Abstracts

The intracarotid amobarbital (Wada) test (IAT) is used to assess cerebral language lateralization in epileptic patients preceding resective surgery. Left-hemispheric language representation predominates in dextral patients. For non-dextrals, higher but widely varying incidences of atypical (right or bilateral) language were reported by previous studies. The purpose of this study was to determine the incidence of left (L), right (R), and bilateral (B) language in dextral and non-dextral subjects as a function of localization and type of lesions on MRI. A retrospective chart review of 445 bilateral IAT (1997 to 2003) was performed. Language lateralization was assessed based on speech arrest times. Localization and type of lesion on presurgical MRI was determined. Left-hemispheric lesions were classified as [ldquo]early[rdquo] (congenital or perinatally acquired: malformations of cortical development, vascular malformations, perinatal encephalomalacia) and [ldquo]late[rdquo] (all others). Chi² test was used for statistical comparisons (significance: 0.05). Out of 391 dextrals, 322 (82%) were L dominant, 16 (4%) were R, 53 (14%) were B. Out of 54 non-dextrals, 26 (48%) were L, 12 (22%) were R, 16 (30%) were B. 97 patients had normal MRI (84 right-handed, 13 left-handed). Of 84 right-handed non-lesional cases, 68 (81%) were L, 3 (4%) were R, 13 (15%) were B. Out of 13 left-handed non-lesional cases, 9 (69%) were L, one (8%) was R, 3 (23%) were B. 49 patients had early left-hemispheric lesions (41 right-handed, 8 left-handed). Of 41 dextrals with early left lesions, 28 (68%) were L, 4 (10%) were R, 9 (22%) were B. Out of 8 non-dextrals with early left lesions, none (0%) was L, 4 (50%) were R, 4 (50%) were B. 65 patients had late-onset left neocortical lesions (54 right-handed, 11 left-handed). Out of 54 dextrals with late-onset left neocortical lesions, 44 (81%) were L, 3 (6%) were R, 7 (13%) were B. Out of 11 non-dextrals with late-onset left neocortical lesions, 3 (27%) were L, 3 (27%) were R, and 5 (46%) were B dominant. The majority of patients without neocortical lesions are L dominant, regardless of handedness (81% of dextrals, 69% of non-dextrals), exclusive R language is rare in this group. Compared to subjects with normal MRI, right-handed subjects with left-neocortical lesions are slightly more likely R dominant (p=0.05). The vast majority of left-handed patients with early left neocortical lesions are R or B dominant; none in this group was L dominant. Left-handed subjects with late-onset left neocortical lesions were most likely B dominant. Thus, most left-handed patients with left neocortical lesions display atypical language representation, with R dominance prevailing in patients with congenital or perinatally acquired lesions, and B dominance prevailing in subjects with late-onset lesions. (Supported by Innovative Medizinische Forschung (IMF), University of Munster, Germany (MO 620202))