Safe Removal Of Gliomas To Preserve Language Requires Less Extensive Brain Exposure Than Previously Thought

Main Category: Cancer / Oncology
Also Included In: Neurology / Neuroscience
Article Date: 28 Jan 2008 - 14:00 PST

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A more limited approach to craniotomy---the procedure through which a patient's skull is opened up to expose the brain---than has traditionally been used by neurosurgeons can maximize resection and minimize lasting side effects when tumours within or near language pathways are removed, according to the results of a prospective study published in the New England Journal of Medicine.

When considering optimal treatment of patients with aggressive brain tumours, neurosurgeons have historically believed that it is essential to identify the areas where language functions are located before surgery in order to avoid damaging these areas and thus preserving the patient's ability to communicate and express themselves---a technique called language mapping. Traditional approaches to this procedure involve neurosurgeons performing a large craniotomy, which exposes a significant portion of the brain, and then using electrical impulses to stimulate numerous different points around the proposed resection area. The procedure is done while the patient is awake so the effect of stimulating each area can be tested by asking the patient to do a selection of simple language tasks. Once the areas associated with language and motor function have been identified (known as "positive sites"), the tumour can be safely resected within the boundaries o! f these points. However, the down side of this technique is that surgeons must expose a lot of the brain and subject the patient to a lengthy series of stimulations and tests to identify language-relevant areas.

To see whether less extensive language mapping might be feasible, Nader Sanai and colleagues from the University of California at San Francisco designed a study in which resection decisions were guided by identifying stimulation points near to the tumour that did not affect language (negative sites), enabling them to keep the amount of exposed brain much smaller than when positive sites are the main frame of reference. "This "negative mapping" strategy represents a paradigm shift in the language-mapping technique by eliminating the neurosurgeon's dependence on the positive sites as controls, thereby allowing minimal cortical exposure, less extensive intraoperative mapping, and a more rapidly performed neurosurgical procedure," explain the authors.

The research team tested their approach for its efficacy in averting new language deficits among 250 patients with gliomas who underwent surgery between June 1997 and September 2005. During the operations, a so-called tailored craniotomy was done, which exposed the tumour and up to 3cm of surrounding brain tissue. A grid electrode was then placed on the surface of the brain, and numerous points in the exposed area were stimulated one by one while the patient was asked to a series of questions to test the effects of stimulation on language function. Language testing constituted of the following tasks: counting numbers from 1 to 50, naming objects pictured on a computer-generated slide show, and reading single words projected sequentially on a computer screen. Each task was done three times as each point in the cortex was stimulated. ! If the patient was unable to count, name objects or read words two out of three times a particular area was stimulated, then the point was labelled a positive site and the location of the site was recorded with the use of magnetic resonance imaging.

Any deficits in language---ie, when the patient was unable to name objects but had fluent speech; when patients retained the ability to write and spell, but made reading errors; or when expression through speech or writing was impaired---were recorded before the operation and at 1 week, 4 to 6 weeks, and 3 to 6 months afterwards.

At presentation, 159 of the 250 patients (63.6%) had no speech problems and 91 patients (36.4%) had some language deficit. One week after surgery, language function was the same or improved in 77.6% of patients, was worse in 8.4%, and new speech deficits had developed in 14%. However, with increasing time since the operation, the new and worsened speech problems seemed to get better. By 3 months, only six of the 245 surviving patients (2.4%) had decreased language function. And at 6 months, just four of the 243 surviving patients (1.6%) had a permanent postoperative language deficit. "Thus, 52 of the 56 patients (92.9%) with new or increased language deficits had a return to baseline function or better," summarise the authors.

Referring to the extensive positive mapping traditionally used to plan resections for patients with gliomas, the authors state: "We have shown that this language localization is no longer needed; nearly half of our patients had no positive language sites in their field of exposure, and more than 94% of the cortical stimulations in these patients were negative, yet their functional outcomes remained acceptable."

"Therefore," they conclude, "resection can be based on the areas where language is not located - that is, on negative mapping."

Functional outcome after language mapping for glioma resection
Sanai N, Mirzadeh Z, Berger MS
N Engl J Med 2008; 358:18-27.

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