The evolution of minimally invasive techniques in pituitary surgery
By Reza Jarrahy, M.D., Hrayr K. Shahinian, M.D.
Surgical approaches to the pituitary gland have become progressively less invasive over the past century. Advances in medical technology have facilitated this trend. This review discusses the evolution of pituitary surgery from open transcranial techniques to the recently described fully endoscopic transnasal procedure.
The purpose of this paper is to review the progress in pituitary surgery that has been made over the past century and to report on the most recent landmark in that progress, the introduction of the fully endoscopic transnasal approach to the pituitary gland.
Summary Background Data
The evolution of pituitary surgery during the last century is characterized by the development of progressively less invasive approaches to the pituitary gland that have been facilitated by simultaneous advances in medical technology. Once performed via an open transcranial operation involving prolonged brain retraction, resection of pituitary tumors can now be performed via a direct transnasal approach under entirely endoscopic imaging.
We have reviewed the relevant historical and clinical literature dating to the turn of the 20th century describing the progression from Cushing's open transcranial technique, to the microscopic transseptal transsphenoidal approach, to the recently described fully endoscopic transnasal method. Published series of patients who received transseptal transsphenoidal surgery were retrospectively reviewed and outcomes were compared to results from trials of endoscopic pituitary surgery.
Endoscopic pituitary surgery compares favorably to transseptal surgery in terms of surgical success and complication rates. The transnasal approach eliminates some of the risks seen in the transseptal technique that are attributable to intraoral and nasal dissection.
Once characterized by open transcranial procedures, surgical management of pituitary disease can now be performed via a minimally invasive endoscopic procedure. The rigid endoscope emerged as a tool that obviates unnecessary invasiveness without compromising surgical success.
The development of pituitary surgery over the past century is largely credited to the pioneering work of Harvey Cushing in the early 1900s.1,2 Cushing accumulated an extensive experience with both transseptal transsphenoidal and transcranial approaches to the pituitary gland, but ultimately came to favor the transcranial technique. He believed the direct and wide exposure of the gland from a suprasellar perspective was paramount to effective surgical management of pituitary disease.2-5 A number of Cushing's contemporaries, however, argued that transsphenoidal exposure of the gland allowed for thorough resection of tumor via a less invasive procedure, making it the technique of choice in pituitary surgery.
This fundamental debate lasted for decades until the introduction of intraoperative fluoroscopy and microscopy effectively put it to rest. With these new imaging techniques, adequate exposure and thorough exploration of the sella turcica became possible without the need for a large frontal craniotomy or prolonged brain retraction. As a result, the transseptal transsphenoidal approach came to be accepted as the procedure of choice for the surgical management of most pituitary lesions. Transcranial techniques came to be reserved for use in the resection of tumors with extensive invasion into the anterior and middle cranial cavities. Indications for microscopic transseptal transsphenoidal and transcranial pituitary surgery have subsequently remained relatively well defined for several decades.
Recently, however, discussions regarding the most effective and least invasive way to perform pituitary surgery have been renewed. Developments in the field of sinus endoscopy6-10 originally prompted surgeons to attempt endoscope-assisted surgery of the pituitary gland via the traditional transseptal approach.9,11-17 Observations regarding the advantages offered by endoscopic imaging of intra- and parasellar structures has culminated in recent descriptions of a fully endoscopic technique for pituitary surgery via a direct transnasal approach to the sphenoid sinus.18-22 This procedure is proving to be equally if not more effective than microscopy as the primary imaging modality in the resection of pituitary adenomas and other pathological lesions in this region. In this paper we review the specific surgical techniques associated with the transcranial, microscopic transseptal, and endoscopic transnasal approaches to pituitary surgery and discuss the indications and advantages associated with each.
Transcranial surgery of the pituitary gland
The majority of pituitary tumors, including those with parasellar and suprasellar extensions, can be successfully treated by microscopic transseptal or endoscopic transnasal approaches to the sella.23-25 These techniques are less invasive, less timely, and associated with fewer complications than transcranial surgery. They provide adequate exposure of the gland, even when tumor extends beyond the boundaries of the hypophyseal fossa. When tumor extension into the anterior or middle cranial fossae is significant, however, approaches from below can only provide limited access to the lesion. In such cases, the transcranial techniques offer a greater chance of complete or near-complete tumor removal. There are two major variations upon the transcranial technique that remain in popular use for the resection of pituitary tumors with extensive suprasellar and parasellar extension: the midline subfrontal approach and the oblique subfrontal approach.
