Cerebellar vascular response to acetazolamide in crossed cerebellar diaschisis: a comparison of 99mTc-HMPAO single-photon emission tomography with 15O-H2O positron emission tomography.

Various observations on the cerebellar vasoreactivity in crossed cerebellar diaschisis (CCD) have previously been reported. The purpose of this study is to clarify the difference between oxygen-15 H2O positron emission tomographic (PET) and technetium-99m hexamethylpropylene amine oxime (HMPAO) single-photon emission tomograph (SPET) findings in CCD and to evaluate the effect of the absolute values of the cerebellar blood flow as measured by 15O-H2O PET on the 99mTc-HMPAO SPET findings. The subjects comprised 15 patients with a supratentorial infarct and CCD. The cerebellar blood flow increased by about 40% at 5 and 20 min after acetazolamide i.v. on both the CCD and the non-CCD side, as measured by 15O-H2O PET. The percentage differences in cerebellar blood flow between the CCD and the non-CCD side were -22.3%+/-5.7% in the resting state, -19. 6%+/-6.4% at 5 min after acetazolamide i.v. and 21.5%+/-6.7% at 20 min after acetazolamide i.v., as measured by 15O-H2O PET, while they were -10.6%+/-5.5% in the resting state and -5.6%+/-5.1% at 5 min after acetazolamide i.v., as measured by 99mTc-HMPAO SPET. After Lassen's linearization correction, the latter two measurements were -16.2%+/-7.7% and -9.6%+/-8.9%, respectively. The effect of acetazolamide did not differ between the CCD and the non-CCD side in 15O-H2O PET, while a greater response on the CCD side was observed in 99mTc-HMPAO SPET, even after Lassen's linearization correction. It is concluded that acetazolamide HMPAO SPET may overestimate the cerebellar vascular response on the CCD side (or underestimate it on the non-CCD side).