Unilateral Endoscopic Endonasal Transsphenoidal Approach For Sellar Tumor: Anatomical And Clinical Study

The transsphenoidal approach for the resection of pituitary tumor was originally used by Cushing in early twenties centuries, however, he later abandoned it in favor of craniotomy. The lack of sufficient magnification and illumination was the major impediment to successful treatment of pituitary tumors via the deep and narrow transsphenoidal approach. After development of operating microscope, Guiot and Hardy were credited for their contribution to the modernization and improvement of the technique, which made it a safe and feasible procedure.During the past century, brain surgery has witnessed the search for less traumatic procedures. Almost all of the surgical approaches were revived again and again followed each evolution of modern techniques. The beginning of the utilization of the endoscope in transsphenoidal surgery has encouraged the attempts of neurosurgeons to make the transsphenoidal approach even more minimally invasive. The first to use the microscope assisted by endoscope in a transsphenoidal approach was Guiot in 1963.Since that time, the endoscope played more and more important role in this procedure. The initial purpose was to overcome the intrinsic limit of microscope, that is, the observation of the so-called blind area undermicroscope. But later, "pure" endoscopic endonasal transsphenoidal approach was introduced by several neurosurgeons, thanks to the rapid development of endoscopic techniques including better illumination, more slender endoscope and more delicate instruments.The popularization of endoscopic technique is due to its minimal invasiveness and panoramic view, especially the blind area surrounding the surgical corridor encountered in conventional microsurgery, can be easily seen under endoscope with different angled lens.Up to now, we can not yet to draw a conclusion that the endoscopic endonasal transphenoidal approach is better than any other transsphenoidal approach, because there are no sufficient data from the literature to compare the results using different transsphenoidal approaches. But the endoscopic endonasal transsphenoidal approach fulfills the principles of the minimal invasive neurosurgery, and certainly will be another milestone in the treatment of sellar tumors.To perform a successful endoscopic endonasal transsphenoidal approach, the surgeon's familiarity with sinonasal endoscopic anatomy is very important. It is vital not only to rapid and uneventful exposure of the lesion, but also to minimal iatrogenic injury to sinonasal and juxtasellar structures. Their iatrogenic injury may lead to serious postoperative nasal and/or intracranial complication. These lead us to study the anatomical landmarks useful in this approach in detail.For many years, neurosurgeons emphasized that confirmation of the sphenoidal ostium is one of the key point in transsphenoidal approach. The majority of neurosurgeons hold the belief that the search for sphenoidal ostium is crucial to locate the opening site of the anterior wall of sphenoid sinus. Although the osteal sphenoidal ostium can be as large as lcm in diameter, the mucosal sphenoidal ostium is much smaller, usually 2~3cm in diameter. If the patient has sinonasal disease, suchas chronic infection in nasal cavity or sphenoid sinus, turbinate hypertrophy, etc, the sphenoidal ostium can be very hard to find intraoperatively, which demand that the surgeon should know how to locate the anterior wall of sphenoid sinus according to more anatomical landmarks. Additionally, using the current standard endonasal transsphenoidal approach, it's difficult to totally remove the sellar tumor with growth outside the sellar and suprasellar region, like the planum sphenoidale, parasellar and retrosellar region. Therefore, familiarity with the endoscopic anatomy surrounding the pituitary fossa and modification of the standard approach according to the growth pattern of the tumor, are crucial for successful endoscopic operation.Objectives:1 Endoscopic anatomy countered in the unilateral endoscopic endonasal transsphenoidal approach was studied to discuss the identification of anatomical landmarks during the procedure, the verification of anterior wall of sphenoid sinus, how to minimize the iatrogenic injury, and the extent of bone exposure of the sellar region according to the different growth patterns of sellar tumors.2 The unilateral endoscopic endonasal transsphenoidal approach was used in 32 patient harboring pituitary adenoma. The clinical record and the results were summarized to present our experience of how to protect the nasal structures and identify the anterior wall of sphenoid sinus. The postoperative complications and the strategy of their prevention and treatment were also discussed.Methods:1 Fifteen adult cadaveric heads were used in anatomical study. Ten heads were fixed by 10% formalin, and five heads were not fixed and were perfused with red silicone in the artery and glass glue in the vein. Ragid endoscope with 30-degree angled lens was introduced in the nasal cavity and the middleturbinate was identified. The position, shape and size of the sphenoidal ostium was inspected and the morphological characteristics of the anterior wall of sphenoid sinus above and below the sphenoidal ostium was observed. The distance between the inferior margin of middle turbinate posterior part and the center of sellar floor was measured. In those that the sphenoidal ostium could not be found, the pharyngopalatine arch was located firstly in the posterior inferior nasal meatus, then the mucosa lateral to nasal septum was incised vertically centered 1.5cm above the pharyngopalatine arch. The mucosa was dissected laterally to expose the osteal sphenoidal ostium. After opening of the anterior wall of sphenoid sinus, the septum within the sinus was removed. The morphological features of sellar floor and the wall of sinus was observed. The sellar floor was opened partially or in standard extent to observe the intrasellar and suprasellar structures. In the study of the modified enlarged endoscopic endonasal transsphenoidal approach, the bone removal was enlarged anteriorly to include the tuberculum sellae. Laterally, the cavernous sinus and its content were exposed. Posteriorly, the upper portion of clivus was removed and the retrosellar structures were exposed. The extent of exposure in different modified enlarged endoscopic endonasal transsphenoidal approach were observed endoscopically. The thickness of sellar floor was measured. Finally, the contra-lateral side of nasal cavity was fully exposed by remove the superficial nasofacial structures to facilitate the macroscopical observation and measurement of the sphenoid sinus, anterior wall of sphenoid sinus, and the distance between the inferior border of the sphenoidal ostium and the pharyngopalatine arch, the angle between nasal septu and the anterior wall of sphenoid sinus was modeled with lead wire and measured. 