Often a transcranial method is reserved for the second stage of a two-stage operation.23,25 The primary procedure is performed via microscopic or endoscopic exposure of the sella turcica, during which the bulk of the tumor is removed transsphenoidally. Residual extrasellar tumor is then resected in a subsequent transcranial operation.
The patient is placed supine on the operating room table and the head of the bed is raised approximately 15 degrees. The position of the patient's head is determined by using the floor of the anterior cranial fossa as a guide to the surgical landmarks of the suprasellar area. The surgeon's perspective of the anatomical relationships between the circle of Willis, optic nerves, optic chiasm, and hypophyseal stalk will vary with the degree of head rotation.
Midline subfrontal approach
The midline subfrontal approach remains the most common method for transcranial pituitary surgery, as it affords a direct exposure of the optic nerves and carotid arteries while providing ready access to the pituitary stalk.25 An incision is made in the scalp on the side of greatest tumor involvement and carried down to bone. A large frontal craniotomy is performed and the frontal lobe is retracted to expose the floor of the anterior fossa. Brain retraction must be kept to a minimum, as postoperative swelling of the frontal lobe can be problematic.25,27,28 Avulsion of the olfactory nerve, which may result in postoperative anosmia, is also a significant risk. 23,29,30
Dissection is carried out in the midline, proceeding posteriorly along the cribriform plate. Once the optic nerve is seen emerging from the optic canal it is fully exposed and used to help dissect the optic chiasm and the contralateral optic nerve. The anatomy of the anterior circle of Willis is also defined in this dissection. Once the neurovascular anatomy is fully detailed, the surgeon can work around the relevant structures to remove tumor from the sella using an assortment of dissecting ring curettes. 25,31-33
In the case of a prefixed chiasm or large tuberculum sellae, direct access to the sella is impeded. If so, the tuberculum may be removed or drilled to gain entry into the sphenoid sinus below.32 The anterior wall of the sella is then removed and resection of tumor progresses. A fat graft may be placed within the space of the sinus after tumor resection is complete.
Following tumor resection, the frontal lobes are released and the dura is reapproximated in a watertight closure. If the frontal sinus is compromised during the initial craniotomy, it is cranialized prior to replacement of the bone flap and reapproximation of the soft tissues of the scalp. The patient is monitored in the intensive care unit for potential sequelae specific to pituitary surgery (diabetes insipidus, visual field deficits, etc.) as well as signs that are suggestive of frontal lobe edema.
Oblique subfrontal approach
The extracranial steps of the oblique subfrontal approach are identical to those described above. However, dissection proceeds along the floor of the anterior fossa at an angle to the midline, in order to allow less aggressive retraction of the frontal lobe and minimize the risk of damage to the olfactory tract.32 Unfortunately, this approach yields incomplete access to the sella turcica, especially on the contralateral side. Thorough tumor removal is therefore more difficult. In addition, the surgeon is forced to work over the optic nerves, increasing the likelihood of a major complication. The beneficial decrease in frontal lobe retraction that this procedure offers must be carefully weighed against the added risks to the regional neurovascular structures that are associated with it and the more limited exposure it provides.
General outcome data from transcranial pituitary surgery is difficult to summarize. Reported results vary according to the specific techniques employed and the parameters used to determine surgical success. These usually focus on postoperative normalization of endocrinological profiles and restitution of visual field deficits.23,40,41
Transseptal transsphenoidal microsurgical pituitary surgery
The traditional transseptal transsphenoidal approach is indicated in the surgical management of pituitary tumors causing hypo- or hyperfunction of the gland that are refractory to medical management. Patients may initially present with endocrinopathies, visual field deficits, or cranial nerve palsies. Visual or cranial nerve symptoms signal involvement of the visual apparatus or the cavernous sinus and indicate an urgent need for decompression of the sella.
