Early False-negative Diffusion-weighted Imaging In Acute Ischemic Stroke

ObjectiveIn this issue, we reported several cases of early false-negative diffusion-weighted imaging(DWI) in acute ischemic stroke in order to investigate the reasons why the early DWI appears to be false-negative in acute ischemic stroke.Subjects and MethodsWe collect 4 early false-negative DWI in acute ischemic stroke patients which had been met in our hospital during 2008-2010, combining with review of literatures, to analysis the possibilities of which may cause early false-negative DWI occurs.ResultsWe can see 1 cerebellar infarction patient,3 brainstem infarction patients in our collection. The cerebellar infarction patient presenting false-negative DWI 8 hours after symptom onset,71 hours later, in cervical vertebra MRI we found cerebellar lesion occasionally, in repeat DWI study we obtained infarction in right cerebellar 81 hours after symptom onset. Among the three brainstem infarction patients (case2-case4), case 2 was midbrain infarction, although the DWI performed 34 hours of symptom onset was negative, the imaging with thinner sections repeated after 5 days despite static neurological symptoms and signs, could demonstrate an acute midbrain infarction; Case 3 diagnosed as top of the basilar syndrome, the initial DWI obtained 10 hours after symptom onset as negative, follow-up studies, performed 29 hours later, showed infarction in regions compatible with the clinical presentation. Case 4 presented as dorsolateral medullary syndrome without identification of a definite lesion on DWI 5 days after syndrome onset.Conclusions1.Several reasons may be support the phenomenon of early false-negative DWI in acute ischemic stroke:First, it is possible that cerebral blood flow (CBF) was at an intermediate level below the threshold for neuronal dysfunction (symptom onset) but above that of reduced diffusion. The second possible mechanism may be that reperfusion had occurred, restoring the diffusion constant to normal but not preventing eventual delayed infarction. Third, in brainstem and lacunar infarction, the lesions could be too small for the resolution of the DWI echo-planar sequence and to recognition, magnetic susceptibility artifacts occurring in echo-planar imaging cause brain stem distortions that could blur image analysis. And last, severe leukoaraiosis may hindering the development of cytotoxic edema.2.The phenomenon of early false-negative DWI in acute ischemic stroke, especially for posterior circulation and lacunar infarction is not rare. High-resolution imaging with thinner sections and combined axial and coronal DWI sequences should be considerd when we highly suspected the occurrence of stroke clinically.