Interpretation of Wada memory test for lateralization of seizure focus by use of (99m)technetium-HMPAO SPECT

Purpose: Although the intracarotid amobarbital procedure (IAP) or Wada test is useful in lateralizing seizure focus in patients with temporal lobe epi lepsy (TLE), the results of the LAP memory test are frequently nonlateraliz ing. An insufficient suppression of the medial temporal region contralatera l to the seizure focus may contribute to the failure of lateralization. We tried to correlate LAP memory results with the functional changes in the co ntralateral medial temporal region as measured by single photon emission co mputed tomography (SPECT)during IAP. Methods: We performed a (99m)technetium-(Tc) hexamethylene-propylene-amine- oxime (HMPAO) brain SPECT in 19 medial TLE patients during a contralateral IAP (sodium amobarbital injected contralateral to the seizure focus). Regio nal cerebral blood flow (rCBF) was measured in the contralateral medial tem poral region. The amount of decrease in the rCBF was calculated by subtract ing the previous measurement from the one obtained with the interictal SPEC T. Results: Ten (53%) patients passed and nine (47%) failed the contralateral IAP. The mean percentage decrease in rCBF was 5.3 +/- 5.3%. There was a sig nificant negative correlation between a decrease in the rCBF and the LAP me mory-retention score by Spearman correlation (p = -0.53, p <0.021). Patient s with smaller decreases in rCBF (<5%) more frequently passed the contralat eral LAP memory test than did those with larger decreases (80 vs. 22%; p < 0.023). Conclusions: We suggest that an insufficient suppression of the contralater al medial temporal function is partly responsible for nonlateralizing IAP m emory tests. An IAP-SPECT may be useful in interpreting IAP memory tests fo r the lateralization of seizure focus in TLE patients.