Abstract WP51: Racial Differences in Salvageable Ischemic Penumbra

Abstract

Objective: African Americans (AA) have a higher incidence of intracranial atherosclerosis than Caucasians. Resulting chronic ischemia may lead to the formation of collateral circulation. Our hypothesis was that AA will have a greater sustainability of their ischemic penumbra from collateral circulation after an acute stroke. Methods: Ischemic stroke patients that underwent perfusion computed tomography (PCT) at admission from August 2011 to March 2012 were reviewed. PCT included 4 supratentorial slices, 8 mm thick. Images were processed using Vitrea® to obtain cerebral blood flow (CBF), cerebral blood volume (CBV) and mean transit time (MTT). Areas of increased MTT were traced and marked as ischemic area. Corresponding area of preserved CBV was labeled as penumbra area. The mean CBF, MTT or CBV for the total ischemic area (or penumbra) was estimated by multiplying each ischemic area (or penumbra) by the corresponding CBF (MTT or CBV), adding the value of four slices and dividing by total area. The ischemic and penumbra areas in four slices were added and multiplied by slice thickness (0.8 cm) to give ischemic volume (IV) and penumbra volume (PV) respectively. Results: Perfusion abnormalities were found in 43 (65.1 % AA vs. 30.2 % Caucasian) patients. The mean ischemic volume was less in AA as compared to Caucasians (63.64 ±36.7 cm 3 vs. 89.57 ±52.6 cm 3 ) as was mean penumbra volume (42.77±28.9 cm 3 vs. 64.36 ± 43.8 cm 3 ). Within the penumbra in AA, CBF was increased (28 ±12.2 ml/100 gm/sec vs. 23.11 ±12.5 ml/100 gm/sec) as was CBV (3.46 ±1.4 ml/100gm vs. 2.98 ±1.1 ml/100gm). The penumbra MTT was faster in AA (8.59 ±2.2 sec vs. 9.46 ±2.72 sec). The trends in CBF, CBV and MTT did not reach statistical significance due to the small sample size. A CBF less than 20 ml/100 gm/sec is conventionally defined as vulnerable ischemic tissue. In the area of ischemia, only 36% of AA had CBF less than 20 ml/100 gm/min as opposed to 61.5% in Caucasians (p=0.17). Conclusion This exploratory analysis showed that AA have a somewhat greater CBF and CBV with faster MTT in the region of penumbra as compared to Caucasians indicating the presence of biological mechanisms to preserve the area at risk. Further analysis to assess collateral cerebral blood flow as a protective mechanism in AA is warranted.