Limitations of Wada memory asymmetry as a predictor of outcomes after temporal lobectomy

The intracarotid amobarbital (Wada) test can be used to evaluate hemispheric memory capacity before anterior temporal lobectomy (ATL). Most patients demonstrate better memory with injection ipsilateral to planned resection (expected asymmetry [EA]), but a substantial minority show better memory with contralateral injection (unexpected asymmetry [UA]). Both degree and direction of Wada memory asymmetry (WMA) have been associated with worse surgical outcome in small series. Reports also suggest that UA is associated with greater decline in verbal memory after left ATL (L-ATL).

The relationship between WMA and surgical outcome (at 3 months, 1 year, and last follow-up) was examined in a large group of ATL patients (108 L, 119 R) with both EA and UA. Also, memory in a subgroup (96 L, 108 R) was examined, comparing subscores of the Rey Auditory Verbal Learning Test obtained preoperatively, at 3 months, and at 1 year.

Thirty-six percent of L-ATL and 8% of R-ATL patients had UA. UA was associated with worse surgical outcome at 1 year for R-ATL patients but was not associated with worse outcome for L-ATL patients. There was no correlation between WMA and persistent postoperative verbal memory change for patients with L- or R-ATL.

Unexpected asymmetry is uncommon in patients with right anterior temporal lobectomy (R-ATL) and may be a risk marker of poor surgical outcome. This relationship may be obscured by language confounds in patients with L-ATL. The results suggest that Wada asymmetry (using mixed stimuli) does not predict postoperative verbal memory; it is unclear whether this finding is generalizable to centers using only nonverbal stimuli.