The procedure is performed under general anesthesia, with the patient placed in a semirecumbent position (Fig. 2A). Some surgeons prefer to operate from the head of the table, with the patient's head in extension, facing toward the patient's feet (Fig. 2B). Because pituitary reserve for the pituitary-adrenal axis may be impaired, it is customary to administer a regimen of "stress dose" exogenous corticosteroids both during surgery and in the immediate postoperative period. The indications for this are reviewed in Chapters 7 and 9. Antibiotic prophylaxis is usually employed, although many leading surgeons dispense with this.
The procedure requires some form of navigational guidance to ensure a safe trajectory to the sella. The standard apparatus for this has been, and continues to be, videofluoroscopy. More recently, there has been increasing reliance on com-
puter-assisted image-guided neuronavigational systems for this purpose (5). Such frameless stereotactic systems give the surgeon more information for transsphenoidal surgery and a safe trajectory in both the sagittal and the coronal plane. In "reoperations," this is invaluable and minimizes the likelihood of loss of the midline, making the procedure considerably safer. After the nose and face have been cleansed with an aqueous-based antiseptic solution, application of decongestants and submucosal infiltration of the nasal mucosa with a dilute (1:200,000) epinephrine solution significantly reduce bleeding and make submucosal dissection easier.
There are three approaches to the sphenoid sinus: the endonasal submucosal approach, the sublabial approach, and the direct transnasal septal pushover approach. Selection of one over the others depends on the size of the nostril, the size of the lesion, the presence of previous nasal surgery, and the surgeon's preference. We tend to favor the basic endonasal approach in most instances. We reserve the sublabial incision for larger and more difficult lesions when a broader corridor of surgical access is required, and tend to use the transnasal septal pushover technique in the setting of previous nasal surgery or among pediatric patients.
Our standard endonasal approach involves a right hemitransfixtion incision over the caudal aspect of the nasal septum, allowing a submucosal plane of dissection to be fashioned on one side of the septum. The dissection continues posteriorly, elevating the nasal mucosa away from the cartilaginous septum back to its junction with the bony septum (Fig. 3). A vertical incision is then made at this junction point, and bilateral posterior submucosal tunnels are created on either side of the perpendicular plate of the ethmoid. The articulation of the cartilaginous septum with the maxilla is then dissected free, and an attempt is made to raise the inferior mucosal tunnel on the opposite side so that the cartilaginous septum can be displaced laterally without creating inferior mucosal tears. A self-retaining nasal speculum can then be introduced to straddle the perpendicular plate of the ethmoid, exposing the face of the sphenoid sinus. A portion of the perpendicular plate is removed and preserved for eventual sellar reconstruction.
Once the anterior face of the sphenoid sinus is reached, videofluoroscopy or neuronavigational image guidance is used to make any necessary adjustments to the final position and trajectory of the retractor blades. The correct orientation is crucial at this stage, with respect not only to the midline but also to the eventual approach window, defined superiorly by the tuberculum and inferiorly by the clivus. Too acute an angle will result in penetration of the anterior fossa floor, whereas too obtuse an angle will direct one toward the midclivus. Identification of the vomer and the sphenoid ostia on either side are useful landmarks, and having them in the center of the field generally prevents misdirection in these early stages of the exposure (Fig. 4). Once the operating microscope has been introduced, the anterior wall of the sphenoid is opened with small-bone rongeurs and Kerrison punches and the sinus is entered.
The mucosa within the sinus is resected, reducing bleeding and decreasing the risk of postoperative mucocele formation. With the internal sphenoid bony landmarks now clearly visible, the surgeon checks orientation with respect to the carotid arteries, the sellar floor, the anterior fossa floor (Fig. 4), and clivus. Correlating the operative anatomy with the neuronavigational data ensures that the trajectory is both midline and within the approach window.
The sellar floor should be clearly visible. With some tumors, the sellar floor is so eroded or thin that it can be fractured with a blunt hook. If the floor of the sella is thick, a small chisel can be used to remove a square of bone. A high-speed drill with diamond burr will gently remove particularly thick fossa bone in safety, a useful maneuver in the underpneumatized fossa and in Cushing's microadenomas. Continuous videofluoroscopic control or image-guidance monitoring ensure safe sellar entry, exposure, and trajectory. Once the sellar floor has been opened, it is widened with a Kerrison punch. Adequate bony exposure is crucial to the success of the transsphenoidal approach, extending from one cavernous sinus to the other in the lateral direction and from just short of the junction of the anterior fossa floor and sella to the clivus in the other, particularly when dealing with large tumors. We advocate wide bony removal in virtually every case.
Exposure within the sella proper is carried out with the operating microscope magnification adjusted so that the sella fills the entire field of vision. An invasive
tumor may erode through the anterior dura of the sella, but in most cases the dura will be intact. Before the dural incision is made, the position of the carotid arteries should be noted from the imaging and thus avoided (Fig. 5). The site of dural opening is selected, cauterized, and incised either in a cruciate fashion or with the excision of a dural window. A subdural cleavage plane between the pituitary gland or tumor and the underlying dura is then developed.
