Making the Transition from Microsurgery to Endoscopic Trans-Sphenoidal Pituitary Neurosurgery

This article reviews the published experience of others and introduces the authors’ insights into the development of an endoscopic pituitary program. While initially challenging, this transition to endoscopic trans-sphenoidal pituitary surgery can yield rewards in the form of superior visualization and potentially more complete tumor resections. With increasing cumulative experience with the endoscopic transsphenoidal technique for pituitary surgery, the improved visualization and less steep learning curve will facilitate more widespread acceptance of endoscopic pituitary surgery as a valid alternative to the trans-septal trans-sphenoidal microscopic approach to pituitary tumors. If not a complete alternative, endoscopic-assisted pituitary surgery will also become more widespread, as endoscopy can easily supplement standard microscopic approaches to pituitary tumors. As transnasal endoscopic approaches to the skull base are increasingly refined in technology and skill, additional applications of this technology may permit skull base approaches through the planum sphenoidale and tuberculum sellae for the removal of giant suprasellar macroadenomas that may otherwise require an open craniotomy for surgical management. The collaboration between otolaryngologists and neurosurgeons is important for further developing successful endoscopic trans-sphenoidal pituitary surgery and improving care for patients. Objective evidence is needed to validate whether the improved visualization results in superior patient outcomes and reduced clinical complications, and if this technique can be reasonably taught in a controlled, supervised setting in residency training programs. Additional outcomes data are needed to evaluate long-term outcomes and define the boundaries of endoscopic trans-sphenoidal pituitary surgery.

Endoscopic technology has revolutionized surgical approaches to the paranasal sinuses and the skull base. Initially limited in its scope of applications, the accepted indications for the use of the endoscope to address various disease pathologies is increasingly being adopted and advocated by both skull base surgeons and patients. The evolution of endoscopic trans-sphenoidal pituitary surgery is the natural development and extension of endoscopic technology to the standard microscopic trans-sphenoidal approach to pituitary surgery.

While endoscopy provides some inherent advantages in its ability to visualize areas of the sella that are otherwise obscured in the microscopic approach, most neurosurgeons were trained to use the microscope for pituitary surgery, and adoption of endoscopic techniques has been limited to date. There are several potential reasons, including unfamiliarity with the equipment and view. At the authors’ institution, a punctuated transition from the traditional, endonasal microscopic technique to the two-surgeon, endonasal endoscopic technique occurred in early 2008. This article reviews the published experience of others plus introduce our insights into the development of an endoscopic pituitary program. While initially challenging, this transition to endoscopic trans-sphenoidal pituitary surgery can yield rewards in the form of superior visualization and potentially more complete tumor resections. The question of whether improved surgical outcomes and reduced complications will materialize will require a comparison of a large series of patients with long-term follow-up.

Trans-sphenoidal pituitary surgery

The intimate proximity of the pituitary gland to critical structures in this central location presents unique challenges in the surgical management of pituitary pathology. Victor Horsley is commonly credited with the first successful transcranial surgical management of a pituitary lesion in the late 1800s. Subsequently, Schloffer is noted to have reported the first trans-sphenoidal approach for tumor removal. Cushing introduced the trans-septal trans-sphenoidal procedure in 1910, and in his series reported difficulty with suprasellar extending tumors, poor illumination, and cerebrospinal fluid (CSF) leakage, which led to the abandonment of this approach by Cushing and his colleagues.

In the late 1950s, Guiot reintroduced this approach with the enhancement of intraoperative fluoroscopy, which permitted an improved ability to guide instruments to the sella and an improved ability to achieve total tumor resection. Hardy is credited with revolutionizing and re-establishing the trans-sphenoidal approach in the 1960s by combining intraoperative fluoroscopy with the use of the operative microscope. The introduction of the microscope to pituitary surgery introduced the modern era of trans-sphenoidal surgery, and the wide adoption of the trans-sphenoidal approach to pituitary lesions. Improving visualization with fluoroscopy and microscopy improved the safety and efficacy of pituitary surgery, which was refined over the subsequent 40 years.

The surgical technique with the microscopic approach is largely limited by the narrow corridor of the nasal speculum. The width of this corridor is a function of the approach, with the purely endonasal approach generally necessitating a narrower speculum compared with the traditional sublabial technique. The speculum creates a line-of-sight view of the sella. For intrasellar microadenomas, the surgeon is provided with complete visualization of the entire tumor with some degree of stereoscopic perspective. For larger macroadenomas, however, the field of view can be incomplete.

