Asymmetries of cerebral perfusion in a stroke-ago population

Cerebral perfusion measurements with Tc-99m-hexamethylpropyleneamine oxime single photon emission computed tomography (HMPAO SPECT) are potentially cl inically useful in the investigation of patients with acute ischaemic strok e. The normal side-to-side asymmetry on Tc-99m-HMPAO SPECT images may be gr eater in the stroke-age population than in younger age groups. To assess th e extent of variation we studied 66 volunteers with Tc-99m-HMPAO SPECT who were closely age matched to a stroke population and who had normal CT and e xtracranial and intracranial vascular ultrasonography. By measuring the sid e-to-side ratios in 19 regions of interest, the normal side-to-side perfusi on asymmetry was determined and, as a secondary aim, variations in regional asymmetry were correlated with age. After repeated measurement analysis of variance (ANOVA), the normal range of side-to-side ratios in this populati on was 1.003+/-0.145 (mean+/-1.96 SD, ANOVA). The two regions with the grea test side-to-side asymmetry values were (1) the superior lateral temporal c ortex (higher on the right relative to the left) and (2) the superior parie tal cortex (higher on the left relative to the right). The orbitofrontal an d posterior temporal cortices demonstrated significantly increased bidirect ional variation with age (P < 0.05). In a stroke-age population hemispheric perfusion is relatively symmetrical and a side-to-side variation of greate r than +/-14.5% may be defined as pathological. This value is higher than t hat reported in younger volunteers suggesting that there is a mild increase in the side-to-side perfusion asymmetry with age. increased variation in t he orbitofrontal and posterior temporal cortices occurs with age and should be borne in mind when interpreting HMPAO SPECT studies.