Учебники / Computer-Aided Otorhinolaryngology-Head and Neck Surgery Citardi 2002
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14.3SPECIFIC CAS APPLICATIONS
14.3.1 Frontal Sinus Mucocele
Frontal sinus mucoceles occur secondary to frontal recess obstruction that most commonly may be attributed to injury to the frontal recess. As mucoceles develop, they tend to be asymptomatic. The frontal recess insult that leads to mucocele formation may be iatrogenic; that is, endoscopic or external frontoethmoid sinus surgery may cause scarring in the frontal recess. Similarly, frontoethmoidal fractures and frontal sinus fractures also may injure the frontal recess.
In these cases the first and preferred approach should be frontal recess dissection to drain the mucocele into the nasal cavity [17]. If this approach fails, then more aggressive alternatives may be necessary. CAS may be of paramount importance to enable safe frontal recess dissection and mucocele drainage, as illustrated in Figure 10.11. Note that the frontal sinus posterior table is missing; in this situation, inadvertent intracranial penetration during intranasal surgery is much more likely. Intraoperative surgical navigation was critical for the determination of the correct area for deliberate penetration of the mucocele.
Occasionally, anatomical variations (due to trauma) and very hard bony lamellae (due to osteoneogenesis) will be encountered in the course of frontal recess dissection. CAS provides to the surgeon additional comfort when working
FIGURE 14.11 This intraoperative CAS screen capture (InstaTrak, Visualization Technology, Lawrence, MA) demonstrates a massive bilateral frontal sinus mucocele with erosion of the entire posterior frontal sinus table and anterior skull base.
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through these areas of greater bone density; in this way, CAS increases the safety of intranasal mucocele drainage. During these procedures, the surgeon should follow the skull base upward from the posterior portion of the frontal recess. The posterior frontal recess table can be penetrated easily creating a CSF leak, especially in the context of an altered surgical field. Consequently the direction of dissection must always be from posterior to anterior—never from anterior to posterior (Figure 14.12). After the frontal sinus is open, vigorous irrigation of the sinus will help remove inspissated mucus and debris (Figure 14.13). If the mucosal lining be damaged severely during this process, placement of a stent to hold the frontal ostium open may be important. Neel and Lake, in a series containing animal studies and clinical experience, suggest thin soft silastic sheeting loosely rolled in a funnel shape [18,19]. Our current recommendations include use of thin silastic sheeting cut into a truncated triangle with a T wing of silastic at the apex (Figure 14.14). The triangular part of the stent is rolled, grasped with a 45or 90-degree frontal sinus side biting forceps, and the wings of the T are pushed up into the frontal sinus and allowed to unfurl. The stent is pulled back down into the frontal recess, leaving the wings to anchor it in the frontal sinus, and the body of the stent is partially unrolled in the frontal recess. This allows
FIGURE 14.12 This intraoperative CAS screen capture (InstaTrak, Visualization Technology, Lawrence, MA) demonstrates a frontal sinus mucocele that occurred previous endoscopic surgery. The frontal sinus is completely closed by remnants of the agger nasi cell anteriorly and a supra bullar cell posteriorly. The endoscopic view is undissected frontal recess.
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FIGURE 14.13 This intraoperative CAS screen capture (InstaTrak, Visualization Technology, Lawrence, MA) demonstrates a left frontal sinus mucocele, which developed after previous endoscopic ethmoidectomy. The sagittal view demonstrates that the mucocele is bounded posteriorly by suprabullar cell and osteitic bone at skull base. Endoscopic view demonstrates widely patent frontal ostium after succesful endoscopic frontal recess dissection for removal mucocele.
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FIGURE 14.14 This schematic illustration shows the basic design (A) and placement
(B) of a simple but efficacious frontal sinus stent.
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the stent to cover a larger part of the mucosa and prevents the tightly rolled stent from acting like a tube. It is important to remember that tube-like frontal stents tend to cause circumferential scarring down to the diameter of the stent.
The stent is left in for at least 6 months, and the patient is followed with serial office endoscopic examinations to check stent placement and to treat any bacterial infections that might arise. Occasionally the stents become infected with a mucoid phase bacterial infection such as Pseudomonas. When this occurs, the infection should be managed with culture-directed antibiotics. Unfortunately, the infection may not clear up until the stent is removed.
Figure 14.13 demonstrates a marsupialised frontal sinus mucocele and open supraorbital ethmoid cell posteriorly—this mucocele was created by scar tissue from previous surgeries. Figure 14.14 depicts the ideal end result after the frontal sinus is irrigated with debris and mucus removed.
