Cryptogenic Infarction

Despite efforts to arrive at a diagnosis, the cause of infarction in a discouragingly large number of cases remains undetermined. Some cases may be unexplained because no appropriate laboratory studies are performed, while others are due to the improper timing of the appropriate laboratory studies. The most frequent circumstances are when normal or ambiguous findings are reached despite appropriate laboratory studies performed at the appropriate time. Results from the Stroke Data Bank indicated that large artery atherosclerotic occlusive disease was a less frequent cause of stroke; small vessel or lacunar and cardioembolic infarction were relatively frequent; and that the cause for the majority of the cases of infarction could not be classified into these traditional diagnostic categories. This forced the creation of a separate diagnostic category for cases whose mechanisms of infarction remained unproven, one known as ‘infarct of undetermined cause’ or ‘cryptogenic infarction.’

Cases categorized as cryptogenic infarction have no bruit or TIA ipsilateral to the hemisphere affected by stroke, no obvious history suggestive of cardiac embolism and usually do not present with a lacunar syndrome. The CT or MRI scan performed within seven days may be normal, show an infarct limited to a surface branch territory or may show a large zone of infarction affecting regions larger than that accounted for by a single penetrant arterial territory. Non-invasive vascular imaging fails to demonstrate an underlying large vessel occlusion or stenosis. No cardiac source of embolism is uncovered by echocardiography, electrocardiography or Holter monitor. If an angiogram is performed, the study may be normal, show a distal branch occlusion or occlusion of a major cerebral artery stem, or the top of the basilar. Because these latter occlusions can be from embolus or thrombosis of an atherosclerotic vessel, their demonstration does not settle the mechanism. Image results for echocardiography

Many of these cases present with a hemispheral syndrome, a surface infarction by CT or MRI and a corresponding branch occlusion documented by angiography or normal angiogram. This constellation of findings has been considered suggestive of embolism. There is ample evidence for many occult sources of emboli, the difficulty proving their existence, and their role in the first or succeeding ischemic strokes. Emerging technologies have led to the suggestions that some cryptogenic infarcts may be explained by hematologic disorders causing hypercoagulable states from Protein C, free Protein S, Lupus anticoagulant or anti-cardiolipin antibody abnormalities. Others have implicated paradoxical emboli through a patent foramen ovale and aortic arch atherosclerosis.

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