Because the surgeon may be unable to directly visualize the entire tumor, various blind resection techniques are used. Sweeping motions with various angled pituitary curettes can effectively deliver soft tumor tissue, particularly if aided by a descending diaphragma sella. There are situations, however, in which the probability of an incomplete resection increases. These include a limited sellar bony opening, particularly exacerbated by an incompletely pneumatized sphenoid sinus. Firm, rubbery tumors can be particularly challenging, especially if adherent to surrounding structures. In general, invasive tumors within the cavernous sinus have been considered off limits with the speculum-based, microscopic approach.

Endoscopic trans-sphenoidal pituitary surgery

Over the past decade, with the improvements in digital video, optics, light sources, and video monitors, endoscopic trans-sphenoidal pituitary surgery has emerged as an important innovation in pituitary surgery. To some, the endoscope is simply an alternative visualization device used instead of the microscope. In many cases, surgeons have opted to use the endoscope in lieu of the microscope, performing the operation in essentially an identical manner. Although angled-lens endoscopes may offer some added value to visualize residual tumor, a smaller sellar opening and exposure is a common limiting factor. In some cases, a hybrid endoscopic-assisted approach is used, essentially augmenting the view, but not the approach, to the sella. Some of the published series of endoscopic pituitary surgery use this limited approach. Whereas the surgical endoscope is an alternative visualization device relative to the microscope, its use allows a virtually completely different surgical approach for larger tumors.

Trans-sphenoidal endoscopic approaches range from:
Endoscopic-assisted surgery using a speculum;
Single-surgeon single-nostril endoscopy with limited sellar opening
Single-surgeon, single or dual nostril endoscopy with expanded exposure
Dual-surgeon, dual nostril expanded approach (so-called expanded, endoscopic endonasal approach, or EEEA ).

The authors adopted EEEA at their institution in early 2008.

The EEEA is a fundamentally different surgical approach compared with the traditional speculum-based transnasal trans-sphenoidal. In the authors’ experience, the removal of a pituitary tumor is more akin to removing a convexity meningioma. It is based on several key concepts. First is wide (expanded) exposure of the entire extent of the tumor involvement. For example, tumor involvement of the anterior cranial fossa requires removal of the tuberculum sella and possibly the planum sphenoidale, whereas wide exposure of the dura over the cavernous sinus is required for tumors involving that compartment. To do so, extensive drilling of the sphenoid sinus is often required, so much so that this technique is more invasive than other so-called minimally invasive techniques. Just as blind dissection is generally unacceptable with open craniotomy approaches to tumors, the same philosophy is applied to pituitary and other parasellar tumors.

A second concept relates to using routine microsurgical techniques, including bimanual manipulation and dissection of neurovascular structures and tumor tissue under direct visualization. The binostril approach allows more degrees of freedom compared with uninostril and endonasal speculum-based approaches. In addition, the endoscope allows the use of standard microsurgical instruments, including the Rhoton microdissectors (Codman, Raynham, MA, USA) and ultrasonic aspirators.

To maintain constant visualization of the area of dissection, the authors use the dual-surgeon technique ( Fig. 1 ). One surgeon holds the endoscope, constantly moving the endoscope to maintain the surgical field centered, as well as avoiding conflict with the instruments used by the surgeon removing the tumor. By using various angled endoscopes, areas not visualized by other approaches can be safely accessed. This improved visualization may enhance the identification of critical neurovascular structures, which may reduce the complications of pituitary surgery and may improve tumor resection by identifying residual tumor in the sella. Endoscopic trans-sphenoidal pituitary surgery also may reduce blood loss and improve operating time for difficult pituitary procedures. This may be due to the reduced injury to the nasal and septal mucosa, which may result in less bleeding. Hence, endoscopic trans-sphenoidal pituitary surgery may allow for access to the sella more quickly and smoothly, and provide enhanced visualization, particularly of the region near the sella turcica. Endoscopic trans-sphenoidal pituitary surgery also may reduce hospital stay, improve patient satisfaction, and decrease the need for postoperative nasal packing.

The expanded exposure does impose added complexity with regard to reconstruction, particularly with patients with intraoperative CSF leaks. With small sellar openings, it is generally easier to support and buttress fat grafts. The wide drilling of the skull base with EEEA surgeries can be extensive, and therefore it may not be possible to secure bone grafts (or other substitutes) to buttress the fat (or other material) grafts. This had led to the wide use of vascularized, nasoseptal flaps for reconstruction.

Finally, a rarely mentioned challenge with the use of endoscopes is the fact that blood, running down the endoscope shaft, can intermittently obscure the view. This requires frequent irrigation of the endoscope with saline. For surgeons accustomed to the continuous view afforded by the speculum and surgical microscope, this can be unnerving. For experienced endoscopic surgeons, this is not a serious issue. This issue should not be confused with the ability to control surgical bleeding. Although one might assume that surgical bleeding would be problematic using the endoscope, it is the authors’ experience that it is far easier to control and stop bleeding with the use of the dual-surgeon, endoscopic approach. The authors routinely enter the cavernous sinus using this technique; this area is actually much harder to control using a speculum and microscope due to the fact it is not generally in the surgical field of view.

