Mapping of visuospatial functions during brain surgery: a new tool to prevent unilateral spatial neglect.

Abstract

To the Editor: In the last decade, major advances in intraoperative functional mapping have dramatically improved the results of brain surgery. When removing a brain tumor, it is common clinical practice to awaken the patient and temporarily inactivate small (approximately 5 mm) brain regions with electrical stimuli, while the patient performs functional tasks. If the patient produces incorrect responses, the surgeon leaves the region intact, to preserve the patient’s functional abilities (3). This procedure allows the surgeon to minimize the residual morbidity while increasing the quality of the resection, and the net result is to improve overall patient survival. However, although sensorimotor and cognitive functions such as language, memory, or calculation have been extensively mapped intraoperatively, visuospatial functions have received less attention. Unilateral spatial neglect (USN) is a dramatic neurological condition resulting from damage affecting the temporoparietal or frontal cortex, or the thalamus or basal ganglia of the right hemisphere (1). Patients with unilateral spatial neglect behave as if the left part of the world does not exist (2). Their functional recovery is poor, and they endure major clinical and social consequences. USN typically results from vascular stroke, but other etiologies are possible. For example, USN was reported after a patient received right inferior parietal cortectomy for intractable epilepsy (4). Although this particular patient recovered from neglect after 2 years, other neurosurgical patients risk suffering from chronic USN as a result of more extensive, corticosubcortical resections, especially as required for cerebral glioma. In a recent series of eight patients who underwent resection of a glioma confined to the right parietal lobe (5), no new USN was clinically observed postoperatively, but there was no formal neuropsychological testing performed, and it is well known that USN may not be apparent at clinical observation (2). To prevent the occurrence of USN in these patients, we propose intraoperative assessment of visuospatial function by asking patients to bisect 20-cm horizontal lines (Fig. 1). If the patient shifts the subjective center more than approximately 6.5 mm rightward (1), then the neurosurgeon leaves the inactivated area untouched. Using this procedure, we were able to avoid postoperative USN in two patients (ages, 27 and 28 years) who underwent resection of low-grade gliomas in the right temporoparietal region (6). These left-handed patients were awakened during surgery because there was functional magnetic resonance imaging evidence of partial language representation in the right hemisphere. Patients gave their informed consent, FIGURE 1. Line bisection tasks performed during brain surgery are simple and feasible. Under test conditions, a 20-cm line (not shown) is presented, aligned to the subjects’ eye axis, in a central position with respect to the patient’s sagittal head plane. The Role of Electrothrombosis in the GDC Technique

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