The Evolution from Open Transcranial to Fully Endoscopic Transnasal Surgery of the Pituitary Gland
By Reza Jarrahy, M.D., Joseph B. Eby, M.D., Hrayr K. Shahinian, M.D.
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 extensive experience with various operative techniques including transcranial (Figure 1) and transseptal-transsphenoidal (Figure 2) approaches to the pituitary gland, but ultimately came to favor the transcranial procedure.3,4 Schloffer in 1907 performed the first transsphenoidal pituitary tumor resection.5 For decades since the introduction of these techniques surgeons have debated which procedure provides the most complete resection of the pituitary lesion with the least risk of complications. Then in the 1960s Jules Hardy introduced intraoperative fluoroscopy and microscopy to transseptal-transsphenoidal pituitary surgery.1,6-8 The improved exposure afforded by these technologies allowed for complete removal of larger pituitary tumors, obviating the need for a complex transcranial operation in most patients.
As a result, the transseptal-transsphenoidal approach came to be the procedure of choice for the surgical management of most pituitary lesions. Transcranial techniques were reserved for use in the resection of large tumors with extensive parasellar and suprasellar invasion. With specific roles for these two approaches thus established, the indications for microscopic transseptal-transsphenoidal and transcranial pituitary surgery have remained relatively well defined for almost forty years.
Recently, however, discussions regarding the most effective and least invasive way to perform pituitary surgery have been renewed. Developments in the field of endoscopic surgery have prompted surgeons to attempt endoscope-assisted surgery of the pituitary gland via the traditional transseptal approach.9-20 Recently, some surgeons have developed methods to perform transnasal-transsphenoidal pituitary surgery using only the endoscope for exposure (Figure 3).21-26 This procedure is proving to be equally if not more effective than the microscope as the primary imaging modality in pituitary surgery.
Transcranial surgery of the pituitary gland
Indications: For large pituitary tumors extending outside of the sella turcica, the transcranial approach offers the greatest chance of complete tumor removal. Often, a transcranial resection is reserved for the second stage of a two-stage operation.27,28 The first operation is performed via microscopic or endoscopic exposure of the pituitary tumor, during which time the bulk of the tumor is removed transseptally or transnasally. Any tumor extending outside the area visualized by the microscope/endoscope, or that is inaccessible during the first operation is then resected in a subsequent transcranial exploration.
Surgical technique: There are two major variations of the transcranial technique that are currently used for the resection of pituitary tumors: Midline Subfrontal Approach and the Oblique Subfrontal Approach.
Midline subfrontal approach: The midline subfrontal approach remains the most common method for transcranial pituitary surgery; providing direct exposure to the optic nerves, carotid arteries, and pituitary gland.27 The operation is performed by first making an incision through the scalp, down to the skull on the side of greatest tumor extension. A craniotomy is then performed and the underlying dura incised; the frontal lobes of the brain are exposed and retracted to gain exposure to the tumor (Figure 1). Retraction must be kept to a minimum to avoid post-operative brain edema.27,29,30 Damage to the olfactory nerve can also occur during this operation, resulting in a decreased sense of smell.28,31,32
Dissection is carried out proceeding anterior to posterior in the midline using skull base landmarks as a guide to the pituitary gland and tumor. The optic nerves are identified and used to help expose the optic chiasm. The blood supply to the front of the brain (anterior circle of Willis) is also visualized. Once the exposure is complete, the surgeon uses an assortment of specialized instruments to work around the relevant structures and resect the tumor.27,33-35 Following tumor removal, the dura is re-approximated to achieve a watertight seal. The craniotomy is closed using microplates and screws, and the soft tissues of the scalp are sutured and stapled.
Oblique subfrontal approach: The oblique subfrontal approach is identical to the procedure described above except that it is performed at an angle to the midline. This approach allows for less frontal lobe retraction and reduces the risk of damage to the olfactory nerves. However, these benefits must be weighed against a reduction in operative exposure and added risks to the optic nerves and carotid arteries.27,28,32,36-38
Microscopically assisted sublabial-transseptal-transsphenoidal pituitary surgery
Indications: This procedure is indicated in the surgical management of pituitary tumors causing hypo- (not enough) or hyperfunctioning (too much) of the gland that have not adequately responded to medical treatment, or tumors growing into adjacent structures, evidenced by visual or other neurologic changes. Micro- and macroadenomas are amenable to resection by this method, including those with mild supra- and parasellar extension.1,39-43 Large parasellar extensions of pituitary tumors, however, are more difficult to manage, as the lateral margins of the microscopic field of view are limited and blind removal of tumor extending beyond the sella is hazardous. Patients with extensive extrasellar extension of their pituitary tumors must be considered for two-stage procedures as described above.28,37,44,45
Surgical technique: While an assistant retracts the upper lip, a sublabial incision is made. Intranasal dissection is carried out separating the nasal tissue and removing a section of the central partition of the nose, forming a large "tunnel" through which the remainder of the procedure is conducted. An adjustable retractor is placed into this tunnel; its blades are advanced to the sphenoid sinus.
