Endoscopic Approaches to Ventricular Tumors and Colloid Cysts

Introduction

The role for neuroendoscopy in the management of intraventricular tumors and colloid cysts is expanding. The endoscope provides an extended range of view not typically seen with microscopy, and it is also a useful adjunct to confirm the completeness of microscopic resection. On its own, it can be used to biopsy tumors, treat hydrocephalus, and definitively resect select tumors.

Endoscopy remains a relatively new tool within the practice of many neurosurgical centers around the world, and it presents a significant learning curve to new practitioners. This chapter outlines how it may be used optimally in the context of colloid cyst and intraventricular tumor management and endoscope-assisted microsurgical procedures.

History

The endoscope has long been used in neurosurgery. The first neuroendoscopic surgical procedure was performed in 1910 by Victor L'Espinasse, who used a cystoscope to treat hydrocephalus in children. Walter Dandy then performed the first endoscopic ventriculostomy in 1922. Though several pioneering neurosurgeons explored the use of the endoscope in ventricular surgery, its use was limited by difficulties in visualization, illumination, and instrumentation. It was not until technologic developments in lenses, electrical conduction, and fiber optics arose that a new generation of endoscopes could be created. Since the 1980s there has been a resurgent interest in neuroendoscopy, initially with regard to endoscopic third ventriculostomy procedures. As this has become increasingly popular, neurosurgeons have further explored the use of endoscopy for the treatment of more complicated pathologies, such as the biopsy and resection of ventricular tumors, the management of skull-base tumors, and even applications in spine surgery. The applications for neuroendoscopy have changed dramatically over the past century and will continue to evolve as technology advances and the next generation of pioneering surgeons is introduced to its use.

Instrumentation

The endoscope consists of a flexible or rigid tube with a lens system and a light source (typically fiber optic). The two main types of endoscopes are rigid lens scopes and flexible fiberscopes. Rigid lens scopes are fixed in length and geometry and come in a variety of viewing angles (0, 30, and 70 degrees to the long axis of the endoscope). They are optically superior and easier to orientate than flexible scopes. Flexible scopes are composed of malleable fiber-optic cables, and thus steerable along three axes, and are able to be used on a curved trajectory. This functionality can be particularly useful in procedures such as pineal tumor biopsies along a curved path traversing the foramen of Monro to the posterior third ventricle, as seen in Fig. 45.1 . Instrumentation is limited, as working channels are smaller and fewer than those with a rigid scope. Surgeons using the flexible fiberscope should also take extra care to not retract the scope while it is bent, as this can cause significant damage to vital surrounding structures. The two different types of scopes have their own unique uses and can be used in conjunction with one another.

Some surgeons opt to use a rigid endoscope holding arm, which eliminates the need for an assistant to hold the scope and allows the surgeon to use both hands to operate. Although the holding arm can reduce tremor and accidental hand movements, small dynamic adjustments can be difficult to achieve.

Frameless stereotactic neuronavigation is useful for the localization of periventricular cysts under an intact ependyma, as well as the selection of a trajectory and burr hole placement in colloid cyst removal. It increases the safety of neuroendoscopic procedures when the surgeon becomes disorientated or when anatomic landmarks are lacking. This may be particularly useful for patients without ventriculomegaly, which, when present, provides a naturally wider operative corridor.

The resection of intraventricular cysts and tumors is currently hindered by limitations in instrumentation. Variable aspiration tissue resectors are emerging as a potential solution to decrease the time involved in the dissection and debulking of tumors. They have been reported to be safe and effective in reaching and removing tumors accessible only through narrow working corridors. One study on their use in neuroendoscopic resections of intraventricular tumors demonstrated feasibility for use with a variety of pathologies, though tumors larger than 20 mm were only subtotally resected. They should be used for nonvascular or devascularized tumors, as tumors cannot be devascularized by the device prior to debulking.

Principles

Endoscopic procedures are categorized as purely endoscopic neurosurgery, endoscope-assisted neurosurgery, or endoscope-controlled microsurgery. Purely endoscopic techniques are performed through a burr hole, and instruments are introduced through the working channels in the sheath. It is considered a coaxial approach, as the components of the endoscopic system (lighting, camera, working channels, irrigant channels, and instruments) are in parallel and enclosed in a single sheath. Damage to surrounding brain from the retraction and introduction of instruments is minimized. Most intraventricular endoscopic procedures are coaxial.

Extra axial approaches involve the introduction of instruments separate from the endoscope. Endoscope-assisted microsurgery and endoscope-controlled microsurgery are considered extra axial. In endoscope-assisted microsurgery, instruments are used in a bimanual technique under the microscope, and the endoscope assists visualization in, and around, corners. With endoscope-controlled microsurgery, the video image is used for guidance of microsurgical instruments rather than the microscope. In this scenario, curved instruments and suckers can be utilized to operate around corners. This results in a greater degree of technical difficulty due to peripheral distortion, disorientation from using an angled scope, and the proximity of the surgical field to the tip of the endoscope. However, mastering this skill can lead to more precise dissections and greater completeness of resection.

For the management of selected colloid cysts and ventricular tumors, purely endoscopic techniques can be used safely and effectively. The scope is introduced through a burr hole under stereotactic guidance to the lateral ventricle. The resection of large or vascular intraventricular or periventricular tumors is enhanced by using both the microscope and the endoscope for visualization. The advantages and disadvantages to both endoscopy and microscopy are summarized in Table 45.1 .

Introduction to Colloid Cysts

The management of colloid cysts has been a topic of contention in neurosurgical practice due to the risk of treatment and the relatively benign nature of these lesions. Colloid cysts are rare and benign lesions of neuroectodermal origin, arising from the roof of the third ventricle. They can cause obstruction of the foramen of Monro and cerebrospinal fluid outflow. This can result in a spectrum of symptoms from headaches to loss of consciousness and, on occasion, sudden death. Forniceal compression can also lead to memory loss.