Most micro- and macroadenomas are amenable to resection by this method, including those with mild supra- and parasellar extension.1,42-46 Patients with extensive extrasellar involvement are candidates for two-stage procedures. In these cases, a primary transsphenoidal procedure serves to debulk as much of the tumor as possible from below, while a secondary operation via one of the aforementioned transcranial approaches allows resection of tumor remnants from above.23,26,47-49
Patient positioning and operating room setup
The patient is placed supine on the operating room table and following the induction of general anesthesia, an absorbent sponge is passed into the posterior oropharynx to collect blood and mucous secretions that collect intraoperatively.
The head of the bed is raised to make a twenty-degree angle with the floor and the neck is extended while the head is rotated approximately fifteen degrees toward the surgeon. The patient's head is then fixed in place with a carbon horseshoe three-pin clamp. In this position, with the microscope in place, the surgeon will be operating along a direct anteroposterior axis toward the pituitary gland.47 The fluoroscopic image intensifier is positioned so that the beam is perpendicular to a sagittal plane through the sella turcica. The contours of the sphenoid sinus and sella turcica must occupy the center of the monitor, which is placed over the patient's right shoulder. An aqueous antibacterial solution is applied to the nares, nose, face, and the upper gingival mucosa. The face is draped so that only the nose and upper lip remain uncovered.
The upper gums are infiltrated with a solution of 1% lidocaine containing epinephrine (1:100,000). This maneuver both lifts the buccal mucosa off of the premaxilla and limits the amount of intraoperative bleeding from the oral incision site. A site on the lower right quadrant of the abdomen is also prepared with antibiotic scrub solution and draped with sterile towels. A fat graft is harvested from this site during the procedure. It is used to pack the sella and sphenoid sinus following extirpation of the tumor. An alternative site for fat harvesting is the periumbilicus, where the resultant scar is more discrete. The lateral thigh may also be used by surgeons who prefer muscle and fascia as graft substrates.50
While an assistant retracts the upper lip, an incision is made in the upper buccal sulcus between the molar roots. (Appropriate placement of the incision is extremely important. Enough soft tissue must be left above the teeth to allow for closure. However, if the incision is made too high, scar contracture may lead to complaints of lip tightness and changes in the aesthetic appearance of the teeth and gums during smiling.) This incision is carried down to the periosteum of the premaxilla and the soft tissues are elevated from the bone to reveal the anterior nasal spine centrally and the pyriform apertures bilaterally.
Intranasal dissection, including elevation of mucoperichondrial and mucoperiosteal flaps, separation and retraction of the nasal septum from its base, and removal of the perpendicular plate of the ethmoid bone, results in a large "tunnel" through which the remainder of the procedure is conducted. An adjustable bivalve retractor is placed into this tunnel. Its blades are advanced to the sphenoid bone and are positioned so that they retract the mucosal flaps off of its surface. Excessive retraction of the blades should be avoided, as fractures to the bony nasal walls, the pyriform apertures, the pterygoid plates, or the palate may result.
Using the sphenoid ostia as reference points, the anterior wall of the sphenoid sinus is resected. Although subsequent examination of the sella is dependent upon this exposure, caution must be used at the lateral boundaries of the sphenoid where the carotid arteries ascend. Additionally, superior dissection must be guarded: injury to the cribriform plate increases the likelihood of a subsequent cerebrospinal fluid leak.51,52 Once the sphenoid is completely exposed, its mucosal lining is stripped to minimize the risk of postoperative mucocele.35 The posterior wall of the sinus, which makes up the floor of the sella turcica, is immediately recognizable. With benign adenomas the floor of the sella is intact. However, it may be thinned, fractured, or even completely obliterated by expanding tumor.35,47 If the floor is indeed intact, it is carefully fractured and resected to provide access to the pituitary gland. Again, serious consideration must be given to the limits of this dissection so as not to disturb the carotid arteries and cavernous sinuses laterally and the optic nerves and chiasm superiorly.35
Deep to the floor of the sella is the dura, identifiable by its pale azure hue. A sharp hook or blade is used to make a cruciate incision in the dura; through this incision ring curettes of different diameters and spatial orientation are introduced to resect the tumor. Suprasellar extensions of a macroadenoma will naturally descend into the sella turcica as the tumor is removed through the sphenoid sinus.1,45,47 This may be facilitated by Valsalva maneuvers conducted by the anesthesiologist, which transiently raise intracranial pressure and cause inferior displacement of the mass. Parasellar extensions of pituitary tumors, however, are more difficult to manage, as the lateral margins of the microscopic field of view are limited. The locations of dissecting curettes placed into the supra- and parasellar spaces can be confirmed fluoroscopically.1 Due to the proximity of the optic nerves, optic chiasm, carotid arteries, and cavernous sinuses to the sella, blind removal of any tumor remnants extending beyond the limits of the sella is potentially catastrophic. Similarly, trauma to the arachnoid membrane increases the risk of damage to neural structures and of postoperative cerebrospinal fluid leak.45 As the sella is emptied of tumor, the boundaries of normal gland are identified. Resection is carried out until all grossly identifiable parts of the lesion are removed.
