TECHNICAL PRINCIPLES FOR PROTOPORPHYRIN-IX-FLUORESCENCE GUIDED MICROSURGICAL RESECTION OF MALIGNANT GLIOMA TISSUE

Malignant gliomas accumulate fluorescing protoporphyrin IX intracellul arly after exposure to 5-aminolevulinic acid, a metabolic precursor of haem. This phenomenon has been exploited for intraoperative identific ation of residual tumour to enable greater completeness of tumour remo val. The present report describes the necessary modifications to the o perating microscope to enable microsurgical, fluorescence-guided tumou r removal. The system consists of a xenon light source coupled to the microscope, which can be switched from normal white light to violet-bl ue excitation light (375-440 nm). A longpass filter is introduced into the observer light path to enable observation of tumour fluorescence. Transmission characteristics of excitation and observation filters ar e chosen to transmit part of the remitted excitation light. Thereby th e observer retains an impression of tissue detail, next to tumour porp hyrin fluorescence. An integrating three chip CCD camera optimized for red light detection enables documentation of fluorescence findings. T he present modifications allow uncomplicated and rapid recognition of red tumour fluorescence and its borders to normal tissue, without inte rrupting the course of the operation. Tissue detail is great enough to enable tumour resection under violet-blue excitation light during par ts of the operation. The system appears to constitute a useful tool fo r optimizing removal of malignant gliomas on a routine basis.