CHAPTER 30 Advantages and Limitations of Cranial Endoscopy
History of Endoscopy
The earliest use of the endoscope intracranially was reported by Lespinasse in 1910 for the treatment of hydrocephalus.1 Dandy2 used the technique more extensively and became known as the “father of neuroendoscopy”. Interest in cranial endoscopy was driven by the lack of alternative treatments of hydrocephalus in the first half of the 20th century. Endoscopic techniques evolved from fulguration or obliteration of the choroid plexus to fenestration techniques involving the ventricles and subarachnoid planes. The first endoscopic third ventriculostomy was reported by Mixter3 in 1923. Limited development in the technology for endoscopes combined with the placement of the first valved shunt by Nulsen and Spitz4 in 1949 decreased the interest in cranial endoscopy until the advent of rod lens endoscopes in 1960.5 Better illumination and resolution of the image enabled the application of the endoscope in the context of cranial neurosurgery. In 1973, Fukushima and colleagues6 introduced the modern endoscope, which could be used for the biopsy of intraventricular lesions, cyst fenestration, and treatment of hydrocephalus. The use of the endoscope in transsphenoidal approaches was introduced by Guiot, although he later abandoned the technique because it offered inadequate visualization.7–9 Bushe and Halves10 were the first to report the use of a modern endoscope in pituitary surgery in 1978. A few other reports emerged in the 1970s describing the use of an endoscope as an adjunct to the microscope in transsphenoidal approaches.10–12 Application of the endoscope to the sella turcica did not grow in popularity until the mid-1990s, when endoscopic sinus surgery had virtually replaced open techniques in use by otolaryngologists.9,13 Modern endoscopic cranial surgery developed from a combination of the growth in popularity of minimally invasive surgery through keyhole approaches14,15 and the development of purely endoscopic approaches to the skull base leading to functional endoscopic pituitary surgery.16
Endoscopic Instrumentation and General Principles
Flexible fiberscopes have the smallest diameter and can be used as a stylet within a ventricular catheter. They do not have a working channel but are appropriate for visualizing catheter placement and ensuring an intraventricular position. They have not been shown to improve the surgical outcome in hydrocephalus as no superiority of any specific location of catheter placement has been demonstrated.17,18
Rod lens endoscopes are used overwhelmingly in cranial endoscopy because of the superior quality of the image obtained. They are heavier because of the mandatory attachment of the camera and fiberoptic cable for the light source. An assortment of viewing angles is available (e.g., 0-, 30-, 70-, 120-degree angled endoscopes; Fig. 30-1). Up to two working channels are available on certain types of rod lens endoscopes through which instrumentation can be used. These working channels can also be used in addition to a trocar sheath, enabling the surgeon to use different viewing-angle endoscopes without the need to reinsert them through brain tissue. Different sheaths are available with one to multiple channels for inserting instruments, providing irrigation, or supplying suction.19 Instrumentation in the form of varying forceps, scissors, suction, or coagulation has been developed. The 0- and 30-degree endoscopes are the most widely used. The 0-degree scope minimizes the risk of disorientation, but the instruments inserted through the working channel remain in the periphery of the field of vision.18 The 30-degree endoscope allows better control of the instruments and, with simple rotation, provides an angle of view with a surface area twice as large as that of a 0-degree endoscope.
