INCOMPLETE BRAIN INFARCTION OF REPERFUSED CORTEX MAY BE QUANTITATED WITH IOMAZENIL

Background and Purpose [I-123]Iomazenil is a specific radioligand for the central benzodiazepine receptor that may be useful as an indicator of the intactness of cortical neurons after focal cerebral ischemia. We evaluated the binding of this receptor in reperfused cortex among p atients with ischemic stroke to detect viable neurons in cortex that a ppeared structurally intact on conventional neuroimaging studies. Meth ods Fourteen patients were selected by (1) angiography within 24 hours of onset showing embolic occlusion of an intracranial artery, (2) cer ebral blood flow showing ischemia of moderate severity in 12 cases and spontaneous reflow in 2 cases, and (3) thrombolysis with reperfusion within 24 hours in most cases. Thirty reperfused cortical areas that r emained structurally intact, 7 infarcted cortical areas, and 6 contral ateral cerebellar areas with reduced blood flow were selected as regio ns of interest to estimate receptor binding 5 days to 23 months after the stroke. A two-compartment model was used to compute the distributi on volume (Vd) of iomazenil in relative units, with Vd proportional to benzodiazepine receptor concentration. The side-to-side asymmetry rat io of Vd was calculated. Results The mean asymmetry ratio was 0.89+/-0 .11 (range, 0.64 to 1.05), 0.50+/-0.15 (range, 0.23 to 0.67), and 0.97 +/-0.05 (range, 0.90 to 1.04) in reperfused cortex, infarcted cortex, and contralateral cerebellum, respectively. Compared with unity, both reperfused cortex and infarcted cortex showed significant decrease of Vd (P<.001). Contralateral cerebellum showing diaschisis had no reduct ion of Vd. On MRI, obtained 3 or 6 months after the stroke, mild corti cal atrophy was observed in two reperfused areas where the asymmetry r atio was moderately reduced (0.64 and 0.80). Conclusions The reduction of benzodiazepine receptor concentration in reperfused cortex that re mained structurally intact is likely to be the result of injury involv ing only a limited number of neurons (ie, incomplete infarction). Our data suggest that the degree of viability of ischemic cortex apparentl y salvaged by early reperfusion can be quantified by iomazenil.