While the surgeon is conducting a final survey of the operative site for any remaining fragments of tumor, an assistant harvests a fat graft from the abdomen or a graft of muscle and fascia from the lateral thigh. There are several models of graft design;46,53-57 each has as a common goal prevention of subsequent leakage of cerebrospinal fluid. In most cases a simple fat graft that plugs the hole in the floor of the sella and obliterates the space of the sphenoid sinus suffices.45 The graft is held in place by a fibrin-based sealant.
With the fat graft in place, the retractor is removed, the septum and mucosal flaps are repositioned, and the gingival incision is reapproximated using absorbable sutures. Both nostrils are packed with Vaseline-impregnated gauze strips. This packing remains in place for up to 48 hours postoperatively, absorbing any draining fluid and providing structural support to the nose as it heals internally.
Outcomes of microscopic transsphenoidal pituitary surgery are measured along several lines, including completeness of tumor removal, correction of visual deficits, restoration of normal hormonal profiles, surgical complications, and recurrence of disease.
Mortality from this procedure is low, generally occurring at a rate of less than 1 percent.53,54,58 The most commonly observed morbidity is cerebrospinal fluid (csf) leak, occurring in approximately 1-3 percent of patients.46,53,54,59 When tumor involves the diaphragma sellae it should be included in the margins of resection; doing so increases the likelihood of a csf leak. In cases where brisk flow of csf is observed following removal of the diaphragma, adequate packing of the sphenoid sinus at the end of the procedure is important. Persistent csf leaks may be treated by placement of a lumbar drain45,46,54 or by re-exploration of the sphenoid and sella.9,50,53
The next most common type of complication is related to glandular injury. Damage to the posterior lobe results in diabetes insipidus of either a transient or permanent nature.46,54,57 Administration of desmopressin acetate (DDAVP) is the indicated treatment. Treatment of postoperative anterior pituitary failure with hormone replacement therapy depends upon the pituitary deficiencies that are observed, but in the majority of cases requires perioperative exogenous steroid delivery.54,57
Complications attributable to the oronasal component of the technique, including aesthetic changes in nasal tip projection, lip contracture, septal perforation, increased nasal airway resistance, and upper lip numbness, occur with varying frequency.54,60-62
Outcome measures used to evaluate surgical efficacy most commonly include clinical parameters such as improvement in preoperative visual deficits and improvement in endocrine function. On average, visual disturbances are improved in approximately 80 percent of cases.46,53,58 Reported rates of normalization of endocrine function vary widely, ranging from 50 to 90 percent depending upon tumor size and histology, the hormonal parameters studied, and the criteria used in analysis.42,46,53,58,59
Fully endoscopic pituitary surgery
The designs of rigid endoscopes have been revolutionized over the past several decades, resulting in endoscopes of varying lengths, diameters, and directions of view. A similar trend has also characterized the development of accessory products, including technologically advanced light sources, video cameras, digital processors, and lens cleansing and irrigation systems.63 Only with the availability of this equipment has the next step in the evolution of pituitary surgery become possible.
Momentum in the field of endoscopic pituitary surgery has derived from the observation that rigid endoscopes provide more comprehensive images of the pituitary gland and its surrounding structures than do operating microscopes. By extension, improved visualization allows for more thorough tumor resection and fewer associated surgical complications.