The optimal use of the endoscope requires a light source combined with a camera and monitor. Halogen, mercury vapor, and xenon light sources are available. The light source is connected to the endoscope through a fiberoptic cable, and its intensity can be modulated. Xenon light sources provide the best illumination for neuroendoscopy.18 The camera is connected to the endoscope by an adapter and transmits the image to a video monitor for viewing by the rest of the surgical team. Cameras are available as a single-chip or a three-chip charge-coupled device. Most systems use a single charge-coupled device because of its lower cost and lighter weight despite a lower quality image.18 A monitor with the highest possible quality should be selected, but its resolution should not exceed that of the camera. The size of the screen should not be excessive; a larger screen limits the quality of the image obtained. The loss of image quality is most pronounced in screens exceeding 13 inches and in cases in which a fiberscope is used.18 Irrigation is useful to optimize visualization and should be used while avoiding entrapment of fluid. Lactated Ringer’s solution is the method of choice for irrigation.20
Rigid endoscope holders may increase the comfort of the surgeon during lengthy procedures but restrict the surgeon’s freedom of movement. Holders have been developed with a combination of pneumatic and electromagnetic brakes, combining the advantages of freehand movements with the possibility of very secure and firm positioning.21,22 Most endoscope holders need continuous manual adjustment at each of their joints, which limits their usefulness. They are usually mounted directly to the side of the operating room table, limiting the range of movement. We have used the Olympus EndoArm (Olympus Europa, Hamburg, Germany), a pneumatic endoscope holder mounted on its own base, extensively (Fig. 30-2). The EndoArm consists of an arm with several ball-and-socket joints that permit movement in all planes. Movement of the joints in either direction is controlled by a single button, giving the surgeon more fluidity in moving the endoscope.23
Endoscopy and Hydrocephalus
Cranial endoscopy was first used in the setting of hydrocephalus before the advent of shunt systems, when the condition was commonly fatal. A renewed interest in the use of endoscopy has arisen because of the high long-term morbidity associated with the use of shunts, most commonly shunt malfunctions and infections. In some cases, to avoid placement of a shunt system, the endoscope can be used to perform a third ventriculostomy or an obliteration of the choroid plexus. Third ventriculostomy has become an important part of the treatment of hydrocephalus, and its long-term success has varied greatly, depending on the cause of the hydrocephalus. Most long-term studies cite success rates of 65% to 75% for third ventriculostomies in the treatment of hydrocephalus.24–41
The endoscope can also be used as an adjunct to a diversion shunt technique when a fiberscope is placed in the ventricular catheter. Adequate placement of the ventricular catheter into the ventricular system is confirmed intraoperatively. Its cost-effectiveness remains questionable, but the technique can be useful in some situations. The endoscope has also been used extensively in cases of multiloculated hydrocephalus to prevent the high rate of shunt infections and revisions encountered in the setting of multiple shunts.42–44 The goal of endoscopic surgery in multiloculated hydrocephalus should be to convert the condition to uniloculated hydrocephalus requiring one or no shunt.42,45 Fenestration of the septum pellucidum by an endoscope may treat an isolated lateral ventricle46,47; in some cases, fenestration of multiple intraventricular membranes may be required,42,45 as well as aqueductoplasty or stenting in cases of fourth ventricular outlet obstruction.48,49
Image guidance is helpful in keeping the surgeon oriented, and a third ventriculostomy can be performed in the same setting if the hydrocephalus is thought to be obstructive. Endoscopic control permits placement of the catheter in an optimal location, and control rates of 62% to 100% can be accomplished in loculated hydrocephalus with one or no shunt.42,43,45,50
Endoscopy and Tumor Resection
Gross tumor resection has been accomplished endoscopically for intraventricular tumors. Favorable factors leading to complete tumor resection include soft tumor consistency, tumor less than 2 cm in diameter, moderate to low vascularity, associated hydrocephalus, low-grade tumor histologically, and tumor situated in the third or lateral ventricle.51 Tumor resection can be time-consuming because it is performed in a piecemeal fashion through the endoscope’s working channel,20 which in most endoscopes is limited to 2.4 mm. Complete tumor resections have most commonly been described in cases of colloid cysts.52–56 Colloid cysts are successfully treated in 60% to 90% of cases51,52,56–69 and seem to carry lower morbidity rates than does open craniotomy57–59; however, few endoscopic series report any long-term follow-up past 5 years.65 Other tumors that have been described as suitable for successful endoscopic resection include subependymal giant cell astrocytoma, exophytic low-grade gliomas into the ventricles, central neurocytoma, small choroid plexus tumors, and intraventricular craniopharyngiomas.32,51,53,70–73
The endoscope can be used effectively in treating intraventricular mass lesions, especially when they cause hydrocephalus.32–34,41,53,74–77 A prime example of the role of an endoscope in tumor resection is illustrated by cases of pineal tumors. In these tumors, the endoscope can be used to obtain CSF for tumor markers and cytologic studies, to inspect the intraventricular cavities to detect gross intraventricular nodules not visible on magnetic resonance imaging, to sample the tumor, and to perform a third ventriculostomy to address the hydrocephalus. Good results in controlling the hydrocephalus have been obtained.33,78,79 Advantages of the endoscopic approach over a stereotactic needle biopsy include the direct visualization of the tumor, a larger biopsy specimen, and the ability to stop the bleeding.51
Endoscopy can also be used as a palliative measure to treat the cystic components of certain inoperable tumors and to implant an Ommaya reservoir in locations more remote from the ventricular system.73
Endoscopy and Arachnoid Cysts
Endoscopy can be used to successfully treat symptomatic arachnoid cysts. Endoscopic fenestration of the cyst into the subarachnoid or intraventricular system enables the procedure to be performed through a smaller opening than is necessary with a craniotomy and alleviates the need for any long-term morbidity of shunt placement. Optimal candidates for endoscopic fenestration should have an area of continuity between the cyst wall and the ependyma or subarachnoid space. A large opening into the cyst wall should be made to prevent reclosure of the stoma. With stable cyst sizes, relief of symptoms without the need for other procedures can be obtained in 71% to 81% of cases.53,73,80–82 Fenestration of the cyst in conjunction with hydrocephalus increases the ease of the procedure and enables the surgeon to perform a concomitant third ventriculostomy.30,73,80,81,83 Fenestration of arachnoid cysts of the middle fossa is possible into the basal cisterns but carries some risk to the vessels of the sylvian fissure and may be best approached through a microsurgical technique.