14.3.2 Lateral Frontal Sinus Lesions
When a lesion is located laterally in the frontal sinus, endoscopic frontal recess dissection should be performed first. At that point, if the lesion cannot be grasped and brought down into the nasal cavity and removed endoscopically, an external approach may be required to remove the lesion completely [18]. Examples of these lesions are laterally positioned cells with chronic sinusitis, frontal sinus osteomas, foreign bodies, or small mucoceles. Most CAS headsets for ENT surgery are positioned directly over the frontal sinus. Repositioning of the headsets from the standard placement often will provide access for external frontal sinus approaches. Alternatively, the tracking system can be moved from the headset so that it is directly attached to the patient’s skull, or a Mayfield head-holder, which tightly secures the patient’s head and mounts the tracking system, may also be used. This latter arrangement is the typical arrangement for neurosurgical procedures. When using these modifications of the standard ENT set-up, it is important that the registration for surgical navigation be completed very carefully. Most systems will require registration based upon anatomical fiducial landmarks or traditional external fiducial markers.
After the CAS system has been prepared for external frontal sinus work, it can guide the placement of a trephination. The CAS probe will add another dimension to the utility of this ‘‘above and below’’ approach. In many cases, the trephine combined with the endoscopic approach will be sufficient to remove any lesions in the frontal sinus.
14.3.3 Osteoplastic Flaps
If the necessary exposure is greater than that provided by a standard trephine, an osteoplastic flap can also be performed. Intraoperative surgical navigation can be especially useful in planning the bone cuts. Drill holes can be designed to
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ensure the safety of the bone cuts and increase their precision. Again, caution must be exercised for correct registration of the CAS system. Since surgical navigation provides greater precision than that afforded by the traditional 6-foot Caldwell plain film, the bone flap may be made larger. The result is better access to the internal frontal sinus. This access will facilitate complete removal of the frontal sinus mucosa if frontal sinus obliteration is planned.
14.4CONCLUSIONS
CAS technology is extremely beneficial in frontal sinus surgery for many reasons. CAS has the capacity to illustrate anatomical abnormalities in the frontal recess; this knowledge can guide more complete frontal recess dissection. The sagittal CT views provided by CAS increase safety when working in the frontal recess and along the skull base. Intraoperative surgical navigation provides confirmation of complete frontal recess dissection. CAS also can be used for placement of external incisions and trephines.
REFERENCES
1.Anderson CM. Some observations on the intranasal operation for frontal sinusitis. Minn Med 1935; 18:744–747.
2.Wright J. A History of Laryngology and Rhinology. 2nd ed. Philadelphia: Lea and Febiger, 1914:271.
3.Ingals EF. Intranasal drainage of the frontal sinus. Ann Otol Rhinol Laryngol 1917; 26:656–668.
4.Mosher HP. The applied anatomy and the intra-nasal surgery of the ethmoid labyrinth. Trans Am Laryngol Assoc 1912; 34:25–39.
5.Van Alyea OE. Ethmoid labyrinth: anatomic study with consideration of the clinical significance of its structural characteristics. Arch Otolaryngol 1939; 29:881–901.
6.Van Alyea OE. Frontal cells. Arch Otolaryngol 1941; 34:11–23.
7.Van Alyea OE. Frontal sinus drainage. Ann Otol Rhinol Laryngol 1946; 55:267– 278.
8.Kuhn FA. Chronic frontal sinusitis: ‘‘the endoscopic frontal recess approach.’’ Oper Tech Otolaryngol Head Neck Surg 1996; 7:222–229.
9.Moriyama H, Yanagi K, Ohtori N, et al. Healing process of sinus mucosa after endoscopic sinus surgery. Am J Rhinol 1996; 10:61–66.
10.Schaeffer JP. The genesis, development and adult anatomy of the nasofrontal region in man. Am J Anat 1916; 20:125–145.
11.Kaspar KA. Nasofrontal connections: a study based on one hundred consecutive dissections. Arch Otolaryngol 1936; 23:322–343.
12.Kuhn FA, Bolger WE, Tisdal RG. The agger nasi cell in frontal recess obstruction: an anatomic, radiologic, and clinical correlation. Oper Tech Otolaryngol Head Neck Surg 1991; 2:226–231.
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13.Bent J, Kuhn FA, Cuilty C. The frontal cell in frontal recess obstruction. Am J Rhinol 1994; 8:185–191.
14.Owen G, Kuhn FA. The supraorbital ethmoid cell. Otolaryngol Head Neck Surg 1997; 116:254–261.
15.Merritt R, Kuhn FA. The interfrontal sinus septal cell. Am J Rhinol 1996; 10:299– 301.
16.Sillers MJ, Kuhn FA, Vickery CL. Radiation exposure in paranasal sinus imaging. Otolaryngol Head Neck Surg 1995; 112:248–251.
