Subgroup Analysis of Patients with Severe Acute Neurological Ischemic Syndromes without Diffusion Weighted Magnetic Resonance Imaging Abnormalities
Several magnetic resonance imaging (MRI) studies have reported correlations of the acute neurological deficit (NIHSS) and lesion size on early diffusion weighted (DWI). The majority of patients falls into this category but as exceptions from the rule patients may present with no or only very small DWI lesions but severe neurological deficits. We analysed serial MRI in this potentially important subgroup of acute ischemic syndromes. Methods: MRI was performed on a 1.5T Siemens Vision unit including T2-, T1-weighted, MR-angiography, echo-planar DWI and perfusion(T2* + Gadolinium injection)- weighted MRI (PWI). Early (8≤hours) and follow-up (at 48–72hours) MRI was analysed in 13 patients with severe acute ischemic neurological syndromes (NIHSS≥8). In all patients there was no or only minimal abnormality on early isotropic DWI (b=1000mm2/sec, ADC maps)and evidence of hemodynamic compromise (MCA main stem, MCA branch, PCA, PICA) on TTP maps and a corresponding lack of flow signal on MRA. Results: Follow-up MRI determined 2 patient subgroups: 1. In 6 patients in whom MRI was performed within 90 minutes after symptom onset the complete DWI lesion had developed only on the follow-up MRI. Those patients showed no or only slight clinical improvement. 2. In 7 patients there was no or only a small DWI lesion on follow-up MRI while there was clinical improvement. In 5/7 patients TTP maps showed resolution or marked improvement of the PWI abnormality on follow-up. Conclusions: Two settings may cause early unrevealing DWI: 1. On early MRI performed within 90 minutes after symptom onset a DWI lesion may not have developed and the extent of an ischemic lesion may be underestimated. 2. The hemodynamic compromise may be less severe (comparable to the concept of the penumbra) causing neurological symptoms without the development of complete tissue infarction.