Near-Infrared Fluorescent Surgery for Skull Base and Intracranial Meningioma

Objective Meningiomas are the most common primary tumor of the central nervous system. Complete resection can be curative, but intraoperative identification of dural tails and tumor remnants poses a clinical challenge. Given data from preclinical studies and previous clinical trials, the authors employ a novel method of localizing tumor tissue and identifying residual disease at the margins via preoperative systemic injection of a near-infrared (NIR) fluorescent contrast dye. This technique, what the authors call “second-window indocyanine green” (ICG), relies on the visualization of ICG 24 hours after intravenous injection.

Methods Thirty-three patients prospectively enrolled in IRB approved study and received 5 mg/kg of second-window ICG the day prior to surgery. A NIR camera was used to localize the tumor prior to resection and to inspect the margins following standard resection. The signal to background ratio (SBR) of the tumor to the normal brain parenchyma was measured in triplicate. Gross tumor and margin specimens were qualitatively reported with respect to fluorescence. Neuropathological diagnosis served as the reference gold standard to calculate the sensitivity and specificity of the imaging technique.

Results Thirty-three patients harbored 27 WHO Grade I and 6 WHO Grade II meningiomas. Fourteen tumors were located in the skull base. Near-infrared visualization during surgery ranged from 18 to 28 hours (mean: 22.9 hours) following second-window ICG infusion. Twenty-eight of the 33 tumors demonstrated a markedly elevated SBR of 5.3 ± 1.8 as compared with adjacent brain parenchyma. Five of the 33 patients showed an inverse pattern of NIR signal, that is, stronger in the adjacent normal brain than in the tumor (SBR 0.41 ± 0.2). The second-window ICG technique demonstrated a sensitivity of 97.9%, specificity of 33.3%, positive predictive value of 71.0%, and a negative predictive value of 87.5% for tumor.

Conclusion Systemic injection of NIR second-window ICG the day before surgery can be used to visualize meningiomas intraoperatively. Intraoperative NIR imaging provides higher sensitivity in identifying meningiomas than the unassisted eye. Skull base meningiomas can be visualized with the exoscope and endoscope systems with high sensitivity. Specificity will be achieved with future targeted near-infrared dyes.