Objective criteria for reporting language dominance by intracarotid amobarbital procedure

We propose a standardized method for reporting language lateralization by intracarotid amobarbital procedure (IAP). We retrospectively reviewed 165 IAPs, and classified language lateralization as left, right, or bilateral by three different methods, all based on the duration of speech arrest following each injection: absolute duration, side-to-side difference, and a "laterality index" defined as (L-R/L+R). Cutoff values were obtained by studying a pure subgroup of left hemisphere dominant right-handed subjects. In 142 patients (86%), the classification remained unchanged among all three methods: left in 112 (79%), right in 19 (13%), and bilateral in 11 (8%). In the other 23 patients (14%), language classification varied among the three criteria used. The change of category was never between left and right, and always involved bilateral language. Thus, this index may be helpful in standardizing and comparing IAP results from different series.