Advances in minimally invasive surgery for brain metastases

Brain metastases (BMs) affect approximately 10-30 % of cancer patients, and their prevalence is growing as patients live longer with controlled primary disease. Surgical resection remains a cornerstone of treatment for both solitary and multifocal lesions. Since the advent of intracranial tumor surgery, neurosurgery has trended towards less invasive surgical approaches, facilitated by a proliferation of surgical innovations ranging from intraoperative MRI to tubular retractors. Minimally invasive cranial surgery (MICS) incorporates approaches such as keyhole craniotomies and tubular retraction with the goal of maximizing extent of resection and reducing iatrogenic tissue injury. Supramarginal resection builds upon this approach, expanding the boundaries of the resection cavity to ensure removal of microscopic tumor fragments and decrease recurrence. Because MICS is generally performed through craniotomies< 5 cm in diameter with limited ability to change predefined surgical corridors intraoperatively, meticulous attention must be given to the preoperative workup. Imaging modalities, including CT, MRI, DWI, and DTI, may reveal characteristics of the intra-tumoral environment and are important in defining the anatomical relationship of BMs to surrounding functional tissue and neurovascular structures. Intraoperatively, neuronavigation helps maintain alignment within predefined surgical corridors, and adjunctive modalities such as intraoperative ultrasound and brain mapping help compensate for brain shift. Advancements in visual augmentation tools such as fluorescence, endoscopes, and exoscopes further enable intraoperative delineation of tumor boundaries and allow for expanded utilization of MICS in deep-seated, complex BMs. The ever-growing armamentarium of minimally invasive surgical tools has made neurosurgery an increasingly safe and effective option for patients with BMs.