For the typical macroadenoma, the tumor is entered with a ring curette, loosened, and then removed with a relatively blunt curette and forceps (Fig. 6). Tumor removal should be done in an orderly fashion. Our practice has been to first remove the tumor in the inferior aspect and then proceed laterally, from inferior to superior on both sides, removing tumor along the medial side of the cavernous sinus.
One must resist coring the central and most accessible portion of the tumor first, because this may cause premature descent of the diaphragma and entrapment of more laterally situated tumor, and delay the superior dissection until the lesion is relatively free elsewhere. This minimizes trauma to the pituitary stalk and secondarily transmitted trauma to the hypothalamus. Occasionally it may be necessary to follow the tumor into one cavernous sinus or the other or to deal with a tumor directly involving the diaphragma. In either instance, any maneuver
more forceful than gentle curetting may be a dangerous move and pulling adherent fragments must be avoided.
Decompression of the intrasellar portion of the tumor frequently permits a suprasellar extension to prolapse into view within the sella. Once this has been resected, the diaphragma subsequently prolapses and generally signifies that the resection is complete. Some surgeons use a temporary increase in intracranial pressure to improve descent of the suprasellar component. The Valsalva maneuver, performed by the anesthetist is popular, although higher and slightly more prolonged pressure increases are achieved with a lumbar drain introduced at the time of the induction of anethesia.
Verification that no residual tumor remains is provided by direct inspection or with the help of dental mirror, a nasopharyngoscope, or a small fiber-optic endoscope. Bleeding from the tumor bed can usually be controlled by tamponade with cotton patties or Gelfoam.
In all cases, a concerted effort is made to preserve normal pituitary tissue. In a large diffuse adenoma, normal glandular tissue usually appears as a thin mem-
brane, situated superolaterally against the sellar wall. The orange-yellow color of the gland, together with its firm consistency, distinguishes it from the grayish color and finely granular texture typical of the tumor. A biopsy of the suspected glandular remnant may be taken for confirmation, but the appearance is often so typical that this tissue can be left behind with confidence.
Microadenomas require a different strategy because it is well recognized that many will not be seen upon opening the dura. In these cases, a systematic search through an apparently normal gland is required. We begin with a transverse glandular incision, followed by subdural dissection and mobilization of the lateral wings. If the incision in the gland is deep enough, lateral pressure with a Hardy dissector usually causes the microadenoma to herniate into the operative field. Its location can then be delineated, its cavity entered, and its removal completed by use of a small ring curette and cup forceps. All suspicious tissue is removed, and a biopsy specimen is occasionally obtained from the residual and presumed normal pituitary gland.
Special mention is necessary for the approach to microadenomas in CD. A careful and systematic dissection of the sellar contents is required. If a tumor is not evident upon opening the dura or after examining all glandular surfaces, the gland must be incised and systematically explored. Subtle changes in tissue color, texture, or the contour of the gland will aid in the identification of an adenoma and distinguish it from the normal gland. If no adenoma is found, excisional biopsies from within the substance of the gland are obtained, beginning with the central mucoid wedge. If an adenoma is not evident in the resected material, the lateral wings of the gland are carefully inspected and resected as necessary. Where no obvious tumor is found in the adult for whom fertility is not an issue, a subtotal hypophysectomy may be performed, leaving only a stump of residual anterior lobe tissue attached to the stalk. If careful examination of the resected tissues still fails to reveal the adenoma, both cavernous sinuses and the posterior lobe must be inspected. The latter has, on rare occasion, been known to harbor a minute adenomatous nodule. Failing to see an adenoma raises the possibility of a supradiaphragmatic tumor nodule. Given the additional operative risks of a diaphragmatic breach, one would not ordinarily contemplate transdiaphragmatic exploration without clear imaging evidence pointing to such a possibility.
After the tumor has been removed and hemostasis has been achieved, the sella must be reconstructed and closed. We prefer not to leave dead space in the sella. If no cerebrospinal fluid (CSF) leak has occurred, the sella is loosely packed with Gelfoam. However, if there is a CSF leak, some form of tissue graft becomes mandatory. Reconstruction of the sellar roof can be attempted with a piece of homologous dural graft material or fascia lata; however, this step probably adds little to the security of the seal. Current practice favors simple packing of the sella with fat taken from the right lower quadrant of the abdomen. The fat is soaked in chloramphenicol solution, rolled in Avitene, trimmed to appropriate size, and snugly placed within the sella. In either case, the sellar floor is then carefully reconstructed using a suitably trimmed piece of cartilage or bone. In cases where previous surgery has been performed and no bone is available, alternative materials for closure include banked bone allograft, slowly resorbable polymer stents, or methylmethacrylate.
If an intraoperative CSF leak has occurred, the sphenoid sinus is packed with fat, but in the absence of a leak, it is left free of foreign material. The posterior septal space may be re-implanted with crushed nasal bone and cartilage. The septal flaps are re-approximated, and the nasal septum is returned to its midline insertion. Any accessible mucosal tears are repaired with fine catgut sutures. Bilateral endonasal packs, consisting of gauze packing within the "fingers" of a rubber glove that have been lubricated with petroleum jelly or antibiotic ointment, are placed in the nostrils. The nasal and/or gingival incisions are closed with interrupted 4-0 catgut sutures, and a gauze mustache dressing is applied.
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