Spencer et al64 have quantified and compared the "volumes of view" of the endoscope and microscope in the setting of pituitary surgery. In their anatomical study, they were able to objectively demonstrate with statistical significance that the 0º endoscope provided more comprehensive views of the sella turcica than did the microscope. The clinical implications of this experiment have been demonstrated in two separate series of patients who underwent endoscope-assisted microscopic resections of pituitary tumors.12,65 In these patients, a traditional microscopic transseptal transsphenoidal approach to the pituitary gland was employed. Following what was believed to be complete microscopic tumor resection, endoscopes were introduced through the blades of the intranasal retractor to conduct a final survey of the surgical field. In both series, an average of 40% of patients was found to have residual tumor fragments that were only discovered with the use of endoscopy. In other words, the microscope alone allowed for complete tumor removal in only 60% of these patients.
These considerations, in addition to the fact that the direct transnasal approach to the sphenoid sinus virtually eliminates the oronasal complications that have been associated with the transseptal method, have contributed to the emergence of fully endoscopic pituitary surgery as the most recent phase in the evolution of pituitary surgery.
Indications for fully endoscopic pituitary surgery are identical to those for the traditional transseptal transsphenoidal microscopic procedure, including the surgical management of productive and non-productive pituitary micro- and macroadenomas that are unresponsive to medical therapy or cause visual or cranial nerve deficits.20-22 Because the fully endoscopic technique entails a less invasive approach to the pituitary gland, it offers a distinct benefit over the traditional methods in terms of operating time, recovery time, and perioperative morbidity. A minimally invasive approach should be considered as the first line of surgical therapy for operative procedures in pediatric populations, surgery for patients with pituitary tumors whose medical histories put them at greater risk for complications of general anesthesia, and biopsies of intrasellar lesions of unknown origin.
The rod lens design of endoscopes, first introduced in the 1960s by English physicist H. H. Hopkins,66,67 provided the basis for the future manufacture of endoscopes and continues to set the standard for the industry. By integrating a series of lens systems within the rod, the endoscope was lengthened and yielded an image of previously unparalleled depth and resolution. Furthermore, the development of endoscopes of varying directions of view has provided for visualization of structures previously hidden from the direct anteroposterior imaging capability of the microscope. Zero-degree, 30°, 70°, and 120° endoscopes offer panoramic perspectives of structures once completely obscured by anatomical "corners." Scopes of different diameters (4.0-mm and 2.7-mm) also provide multiple options to the surgeon faced with variations in surgical anatomy.63
Illumination of tungsten halogen, metal halide, or xenon arc origin is generated by a light source and transmitted to the telescope via a fiberoptic cable. Light then travels along the length of the telescope – also fiberoptically – to illuminate the surgical field.63,66,67 Different types of illumination devices offer light of varying brightness and whiteness and also offer hardware in a range of prices and sizes.
Hopkins rod telescopes are manufactured with standard eyepieces through which the endoscopic image can be directly viewed or to which video cameras can be attached. Images are then be projected onto one or several monitors or electronically processed and recorded. Three-chip cameras contain individual chips for each of the primary colors. These produce the highest quality images and feature automatic control over color, exposure, white balance, and digital contrast enhancement. Single-chip cameras are less expensive and offer fewer options, but also produce high quality images that are more than adequate for the operating room.63,66
Devices that digitally process the endoscopic image allow real-time detail enhancement and image manipulation. Video processing systems have also made "picture-in-picture" viewing--simultaneous viewing of endoscopic and microscopic images on one monitor – possible.68,69 All of these options contribute to the great versatility of endoscopy as a surgical tool and make it easily adaptable to highly specialized and intricate procedures.
Bimanual operating is a necessity in pituitary surgery. Multiple instruments are needed to execute a transnasal approach and tumor resection. The development of endoscope holding arms has obviated the need for surgeons to dedicate one hand to holding the camera.
In general, holding arms must be sturdy, stable, and adjustable. They must be able to hold the endoscopes securely in place but must allow the surgeon to manipulate them at will and with ease. Early designs combined long metal rods at movable joints and placed clamps on each end: one to grip the operating table and the other to hold the endoscope. The latest generation of holding arms is designed to work using ball bearing joints that are pneumatically powered. These devices are remarkably flexible and extremely reliable.
