Evaluation of Language Function under Awake Craniotomy

Abstract

Awake craniotomy is the only established way to assess patients' language functions intraoperatively and to contribute to their preservation, if necessary. Recent guidelines have enabled the approach to be used widely, effectively, and safely. Non-invasive brain functional imaging techniques, including functional magnetic resonance imaging and diffusion tensor imaging, have been used preoperatively to identify brain functional regions corresponding to language, and their accuracy has increased year by year. In addition, the use of neuronavigation that incorporates this preoperative information has made it possible to identify the positional relationships between the lesion and functional regions involved in language, conduct functional brain mapping in the awake state with electrical stimulation, and intraoperatively assess nerve function in real time when resecting the lesion. This article outlines the history of awake craniotomy, the current state of pre- and intraoperative evaluation of language function, and the clinical usefulness of such functional evaluation. When evaluating patients' language functions during awake craniotomy, given the various intraoperative stresses involved, it is necessary to carefully select the tasks to be undertaken, quickly perform all examinations, and promptly evaluate the results. As language functions involve both input and output, they are strongly affected by patients' preoperative cognitive function, degree of intraoperative wakefulness and fatigue, the ability to produce verbal articulations and utterances, as well as perform synergic movement. Therefore, it is essential to appropriately assess the reproducibility of language function evaluation using awake craniotomy techniques.

Fig. 1.

Pre- (a) and postoperative (b) gadolinium-enhanced magnetic resonance images in a patient with anaplastic oligodendroglioma located in the left frontal lobe.

Fig. 2.

Preoperative functional magnetic resonance imaging (fMRI) during reading (a), mouth motion (b), and right hand motion (c).

Fig. 3.

Intraoperative evaluation of language function by electrical stimulation. a and b: A 4 × 5-electrode plate was placed on the temporo-parietal lobe and a 2 × 8-electrode plate was placed on the frontal lobe to identify the language cortex. The small red circle represents the area of stimulation and the large circle indicates the area in which cortico-cortical evoked potentials (CCEPs) were recorded. (1–3): CCEPs during operation. (1) CCEPs recorded from the temporoparietal lobe (the posterior language area: 4 × 5-electrode Nos. 7, 8, 9, 11, 12, 13, 16, 17) in response to bipolar stimulation of the frontal lobe (the anterior language area: 2 × 8-electrode Nos. 15–16). (2) CCEPs also recorded from the anterior opercular region (the anterior language area: 2 × 8-electrode Nos. 7, 8, 14, 15, 16) in response to bipolar stimulation of the inferior parietal lobule (the posterior language area: 4 × 5-electrode Nos. 12–13), the area where the maximum reaction was recorded in the previous stimulation (1). The electrophysiological connection between these two areas appeared to be bidirectorial. (3) Monitoring of CCEPs from the posterior language area (4 × 5-electrode) by stimulating Nos. 15–16 of the 2 × 8-electrode plate intraoperatively. The N1 peak was slightly reduced compared with the control amplitude shown in (1) during awake resection of the anterior base of the tumor (orange circle), when impaired auditory comprehension and visual naming were observed.