Frequency of various brain parenchymal findings of early cerebral ischemia on unenhanced CT scans.

The purpose of the study was to determine the frequency of various unenhanced computed tomography (CT) findings of early cerebral ischemia within brain parenchyma, which could be useful to the radiologist who is interpreting CT studies by indicating the CT finding that is most likely to be present in early cerebral ischemia. We analyzed articles reporting the use of unenhanced CT in acute cerebral ischemia over the period 1976-2009 for frequency of the following brain parenchyma signs: loss of insular ribbon, obscuration of lentiform nucleus, sulcal effacement, and parenchymal hypodensity. We recorded data for the 2-, 3-, 6-, and 12-h intervals after symptom onset from various studies and (1) calculated percent of time intervals in which >50% of patients exhibited the finding in any study and (2) pooled results for patients reported as having a specific CT finding during a specific time interval. We hypothesized that CT findings indicating brain swelling, which would be expected to be a relatively late phenomenon, would be detected at a lower rate in the first 6 h than changes of decreased density of brain tissue and increased density of arteries. The loss of insular ribbon sign (83% of time intervals reported) and obscuration of lentiform nucleus sign (75%) were the most common signs present in >50% patients in a time interval in any article. Pooled results showed that the two most common findings in the first few hours were loss of insular ribbon (70% at 2 h; 77% at 3 h) and obscuration of lentiform nucleus (60% at 2 h; 82% at 3 h). At 6 h, parenchymal hypodensity (53%), loss of insular ribbon (46%), and obscuration of lentiform nucleus (46%) were most common, which validated our hypothesis. At 12 h, loss of insular ribbon (65%) and sulcal effacement (63%) were most common. Loss of insular ribbon and obscuration of lentiform nucleus appear to be the most common signs of early cerebral ischemia identified on unenhanced CT.