Making the Transition from the Microscope to the Endoscope

An early study by Stankiewicz initially suggested a steep learning curve to endoscopic surgery with a higher complication rate for less experienced surgeons. His experience suggests a learning curve of approximately 90 cases. Other studies also suggest a similar number for the learning curve for standardization of this novel approach and for gaining ease and familiarity with endoscopic trans-sphenoidal surgery.

More recently, Sonnenburg and colleagues reported their series of the first 45 minimally invasive pituitary cases done at the University of North Carolina by both otolaryngology and neurosurgery in joint cases. In their series, they reported an overall CSF leak rate of approximately 4% and suggested that there is not a steep learning curve to minimally invasive pituitary surgery with the collaboration between otolaryngology and neurosurgery at an academic medical center. In another retrospective analysis of the otolaryngology experience for the endoscopic trans-sphenoidal learning curve, Marks also suggested that the learning curve is not steep and that significant advancement on this curve can be achieved during residency training. Other recent reports additionally have suggested that the learning curve to endoscopic surgery is not a steep one and that significant advancement on this curve can occur during a rigorous residency training program.

Kabil and colleagues reported on their retrospective analysis of endoscopic and trans-septal approaches to pituitary surgery. In their experience, they suggested that the enhanced visualization of the endoscope improves the ability to differentiate normal pituitary from tumor tissue and also permits exceptional visualization of the suprasellar and parasellar regions of pituitary tumor extension. Their series of 300 endoscopic trans-sphenoidal pituitary surgeries reported a CSF leak of less than 2% with improvement as the surgeon advances along the learning curve. Furthermore, their large retrospective analysis suggested that it may be possible to improve tumor resection and reduce complication rates using the enhanced visualization of endoscopy to trans-sphenoidal pituitary surgery. Another recent report by Jarrahy and colleagues in a small series of consecutive patients also suggested that tumor fragments that can only be identified endoscopically may be present in over one-third of pituitary tumor cases. In a recent large cohort, Cappabianca and colleagues reported their postoperative complications in a series of 146 consecutive cases of endoscopic trans-sphenoidal surgery for pituitary adenomas. Their CSF leak rate was only 2%, and their morbidity and mortality rate was comparable to modern microscopic trans-sphenoidal results.

A recent systematic review of the reported literature on endoscopic trans-sphenoidal pituitary surgery indicates that over 800 patients have now been treated with endoscopic trans-sphenoidal approaches with little morbidity and even less mortality. The overall rate of CSF leak was 6% (the most common complication), and the mortality rate was 0.2% in this data analysis. This large analysis of a pooled cohort of patients suggests that endoscopic trans-sphenoidal pituitary surgery can be performed safely with minimal complications and almost no mortality. In comparison to traditionally reported results from trans-sphenoidal surgery, this meta-analysis suggests that endoscopic trans-sphenoidal surgery is similar in effectiveness and risk as traditional approaches to pituitary surgery. It has been suggested that outcomes with endoscopic trans-sphenoidal pituitary surgery may improve as it becomes widely adopted and neurosurgeons advance along the learning curve and aggregate cumulative experience over time. Among limitations of the literature reporting on endoscopic trans-sphenoidal pituitary surgery are the limited long-term results, as this approach has only been widely employed for the past decade.

Over the past 2 years, the authors have successfully made the transition from microscopic to fully endoscopic pituitary surgery at their institution, having performed over 180 operations in this time. The authors’ ability to adopt this approach was facilitated by the fact that both surgeons (MB, MBW) were already adept and highly experienced with endoscopic operations. As such, there was virtually no learning curve with respect to the use of an endoscope.

What was required in the authors’ case was formal training in the EEEA technique, which they acquired over an intense 4-day hands-on course. Understanding the unique surgical anatomy, surgical techniques, and teamwork training were key to the authors’ successful transition. In the authors’ opinion, it is not a procedure that should be casually adopted. It requires a dedicated team, including surgical nurses and ancillary personnel familiar with the equipment and procedure.

For their team, the authors incorporated an experienced rhinologic surgeon (MBW) in these cases. Although not necessary for the surgical approach for many routine cases, the rhinologic surgeon can be invaluable for complex or repeat operations. Because the seamless dual-surgeon teamwork is most important for these difficult cases, the authors use the dual-surgeon technique for all cases. Preoperative discussion of the sinonasal sequelae of the surgery by the rhinologic surgeon is also helpful in preparing patients for expectations during the recovery period. Furthermore, they can provide the optimal postoperative care with outpatient endoscopic nasal lavages and surveillance.