The operating microscope is utilized for the remainder of the case, providing magnification and improved illumination of the limited operating field. The anterior wall of the sphenoid sinus is cautiously resected as it boarders the carotid arteries, cavernous sinuses, and optic chiasm.46-48 Once the anterior wall is removed, its mucosal lining is resected, exposing the posterior wall of the sinus (floor of the sella turcica). Benign adenomas usually do not invade the floor of the sella, however, expanding tumors may erode through the floor. If intact, the floor of the sella (posterior wall of the sinus) is removed. Dissection of this region determines the operative exposure, and is crucial for adequate visualization and thorough tumor removal. Deep to the floor of the sella is the dura. A sharp hook or blade is used to incise the dura, and through this incision specialized dissecting instruments are used to remove the tumor. Resection of tumor is carried out until all visually identifiable tumor is removed. As the sella is emptied of tumor, the boundaries of normal pituitary gland are identified.
The hole in the floor of the sella is then plugged using a fat graft from the abdomen, or muscle and fascia graft from the lateral thigh. This plug obliterates the space of the sphenoid sinus and helps prevent post-operative cerebrospinal fluid leakage.49 There are several models of graft design, in most cases a simple fat graft suffices.42,43,50-54 With the fat graft in place, the retractor is removed, the central bridge of the nose and flaps of tissue are repositioned, and the gum line 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.
Fully endoscopic pituitary surgery
With the advent of modern endoscopic equipment, momentum in the field of endoscopic pituitary surgery has stemmed from studies, which show endoscopes provide more comprehensive images of the pituitary gland and its surrounding structures than does the operating microscope.38,55 This in turn should allow for a more thorough tumor resection and fewer associated surgical complications.
The clinical implications of these findings have been reflected in two separate studies of patients who underwent endoscope-assisted microscopic resections of pituitary tumors.15,38,55,56 These patients underwent a traditional microscopic transseptal-transsphenoidal approach to their pituitary gland tumor. Then, following what the surgeon believed to be complete tumor resection using the microscope, endoscopes were introduced into the pituitary region looking for residual tumor. In both series, an average of 40% of patients were found to have tumor left behind that was only discovered and resected during the endoscopic surveys. In other words, the microscope alone allowed for complete tumor removal in only 60% of patients.
Improved tumor resection, elimination of intraoral and transseptal dissection along with reductions in operating time, recovery time and complications, have ushered in the completely endoscopic transnasal approach to the pituitary gland as the most recent phase in the evolution of pituitary surgery.
Indications: Indications for fully endoscopic pituitary surgery are identical to those for the traditional transseptal-transsphenoidal microscopic approach.16,23-26
Surgical technique: The first step in the endoscopic procedure is to choose the appropriate endoscope. Preoperative physical examination of the nasal passages provides the surgeon with an idea of which endoscopes will be most appropriate. The surgeon must have scopes of varying diameters available, and must improvise intra-operatively depending upon the intranasal and skull base anatomy of the patient.
Furthermore, every endoscope must be fitted with an irrigation sheath to clear the lens of blood or debris during dissection. This avoids the redundant removal and replacement of endoscopes for cleaning, which 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 passageway. The ultimate target of the endoscope is the sphenoid sinus. Therefore, the goal of the intranasal portion of the procedure is to create a passage to the sinus 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 visualization posteriorly.
The endoscope is advanced to the anteroinferior border of the middle turbinate. An elevator (dissecting instrument) is used to displace the nasal septum medially and middle turbinate laterally. A long straight suction device may also be introduced to clear the naris of any blood or mucoid secretions. As the nasal passage is widened, the holding arm is released and the endoscope advanced further posteriorly. Ultimately, the anterior wall of the sphenoid sinus is exposed, marking the extent of the intranasal dissection. The mucosal lining of the anterior wall of the sphenoid sinus is dissected away from the bone with a combination suction-cautery device and then lifted from the surface of the bone. Resection of the anterior wall of the sphenoid, the mucosal lining of the sinus, and the floor of the sella (back wall of the sinus) proceeds under endoscopic visualization. The surgical instruments are passed through the nostril, below the shaft of the endoscope, and into the surgical field to gain access to the sphenoid sinus and sella turcica. The same principles of awareness for the limits of dissection apply.16 Injuries to the cavernous sinuses, carotid arteries, optic nerves and chiasm 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 proceeds as previously described. All imaging up until this point is provided by the 0º endoscope, which provides near complete visualization of the sella turcica, but only a limited view of the suprasellar structures. Therefore, once tumor resection is deemed complete, the 0o scope is replaced with a 30º endoscope. The 30º endoscope is advanced into the sella turcica and rotated clockwise and counterclockwise, thoroughly visualizing the supra- and parasellar regions. Such a comprehensive survey of these regions is not possible with the operating microscope.16,23-26 Tumor remnants in these areas are then removed, thereby eliminating sources of potential tumor recurrence. Resection is considered complete only after examination with the angled endoscope. A fat or muscle graft is then used to reconstruct the floor of the sella as previously described. No postoperative nasal packing is necessary. A small gauze sponge loosely taped beneath the nose collects any fluid that may drain from the nostril. Patients are discharged from the hospital within 24 to 36 hours of surgery.
