Use of I-123-IMP brain SPET to predict outcome following STA-MCA bypass surgery: cerebral blood flow but not vasoreactivity is a predictive parameter

Superficial temporal artery - middle cerebral artery (STA-MCA) bypass surge ry might improve the cerebral blood flow (CBF) but fail to reduce the risk of post-surgical events such as ischaemic stroke. In this study, we studied retrospectively whether the risk of postsurgical events corresponded to th e change in resting CBF and/or the change in vasoreactivity observed before and after STA-MCA surgery using N-isopropyl-I-123-p-iodoamphetamine (I-123 -IMP) brain single-photon emission tomography (SPET). I-123-IMP brain SPET images obtained at rest and following acetazolamide challenge both before a nd after STA-MCA surgery were studied in 30 patients. Resting CBF was estim ated semiquantitatively using the resting count ratios of the middle cerebr al artery (MCA) area to the cerebellum. Acetazolamide challenge was assumed to result in an average increase in flow of 40% in the cerebellum. The vas oreactive response was then estimated as the ratio of the change in counts (acetazolamide - rest) to the resting cerebellar counts multiplied by 1.4, We classified 14 patients (50.5+/-19.3 years) into group I, who had a chang e in their resting CBF from before to after surgery of >10%, and 16 patient s (54.0+/-18.8 years) into group II, who had a change in their resting CBF from before to after surgery of less than or equal to 10%. Oxygen-15 positr on emission tomography (PET) studies were performed in five patients from g roup I and five patients from group II. One post-surgical event occurred in group I while there were eight post-surgical events in group II (P<0.05). Resting CBF improved by 20.4%+/-7.5% in group I and by 0.9%+/-6.9% in group II patients after surgery (P<0.001), No significant difference in the impr ovement in vasoreactivity was observed between group I patients (32.6%+/-17 .7%) and group II patients (24.6%+/-15.6%) following surgery. Patients in t he group I PET subset showed normalization of oxygen extraction fraction (O EF) from 0.59+/-0.09 before surgery to 0.46+/-0.06 after surgery (P<0.05), while patients in the group II PET subset showed no statistical difference in OEF before surgery (0.58+/-0.14) and after surgery (0.54+/- 0.05). We co nclude that the outcome of STA-MCA bypass surgery can be predicted by the i mprovement in resting CBF but not by the improvement in vasoreactivity.