INTRODUCTION

Technological advances in the field of neurosurgery have made new surgical techniques possible for meningioma treatment that may provide effective precise image-guided minimally invasive resection. This chapter covers four surgical initiatives that may significantly change meningioma management in the future:

INTRAOPERATIVE IMAGING

Image-guided neurosurgery using a navigation system in the traditional operating room is important in the management of many meningiomas because it can localize the tumor and critical structures around it. Intraoperative imaging is a useful further development because it compensates for brain shift, allows accurate navigation, and gives verification of what has been done surgically before the patient leaves the operating room.¹ Current intraoperative imaging modalities offering real-time imaging are computed tomography (CT), magnetic resonance imaging (MRI), and ultrasound. Other modalities may help define the tumor by cellular techniques—these include photodynamic imaging, radio immune imaging, and infrared imaging with ala or other material. These extend the capacity of the surgeon significantly but are not discussed here.

Present frameless navigation systems used in the traditional OR can localize a tumor with great accuracy and can even track the movement of surgical instruments in the operative field. They generally involve infrared or magnetic sensors that relate to a receiver attached to skeletal fixation device. A small incision, preservation of eloquent areas, and clean resection margins are possible using these techniques.

Despite the power of navigation systems, there are several potential problems with them including system failure and inaccurate registration. The registration of scalp to the preoperative image may be done either with fiducials or landmarks such as the nose, inion, and orbital rim. These may be inaccurate because of scalp movements as the patient changes position or as the skeletal fixation distorts the scalp even in the supine position. Other sources of inaccuracy include geometrical distortion in images, movement of patient with respect to the system during surgery, and brain shift.

Brain shift may result from fluid shifts, reduction in tumor volume as the tumor is resected, changes in arterial pCO_2, and cerebrospinal fluid (CSF) loss after opening of the dura.^2–5 It makes guidance from preoperative images potentially and variably inaccurate. Intraoperative brain surface deformations greater than 10 mm have been documented within 1 hour of opening the dura. The error induced by this type of shift may be even larger in the presence of hydrocephalus or preexisting loss of parenchymal volume. Intra-operative imaging was in part created to overcome the effect of brain shifting.