Preoperative predictors of anterior temporal language areas

Object. Although it is known that 5 to 10% of patients have language areas anterior to the rolandic cortex, many surgeons still perform standard anter ior temporal lobectomies for epilepsy of mesial onset and report minimal lo ng-term dysphasia The authors examined the importance of language mapping b efore anterior temporal lobectomy. Methods. The authors mapped naming, reading, and speech arrest in a series of 67 patients via stimulation of longterm implanted subdural grids before resective epilepsy surgery and correlated the presence of language areas in the anterior temporal lobe with preoperative demographic and neuropsychome tric data. Naming (p < 0.03) and reading (p < 0.05) errors were more common than speec h arrest in patients undergoing surgery in the anterior temporal lobe. In t he approximate region of a standard anterior temporal lobectomy, including 2.5 cm of the superior temporal gyrus and 4.5 cm of both the middle and inf erior temporal gyrus, the authors identified language areas in 14.5% of pat ients tested. Between 1.5 and 3.5 cm from the temporal tip, patients who ha d seizure onset before 6 years of age had more naming (p < 0.02) and readin g (p < 0.01) areas than those in whom seizure onset occurred after age 6 ye ars. Patients with a verbal intelligence quotient (IQ) lower than 90 had mo re naming (p < 0.05) and reading (p < 0.02) areas than those with an IQ hig her than 90. Finally, patients who were either left handed or right hemisph ere memory dominant had more naming (p < 0.05) and reading (p < 0.02) areas than right-handed patients with bilateral or left hemisphere memory latera lization. Postoperative neuropsychometric testing showed a trend toward a g reater decline in naming ability in patients who were least likely to have anterior language areas, that is, those with higher verbal IQ and later sei zure onset. Conclusions. Preoperative identification of markers of left hemisphere dama ge, such as early seizure onset, poor verbal IQ, left handedness, and right hemisphere memory dominance should alert neurosurgeons to the possibility of encountering essential language areas in the anterior temporal lobe (1.5 -3.5 cm from the temporal tip). Naming and reading tasks are required to id entify these areas. Whether removal of these areas necessarily induces long -term impairment in verbal abilities is unknown; however, in patients with a low verbal IQ and early seizure onset, these areas appear to be less crit ical for language processing.