Fluorescent-guided surgery allows surgeons to visualize entire solid tumors intraoperatively using glowing substrates in conjunction with a near-infrared (NIR) microscope. One that has gained considerable attention is indocyanine green (ICG), an FDA-approved angiography contrast agent. In 2016, our lab developed a novel technique known as Second Window Indocyanine Green (SWIG) which allows surgeons to utilize the enhanced permeability and retention effect (EPR) of tumor tissue to accumulate the dye during a “second window” of fluorescence that occurs several hours after injection [1]. SWIG has been utilized in other neurological tumors including pineal tumors, hemangioblastomas, meningiomas, skull base tumors, intraventricular tumors, and high-grade gliomas [2], [3], [4], [5], [6], [7].

Schwannomas are benign neoplasms of peripheral nerves that usually incorporate the nerve into the encapsulated tumor [8]. Sporadic schwannomas affect patients of all ages with a peak between ages 20 and 50. Symptoms of cranial nerve schwannomas include loss of hearing and balance, facial paralysis and/or paresthesia, and difficulty swallowing [9]. Schwannomas are typically slow-growing, and are often undetected until they begin to impinge on the nerve or adjacent neural structures [10]. As such, fluorescence-guided surgery could be useful for the resection of tumor tissue while leaving functional nerve intact.

Other fluorescent agents have been used in the past to assist in the resection of schwannomas. Sodium-fluorescein (SF) is a fluorescent dye that has seen a renaissance in neurosurgery in the early 2000s [11]. In 2021, Pedro and colleagues found that SF was able to detect tumor remnants and enhanced tissue differentiation between affected and unaffected nerve segments in schwannoma resection; however, intraneural tissue differentiation was not possible [12]. Additionally, SF has been underutilized in the past due to a lack of appropriate light source or filter and additional required equipment. Prior studies assessing SF have also found that it is limited by poor specificity, although these data are scarce [13].

Because ICG is an FDA-approved dye that is readily available and has low rates of adverse events, SWIG proves to be a more accessible tool for surgeons. Additionally, the NIR light used to detect SWIG permits sensitive detection at greater tissue depth due to superior penetration while minimizing light absorption and scattering [14]. In the present paper, we report three patients undergoing resection of cranial nerve schwannomas who were infused with SWIG prior to surgery. We believe this technique allows for more complete resection, better outcomes, and a new approach to schwannoma resection. This case series suggests another potential application for SWIG in the resection of brain tumors.