5-ALA complete resections go beyond MR contrast enhancement: shift corrected volumetric analysis of the extent of resection in surgery for glioblastoma

Background The technique of 5-aminolevulinic acid (5-ALA) tumor fluorescence is increasingly used to improve visualization of tumor tissue and thereby to increase the rate of patients with gross total resections. In this study, we measured the resection volumes in patients who underwent 5-ALA-guided surgery for non-eloquent glioblastoma and compared them with the preoperative tumor volume. Methods We selected 13 patients who had received a complete resection according to intraoperative 5-ALA induced fluorescence and CRET according to post-operative T1 contrast-enhanced MRI. The volumes of pre-operative contrast enhancing tissue, post-operative resection cavity and resected tissue were determined through shift-corrected volumetric analysis. Results The mean resection cavity (29 cm 3 ) was marginally smaller than the pre-operative contrast-enhancing tumor (39 cm 3 , p = 0.32). However, the mean overall resection volume (84 cm 3 ) was significantly larger than the pre-operative contrast-enhancing tumor (39 cm 3 , p = 0.0087). This yields a mean volume of resected 5-ALA positive, but radiological non-enhancing tissue of 45 cm 3 . The mean calculated rim of resected tissue surpassed pre-operative tumor diameter by 6 mm (range 0–10 mm). Conclusions Results of the current study imply that (i) the resection cavity underestimates the volume of resected tissue and (ii) 5-ALA complete resections go significantly beyond the volume of pre-operative contrast-enhancing tumor bulk on MRI, indicating that 5-ALA also stains MRI non-enhancing tumor tissue. Use of 5-ALA may thus enable extension of coalescent tumor resection beyond radiologically evident tumor. The impact of this more extended resection method on time to progression and overall survival has not been determined, and potentially puts adjacent and functionally intact tissue at risk.