With help from navigational MRI, researchers at the University of California, San Francisco have assembled the largest composite map of the brain’s language sites ever to appear in the medical literature. They found far greater variability in the location of these sites than other models of language organization suggest.
With help from navigational MRI, researchers at the University of California, San Francisco have assembled the largest composite map of the brain's language sites ever to appear in the medical literature. They found far greater variability in the location of these sites than other models of language organization suggest.
The study of language mapping was based on navigational MR images from 250 consecutive conscious patients during glioma surgery.
Prior to the study, the understanding of where language sites were localized was limited, according to first author Dr. Nader Sanai, a senior resident in neurological surgery at UCSF. Historically, it was based on case reports of injuries due to impact trauma, stroke, projectile injury, or surgery, when those injuries caused language problems.
"What this composite map showed us was there is a much larger degree of variation than what had previously been acknowledged," Sanai said.
In the study, surgeons found nearly half of their patients had no positive language sites within 2 cm of the surgical site. More than 94% of cortical stimulations in these patients were negative, yet their functional outcomes remained acceptable. Only 1.6% of surviving patients had a persistent language deficit six months after surgery.
Sanai found during a literature search that no previously published composite brain map of language employed data from as many patients as the UCSF study.
Brain images for the study were acquired in a standard clinical MR scanner before surgery. The resulting images depicted the patient's brain as well the spatial relationship between brain anatomy and fiducial markers that were placed on the patient's scalp before the procedure.
Patients were transported to the operating room after their heads were immobilized using three-point fixation. The surgeon used a wireless wand with an infrared aiming mechanism on its tip to identify the location of the fiducial marks. A computer created a map establishing the spatial relationship of the markers and brain anatomy in 3D space.
The surgeon again employed the wand for real-time guidance during surgery. With the wand aimed at a region of interest, software automatically displayed the corresponding axial, coronal, and sagittal images with a cross-hair on the point that was localized.
During the mapping procedures, surgeons sequentially stimulated each square centimeter of the patient's cortex to determine presence of a language site. Then, for each square centimeter, they put down a sterile piece of paper with a number to form a grid of markers across the surface of the brain, with each marker corresponding to where language did and did not reside.
Sanai and colleagues compiled data for the composite map from glioma resections performed at UCSF from 1997 to 2005. Their results were reported in the Jan. 3 issue of The New England Journal of Medicine (2008;358:18-27).
Clinically, the mapping technique proved effective. Overall, 159 of 250 patients (63.6%) had intact speech, and 91 (36.4%) has some language deficit before surgery. One week after resection, the language function of 194 patients was unaffected from surgery or had improved. Language problems appeared for the first time for 35 patients and worsened for 21 patients. After one month, however, the number of patients with exacerbated preexisting language deficits dropped to 16 (6.4%), and only eight patients (3.2%) who were free of language deficit before surgery developed a new language deficit afterward.
The composite will be used to provide a template for future operative planning and analysis for how language is organized, Sanai said. It already has implications for neurosurgeons.
"Historically, neurosurgeons believed it was essential to identify the areas where language was located before any nonfunctional area could be safely resected," the researchers wrote. "That's no longer the case."
Now, instead of seeking to identify every possible language site on the surface of the cortex prior to resection, surgeons may safely restrict their language mapping activities to a 2-cm area immediately bordering a tumor, Sanai said.
The protocol saves time because less brain is exposed and a smaller area of the brain's surface must be mapped, he said.
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