Учебники / Computer-Aided Otorhinolaryngology-Head and Neck Surgery Citardi 2002

It should be emphasized that direct midline approaches to the sella (i.e., transseptal routes) provide direct access and afford less perceptual distortion. For this reason, they represent the preferred alternative, although other modifications (such as an endoscopic transnasal route) may also be used. If the route is off of the nasal midline, the potential for inaccurate recognition of relevant landmarks becomes greater. In these instances, CAS may have an even greater role.

After induction of general anesthesia and CAS system calibration and registration, the actual surgery is started. The septum may be used as the direct dissection plane to the sphenoid rostrum in any of the transseptal approaches. Cartilage, mucosa, and the sphenoid keel are removed to open into both sphenoid sinuses. Ante- rior-to-posterior septal flap elevation at the sphenoid rostrum may be avoided by creating a posteriorly based perforation approximately 1 cm anterior to the rostrum. At this point, a midline sphenoidotomy has been created via the transseptal route.

After completion of the midline sphenoidotomy, the anterior wall of each sphenoid sinus is removed from medial to lateral. During this removal, care should be taken to avoid injury to branches of the sphenopalatine artery, which cross the anterior sphenoid wall (Figure 15.2). The lateral and superior extent of dissection at the sphenoid sinus anterior wall may be guided by CAS surgical navigation.

After removal of the anterior sphenoid walls, the interior surface of the sphenoid sinus should be carefully inspected. The sphenoid intersinus septum may insert on the sella or the internal carotid artery (Figure 15.3). The internal carotid artery and the optic nerve may indent or actually pass through the sphenoid sinus. These anatomical variations, if present, should be identified. Direct visualization (via the operating microscope or nasal telescope), coupled with CAS surgical navigation, serves to accomplish this objective. The angled telescopes (namely, 30°, 45° and 70° telescopes) allow the surgeon to look ‘‘around the corner’’ prior to dissection. This may be very useful for dissection at the most lateral aspects of the sphenoid sinus. Other instruments used during this dissection may also include nasal specula, suction bipolars, suction curettes, sickle knives, and hooks. Suction sphenoid mushroom punches are also available.

The pituitary gland is located in the sella, which is just deep to the posterosuperior wall of the sphenoid sinuses (Figure 15.1). The posterior sphenoid wall may vary in thickness and orientation with respect to the pituitary. Hardy described three types of sphenoid sinus variants with respect to the pituitary [7]. The most common variant (86%) is the sellar type, in which a thin posterior sphenoid wall surrounds the pituitary gland. In the presellar type (11%), the anterior boundary of the sella is the thin posterior sphenoid sinus wall, and the sella’s inferior boundary is thick bone. In this anatomical arrangement, sphenoid pneumatization does not extend beyond the vertical plane defined by the anterior sella wall. In the concha type (3%), the sella is surrounded by thick bone, and sphenoid pneumatization is minimal. The last variant may require usage of a drill for removal of thick bone for access to the sellar contents. Some CAS systems support

the tracking of drill tip position; obviously, this may be helpful in the dissection of the conchal variant. The sphenoid posterior wall position can be determined by review of the preoperative sagittal CT images, which are reconstructed from the axial CT data on the CAS computer.

After a suitable opening into the sphenoid sinuses has been created, the sella itself must be opened. The mucosa from the posterior sphenoid sinus wall is carefully elevated and preserved. Then the thin bone that defines the boundary between the sella and the sphenoid sinuses is removed. A bipolar cautery is used to gently cauterize the underlying dura. Next the dura is incised for access to the pituitary fossa. Standard microdissection permits removal of the pituitary pathology. Violation of the sellar boundaries must be performed to minimize risk to the adjacent parasellar structures. The neurosurgeon usually performs the intrasellar dissection after the otorhinolaryngologist has provided the surgical access.

After completion of the pituitary dissection, surgical closure of the sellar defect is necessary. Autografts of fat, muscle, and/or fascia may be placed in the sella, but if the adjacent parasellar structures prolapse into the sellar space, the sella may not require packing with autografts. In fact, the avoidance of sellar packing may permit for clearer postoperative imaging for the early detection of recurrence. The posterior sphenoid wall (i.e., the sellar anterior wall) should be repaired to decrease the risk of cerebrospinal fluid leak, encephalocele, pneumocephalus, or meningitis [25–27]. Often the otolaryngologist completes this portion of the surgery. Otologic microinstruments may be helpful during the repair of the sellar wall. A layered reconstruction of the sellar wall is desirable. Temporalis fascia or other autogenous fascia may be placed on the intracranial side of the sellar defect in an ‘‘underlay’’ technique (which is similar to fascial graft placement in tympanoplasty). Acellular dermal allograft (AlloDerm, LifeCell Corporation, Branchburg, NJ) may be substituted for the fascial autografts [28]. Obviously, the use of allografts avoids the potential issues associated with the surgical harvest of autografts. The second layer consists of the positioning a piece of septal bone and/or cartilage (or an autogenous bone graft from the sphenoid anterior wall) so that this graft is wedged into position just deep to the posterior sphenoid wall. Sphenoid mucosa can then be redraped over the anterior sella wall defect. Alternatively, a free mucosal graft from the inferior or superior turbinate may be used for this purpose. Fibrin glue or Tisseel surgical sealant (Baxter Healthcare Corporation, Glendale, CA) may be applied over the reconstruction. Finally, dissolvable hemostatic packing (such as Avitene [MedChem Products, Inc., Woburn, MA], Merogel [Medtronic Xomed, Jacksonville, FL] and/or Surgicel [Johnson & Johnson, New Brunswick, NJ]) is then placed in the sphenoid. Anterior sellar wall reconstruction avoids the need for formal sphenoid sinus obliteration, which is now reserved for selected cases only.

