Chapter 7

Is the Endoscope Useful for Pituitary Tumor Surgery?

Giant pituitary tumors are among the most complex neurosurgical challenges. Despite their histologically benign nature, some of these tumors grow to a massive size. Because of the invasiveness and size of such tumors, surgical resection is difficult and, in some cases, dangerous.1 But because the results of radiation therapy are inconsistent, surgery forms the mainstay of treatment.

The diagnosis of a pituitary tumor usually can be made on the basis of clinical features and their classic anatomic extensions seen on imaging.² Surgical biopsy for histological confirmation has no relevance. Small or partial resections can be dangerous, as bleeding from the residual tumor is frequent, an event defined earlier as “post operative pituitary apoplexy.”¹ Successful radical resection of the tumor can rapidly dispel symptoms and lead to an excellent long-term clinical outcome. After such resection, the recurrence rate of these tumors is low.

Anatomic Grading of Giant Pituitary Tumors^3,4

Giant pituitary tumors have a maximum transverse dimension of at least 3 cm and can be divided into four grades:

The Use of the Endoscope in Pituitary Tumor Surgery

In use for quite some time now, endoscopes are currently being recommended for several neurosurgical operations. The superiority of the endoscope in treating tumors of the paranasal sinus and clival regions and medial extradural cavernous sinus tumors is now accepted. The campaign in favor of the use of the endoscope has been quite intense. Even the general population has come to know this tool, and some patients even demand that their pituitary surgery be done with an endoscope. Several surgeons who are accustomed to using the microscope for pituitary tumor surgeries have acknowledged the value of the endoscope.

I expose the anterior sellar wall and then resect it widely, initially using a chisel and then rongeurs. After the wall is open, I make a cruciate incision in the dura. The tumor is then progressively debulked. These tumors are usually soft, friable, and necrotic, which makes debulking safe and relatively quick. Despite the occasional high vascularity of these lesions, it is relatively easy to control bleeding with hemostats like Gelfoam and Surgicel, and intra- tumoral coagulation can be avoided.

Endoscopic Removal of Pituitary Macroadenoma

The ancient Egyptians were the first to recognize the possibility of accessing the brain endonasally without disfigurement. Computed tomography scans of mummies and archaeological findings confirm that the Egyptians used specialized instruments to perform the earliest transsphenoidal approaches, albeit postmortem.6 It would be several thousand years before Schloffer, Von Eiselberg, and Kocher would carry out, in 1907, the earliest transsphenoidal surgeries to access a pathological lesion.7 The sublabial transseptal approach was used by Cushing⁸ in 1909 and was less traumatic than the endonasal and sublabial approaches introduced in 1910 by Hirsch and Halstead, respectively.⁷ Cushing abandoned the approach, however, in part because of inadequate illumination, but in the late 1960s, Hardy overcame this obstacle by making use of the operating microscope. Since then, approaches have been modified with improved visualization for the surgeon and decreased postoperative discomfort for the patient.

The approaches done with the microscope essentially differ according to where the mucosal incision is made (sublabial, hemitransfixion, Killian, or direct sphenoidotomy) and the width of the sellar exposure each provides. Whereas the sublabial approach provides the widest exposure, it also requires the most soft tissue and mucoperichondrial dissection. By contrast, the direct endonasal sphenoidotomy requires no anterior septal dissection but has the narrowest exposure. The endonasal approaches decrease both the postoperative discomfort for the patient and the chances of anterior septal complications. However, the downsides of more direct approaches include diminished working room, a more limited sellar exposure, and an approach from an angled trajectory.⁷

Evolution of the Endoscopic Approach

The role of the endoscope has evolved over time. Initial reports describe the use of the endoscope as an adjunct to the standard approach with the microscope.^9,10 For example, the endoscope could be used for the anterior sphenoidotomy before introducing the microscope, or it could be simply introduced at the end of resection to inspect for residual tumor. The pure endoscopic transsphenoidal approach was introduced by Jho and Carrau¹¹ in the late 1990s, with modifications by Kassam and colleagues^12,13 that allowed the scope of the approach to expand to surgery for complex skull-base tumors. Other pioneers include Cappabianca and de Divitiis^14,15 in Italy, as well as Frank, Pasquini, Locatelli, and others who have made significant contributions to the development of endoscopic techniques and transsphenoidal surgery.^16–18

