Early computed tomographic (CT) findings (scans obtained within 6 hours of the onset of stroke) were retrospectively analyzed in 25 patients with embolic cerebral infarction of the middle cerebral artery or internal carotid artery distribution, including the lentiform nucleus, diagnosed on the basis of findings at sequential CT. CT scans were analyzed for the following: (a) an obscured outline or partial disappearance of the lentiform nucleus, (b) a slight decrease in tissue density, or (c) effacement of the cortical sulci. One or more of these findings was recognized in 23 of 25 patients (92%). The first finding was noted most frequently, and it appeared earliest. Obscuration of the lentiform nucleus was thought to be an important early sign of cerebral infarction, including the lentiform nucleus.

MR imaging is useful in evaluating secondary thalamic degeneration after cerebral infarction. In clinical practice, this secondary degeneration should not be mistaken for other lesions such as further cerebral infarction.

Degeneration of the substantia nigra ipsilateral to the striatal infarction was clearly demonstrated at MR imaging. This finding should not be mistaken for further cerebral infarction.

Using quantitative autoradiography, we studied sequential changes in regional cerebral blood flow during and after 2 minutes of bilateral common carotid artery occlusion in 18 gerbils. Occlusion (n=4) led to severe ischemia in the forebrain (regional cerebral blood flow <5% of control [ft=4]) and midbrain (regional cerebral blood flow <10% of control), but was morphologically nonlethal. Reperfusion of the brain was complete, and regional cerebral blood flow was not different from control 1 minute after ischemia (ft=4), but hypoperfusion (regional cerebral blood flow 30-50% of control) occurred at 5 minutes (ft=3) and was pronounced at 1 hour (n=4); at this stage blood flow was inhomogeneous. Hypoperfusion had disappeared at 4 hours (n=3 This damage occurs not only in forebrain regions (such as the hippocampal CA1 subfield, the striatum, thalamus, and neocortical layers 3 and 5) but also in midbrain structures (i.e., the medial geniculate body, substantia nigra, and inferior colliculus). 5On the other hand, repeated brief bilateral carotid artery occlusions in gerbils produce cumulative damage to the brain. Tomida et al 6 found that damage following three 5-minute ischemic insults at 1-hour intervals is greater than that following a single 15-minute ischemic insult and concluded that postischemic hypoperfusion plays an important role. We have reported that repeated 2-minute ischemic insults, each of which is nonlethal to the brain when given singly, produce severe neuronal damage. 78 However, whether hypoperfusion takes place after nonlethal 2-minute ischemic insults is not known. The purpose of this study was to visualize and quantify using autoradiography the extent and degree of regional cerebral blood flow (rCBF) changes during and after 2 minutes of cerebral ischemia in gerbils. Materials and MethodsWe used a total of 33 adult male Mongolian gerbils weighing 70-90 g. Anesthesia was induced with 2% halothane and maintained with 1% halothane in 30% O 2 and 70% N 2 O. A midcervical skin incision was made, and both common carotid arteries were gently exposed. Nine control gerbils received no occlusion, but in the remaining 24 experimental gerbils the arteries were occluded with aneurysm clips for 2 minutes. In 14 gerbils for autoradiography the carotid arteries were reperfused by removing the clips for 1 (n=4) or 5 («=3) minutes or 1 (w=4) or 4 (n=3) hours. In all gerbils rectal temperature was maintained at around 37° C using a heating pad and a lamp.For the autoradiographic determination of rCBF, a femoral artery and vein were cannulated for arterial blood sampling and radioisotope injection, respectively, in four control and 18 experimental gerbils. At the indicated time, 10 fxCi of [ 14 C]iodoantipyrine (Amersham, Tokyo, Japan) dissolved in approximately 0.7 ml saline was injected intravenously over 30 seconds, and six to eight-ju.1 timed arterial blood samples were collected. The gerbils were then decapitated, and the brains were quickly removed and frozen in powdered dry ice. Frozen sections 20 fim thick ...

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