Last Updated: 2008-01-02 18:23:04 -0400 (Reuters Health)

NEW YORK (Reuters Health) – An intraoperative technique called negative language mapping allows for the radical resection of brain tumors without causing persistent language deficits in the majority of patients, new research shows.

In the past, surgeons have relied on positive language mapping to indicate what areas in the brain could be resected without impairing language function. With this technique, a large craniotomy is made that exceeds the borders of the target tumor. Cortical sites are then stimulated to identify those that produce a language deficit. These "positive" sites are then avoided (if feasible) during surgery.

The conventional wisdom had been that surgeons needed the positive sites as a control to facilitate a safe resection. In the present study, Dr. Nader Sanai and colleagues, from the University of California at San Francisco, used a different approach: negative language mapping.

With negative language mapping, a smaller craniotomy is made and the surgeons plan their resection based on the identification of negative sites: those that do not cause a language deficit when stimulated. No exhaustive effort is made to identify sites that cause a language deficit when stimulated. In short, the surgeon can begin the resection without identification of a positive site.

Without the need to look for positive control sites, cortical exposure can be more limited, intraoperative mapping is less extensive, and the operative time is decreased.

The present study, which is reported in January 3rd issue of The New England Journal of Medicine, involved 250 consecutive patients with gliomas potentially involving language regions in the brain. The resections were performed using tailored craniotomies with negative language mapping.

Fifty-eight percent of patients had at least one site that caused speech arrest when stimulated during surgery. Still, the majority of cortical sites tested-94%–did not produce a language deficit when stimulated.

Prior to surgery, 159 (63.6%) patients had intact speech. In the first postoperative week, language function was unchanged in 194 (77.6%) patients, worse in 21 (8.4%), and a new speech deficit had developed in 35 (14.0%). By 6 months, however, just 4 of 243 surviving patients (1.6%) had a persistent language deficit.

The cortical maps that were created with the operative language data indicated "surprising variability" in the localization of language within the dominant hemisphere, the authors note. This suggests "that our current models of human language organization insufficiently account for observed language function," they add.

"Our findings suggest that a tailored craniotomy in conjunction with negative language mapping can be relied on to maximize resection and minimize morbidity when gliomas within or near language pathways are removed," Dr. Sanai’s team concludes.

N Engl J Med 2007;358:18-27.