Advantages of the Endoscopic Approach

The primary advantages of the endoscopic removal of adenomas lie in the panoramic field of view and the ability to attain an extreme close-up point of view. During the approach, the panoramic view allows superior visualization of the sphenoid anatomy. Unlike the approach with the microscope, in which a localization X-ray is necessary after speculum placement, image guidance is rarely needed during a standard endoscopic approach, which decreases the dose of radiation to both the patient and operator. Anatomic landmarks are clearly identifiable, even by the novice endoscopist, which increases the surgeon’s confidence and decreases the learning curve.¹⁹ In the case of a repeated operation, distorted anatomy can be more clearly identified, and the existence of an operative corridor facilitates surgery with less risk of complications.^7,15 In addition, because there is no submucosal dissection, nasal packs are not routinely used, which improves overall patient satisfaction with the procedure.

Most significantly, the panoramic view allows a greater portion, if not all, of an adenoma to be removed under direct visualization. Tumor extensions toward the cavernous sinus walls and the suprasellar portions, which are often removed blindly by feel during an approach with the microscope, are instead removed with certainty. The magnification allows excellent visualization of the interface between the tumor and pituitary gland, potentially facilitating adenomectomy with minimal disruption of the surrounding tissues.¹⁵ With the wide-angle lens view of the zero-degree endoscope and the use of angled endoscopes, the endoscopic surgeon can see around corners, which is not possible with the microscope.¹⁶ This ability can be particularly helpful in patients with a macroadenoma that extends into the cavernous sinus or suprasellar space.¹⁷ For tumors that invade the cavernous sinus, the endoscope affords a wider view when compared with the microscope and unrivaled maneuverability in the lateral compartment of the cavernous sinus.¹⁷ Moreover, only the endoscope allows the surgeon to use the diving technique described by Locatelli and colleagues.¹⁸ Intrasellar hydroscopy allows for more complete assessment of the surgical bed, during and after resection, with improved hemostasis. Blind curettage is therefore minimized and a larger extent of the tumor can be removed under direct visualization.

Disadvantages of the Endoscopic Approach and Strategies for Their Management

Despite its advantages, there are several disadvantages of the endoscopic approach, many of which can be overcome with training and experience. Neurosurgeons are comfortable using the operating microscope and the three-dimensional view it provides. When using the endoscope, a new skill set with a different type of hand–eye coordination must be learned and practiced. Some surgeons find the two-dimensional view on a monitor challenging, particularly with regard to depth perception.^19,20 This problem can be partly overcome with the help of a skilled endoscopist as the assistant. Such an assistant can help the surgeon with opportune in-and-out movements of the camera to create an artificial perception of depth. This notion of the endoscope as part of a “clock gear” mechanism was aptly described by Cavallo and associates.²¹ Each part of the system depends on the others. If one part fails then the whole system fails. In addition, proprioception allows the surgeon to perceive the location of an instrument in one hand as it relates to the instrument in the other. Because of the current constraints with rigid endoscopes, there is a slight “barrel distortion” effect at the edges of the field of view. When the endoscope cannot be repositioned, an angled scope can overcome these distortive effects so that the surgeon can examine the edges and beyond the resection bed.

The case presented is that of a 45-year-old man with a nonfunctioning pituitary macroadenoma causing bitemporal hemianopsia. The representative magnetic resonance imaging (MRI) shows a large macroadenoma with a suprasellar extension (Fig. 7.5). Coronal images show likely cavernous sinus involvement bilaterally. Therefore, a complete resection is unlikely regardless of whether an endoscope or microscope is used. The primary goal of surgery is to decompress the optic chiasm. Secondary goals are to remove enough of the tumor to prevent recurrence and to preserve pituitary function. Because the patient is relatively young, these goals require as thorough a removal of tumor as possible.

Surgical Technique