35 Image-Guided Surgical Techniques for Meningiomas
The skin opening must be bigger than the bone opening. The bone opening must be bigger than the dural opening. The dural opening must be bigger than the tumor.
—Patrick J. Kelly, MD
Meningiomas are one of the more common brain tumors. Given their typically benign histopathology, optimal treatment remains complete resection when it can be accomplished with no or minimal morbidity. For difficult tumors with higher-risk profiles, other treatment options include radiosurgery and radiation therapy—with or without surgical debulking.1–5 Nevertheless, even completely resected benign meningiomas can recur in nearly 10 to 30% of cases with long-term follow-up, and progression of incompletely resected tumors is quite high6–10 ( Table 35.1 ). Incomplete resections predispose patients not only to a high probability of recurrence but also to a decreased chance of successful resection at subsequent operations7 and worse overall survival.11 These findings underscore the need for attempted complete removal at the initial operation—including removal of the bulky tumor in addition to the dural tail, sinus invasion, and bony involvement when possible. To better achieve this end safely and in a manner as minimally invasive as possible, image guidance surgery (IGS) systems have become an increasingly important and utilized tool.
Stereotactic neurosurgery was originally conceived for the treatment of intraparenchymal lesions and utilized a headframe-based platform. With engineering advances in imaging, optical, and infrared technologies, “frameless” stereotaxy systems (neuronavigation) were developed12 and, given their ease of application, have grown in prominence for the treatment of all types of intracranial lesions—including meningiomas.13 Many centers now routinely use IGS for resection of meningiomas to minimize skin incision and craniotomy size,8 but few centers have reported on their experience.14–19 This chapter discusses the techniques of IGS for intracranial meningiomas and their utility beyond minimally invasive neurosurgery.
Rationale for Use of Image Guidance Surgery Systems in Meningioma Resection
IGS systems use the information obtained in a two-dimensional (2-D) plane to re-create and display the patient’s anatomy in a three-dimensional (3-D) space. This reconstructed 3-D volume can then be analyzed and manipulated, allowing visualization of the target lesion in multiple planes, planning of the optimal surgical trajectory, and accurate localization of critical nearby structures. All of this can be accomplished before the patient enters the operative suite and can be updated with real-time positional feedback with tracked instruments as the surgery progresses.
To date, however, no prospective, randomized studies have demonstrated improved outcomes using IGS for meningioma resection. Paleologos et al17 retrospectively reported on 270 patients who underwent meningioma re-section (100 with IGS, 170 with standard surgery). Matching 100 patients with similar baseline characteristics (50 in each group), they noted shorter operative times, fewer major complications, shorter hospital stays, and lower costs in the patients in whom IGS was used. In agreement with other centers,13,15,17,20–23 we believe neuronavigation not only enhances surgeon confidence but can result in improved patient outcomes and satisfaction, with smaller scalp flaps and craniotomy sizes, shorter operative times, more complete resections, less trauma to the surrounding structures, lower surgical morbidity, and shorter hospital stays.
Types and Overview of Image Guidance Surgery Systems
Table 35.2 summarizes the major IGS platforms and the commercially available products. No objective, prospective studies have determined the benefits of using IGS systems compared with not using neuronavigation for meningioma resection nor the superiority of one system over another. Ultimately, the choice of IGS device depends on surgeon preference and institutional availability.
Original frameless IGS devices involved articulated arms with multiple electropotentiometer position-sensors within the joints that allowed simple patient-to-image registration. They can be cumbersome to move into and out of the operative field—especially during use of the microscope for skull base tumors. Their bulk and frequent collisions with the microscope led to their demise. Nevertheless, accuracy on the order of 2 mm had been reported by multiple authors using these systems—adequate for most meningioma surgeries20 and rivaling the accuracy of later systems.
Light-Emitting Diode Systems
Light-emitting diode (LED) neuronavigation systems are optically based systems that use an infrared camera array to monitor instrument and head position. The camera tracks the location of LEDs mounted to surgical instruments and to the reference array attached to the head holder or directly onto the skull. Rigid fixation is required with LED systems to maintain the 3-D coordinate space created during registration. These systems require maintenance of line of sight between the camera, head holder array, and probe but allow stereotactic integration with the operating microscope (using the focal point as the “pointer position”).
Passive Infrared Sensors
Systems utilizing passive infrared sensors use cameras that flash pulses of infrared light reflected from specially coated spheres attached to a pointing probe or from an array of spheres attached to surgical instruments. Surgical instruments (e.g., endoscopes, ventricular catheters, biopsy probes, etc.) can be registered and calibrated using both device length and diameter to be used during surgery. Importantly, these systems allow a wide array of instruments to be registered and require no cable attachments for ease of use. Similar to LED systems, however, rigid fixation is required, line of sight must be maintained, and the spheres must be cleaned periodically to maintain their reflective properties. Infrared systems also allow stereotactic integration with the operating microscope (using the focal point as the “pointer position”).
Electromagnetic IGS systems involve the creation of a small magnetic field enveloping the cranial space and allow tracking of a magnetically active pointing device in the registered field. Magnetic systems avoid line-of-site issues but are prone to magnetic field distortion and disruption of navigation if instruments composed of ferromagnetic materials are brought into the field. Both the Cygnus Stereotactic System (Compass International, Inc., Rochester, MN) used at our center for years and the StealthStation AxiEM (Medtronic Navigation, Louisville, CO) can be used with or without a head holder attachment. The latter has been used successfully in small children where pinning is not advisable.