Chronic cerebrovascular insufficiency on the xenon CT scan.

Several investigators have described CT-negative low flow areas in TIA and stroke patients in the chronic phase. The emission tomographic SPECT image they employed has, in contrast to the xenon CT method, no direct relation to the x-ray transmission CT scan. The aim of our study was to study the phenomenon of CT-negative low flow areas using the xenon CT method, a method especially well suited for such cases. 57 xenon CT examinations were performed in 40 TIA patients. Flow data from brain tissue which appeared to be anatomically intact in a slice 5 cm above the canthomeatal plane were analyzed. In the TIA group, the flow in the gray matter was found to be significantly lower on the clinically affected side: symptomatic side, 61.8 +/- 14.7 ml/100 g/min; asymptomatic side, 66.4 +/- 15.8 ml/100 g/min (p less than 0.001). In the stroke group, the flow in the white matter was also affected; symptomatic side, 31.2 +/- 9.8 ml/100, g/min; asymptomatic side, 35.3 +/- 11.1 ml/100 g/min (p less than 0.01). Gray matter: symptomatic side, 56.1 +/- 11.4 ml/100 g/min; asymptomatic side, 66.0 +/- 11.0 ml/100 g/min (p less than 0.001). The findings indicate that the appearance of CT-negative low flow areas in TIA and stroke patients during the chronic phase is the rule rather than the exception. Flow adaptation to anatomic changes not discernible by CT can be differentiated from clinically relevant flow impairment only by testing the cerebrovascular reserve.