Blood, debris, mucous, and mist invariably cover the lens of the endoscope during the operation and obscure the image. Irrigation sheaths are available in different diameters to accommodate different sized endoscopes. They are connected to a reservoir of sterile saline via tubing that threads through a motorized pedal-activated gear system. Upon demand, the sheath delivers a cleansing stream of saline over the tip of the endoscope. With this system in place, the continual clarity of the image is guaranteed.
Positioning and operating room setup
Patient positioning in the fully endoscopic procedure is similar to that used in the traditional transseptal transsphenoidal microscopic technique. The patient is placed supine with the head of the bed raised, the neck extended, and the head rotated and fixed in position with a carbon horseshoe three-pin clamp. The C-arm fluoroscopy image intensifier is brought to the head of the table and rotated so that the trajectory of the beam yields centrally positioned sphenoid and pituitary contours on the fluoroscopy monitor. Next, the endoscopic tower (housing the camera, light source, and video recording and processing equipment) is placed over the patient's shoulder, directly in the line of vision of the surgeon. Finally, an endoscope holding arm is affixed to the bed on the side opposite the surgeon and wrapped in a sterile drape. The arm reaches over the patient's upper body to rest above the patient's nose. Its orientation can be adjusted to alter the position of the endoscope as necessary.
The face, nares, and abdomen or thigh are prepared with antibacterial surgical scrub, as in the transseptal transsphenoidal technique. Some authors14,19,20,70 support the use of intranasal epinephrine- or cocaine-soaked sponges in order to obtain mucosal vasospasm. Sterile towels are used to cover the face, leaving only the nose exposed during surgery.
The first step in the endoscopic procedure is to choose the appropriate endoscope. The initial intranasal dissection is invariably performed with a 0-degree lens, but the diameter of the scope may vary. The advantages of the 4.0-mm endoscope over the 2.7-mm include higher resolution of the image and better illumination of the surgical field. The 4.0-mm endoscope, however, occupies a significantly greater amount of space within the nostril. Preoperative physical examination of the nasal passages may provide the surgeon with an idea of which instrument will be more appropriate. Nevertheless, nasal passages that initially appear sufficiently large may front a deeper surgical anatomy that precludes the advancement of multiple surgical instruments alongside a 4-mm endoscope. The surgeon must have scopes of both diameters available and must be able to improvise intraoperatively, depending upon the intranasal and skull base anatomy of the patient. Furthermore, every endoscope must be fitted with an irrigation sheath prior to use, as described above. Operation without a properly functioning lens irrigation system is extremely difficult, as the redundant removal and replacement of endoscopes for cleaning is both tedious to the surgeon and hazardous to the patient.
The endoscope is attached to the grasping end of the holding arm, advanced into the right nostril, and used to conduct a brief survey of the anterior nasal vestibule. The middle turbinate and the architecture of the nasal septum are identified. As the ultimate target of the endoscope is the sphenoid sinus, the goal of the intranasal portion of the procedure is to create a passage to the sphenoid that is wide enough to accommodate the endoscope and accompanying instruments. This goal can be achieved rapidly, but should be meticulously and atraumatically performed, as bleeding from traumatized mucosa anteriorly can obscure posterior visualization.
The endoscope is advanced to the anteroinferior border of the middle turbinate. An elevator is passed under the shaft of the endoscope until it is visualized on the monitor. A long straight suction device is also introduced to clear the naris of any blood or mucoid secretions that accumulate during the subsequent steps. The elevator is placed flatly against the surface of the septum and firm, sustained pressure is applied in a medial direction. The spongy septal mucosa is flattened and the underlying cartilage is moved. This maneuver is repeated along the entire face of the septum until it yields and is definitively displaced. The elevator is then carefully rotated intranasally and a similar force is applied to the middle turbinate in a lateral direction. As the nasal passage is widened, the holding arm is released and the endoscope is advanced. Ultimately, the posterior nasopharyngeal wall and the sphenoid ostium are revealed, marking the posterior extent of the intranasal dissection.
The mucosal lining of the anterior wall of the sphenoid sinus is cauterized and then lifted from the surface of the bone using an elevator. This dissection is carried out bilaterally to expose both sphenoid ostia. The superior and inferior limits of the anterior sphenoid, as defined by the cribriform plate and vomer, delineate the limits of mucosal dissection. The vomer may be removed with a rongeur to more completely expose the surface of the sphenoid bone.