Several variations in the traditional sublabial, transseptal, transsphenoidal approach have been introduced. The introduction of endoscopic visualization now

minimizes the risk of septal perforations, which are quite common with the use of the operating microscope. Inadvertent septal trauma is minimized if the telescope is passed between the septal flaps, since the porthole necessary for the telescope is much smaller than the corresponding access needed for the selfretaining nasal speculum and the nasal telescope. Alternatively, the septum may also be left completely undissected; instead the posterior wall of the sphenoid sinus may be exposed via a direct endoscopic unilateral sphenoidotomy. Bilateral endoscopic sphenoidotomies without septoplasty can also be used. Badie et al. [14] studied two groups of patients who underwent standard transseptal transsphenoidal hypophysectomy (n 21) and direct endoscopic transsphenoidal hypophysectomy (n 20). They found that the exposure was equivalent. The endoscopic approach was associated with less facial pain, shorter operative time, and shorter hospitalization. The sublabial technique may be associated with a significant postoperative pain wound infection and nasal deformity. Koren et al. [13] compared the endoscopic transnasal and the sublabial approaches. The endoscopic technique had shorter operative time, shorter hospital stay, and lower incidence of nasal complications.

Today, most otorhinolaryngologists prefer the surgical nasal telescope for visualization during sinonasal procedures, since this instrument offers excellent illumination, visualization, and magnification. Some neurosurgeons have also adopted the telescope for hypophysectomy. The telescope may also supplement the operating microscope during sellar dissections. In particular, the telescope may be used during suprasellar dissections, since the angled telescopes affords visualization that the operating microscope cannot offer. It may be anticipated that the telescope may supplant the operating microscope as more experience with the telescope in pituitary procedures is acquired.

Sethi et al. [21] have developed an entirely endoscopic approach using cadavers. They have utilized this technique in over 40 hypophysectomies and state that it is the preferred technique at their tertiary referral hospital [9]. Carrau and Jho have also instituted a program for similar minimally invasive, endoscopic hypophysectomy at their university-based hospital [10–12]. Both groups believe that actual sella dissection with the 0° and 30° endoscopes permits more thorough dissection since the differences between normal and pathological tissues may be seen more clearly and easily. In addition, the 45° and 70° angled telescopes may also be used to further the extent of dissection in the suprasellar region. A variety of telescope holders and irrigation devices have been introduced; these products allow easier handling of the telescopes and may even permit bimanual dissection.

Vaughan et al. examined the differences among the choices of instruments by three different neurosurgeons who worked in conjunction with a single otolaryngologist [24]. One neurosurgeon preferred the microscope and C-arm, the second neurosurgeon used the operating microscope with CAS surgical navigation, and the third neurosurgeon had chosen the nasal telescope and CAS surgical

navigation. Complications, operative times, blood loss, and length of hospital stay were similar in all patients, regardless of the intraoperative preferences of the operating neurosurgeon.

15.6FUTURE DEVELOPMENTS

Transsphenoidal hypophysectomy has established itself as an effective and welltolerated approach for pituitary surgery. With additional refinements of endoscopic techniques as well as their greater adoption by both neurosurgeons and otorhinolaryngologists, transsphenoidal hypophysectomy will grow to reflect the trend to minimally invasive surgery.

CAS software modifications will drive additional advances in pituitary surgery. Ideally, the next generation of CAS will support better radiology data set management. Furthermore, modified registration protocols may permit greater surgical navigation accuracy but offer simpler strategies for their routine use. CAS surgical planning modules also need additional revision. In particular, surgical planning should include virtual preoperative dissections, which would facilitate the identification of critical structures. In theory, intraoperative surgical navigation could be integrated with preoperative planning so that the CAS computer becomes a surgical warning system. This future CAS system would warn the surgeon of the close proximity of a critical structure (such as the internal carotid artery or the optic nerve) as the surgeon’s instruments approached the structure. Furthermore, robotic instruments, which may be programmed with both preoperative and intraoperative data, may also be developed for hypophysectomies.

15.7CONCLUSION

Many years ago transsphenoidal hypophysectomy emerged as the preferred approach for pituitary gland surgery. All of the various techniques share the common theme of access to the sella through the sphenoid sinus. Anatomical variability and the close proximity of critical structures represent the key surgical challenges during these procedures. To the extent that CAS facilitates the surgeon’s three-dimensional understanding of this anatomy (both through preoperative planning and intraoperative localization), CAS may greatly reduce the potential morbidity and enhance the surgical results of transsphenoidal hypophysectomy.

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