Surgery of Small Anterior Skull Base Meningiomas by Endoscopic 5-Aminolevulinic Acid Fluorescence Guidance: First Clinical Experience

BACKGROUND: Minimally invasive surgery of small skull base meningiomas is technically challenging. We report the role of endoscopic 5-aminolevulinic acid fluorescence guidance (e-5-ALA-FGS) for small and deep-seated anterior skull base meningiomas. METHODS: We report the cases of 2 patients. The first case was a small olfactory groove meningioma resected via a trans-eyebrow, subfrontal approach. The second case was a clinoid meningioma with invasion of the optic canal resected via a small frontolateral approach. Intraoperative documentation demonstrated the usefulness of 5-ALA endoscopy. In either case, residual fluorescing tumor tissue was detected. No complication was encountered. The clinical and radiological outcomes were good. No regrowth had occurred after 54 and 17 months of follow-up, respectively. RESULTS: Residual meningioma tissue on the far side of a keyhole approach (e.g., in the olfactory groove or at the optic canal) can be difficult to visualize. Visualization can be improved by use of an endoscope. To date, fluorescence guidance with a microscope was limited by insufficient fluorescence signals in deep corridors. With a specially equipped 5-ALA fluorescence endoscope, one can combine the advantages of both endoscopic vision and fluorescence guidance. The results of present report have demonstrated the usefulness of 5-ALA endoscopy for difficult to visualize areas. CONCLUSION: Endoscopic 5-ALA fluorescence guidance was shown to be feasible when resecting small and deep-seated skull base meningiomas via minimally invasive approaches. Based on this proof of principle, we encourage its evaluation for the middle or posterior fossa (e.g., internal auditory canal) and other difficult areas (e.g., behind neurovascular structures or the brainstem). The sensitivity and specificity of this method should be prospectively and systematically investigated.