Endoscopy and the Skull Base
The endoscope has increasingly been used in skull base surgery since the 1970s.9–13 First introduced in 1978 by Bushe and Halves,10 the endoscope was used to better visualize and reach the suprasellar extension of sellar lesions.84–91 The speculum used in the microscopic transsphenoidal approaches limits the working space of the endoscope and instruments, especially in reaching far superiorly, laterally, or posteriorly into the suprasellar space.84–89,91–94 Several variations involving the use of the endoscope in transsphenoidal surgery have been reported. The endoscope has been used to perform the initial approach in the sphenoid sinus, with decreased nasal morbidity to the approach.95 Other purely endoscopic endonasal transsphenoidal approaches have also been developed as an alternative to the microscopic techniques, alleviating the use of a nasal speculum.16,87,96–101
Among the advantages of the endoscope over the microscopic technique in transsphenoidal approaches are a panoramic view with better illumination.102,103 The addition of the endoscope consistently increases the area of visualization of the sellar and parasellar areas when a transethmoidal, transcolumellar, or sublabial approach is compared with its corresponding microscopic approach (Table 30-1; Fig. 30-3).102 In the microscopic approaches, the advantage of the sublabial approach over the transcolumellar approach, which, in turn, improves on the transethmoidal approach, is a better anterior and superior view to address the suprasellar area.104 The endoscope offers wider visualization in all axes with a maximal benefit in the superior and anterior aspects (Fig. 30-4). It is of note that a larger volume of visualization has been reported with an endoscopic transcolumellar approach than with a microscopic sublabial microscopic approach (see Fig. 30-3). Better detail in the image can be obtained with an endoscope than with a microscope because the camera source is closer to the structures of interest. Visualization in the microscopic technique is restricted by the “fixed tunnel” views offered through the openings of the nasal speculum. The microinstruments have to be used in a coaxial fashion, and their reach is limited by the nasal speculum. In addition, the microscopic technique often uses a sublabial or transseptal route, which may cause more trauma to the nasal mucosa,105 and vigorous opening of the speculum may cause optic nerve damage, facial pain, and swelling.106 A disadvantage of the endoscopic technique is the lack of depth perception compared with the binocular stereoscopic vision of the microscope. The endoscope’s image is also distorted, with maximal magnification at its center and contraction at the periphery (barrel effect). Continuous in-and-out movement of the endoscope can accommodate for the barrel effect and lack of depth perception.102
| Advantages |
| Wide-angle view |
| Placement of the surgeon’s eye at the site of surgery |
| Angled scopes look around corners |
| Increased volume of visualization at the site of surgery |
| Disadvantages |
| Lack of binocular vision with current technology |
| Endoscope occupies space in surgical corridor |
| Assistant or holder for scope is required for bimanual surgery to be performed |
| Lack of instrumentation to work through operative channel |
The endoscope’s initial use in transsphenoidal approaches to the sella was quickly expanded to address other midline skull base lesions because of their accessibility endonasally.107–123 The initial experience with these procedures was mixed because of high rates of postoperative CSF leaks, which remain the biggest limitation to the use of an endonasal technique compared with other transcranial neurosurgical approaches.94,121 The incidence of CSF leaks varies greatly with the nature of the condition treated and the degree of disruption of the arachnoid or ventricular system involved.121 Improvement in closure techniques has resulted in decreased rates of CSF leaks over time,121 as the use of fat, fascia lata, mucoperiosteum,124 and vascularized nasal septal flaps125 has been combined with the lumbar drainage, suturing,126 and balloon buttress techniques and fibrin glues.
