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Endoscopic Endonasal Transsphenoidal Surgery:
Review of the Literature

St. Dimitrov, M. Marinov

Neurosurgical Clinic, University Hospital "St. Anna", Sofia, Bulgaria

ABSTRACT

Objective: Our goal was to review the current literature on the subject and to make conclusions regarding the application and usefulness of this new method in daily neurosurgical practice.
Data sources: Review of accessible English-language literature was done, predominantly for the last five years.
Study selection: Articles were selected according to the applied technology, number of selected cases, depth of analysis and the impact of referred journals.
Data extraction: All facts concerning the endoscopic transsphenoidal operations were selected.
Data synthesis: The value of data selected was estimated according to their contribution to the development of the method.
Conclusions: Endoscopic transsphenoidal surgery seems to be very promising in the future pituitary surgery.
Key words: Endoscopic endonasal surgery, Pituitary adenoma, Transsphenoidal surgery.
Pro Otology 1: 30-33, 2002

The history of transsphenoidal surgery is a fairy tale of innovative steps towards developement of sublabial and endonasal approaches, which became a standard surgical routine. The establishment of a single universally accepted procedure was one of the first major steps in the development of transsphenoidal surgery. During the revival of the approach in the 1950s, use of radiofluoroscopy and the operating microscope greatly improved the illumination and clarity of intraoperative imaging. Innovations in technology in the form of endoscopy offered even more advanced methods to visualize the operative field. Since it allowed surgeons to see otherwise blind corners and provided a variety of panoramic and close-up views, it became popular during the past decade.

Our aim was to review the contemporary literature on the subject and to make a conclusion towards the application of the endoscopic endonasal transsphenoidal surgery to our current neurosurgical practice.

Historical movements: The concept of endoscopy is not new in neurosurgery. Most commonly it is applied to procedures within the ventricular system and selected intraventricular tumors, typically in pediatric population. Otolaryngologists have used endoscopic techniques for the treatment of most inflammatory sinonasal disorders, nasal polyps, neoplasms and repair cerebrospinal fluid leaks. There are clinical demands for less-invasive procedures because of the reduced recovery time, potential benefits and theoretical decreased cost of medical care. Nevertheless, transsphenoidal surgery for pituitary tumors still presents unique surgical challenge. First, the surgical corridor is relatively narrow, limiting the surgeon's view in lateral and rostrocaudal directions. Second, during tumor removal only a small portion of the lesion is seen at any given time but in many cases lateral and suprasellar growth is considerable. A panoramic view of the sellar contents is not possible with the microscope. On the other site, rhinological complications due to the surgical approach itself are not rare but are often underestimated by neurosurgeons (1,2). It is thought that endoscopy can solve some of this problems.

In the beginning, endoscopy was employed to assist visualization during microscopic pituitary surgery through a standard transseptal, transsphenoidal approach. At the end of the operation surgeons were eager to "look around the corner". In 1978 Busche and Halves (3) used an endoscope as a supplement to the standard microscopic transsphenoidal procedure with considerable contribution to complete tumor extirpation. Gamea et al. (4), postulated that the use of rigid endoscope during transsphenoidal microsurgery allowed close inspection and differentiation between tumor tissue and glandular remains and the angled view of endoscope helped total gross removal of tumor from less accessible supra- and parasellar extensions. Helal in 1995 (5) confirmed the potential of the method in 37 patients with pituitary macroadenomas. In 1996 Rodziewicz et al., (6) reported their results in 10 patients. They used biportal submucosal approach through self-retaining speculum and nasal stents along the septum after completion of the procedure. Debulking of the tumor was achieved using the endoscope. Cusimano and Fenton (7) resected the middle turbinate using a rigid endoscope and entered the sphenoid sinus via the ethmoidal bulla and sinus or through the sphenoid ostium. The following steps of the procedure were not different form standard microsurgical operation. Teo et al., (8) entered the sphenoid by performing anterior ethmoidectomy and posterior middle turbinectomy. Yaniv and Rappaport (9) used an endoscope only until opening of the sphenoid sinus. The next steps were done towards reducing the invasiveness of nasal stage of operation, saving the middle turbinate, ethmoid and septum (10), developing specific instruments (11) and eliminating microscope and intraoperative radiofluoroscopy (12,13).