Resection of the anterior surface of the sphenoid, the mucosal lining of the sinus, and the floor of the sella proceeds under endoscopic visualization as in the transseptal approach. The same instruments are passed through the nostril, below the shaft of the endoscope, and into the surgical field to gain access to the sella turcica. The holding arm is released and the endoscope is advanced further toward the pituitary with each subsequent step. The same principles of awareness for the limits of dissection apply.13 Injuries to the cavernous sinuses, carotid arteries, optic nerves and chiasm, and cribriform plate are still possible if caution is not exercised while working within the sinus or sella. With the endoscope fixed in the sphenoid sinus, incision of the dura and removal of tumor also progresses as previously described, using suction and ring curettes of varying diameters and orientations and strategic Valsalva maneuvers.21
The 0º endoscope provides near complete exposure of the sella turcica and a partial view of the suprasellar structures, including the optic chiasm and the arachnoid membrane. Once tumor resection under the 0º endoscope is thought to be complete, it is replaced with a 30º endoscope. By advancing the 30º scope into the sella turcica and then rotating it in clockwise and counterclockwise directions about the anteroposterior axis, the parasellar and suprasellar areas are even more thoroughly visualized.21,22 These maneuvers underscore the strength of endoscopy in pituitary surgery: areas that are not revealed during microscopic examination are directly exposed using a combination of rigid endoscopes of different angles of view. Tumor remnants in these areas are removed and sources of potential tumor recurrence are thereby eliminated. This is accomplished with a superb visual appreciation of the critical surrounding structures.
Once tumor resection is complete, a fat graft from the abdomen or a graft of muscle and fascia lata from the lateral thigh is harvested and used to reconstruct the floor of the sella and fill the sphenoid sinus.18-22,70 Fibrin sealant is used to secure the graft in place. With no mucoperichondrial or mucoperiosteal dissection to speak of, the need for postoperative nasal packings is eliminated.14,18,20 A small gauze sponge loosely taped beneath the nose ("mustache" dressing) collects any fluid that may drain from the nostril overnight. Patients are discharged from the hospital within 24 to 36 hours of surgery.
Because this procedure is relatively new, the amount of data that has been generated by the few centers using this technique to perform pituitary tumor resection is limited. However, preliminary evidence suggests that complication rates and surgical outcomes compare favorably to those that have been reported for the transseptal transsphenoidal microscopic procedure.
Cappabianca18 reports evidence of complete tumor removal on follow up MRI in all cases except those with tumor invasion of the cavernous sinuses in his series. All patients with preoperative visual field deficits experienced improvement of their symptoms, and greater than 80% of patients with endocrinopathies characterized by elevated levels of growth hormone, IGF-1, and prolactin had normalization of these levels postoperatively.
In a series of 46 patients who received a fully endoscopic transnasal approach to the pituitary gland, Jho20 reported similar results. All nonfunctional adenomas were completely resected except those involving the cavernous sinuses. Six of 8 patients with Cushing's disease and 10 of 17 patients with hyperprolactinemia exhibited normal postoperative hormonal profiles.
Sheehan71 conducted a retrospective review comparing 26 patients with nonproductive pituitary tumors resected via an endoscopic transnasal approach to 44 matched controls that received a transseptal transsphenoidal operation. He found similar complication rates and postoperative outcomes between the two groups as well as a statistically significant decrease in operative times when the endoscopic technique was employed. Common to the experience of all of these authors is the elimination of the oral and nasal complications associated with the transseptal surgery.
While more extensive data over longer follow-up periods is required to further substantiate these early trends, it is clear that transnasal endoscopic pituitary surgery does offer an equally effective if not superior alternative in the surgical management of pituitary disease that emphasizes the beneficial principles of minimally invasive surgery.
The evolution of pituitary surgery over the past century has been characterized by a progressive trend toward less invasive approaches to the gland. Cushing's transcranial approach was superseded by the transseptal technique to achieve equivalent surgical results. The endoscopic transnasal approach offers even less invasive access to the pituitary gland and surrounding area while providing improved visualization. With surgical outcomes comparing favorably to data from transseptal pituitary surgery series, transnasal endoscopic pituitary surgery represents the most recent advance in the evolution of surgical management of pituitary disease.
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