Subcortical injury is an independent predictor of worsening neurological deficits following awake craniotomy procedures

BACKGROUND: Tailored craniotomies for awake procedures limit cortical exposure. Recently we demonstrated that the identification of eloquent areas increased the risk of postoperative deficits. However, it was not clear whether the observed neurological deficits were caused by proximity of functional cortex to the tumor [cortical injury] or subcortical injury. OBJECTIVE: We hypothesize that subcortical injury during tumor resection is an important predictor of postoperative neurological deficits compared to cortical injury. METHODS: A retrospective review of 214 patients undergoing awake craniotomy was carried out in whom preoperative functional magnetic resonance imaging (fMRI) and cortical mapping (CM) were performed. A radiologist blinded to the clinical data reviewed and graded the postoperative changes on diffusion-weighted MR-imaging (DWI). RESULTS: Of the 40 cases who developed new intraoperative neurological deficit, 36 (90%) occurred during subcortical dissection, 3 (7.5%) during both subcortical and cortical dissection, and 1 (2.5%) during cortical dissection. Neurological dysfunction acquired during subcortical dissection was an independent predictor of postoperative deficits both in the immediate postoperative period (P, .001) and at the 3-month follow-up (P , .001). Significant DWI restriction in the subcortical white matter was predictive of neurological deficits both immediately and at 3 months, P = .011 and P , .001, respectively. New or worsening deficits were seen in 38% of patients; however, at 3 months 13% had a mild persistent neurological deficit. CONCLUSION: Subcortical injury with significant DWI changes result in postoperative neurological decline despite our efforts to preserve cortical areas of function. This underscores the importance of preserving subcortical fiber tracts during awake craniotomy procedures.