The evolution of pituitary surgery over the past decade has been characterized by a progressive trend toward less invasive surgical approaches to the gland. Innovations in medical technology have, in part been responsible for these advances. The transcranial method was abandon for the transseptal technique when surgeons documented their ability to achieve equal surgical results without the need for removal of the skull or retraction of the brain. The endoscopic transnasal approach offers even less invasive access to the pituitary gland and surrounding area, in addition to providing better intraoperative imaging of the region. Preliminary evidence suggests that complication rates and surgical outcomes of endoscopic pituitary surgery compare favorably to those that have been reported in large series of patients who have undergone microscopic transseptal pituitary surgery.18-21 More extensive data over longer periods of follow-up will further substantiate these early trends. It is clear that transnasal endoscopic pituitary surgery represents significant progress in the surgical management of pituitary disease.
Glossary of Terms
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- Transcranial – Surgical exposure for pituitary surgery by way of opening the skull (Craniotomy), and retracting the front of the brain to access the pituitary gland
- Transseptal – Surgical resection of a portion of the central partition of the nose to access the sphenoid sinus. (exposed either transnasally or through sublabial incision)
- Sphenoid sinus – Sinus – (cavity lined with mucosa) that lies directly behind the nose and in front of the pituitary gland – the back wall of which makes up the anterior wall of the sella tursica.
- Transsphenoidal - Surgical dissection through the sphenoid sinus to access the pituitary gland
- Transnasal - Surgery through the nostril providing access to the sphenoid sinus and pituitary gland
- Sublabial – Surgical incision below the lip, above the front teeth in the gum line, providing access to the nostril, or followed by splitting the palate (bone) to eventually access the sphenoid sinus.
- Sella Tursica – Bony structure at the base of the skull in which the pituitary gland rests
- Intrasellar – Within the sella tursica
- Subsellar – Extending below the sella tursica
- Suprasellar – Extending above the sella tursica
- Parasellar – Extending into the area surrounding the sella tursica – (beside, behind or in front of)
- Adenoma - Benign tumor - referring to a non-functioning mass in the pituitary gland (this paper)
- Microadenoma – Small adenoma – Less than 10mm in size
- Macroadenoma – Large adenoma – Greater than 10mm in size
- Anterior – Pertaining to being in front of another structure – toward the front of the body
- Posterior – Pertaining to being behind another structure – toward the back of the body
- Medial – Toward the midline of the body
- Lateral – Toward the periphery of the body (away from the midline)
- Carotid arteries – Arteries which carry blood up through the neck, eventually supplying the brain with its major blood supply – these vessels are also found within the cavernous sinus.
- Cavernous sinus – Area adjacent to the sphenoid sinus containing several vital nerves and blood vessels.
- Dura – Thin membrane surrounding the brain, which acts as a bag to contain the cerebrospinal fluid.
- Cerebral Spinal Fluid/Leak – Clear fluid which surrounds the brain/a hole in the dura which allows the leakage of this fluid – (the dura must be opened to access the pituitary gland)
- Endoscopy/Endoscopic Surgery – Surgery performed using small illuminated lenses on long rods connected to cameras to magnify/better visualize an operating field
- Fluoroscopy – Video x-rays
- Frontal Lobes/edema – The region of the brain in the front of the head which lies above and in front of the pituitary gland/a swelling of some tissue due to injury & accumulation of fluid.
- Indication – Scientific/medical reason for performing a certain procedure
- Microscopy - Using an operating microscope to better visualize a small operating field or perform delicate surgery.
- Olfactory Nerves – Nerves which connect to the nostrils to provide one's sense of smell
- Optic Chiasm – Area where optic nerves cross over, located just above the pituitary gland, which can be compressed by pituitary tumors
- Optic Nerves – Nerves which connect to the eyes providing one's sense of sight
- Resected – Cut out or removed surgically
- Turbinate (superior, middle, inferior) – Bony prominences in the nasal passage way