One of the suggested disadvantages of the endoscopic approach to the sella is a monocular view instead of the binocular view neurosurgeons have become accustomed to, particularly among neurosurgeons who have received minimal training in the use of the endoscope. These limitations, however, are mitigated with improving endoscope technologies, significantly larger high-definition visualization video screens, and the increasing incorporation of endoscopic training in neurosurgery residencies. Dynamic interaction between the left- and right-handed instruments and coordinated movement of the endoscope give the surgeon visual and tactile clues that help to compensate for the monocular view. The authors have found that a significantly large (50 in or greater size) high-definition screen ( Fig. 2 ) can be immersive in its visualization, and can mitigate many of the problems caused by the monocular view provided by the endoscope. The extra space that endoscopic videos and monitors used to take now can be minimized by flat screen high definition visualization technology. Furthermore, digital imaging improvements with dual chips at the tip of the endoscope may permit three-dimensional visualization with technological advancement. Lastly, as the value of endoscopic techniques becomes more apparent, the use of the endoscope during residency training may also improve, and eventually begin to incorporate virtual reality surgery training similar to what pilots use for virtual reality flight simulators in their training.

Endoscopic trans-sphenoidal pituitary surgery

Over the past decade, with the improvements in digital video, optics, light sources, and video monitors, endoscopic trans-sphenoidal pituitary surgery has emerged as an important innovation in pituitary surgery. To some, the endoscope is simply an alternative visualization device used instead of the microscope. In many cases, surgeons have opted to use the endoscope in lieu of the microscope, performing the operation in essentially an identical manner. Although angled-lens endoscopes may offer some added value to visualize residual tumor, a smaller sellar opening and exposure is a common limiting factor. In some cases, a hybrid endoscopic-assisted approach is used, essentially augmenting the view, but not the approach, to the sella. Some of the published series of endoscopic pituitary surgery use this limited approach. Whereas the surgical endoscope is an alternative visualization device relative to the microscope, its use allows a virtually completely different surgical approach for larger tumors.

Trans-sphenoidal endoscopic approaches range from:
Endoscopic-assisted surgery using a speculum;
Single-surgeon single-nostril endoscopy with limited sellar opening
Single-surgeon, single or dual nostril endoscopy with expanded exposure
Dual-surgeon, dual nostril expanded approach (so-called expanded, endoscopic endonasal approach, or EEEA ).

The authors adopted EEEA at their institution in early 2008.

The EEEA is a fundamentally different surgical approach compared with the traditional speculum-based transnasal trans-sphenoidal. In the authors’ experience, the removal of a pituitary tumor is more akin to removing a convexity meningioma. It is based on several key concepts. First is wide (expanded) exposure of the entire extent of the tumor involvement. For example, tumor involvement of the anterior cranial fossa requires removal of the tuberculum sella and possibly the planum sphenoidale, whereas wide exposure of the dura over the cavernous sinus is required for tumors involving that compartment. To do so, extensive drilling of the sphenoid sinus is often required, so much so that this technique is more invasive than other so-called minimally invasive techniques. Just as blind dissection is generally unacceptable with open craniotomy approaches to tumors, the same philosophy is applied to pituitary and other parasellar tumors.

A second concept relates to using routine microsurgical techniques, including bimanual manipulation and dissection of neurovascular structures and tumor tissue under direct visualization. The binostril approach allows more degrees of freedom compared with uninostril and endonasal speculum-based approaches. In addition, the endoscope allows the use of standard microsurgical instruments, including the Rhoton microdissectors (Codman, Raynham, MA, USA) and ultrasonic aspirators.

To maintain constant visualization of the area of dissection, the authors use the dual-surgeon technique ( Fig. 1 ). One surgeon holds the endoscope, constantly moving the endoscope to maintain the surgical field centered, as well as avoiding conflict with the instruments used by the surgeon removing the tumor. By using various angled endoscopes, areas not visualized by other approaches can be safely accessed. This improved visualization may enhance the identification of critical neurovascular structures, which may reduce the complications of pituitary surgery and may improve tumor resection by identifying residual tumor in the sella. Endoscopic trans-sphenoidal pituitary surgery also may reduce blood loss and improve operating time for difficult pituitary procedures. This may be due to the reduced injury to the nasal and septal mucosa, which may result in less bleeding. Hence, endoscopic trans-sphenoidal pituitary surgery may allow for access to the sella more quickly and smoothly, and provide enhanced visualization, particularly of the region near the sella turcica. Endoscopic trans-sphenoidal pituitary surgery also may reduce hospital stay, improve patient satisfaction, and decrease the need for postoperative nasal packing.