Real progress was achieved by the work of H-D. Jho et al., (12-16) and P. Cappabianca et al., (11,17). They converted the endoscopy from a supplement of the classical microsurgery to an independent surgical method. Different interpretation of normal anatomy was imperative (18). This was necessary because of the need to accommodate for intrinsic optical distortion of the structures related to endoscopic optics, two-dimensional (2-D) images and image characteristics related to varied lens angulations. When using an endoscope, a surgeon may face difficulty in correlating distorted 2-D sinus anatomy to its 3-D relationship with surrounding anatomy. Due to its panoramic view, all surrounding structures are compressed (18). The optical distortion is not uniform, because the periphery is more compressed than the central area. The compressed peripheral structures appear to be significantly smaller than their actual size. This "barrel-type" of spatial distortion is further accentuated eccentrically when an angled lens is introduced. In addition, the direct light projected from the tip of an endoscope produces images that interfere with proper depth perception (2-D vision) because of the absence of shadows. The artificial image distortion is more evident when the image is magnified by the closeness to the target, along with the increased light intensity. The distorted anatomy can be confusing when the surgeon is not familiar with the manner in which the structure can be affected by this optical distortion.

Anatomical considerations: During the last two years a growing number of endoscopic operations were reported (13,17) and some new approaches were introduced (19). It was estimated that sinonasal anatomy located laterally to the middle turbinate is vital for sinonasal function. These structures should neither be traumatized nor disrupted during or after endoscopic pituitary surgery (13). Lateral to the middle turbinate is the uncinate process, behind which is a groove called the hiatus semilunaris. Along the posterorostral bank of the hiatus semilunaris is the ethmoidal bulla, which are anterior ethmoidal air cells. The maxillary sinus ostium is located at the caudal end of the hiatus semilunaris just lateral to the middle turbinate. Once the endoscopic endonasal pituitary operation is complete, the middle turbinate that was laterally displaced during the surgery must be placed back in its normal position so that it is kept away from the lateral wall. The nasal mucosa at the middle meatus between the middle turbinate and the lateral wall should not be traumatized during the operation because a postoperative adhesion at the middle meatus can cause sinonasal dysfunction function.

Since a bloodless operative field is required for endoscopy some attention must be paid to septal vascularisation. The posterior septal artery arises from the sphenopalatine branch of the internal maxillary artery and passes to the posterior nasal septum at the inferior medial aspect of the posterior middle turbinate. When surgical access is made between the middle turbinate and nasal septum for anterior sphenoidotomy, the posterior septal artery often needs to be coagulated and divided to prevent intraoperative or postoperative nasal bleeding. Delayed copious nasal bleeding after transsphenoidal surgery is often caused by rebleeding from this artery (13).

Eliminating the necessity of intraoperative fluoroscopy H-D. Jho and A. Alfieri (13) pointed out to some anatomical landmarks to follow during the procedure. The surgical trajectory to the sella via a patient's nostril is a few degrees off the midline. They approach through the contralateral nostril in patients who have an adenoma located laterally. However, the size of the nasal cavity dictated which nostril was to be used regardless of the laterality of the tumor. They postulated that the inferior margin of the middle turbinate is a consistent landmark leading to the floor of the sella rather than the sphenoidal ostium which is not always visible through the space between the middle turbinate and the nasal septum. The inferior margin of the middle turbinate leads to the sphenoidal sinus at approximately 1 cm below the floor of the sella. The surgeon's frequent reference to this anatomical landmark is very important for the precise placement of an anterior sphenoidotomy. An inadvertent rostral tilt of the surgical trajectory can easily occur with this endoscopic technique, leading to the anterior cranial fossa.

Evolution of surgical technique: The important steps toward the adoption of endonasal route were made without the use of a transsphenoidal retractor (11-17,20). Although a nostril is small, the space in the nasal cavity is ample when the retractor is not used. The working angle is extremely wide. The elimination of a transsphenoidal retractor not only allowed the use of surgical instruments more freely adjacent to the endoscope shaft but also provided easy access to the skull base from crista galli to the foramen magnum. H-D. Jho and A. Alfieri (13), P. Cappabianca et al., (17) have eliminated the topical use and the local infiltration of vasoconstrictors. They saw fewer nasal bleeding postoperatively when the use of vasoconstrictors was abandoned. Mucosal bleeding was meticulously controlled with electrocoagulation. This is an essential part of the procedure in order to make it easy and clean. The necessity of inserting and withdrawing surgical instruments must be reduced in order to minimize mucosal trauma at the nasal cavity. In earlier series (12,14-16), the sphenoidal mucosa was stripped completely and the sphenoidal sinus was packed with an abdominal fat graft, a gelatine sponge or an oxidized surgical sponge. This has evolved into a technique that minimizes disruption of the mucosal anatomy in the sphenoidal sinus. When an anterior sphenoidotomy is made at the bony anterior wall of the sphenoidal sinus, the mucosal opening is limited to the area of the anterior sphenoidotomy hole (13,17,20). In the sella, mucosal removal is limited to the anterior wall of the sella and the mucosa at the remaining sphenoidal sinus wall is kept intact as much as possible. At the end of the operation, every effort is made to maintain the sphenoidal sinus aerated without leaving behind any foreign material. When needed, sellar reconstruction is performed with an autogenous bone graft or titanium mesh at the anterior wall of the sella. This bony sellar reconstruction provides relatively firm support for the fat graft placed at the tumor resection cavity. It enhances water-tight closure and makes packing unnecessary, thus allowing the sphenoidal sinus to remain aerated. D. Moreland et al., in 2000 (20) described a variation, which they called "hemisphenoidotomy approach". Its key technical feature is that bone is removed from the sphenoid ostium to the middline rather than all the way to the contralateral ostium, until an opening approximately 1,5 cm by 1,5 cm is made. By taking advantage of the fact that the sphenoid septum is either absent or deviated in 75% of the cases (21), many patients with pituitary lesions confined to the sella can be considered candidates for the hemisphenoidotomy.

