Regional cerebral perfusion and amytal distribution during the Wada test

The distribution of sodium amytal and its effect on regional cerebral perfu sion during the intracarotid amytal (Wada) test were investigated using hig h-resolution hexamethyl propyleneamine oxime (HMPAO) SPECT coregistered wit h the patient's MRI dataset. Methods: Twenty patients underwent SPECT after intravenous HMPAO injection, and 5 patients had both intravenous and intra carotid injections in a double injection-acquisition protocol. Results: All patients had hypoperfusion in the territories of the anterior and middle c erebral arteries. Basal ganglia perfusion was preserved in 20 of 25 patient s. Hypoperfusion of the entire mesial temporal cortex was seen in 9 of 25 p atients. Partial hypoperfusion of the whole mesial cortex or hypoperfusion of part of the mesial cortex was seen in 14 of 25 patients. In 2 of 25 pati ents, mesial temporal perfusion was unaffected. In 5 patients, the double a cquisition showed a distribution of HMPAO delivery matching that of hypoper fusion, except for the following: (a) HMPAO was delivered to the basal gang lia and insula, where there was no hypoperfusion; (b) HMPAO was not deliver ed to the contralateral cerebellum, which did show hypoperfusion; and (c) i n 1 patient, perfusion of the mesial temporal cortex was preserved despite intracarotid delivery of HMPAO. Conclusion: Some degree of hypoperfusion of medial temporal structures occurs in the great majority of patients during the Wada test. Partial inactivation of memory structures is therefore a cr edible mechanism of action of the test. The double acquisition protocol pro vided no evidence that mesial temporal structures are inactivated remotely by diaschisis. Perfusion in the basal ganglia and insular cortex is not aff ected by amytal.