisons to generate a probabilistic estimate of the IBZ. The IBZ extended from the insular cortex to the internal capsule and the anterior part of the caudate nucleus head. The IBZ showed the highest lesion frequencies (~30% on average across IBZ voxels) in our chronic stroke patients but also in an independent sample of 87 acute patients. Additionally, the most important apparent diffusion coefficient reductions (−6%), which reflect stroke severity, were situated within our IBZ estimate. The IBZ was most severely injured in case of a territorial infarction. Then, our results are in favour of an increased IBZ vulnerability to ischemia. Moreover, our probabilistic estimates of deep, superficial and IBZ regions can help the everyday spatial classification of lesions.

Is Hypoperfusion an Important Cause of Strokes? If So, How?

Traditionally hypoperfusion and embolism are considered separate important causes of stroke in patients with arterial occlusive disease. However, although hypoperfusion and embolism differ in mechanisms and location, they generally coincide in severe obstructive lesions and cause washout disturbances of embolism in low perfusion territories distal to stenosis. Unless the collateral blood supply is sufficient to prevent ischemia, multiple remote spot-like infarctions occur within the hypoperfused brain territory. In border-zone distributed infarction - long suspected to result from hemodynamic compromise alone - complementary interaction of embolisation and hypoperfusion territories has to be considered. Thus hypoperfusion with embolism or embolism alone are the most common explanations for stroke, the former often associated with less severe clinical deficits than the latter.

Topography of cerebral infarction associated with carotid artery dissection

Because the pathogenesis of cerebral ischaemia in internal carotid artery dissection (ICAD) is controversial we studied the topography of cerebral infarction that results from ICAD according to pathophysiology of embolic and haemodynamic stroke. Sixty-four patients with 67 ICADs diagnosed by angiography, Doppler duplex sonography and magnetic resonance imaging (MRI) were studied prospectively during the past decade. According to current pathophysiological concepts, cortical territorial infarcts and large subcortical lenticulostriate infarcts revealed by CT or MRI were classified as embolic, while smaller infarcts in the subcortical junctional zone and infarcts in the cortical borderzone between the middle (MCA) and anterior cerebral artery were interpreted as haemodynamic infarcts. Of the 67 dissections 37 (55%) were associated with brain infarcts, of which territorial MCA infarcts of variable size accounted for 60%. These were combined with infarcts of the anterior and posterior cerebral artery in 5%; 8% of the patients had complete MCA infarction. Large lenticulostriate infarcts were present in 11%. Haemodynamic infarcts involved the subcortical junctional zone in 16% but never the anterior cortical borderzone. Although different abnormal Doppler findings indicated haemodynamically significant carotid obstruction in all symptomatic ICADs, only the characteristic high-resistance Doppler signal was significantly associated with the occurrence of brain infarction (in 66%, P < 0.01). The angiographic features of ICAD did not correlate with the incidence or with the topography of cerebral infarction. Patterns of infarction in ICAD indicate a predominantly embolic causation probably due to thrombus formation in the dissected carotid artery in the presence of severe haemodynamic obstruction, as demonstrated by Doppler sonography.