Features of various parts of the arcuate fasciculus mapping in patients with left hemisphere gliomas: analysis of 23 awake brain surgeries

Background . Awake craniotomy is a modern technique of neurosurgical operations allowing to preserve speech while trying to achieve maximal tumor resection. For a long time, during awake surgeries the main importance was assigned to electrostimulation of the language centers. Currently, the mapping of the long association tracts during resection of gliomas of the speech-dominant hemisphere is the necessary requirement for speech preservation. Aim . To analyze the results of intraoperative electrostimulation of the arcuate fasciculus in comparison with magnetic resonance tractography data (MR tractography), as well as speech disorders before and after surgical interventions in patients with left hemisphere gliomas adjacent to the arcuate fasciculus who underwent awake craniotomy. Materials and methods . Awake surgeries were performed in 23 patients aged between 19 and 67 years old (mean age 41) with left hemisphere glionas. Tumor was located in the frontal lobe in 11 patients, in the temporal lobe - in 8 patients, in the parietal lobe - in 4 patients. The malignancy grade was the following: Grade 2-7 patients, Grade 3-12 and Grade 4-4 patients. In all patients, the cortical electrophysiological stimulation to control localization of the cortical language centers and subcortical electrophysiological stimulation for identification of the arcuate fasciculus were performed during awakening. Speech disorders before and after surgery were evaluated by a neuropsychologist using the Luria method; intraoperatively, automated test with picture naming was additionally used. The mean current intensity during direct subcortical electrostimulation was 4 mA. MR tractography with reconstruction of the arcuate fasciculus and volumetry using magnetic resonance imaging (MRI) were performed in all 23 cases before and after surgery. Results . During intraoperative electrostimulation, Broca's area was identified in 8 of 11 patients with frontal lobe tumors, cortical temporal speech areas were identified in 5 of 8 patients with temporal lobe tumors. In 16 (70 %) of 23 patients, the arcuate fasciculus was mapped in the form of mixed speech abnormalities in the depth of operative wound in the frontal, parietal and temporal lobes. In 17 (75 %) of 23 patients, worsening the speech function was observed in the early postoperative period: in 13 of them a combination of frontal and temporal types of speech disorders (conduction aphasia caused by the surgery near the arcuate fascisulus) was observed. The postoperative MR tractography performed in 23 patients showed the direct intraoperative injury of the arcuate fasciculus in 3 (13 %) cases and adjacent ischemia - in 2 (9 %) cases. The MR volumetry showed total tumor resection in 8 cases, subtotal - in 9 cases, and partial - in 6 cases. Conclusion . During awake surgeries for left hemisphere tumors, it is important to map the arcuate fasciculus in the deep parts of the frontal, temporal and parietal lobes. The subcortical stimulation allowed to identify the arcuate fasciculus in 70 % of presented cases; the MR tractography showed the damage of the anatomical integrity of the arcuate fasciculus in 22 % of cases (direct injury or ischemia). Worsened speech function after surgery was observed in 75 % of patients. In the early postoperative period, the main cause of worsened speech function related to the arcuate fasciculus is its functional insufficiency but not an anatomical damage. These speech disorders regress in the majority of patients (85 %) in 3-6 months after surgery.