32 patients, 14 man and 18 women, harboring pituitary adenoma was includedin the clinical study. All the patients underwent the CT and MRI examination. After general endotracheal anesthesia is administered, the endoscope was introduced into the nasal cavity. The sphenoidal ostium was inspected for verification of the site where the initial opening of the anterior wall of sphenoid sinus was located. But if any difficulty, we directly incised the nasal mucosa of the septum vertically centered at the expected level of the sphenoidal ostium. The nasal mucosa is dissected bilaterally to exposed the bony ostium of sphenoid sinus. The upper limit of the opening of anterior wall of sphenoid sinus should not beyond the sphenoidal ostium, and the lower limit should not below a line lcm above the pharyngopalatine arch. After the confirmation of midline position, the sellar floor was opened. The tumor was removed piece by piece under the endoscopic control. The tumor bed was inspected endoscopically for residual tumor, especially the suprasellar and parasellar region. The tumor bed was packed with Surgicel or Gelfoam. Whether the sellar floor need reconstruction and how to accomplish it depend on the presence of cerebrospinal fluid leak and the site of the leakage. When the operation is completed, the displaced mucosa was repositioned. The surgical corridor was packed with iodoform strings without impediment of inferior nasal meatus. The diagnosis was confirmed histologically and all patients underwent followup. 3 The surgical results were summarized and the relative literatures were reviewed. The surgical complications and their prevention were analyzed.Results:1 The structure within the nasal cavity can be well visualized endoscopically. The sphenoidal ostium can be found in the sphenoidoethmoid recess between the upper and middle turbinate lateral to the nasal septum in most of the cases. In cases with difficulty to locate the sphenoidal ostium, the anterior wall ofsphenoid sinus can be easily located with reference to surrounding structures. It is feasible to locate the opening site on the anterior wall of sphenoid sinus first, then to locate the osteal sphenoidal ostium after dissection of overlieing mucosa. The upper limit of the opening of anterior wall of sphenoid sinus should not beyond the sphenoidal ostium to avoid subsequent opening of tuberculum sellae and planum sphenoidale. The lower limit of the opening of anterior wall of sphenoid sinus should not below a line lcm above the pharyngopalatine arch to avoid injury to sphenoidopalatine artery and clivus.2 The lateral wall of the sphenoid sinus is high risk area due to the adjacent to the optic nerve, internal carotid artery, and cavernous sinus. The boundary of sellar floor can be identified by its arched prominence and the surrounded osteal protuberance and recess. With half opening of the sellar floor, the intrasellar pituitary gland can be well visualized, but not the suprasellar and parasellar structures. With full opening of the sellar floor and removal of pituitary gland, the pituitary stalk and and superior pituitary artery are well exposed. After the diaphragm sellae is incised, the suprasellar and parasellar structures can be exposed. When the tuberculum sellae was removed, the optic chiasm, optic nerve, anterior cerebral artery, anterior communicating artery, etc, are brought into view. If the bone window is extended laterally, the cavernous sinus and its content can be exposed. And if the bone window is extended postero-inferiorly to the upper clivus, the structures within interpeduncular and prepontine cistern and the brain stem can be seen.3 In this series, total tumor removal was achieved in 24, subtotal in 6, partial in 2. the followup results revealed gradual improvement of preoperative symptom in all cases. There is no mortality. Cerebrospinal fluid leak occurs in 2 patients and the delayed nasal bleeding from the mucosa in 2,and inflammation of phenoidsinus in 3. Twelve patients experienced temporary diabetes incipidus and 1 patient developed hyperthermia and fluid electrolyte disturbance in the early postoperative period.Conclusions:1 The sphenoidal ostium is an important landmark of the anterior inferior wall of sphenoid sinus. When it is difficult to locate the sphenoidal ostium, the opening site can be located by the peculiar oval protuberance of the anterior wall of sphenoid sinus, the relationship between the anterior wall of sphenoid sinus and the middle turbinate, and the average distance from the superior limit of pharyngopalatine arch to the sphenoidal ostium.2 The lateral wall of sphenoid sinus is high risk area which need particular attention during the opening of sellar floor. The location of septum in the sphenoid sinus varies and can not be used as midline. The vomer has midline position and can be used as landmark of midline.3 The standard sellar floor opening provide an excellent endoscopic visualization of the intrasellar, suprasellar and parasellar structure. It can be used in most sellar tumor with confined within the pituitary fossa with or without suprasellar extension. When the tumor has extrasellar portion, like the planum sphenoidale, the modified enlarged approach.can be the choice.4 Preservation of the nasal structure is vital for success of this procedure. The mucosa of nasal septum is incised vertically and dissected laterally. When the operation is completed, the mucosa can be repositioned which preserve the natural nasal structure. It leads to less postoperative nasal complication. Whether the sellar floor need reconstruction and how to accomplish it depend on the presence of cerebrospinal fluid leak and the site of the leakage. The postoperative package of the nasal meatus can be confined to the middle nasalmeatus to preserve the patency of inferior nasal meatus.5 The endoscopic endonasal transsphenoid approach has pros and cons. The minimal invasiveness, good surgical results and the panoramic vision make it an excellent approach for sellar tumor resection. But the neurosurgeon must overcome some limits of the procedure, such as two-dimensional vision, small space for manipulation, and the difficulty in coagulation.