Concerning intrasellar stage of the operation the advantage of the endoscope is that it can be advanced into the empty pituitary fossa and rotated to determine the extent of tumor removal (8,10,12-17). This maneuver with 30° endoscope distinguishes this technique from the standard microscopic approach. It has proven to be essential for meticulous tumor removal. When the suprasellar portion of the tumor is fibrotic and solid and does not descend into the sellar cavity, further rostral exposure is made at the bony skull base of the tuberculum sellae or planum sphenoidale in order to directly access the tumor.

No nasal packing is necessary after completion of the operation, which is a great advantage over the standard microsurgical procedure.

Refinements of surgical instrumentation: In the field of endoscopic surgery, dedicated instruments are needed (22). There are some technical problems inherited in this new method (11): 1) there is less room for work; 2) a conflict between the surgeon's hands and the endoscope may easily arise; and 3) introduction of the instruments into the nostril during the sphenoid and sellar phases of the operation, when the endoscope is secured to an endoscope-holder for a stable view, carries a risk of possible damage to the nasal structures. According to P. Cappabianca et al. (11), ensuring a secure grip is necessary by means of quadrangular section of the handle and by positioning the barycenter of the instrument within the surgeon's hand to enhance the balance. For removal of the parasellar portion of the tumor under direct endoscopic view, a stirrup-like tip was designed for more aggresive curettage of the lateral wall of the sella. To address the second point, the handle was bent 10° to 30° horizontally to enable work with two instruments in the operative field, introduced parallel and tangential to the endoscope and working laterally, above or below it. Concerning the third point, two main solutions were adopted to lower the risk of damage to the nasal structures: elimination of the bayonet-like shape and hiding of the cutting tip in the handle and drawing it out by pressing the rear plunger.

The optics and video images of endoscopy have been continuously improved. Digital enhancing mechanisms have improved the clarity of monitored endoscopic images. Although a high-definition camera is available, it is not widely used yet. Endoscopic holders are available commercially in two different types, a hand-tightening mechanical holder and an one-button controlled pneumatic-powered holder. A lens-cleansing device was adopted in order to maintain clean endoscopic images during an operation. Recently, a frameless navigation has been applied to endoscopy in order to enhance intraoperative orientation and reduce potential complications (23).

Patient selection: The indications for endoscopic endonasal transsphenoidal surgery are identical to that of standard microsurgical approach. In recurrent and residual pituitary adenomas endoscopic surgery has some prominent advantages (17,24). The endonasal surgical stage is very fast because the sphenoid ostium has been already enlarged in the former operation. The wider anatomical orientation provided by the 30° endoscopes allows a safer progress in the sphenoid sinus, which minimizes the risk of damage to the carotid artery and other parasellar structures in a condition of mucosal rearrangement. In recurrent pituitary adenomas requiring reoperation, endoscopic approach has significant advantages during intrasellar phase as compared to microsurgery (17).

The referred authors gave no specific contraindications for the endoscopic technique.

Endoscopic method proved to be suitable also for treatment of cerebrospinal fluid leaks (25-27), endo- and infrasellar craniopharyngeomas (28,29) and clival chordomas (14).

After the review of the literature we can point out to some advantages and limits: The main advantages of this minimally invasive method are:

1. Wide-angled panoramic view of the sphenoidal sinus and the anatomical corners.

2. Easy accessibility to the skull base ranging from crista galli to foramen magnum.

3. Quick postoperative recovery with minimal postoperative discomfort and short hospital stays.

The main limitations are:

1. Two-dimensional view.

2. Requirement for bloodless operative field.

3. Quality and size of endoscopes and inadequacy of surgical instruments.

4. Steep learning curve.

CONCLUSION

The future of endoscopic endonasal surgery seems to be very promising. Presently, we are still limited by size and maneuverability of the endoscope and the instrumentation. Nevertheless, the endoscopic technology available today offers sufficient advantages for its use as a part of the neurosurgical armamentarium. We expect the modality to improve significantly in near future, which will allow removal of larger and deeper lesions through smaller less traumatic avenues than are currently attainable.

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