Watershed cerebral infarctions, also known as border zone infarcts, occur at the border between cerebral vascular territories where the tissue is furthest from arterial supply and thus most vulnerable to reductions in perfusion.
Watershed cerebral infarction account for 5-10% of all cerebral infarctions 8. They tend to be seen in the elderly, who have a higher incidence of arterial stenosis and hypotensive episodes, as well as microemboli.
It has been proposed that both, episodes of hypoperfusion and microembolisms from inflamed atherosclerotic plaques, play a role in pathophysiology of this entity, although the later is less well established 5.
Episodes of systemic hypotension particularly with severe stenosis or occlusion of the feeding arteries, in particular intra and extracranial carotid arteries, is the typical scenario in which watershed infarction is encountered.
Clearance of the microemboli, which may form on the surface of inflamed plaques, or are the result of an embolic shower, are most likely to be impaired in watershed zones due to poorer perfusion.
Watershed zone infarct in an isolated area is more likely to be secondary to microembolism, particularly in the absence of significant systemic hypotension and/or arterial stenosis. In a severe carotid stenosis, lesions are usually ipsilateral to the stenosis. Prolonged hypotension such as cardiac surgery or cardiac arrest commonly gives a bilateral pattern in the absence of severe stenosis 5.
Watershed infarction has been classified to:
- cortical (external) border zones infarct
deep (internal) border zones infarct:
- between ACA, MCA, and PCA territories, and perforating medullary, lenticulostriate, recurrent artery of Heubner and anterior choroidal arteries
CT and MRI
The exact pattern depends on the bordering territories which is usually variable in different individuals. Imaging of watershed infarction should also aim to determine presence and severity of arterial stenosis or occlusion.
Cortical (external) border zones infarct
These are usually wedge-shaped or gyriform:
- ACA/MCA: in frontal cortex extending from anterior horn to the cortex
- MCA/PCA: in parieto-occipital region extending from posterior horn to the cortex
- parallel parafalcine stripes in subcortical white matter at the vertex- this type is seen when there was profound diffuse hypoperfusion
Triple watershed zone: most vulnerable region where ACA, MCA, and PCA converge posterior to lateral ventricles in parieto-occipital region.
Deep (internal) border zones infarct
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- 5. Gottesman RF, Sherman PM, Grega MA et-al. Watershed strokes after cardiac surgery: diagnosis, etiology, and outcome. Stroke. 2006;37 (9): 2306-11. doi:10.1161/01.STR.0000236024.68020.3a - Pubmed citation
- 6. Mangla R, Kolar B, Almast J et-al. Border zone infarcts: pathophysiologic and imaging characteristics. Radiographics. 2011;31 (5): 1201-14. Radiographics (full text) - doi:10.1148/rg.315105014 - Pubmed citation
- 7. Derdeyn CP, Khosla A, Videen TO et-al. Severe hemodynamic impairment and border zone-region infarction. Radiology. 2001;220 (1): 195-201. doi:10.1148/radiology.220.1.r01jl09195 - Pubmed citation
- 8. Naidich TP, Castillo M, Cha S et-al. Imaging of the Brain,Expert Radiology Series,1. Saunders. (2012) ISBN:1416050094. Read it at Google Books - Find it at Amazon
- 9. Kumar V, Abbas AK, Aster JC. Robbins & Cotran Pathologic Basis of Disease. Elsevier Health Sciences. (2014) ISBN:0323296351. Read it at Google Books - Find it at Amazon