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5-aminolevulinic acid induced protoporphyrin IX fluorescence in high-grade glioma surgery: a one-year experience at a single institutuion.

OBJECTIVE
Among the factors determining prognosis in patients with malignant glioma, the extent of resection has long been controversial. However, recent data have shown that patients derive a survival benefit from extensive tumour resection. 5-aminolaevulinic acid (5-ALA)-induced fluorescence renders more complete resection possible in malignant glioma. We report on the feasibility of the method in daily clinical practice, the benefits for patients and surgeons, the technical limitations and the methods we have devised of overcoming these limitations.


METHODS
We describe our initial experience in 74 cases undergoing gross total resection, partial resection and biopsy. Fluorescence intensity and histological data are analysed, specificity and sensitivity are calculated according to fluorescence intensity, and the pitfalls and limitations are defined. The fluorescence signal was quantified via digital video data and by single photon count.


RESULTS
Solid fluorescence signals define tumours with a sensitivity of 0.98 and a specificity of 1.0. Vague fluorescence reduces sensitivity to 0.76 and specificity to 0.85. Limitations of 5-ALAassisted surgery are apparent within the inter-observer interpretation of solid or vague fluorescence, heterogeneity of gliomas, invasion beyond the resection cavity and intercell heterogeneity of porphyrin IX fluorescence.


CONCLUSION
5-ALA-induced PIX fluorescence improves the results in high-grade glioma surgery for gross total resection. Specificity and sensitivity in regions of solid fluorescence are very high. Quantitative analysis of fluorescence intensity corrects the reduced reliability of the method in areas of vague fluorescence and renders gross total resection more feasible without additional risk to the patient. PIX fluorescence is easy to implement in daily neurosurgical practice and side effects are very few. Heterogeneous tumours with lower grade elements and satellite lesions cannot be reliably resected using fluorescence-assisted surgery alone. In these cases the additional use of intra-operatively updated imaging-based neuronavigational methods (MR, ultrasound) is needed.