Non-enhancing gliomas: does intraoperative ultrasonography improve resections?

PURPOSE: Non-enhancing diffuse gliomas are a challenging surgical proposition. Delineation of tumour extent on preoperative imaging and intraoperative visualization are often difficult. METHODS: We retrospectively analyzed all cases of non-enhancing gliomas that were operated on using navigated 3-dimensional ultrasonography (US). Tumour delineation (good, moderate, or poor) on preoperative magnetic resonance imaging (MRI) and intraoperative US was compared. Post-resection US findings with respect to residual tumour status were compared to the postoperative imaging findings. The extent of resection was calculated and recorded. RESULTS: There were 55 gliomas (43 high-grade, 12 low-grade). Forty were close to eloquent areas. The pre-resection concordance of MRI with US was 56%, with US defining more tumours as well-delineated (n=26) than MRI (n=13). US was used for resection control in 50 cases. Gross tumour resection was achieved in 24 cases (51%). US correctly predicted the residual tumour status in 78% of cases. The use of US led to radical resections even in some tumours preoperatively deemed to be unresectable. However, eloquent location was the only independent predictor of the extent of resection. CONCLUSION: Intraoperative US is a useful tool for guiding resection of non-enhancing gliomas. It may be better than MRI for delineating these tumours, and may thereby facilitate improved resection of these otherwise poorly delineated tumours. However, functional boundaries remain the main limiting factor for achieving complete resection of non-enhancing gliomas.