Preoperative navigated transcranial magnetic stimulation (nTMS) analysis of motor areas improves the prognosis of patients with malignant brain tumors. These findings were published in BMC Cancer (2015; doi:10.1186/s12885-015-1258-1).

nTMS has been gaining importance in neurosurgery for some time now. Among other applications, it is used to map brain tumors before surgery and to test whether important regions of the brain, motor or language areas, for example, are affected.

With the help of nTMS, it is possible to identify what areas of the brain control motor or language function to an accuracy of 4 mm.

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The method enables tumor resection without affecting functional areas, while at the same time removing as much of the malignant tissue as possible, explained senior author Sandro Krieg, MD, working group leader at the Department of Neurosurgery of the Technische Universität München (TUM) University Hospital Klinikum rechts der Isar in Munich, Germany.

Mapping must be performed separately for each patient, as tumors can displace important brain areas from their original sites.

To determine motor areas with the nTMS technique, the physician scans points at defined positions on the patient’s head using a coil. The coil induces brief painless electrical pulses in the brain, which stimulate brain neurons at those positions.

If the pulses at a given position point activate neurons that trigger muscle movements, the scientists are able to measure the muscle activities with the help of electrodes fastened to the patient’s arms and legs. That position is then regarded as an essential location for motor activity.

The technique can analyze and map up to 150 individual position points per patient.

“In this way, we can draw up a map of important motor areas and nerve pathways in the vicinity of the tumor. During the operation, this data is a good guide as to where we can and cannot cut,” explained Krieg.

In their recent study, Krieg and his team scanned and mapped motor areas in patients with high-grade gliomas (HGG), which are usually associated with a poor prognosis. They compared two groups: 70 patients who underwent preoperative nTMS analysis and 70 patients who underwent tumor resection in 2010, before nTMS became a standard procedure in the hospital.

The results of the study show the advantage of nTMS mapping: surgery required smaller openings in the skull and residual tumor tissue was left behind less frequently. In addition, thei average hospitalization period was 2 days shorter for patients who underwent nTMS tumor analysis.

Because the general state of health of the nTMS-treated patients was also better, an increased number of them were subsequently able to receive radiotherapy. Above all, those patients survived several months longer than the control group.

“Of course, we need to confirm the findings in larger patient groups, but one important thing is clear: preoperative tumor mapping positively influences many aspects of the procedure,” Krieg said about the results, adding: “Some tumors that are otherwise thought to be inoperable can be removed by this method.”

The scientists now aim to improve standard protocols for nTMS and the mapping of language areas.