Comparison of intraoperative fluorescence and MRI image guided neuronavigation in malignant brain tumours, a prospective controlled study.
INTRODUCTION
MBT carry poor prognosis and more than 80% of MBT recur locally within 2 cm of the resection margin because of inadequate surgical removal. A number of techniques have been implemented in recent years to improve surgical removal of MBT with variable success. We examined two methods commonly used to resect MBT to establish which one offered the best chances of gross total removal; MRI guided technology and ALA-induced fluorescence.


PATIENTS AND METHODS
Twenty consecutive patients diagnosed with MBT were included in this study. They were given 20mg ALA per kg body weight 3h before anaesthesia orally mixed in water. Surgery was planned using preoperative enhanced MPR age images. Surgery was executed using the Stealth Station image guidance system and ALA-induced fluorescence microsurgical techniques. During surgery the intensity of fluorescence was graded into red, pink or blue. The intensity of fluorescence was also measured using pulsed 405 nm laser and a compact spectrometer using a touch probe directly placed on the tissue. The extent of tumour invasion was assessed intraoperatively using standard white light, blue light and spectroscopic measurements. Postoperative enhanced MRI was used to assess the extent of resection and the volume of residual tumour was measured.


RESULTS
There were six newly diagnosed GBM, eight recurrent GBM, one oligodendroglioma (ODG) and five metastases (MET). On enhanced MRI, the mean diameter of new GBM, recurrent GBM, ODG and MET was 2.3 cm, 2.3 cm, 1.5 cm, and 2.3 cm respectively. Under the blue light, the mean diameter of new GBM, recurrent GBM, ODG and MET was 2.9 cm, 3 cm, 1.5 cm and 2.3 cm respectively. The results of quantitative measurements of fluorescence ratios revealed that red fluorescence corresponded to 5.9-11.6 (solid tumour on histology), and pink fluorescence measured 0.8-1.9 (infiltrating edge of tumour on histology). When we compared the maximum tumour diameter of GBM we found on average it was 10mm wider on spectroscopy compared to standard white light microscopy and 6mm wider than what the enhanced MRI demonstrated.


CONCLUSIONS
Fluorescence technology revealed that GBMs are wider than the enhanced MRI had demonstrated, while MET enhanced MRI was similar in size to fluorescence. Furthermore, solid tumour can be identified intraoperatively and can be measured using fluorescence and spectroscopy techniques and it can be removed safely. Infiltrating tumour can also be identified intraoperatively using this technology and can be removed in non-eloquent areas to maximise surgical resection.