Development of a Fluorescein Operative Microscope for use During Malignant Glioma Surgery: A Technical Note and Preliminary Report

Abstract

Background Fluorescein has been used in the field of neurosurgery; however, fluorescein enhancement or contrast proved to be inadequate because of a lack of appropriate light sources or filters. A new operative microscope system, in which the microscope itself is equipped with excitation and barrier filters, and the application of this system to surgery for malignant glioma are reported. Methods BP 450-490, a glass interference filter used as the excitation filter for the light source optical system, and a Kodak Wratten No. 12 filter used as the barrier filter for the microscope optical system, were incorporated in the operative microscope. A switching apparatus was devised so that filters could be inserted instantly when fluorescence was to be observed. Ten cases in which the location of malignant glioma was enhanced by computed tomography (CT) or magnetic resonance imaging (MRI) were selected for this study. After incision of the dura mater, 8 mg/Kg body weight of fluorescein Na was injected intravenously. Tumor removal was begun some 20 min after the injection with the aid of this newly developed fluorescein operative microscope system. Results Fluorescence enhancement and contrast were remarkable when this system was used. It enabled surgical maneuvering while viewing the fluorescent image of objects. The boundaries between the tumor areas enhanced by CT or MRI and the surrounding brain could be clearly distinguished in the fluorescent image; the tumor was totally removed, except for deep lesions, without any neurological deterioration. When the tumor was relatively hard, the area surrounding the tumor was aspirated with a cavitron ultrasonic surgical aspirator; as a result, the tumor could be removed en bloc; otherwise, the fluorescent tumor was removed piece by piece. Conclusions This system provides adequate fluorescent enhancement and contrast and is useful for observing intravenously injected fluorescein during an operation. Though long-term follow-up of such cases is needed, the conditions of our patients immediately after surgery for malignant glioma were satisfactory. These results suggest that our fluorescein operative microscope system is highly effective in surgery for malignant glioma.