99mTc HM-PAO SPECT in pediatric migraine. 99mTC HM-PAO SPECT brain imaging was performed during the headache-free period in 19 young migraineurs, affected by common migraine (CM, 10 cases), classic migraine (CLM, 6 cases) and hemiplegic migraine (HM, 3 cases). SPECT findings were negative in all 10 patients with CM, in 3 cases of CLM and in 2 cases of HM. Positive findings in the remaining 4 patients (3 cases of CLM and 1 of HM) showed a decreased tracer distribution in the temporo-occipital regions (2 cases) and parietal regions (2 cases): the two with decreased temporo-occipital perfusion reported prodromal symptoms exclusively contralateral to the areas of hypoperfusion. An impaired regional cerebral vascular autoregulation may exist even during headache-free intervals in patients suffering from classic and hemiplegic migraine. 