Comparison of cerebral blood flow in computed tomographic hypodense areas of the brain in head-injured patients

OBJECTIVE: Hypodense lesions identified on computed tomographic (CT) scans are often assumed to indicate ischemia. The purpose of this study was to investigate regional cerebral blood flow, (rCBF) in hypodense areas of the brain after severe traumatic brain injury. METHODS: CBF was measured by stable xenon-enhanced CT scans. Hypodense areas were identified, and rCBF values as well as CT density were averaged for the region. RESULTS: Thirty (60%) of the 50 patients had a total of 45 hypodense regions; which were associated with either contusion (n = 30) or areas of infarction (n = 15). rCBF in the hypodense regions was variable, ranging from a low of 3.3 to a high of 72.5 ml/100 g/min. The cause of the lesion was the major factor associated with the. level of rCBF. Although the average decrease-in CT density was similar for the two types of lesions, the average rCBF was significantly lower and the difference in rCBF between the lesion and the contralateral side was greater when the,hypodense lesion was associated with a contusion. A critical reduction in rCBF (<20 ml/100 g/min) was found in 19 (63%) of the hypodense regions associated with contusions but in only 4 (27%) of those from areas of infarction. CONCLUSION: Hypodensity on plain CT scans does not always indicate reduction in CBF. This association was found more commonly when the low-density area was associated with a contusion. In hypodense areas associated with infarction, rCBF was variable and not commonly in the ischemic range at the time the CBF measurement was obtained.