Cerebral blood flow thresholds predicting new hypoattenuation areas due to macrovascular ischemia during the acute phase of severe and complicated aneurysmal subarachnoid hemorrhage. A preliminary study.

BACKGROUND: Focal ischemia may affect patients with aneurysmal subarachnoid hemorrhage (SAH), and the potential evolution of cerebral infarction may greatly influence the patients' outcome. The aim of the study was to assess the values of regional cortical cerebral blood flow (rCBF) thresholds predictive for ischemia during the acute phase of SAH.
METHODS: In 34 patients affected by poor grade or complicated SAH, 52 pairs of Xenon-CT (Xe-CT) studies of regional CBF were analyzed, in which the follow-up Xe-CT study was obtained no later than 72 hours after the baseline study. Corresponding cortical ROIs were placed in the perimeter of the cortex on both the Xe-CT studies. A blinded, experienced neuroradiologist classified for each ROI, the development of a new hypoattenuation at the unenhanced CT images included in the follow-up Xe-CT, while another independent investigator collected rCBF levels of the ROI in the baseline Xe-CT study.
FINDINGS: New hypoattenuation developed in 3.94% of the ROIs in the paired follow-up Xe-CT studies, and these evolving ROIs were associated with a lower rCBF in baseline Xe-CT. However, the positive predictive value of rCBF levels for the development of new hypoattenuation was only moderately predictive (28.3%) for very low physiological values (5 ml/100gr/min).
CONCLUSIONS: The results suggest that there is no absolute rCBF threshold ofischemia in severe and complicated SAH patients and that the rCBF values are only moderately predictive at levels lower than previously described.