Brain shift refers to the movement or displacement of brain tissue during neurosurgery. This phenomenon is a concern because it impacts the accuracy of surgical navigation and the ability to precisely target specific brain areas. This can lead to reduced accuracy in tumor removal or potential harm to surrounding healthy tissue.
What is Brain Shift?
Brain shift describes the dynamic, three-dimensional displacement of brain tissue relative to its position on preoperative images. This movement can range from a few millimeters to over 25 millimeters and is specific to each patient. It invalidates the patient-to-image mapping used by navigation systems. This discrepancy makes it challenging for surgeons to accurately locate targets and critical structures, potentially leading to incomplete tumor removal or injury to healthy tissue.
Factors Contributing to Brain Shift
Several factors contribute to brain tissue displacement during neurosurgery. One common cause is the drainage of cerebrospinal fluid (CSF), which can lead to a decrease in intracranial pressure and subsequent brain collapse. Patient positioning on the operating table also plays a role, as gravity can cause the brain to sag, particularly when the head is elevated.
Surgical interventions directly affect brain shift. The removal of brain tissue, such as during tumor resection, creates a cavity that allows surrounding brain tissue to move into the newly formed space. Surgical retraction, where instruments gently hold tissue aside, can cause localized deformation. Edema or swelling of brain tissue can contribute to the brain’s expansion and movement within the skull.
Measuring Brain Shift in Real-Time
Neurosurgeons use various technologies to monitor brain shift. Intraoperative Magnetic Resonance Imaging (iMRI) provides frequent, high-resolution image updates for real-time estimation of brain shift. This technology helps assess tumor resection and identify surrounding functional structures, though it can be expensive and prolong surgery.
Intraoperative Ultrasound (iUS) is another imaging modality. It is more time-efficient and cost-effective than iMRI, with image acquisition taking approximately five minutes for a dataset. Live 2D ultrasound images can be overlaid onto preoperative MRI data, enabling surgeons to visualize and assess brain movement. Optical tracking systems, in conjunction with neuronavigation, track surgical instruments and construct real-time models of the resection cavity.
Strategies to Minimize Brain Shift
Neurosurgeons employ several approaches to mitigate or compensate for brain shift. Preoperative planning involves high-resolution MRI or CT scans to detail brain anatomy and anticipate potential areas of shift. Surgical simulation can also help predict brain shift and inform planning.
During the procedure, specific surgical maneuvers are used. Controlled CSF drainage and strategic patient positioning can help manage intracranial pressure and gravity-induced shifts. Minimally invasive surgical approaches are favored to reduce tissue trauma and CSF loss, while gentle tissue handling minimizes localized deformation. Real-time imaging, such as iMRI and iUS, is integrated with surgical navigation systems to update the brain’s position and maintain accuracy throughout the operation.