Transcallosal and Endoscopic Approach to Intraventricular Brain Tumors

Introduction

Endoscopic surgery for intraventricular brain tumors is a logical application of endoscopic technology. Because of the central and deep location of intraventricular brain tumors, conventional neurosurgical approaches have a relative increase in potential morbidity. Traditional approaches involve a craniotomy and opening of the lateral ventricle through a transfrontal approach, opening of the third ventricle through a transfrontal transforaminal approach, or an interhemispheric, interforniceal approach and opening of the atrium of the ventricle through the superior parietal lobule. The downside of these open approaches includes damage to deep white matter tracts, memory loss from damage to the fornix, and the risk of external hydrocephalus resulting from a persistent opening between the ventricles and the subdural space.

With the use of intraventricular endoscopes, many of these risks and drawbacks are avoided. However, the limits of the intraventricular endoscopic approach include limited ability for bimanual surgery and hemostasis, so the tumors that can be removed this way must be carefully selected. Auspiciously, the location of intraventricular tumors being within a cerebrospinal fluid (CSF) compartment affords excellent light and image transmission. The fact that most intraventricular tumors cause hydrocephalus makes endoscopic surgery particularly attractive because simultaneous procedures can be employed for both CSF diversion and tumor management. In addition, the inherent benefits of minimally invasive techniques, including reduced surgical time, improved cosmetic results, shortened hospital stay, and reduced cost also factor into the appeal of neurosurgical endoscopy for managing intraventricular tumors. Five commonly employed endoscopic procedures are highlighted, including endoscopic fenestration, endoscopic tumor biopsy, simultaneous tumor biopsy with endoscopic third ventriculostomy (ETV), endoscopic removal of solid tumors, and endoscopic removal of colloid cysts.

Patient Selection

Patient selection is critical in optimizing the desired surgical goal, avoiding unnecessary procedures, and minimizing surgical morbidity. The intended surgical goal must be carefully established prior to surgery. Many patients who can undergo endoscopic surgery may not be logical candidates since they will ultimately require conventional surgical tumor removal or no surgery. Examples that serve to highlight this point are the patient with a large intraventricular tumor of the ventricular atrium or the patient with a biochemically proven malignant germ cell tumor. In selecting patients, the less experienced surgeon should begin with less demanding cases (septal fenestration and ETV) and eventually incorporate more complex cases (colloid cyst and solid tumor resection).

Equipment

Endoscopes vary in the type of optics (fiberoptic or solid lens), diameter of the scope, and the dimension and number of working portals. While the fiberoptic systems are appealing for their light weight and reduced cost, the greater image resolution with a solid lens system is preferred by the author for most endoscopic tumor surgery. For all procedures featured in this article, scopes should have at the very least one working channel, one irrigation port, and a dedicated egress channel. Navigational guidance is strongly encouraged for ventricular cannulation and for selecting an optimal trajectory ( Figs. 20.1 and 20.2 ). This simple integration greatly reduces the tendency to torque once in the ventricular compartment, thus reducing potential hemorrhage and neurologic injury.

Use of Emerging Novel Technologies in Intraventricular Surgery

There have been many recent advances in the field of intraventricular surgery, including improved instruments that aid in microdissection and laser interstitial thermal therapy (LITT) both of which provide better visualization of normal and abnormal structures. Recent advances in MRI-guided LITT technology have made it possible for its application to be explored in the resection of ventricular tumors. The full range of the benefits and complications associated with LITT dissection still need to be better illuminated. However, Karsy et al. have described a case of stereotactic LASER ablation of a subependymal giant cell astrocytoma at the level of the foramen of Monro in a patient with tuberous sclerosis complex resulting in obstructive hydrocephalus from gadolinium extravasation.

As is true for endonasal endoscopy, better visualization during intraventricular endoscopy has been a continuous effort in the field. In recent studies, the use of endoscope-integrated indocyanine green fluorescence and narrow-band imaging technology satisfactorily enhanced the visualization of the vascular structures within the ventricles. They also allowed for the identification of the abnormal hypervascularized tissue in ventricular tumors. ^, There has also been an increasing interest in the use of augmented reality for surgical planning and navigation. Augmented reality-navigated neuroendoscopy may integrate relevant planning information directly into the endoscope’s field of view, thus improving the safety and efficacy of intraventricular neuroendoscopic surgery. Augmented reality-enhanced navigated endoscopy was favorably tested in 29 patients with different cerebral spinal fluid circulation pathologies, helping in the more accurate identification of the best entry point, trajectory, and regions of interest ( Fig. 20.3 ).