gms | German Medical Science

Objective: A gross total resection in non-eloquent high grade gliomas is the surgical goal for most neurosurgeons. In order to maximize the extent of resection, intraoperative imaging is required. Evidence for overall survival exists for two techniques so far: intraoperative MRI and 5-aminolevulinic acid. However both methods are based on distinctly different principles which mayt lead to unliklye results in detecting residual tumor. The aim of the study was to perform a prospective comparative study assessing sensitivity and specificity of ioMRI and 5-ALA based on a histopathological assessment.

Method: We included 32 patients harboring contrast-enhancing cerebral lesions in whom a gross total resection was intended. After microsurgical resection, the resection cavity was inspected with 5-ALA and positive areas were marked in the neuronavigation system followed by a contrast-enhanced ioMRI scan. Congruencies of ioMRI and 5-ALA tumor positive areas were recorded. 86 histopathological specimens were harvested according to acquired points and a further resection of residual tumor was performed, whenever ioMRI or 5-ALA showed positive results. Histopathological assessment included distribution of tumor, infiltration zone and tumor-free tissue in the specimen as well as MIB index and vascular proliferates. Rate of resection was recorded based on post operative MRI.

Results: The final histopathological diagnosis of the majority of patients was a glioblastoma multiforme. 6 patients had a cerebral metastasis and two patients an anaplastic astrozytoma. Sensitivity to detect residual tumor tissue after microsurgical resection was higher for ALA at 87% in comparison to ioMRI at 35%. This difference was statistically significant according to McNemar's test (p< .005). However, specificity was significantly lower (p<0.038) in 5-ALA at 17% in comparison to ioMRI at 60%. The accuracy for detecting tumor-including infiltration zone was 92% for 5-ALA and 50% for ioMRI. The mean share of solid tumor in ioMRI negative specimens was 31% of infiltration zone 56%. The rate of gross total resection with combined use of ioMRI and 5 ALA in our series was 94%.

Conclusions: 5-ALA exceeds the sensitivity for detecting residual tumor of ioMRI significantly. However, 5-ALA has a low specificity since the differentiation between solid tumor and infiltration zone is poor. ioMRI shows a gap in detecting the infiltration zone of the tumor. Since these areas may be the base for an early recurrence of tumor, we favor a combined use of both techniques.