17.Kennedy DW, Josephson JS, Zinreich SJ, et al. Endoscopic sinus surgery for mucoceles: a viable alternative. Laryngoscope 1989; 99(9):885–895.
18.Neel HB, Whicker JH, Lake CF. Thin rubber sheeting in frontal sinus surgery: animal and clinical studies. Laryngoscope 1976; 86:524–536.
19.Neel HB, McDonald TJ, Facer GW. Modified Lynch procedure for chronic frontal sinus disease: rationale, technique and long term results. Laryngoscope 1987; 97: 1274–1279.
20.Bent JP, Spears RA, Kuhn FA, Stewart SM. Combined endoscopic intranasal and external frontal sinusotomy (the above and below approach to chronic frontal sinusitis: alternatives to obliteration). Am J Rhinol 1997; 11:349–354.
15
Computer-Aided Transsphenoidal
Hypophysectomy
Winston C. Vaughan, M.D.
Stanford University, Stanford, California
15.1INTRODUCTION
The biopsy and removal of pituitary pathology is usually a joint procedure performed by the otorhinolaryngology and neurosurgery services. The transsphenoidal route to the pituitary fossa has become the preferred approach, since it has been shown to offer faster recovery and fewer complications when compared to traditional craniotomies. However, significant complications remain, which usually relate to the close proximity of critical structures. The removal of sellar pathology without injury to the adjacent structures is the main aim of transphenoidal surgery.
Computer-aided surgery (CAS) technology has been implemented in many centers in these procedures, since it offers improved surgical precision and potentially improved surgical outcomes.
15.2HISTORICAL PERSPECTIVE
The early history of pituitary surgery is filled with renowned surgeons from multiple specialties and countries. It is interesting to consider that these early procedures occurred at a time when antibiotics were not available, microscopes were
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new devices, and the C-arm image intensifier was considered a major advance in surgical navigation.
Schloffer [1] and Kanavel [2] described an intranasal route that used a subnasal and lateral rhinotomy incision. Halstead introduced the sublabial transnasal route [3]. Cushing followed with the sublabial transeptal approach [4]. He operated on over 240 pituitary masses from 1910 to 1929. This approach lost favor for several years and was replaced by intracranial approaches. Guiot and Thebaul in France, followed by Hardy in Montreal in the 1960s, reintroduced the sublabial, transeptal transsphenoidal route, using the operating microscope and intraoperative fluoroscopy [5–7]. Approximately 40 years later, the sublabial, transseptal, transsphenoidal route to the sella remains the preferred approach for most neurosurgeons.
Over the last decade, otorhinolaryngologists have begun to use endoscopic techniques extensively. More recently, neurosurgeons have started to adopt these techniques. Several joint otorhinolaryngology and neurosurgery teams have published their experiences with these minimally invasive endoscopic applications [8–14].
Endoscopic approaches in the management of sinus inflammatory disease are now some of the most common procedures performed by otorhinolaryngologists. Implementation of CAS surgical navigation during these difficult dissections has improved the safety and efficacy of these procedures.
15.3COMPUTER-AIDED SINUS SURGERY OVERVIEW
CAS involves the use of an imaging data set for the confirmation of anatomical location during surgical dissection. CAS-based surgical navigation is usually considered a purely semiconductor-based technology; however, use of intraoperative fluoroscopy for localization of instrument positions really is a primitive form of surgical navigation. In this regard, the first real application of this approach involved the use of the C-arm image intensifier to localize the skull base position during sinus dissections. Today computed tomography (CT) scans and magnetic resonance imaging (MRI), coupled with sophisticated tracking systems, are now used.
In early CAS systems, articulated arms provided positional information for the computer system. More sophisticated CAS systems incorporate electromagnetic or optical emitters and sensors for the tracking of instrument positions. Real-time intraoperative imaging is also possible using portable CT scanners [15]. Standard operating rooms have been adapted to accommodate a modified open MRI scanner so that surgical dissection can occur under MRI guidance [16]. (These systems are described in other chapters throughout this book.)
The main indication for CAS in sinus surgery that targets refractory inflammatory rhinosinusitis includes dissection in areas surrounded by vital struc-
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tures. Furthermore, CAS also offers advantages in the situation where the usual surgical landmarks have become distorted. In a similar fashion, CAS may be useful in transsphenoidal hypophysectomy, since the close proximity of vital structures (namely, the internal carotid arteries, the cavernous sinus and its contents, the brain, and the optic nerve) leads to a very small surgical margin of error. Complications related to inadvertent injury to these structures can be devastating. The guidance provided by CAS cannot substitute for knowledge of anatomy or careful dissection, since CAS is not an infallible technology.
15.4DEVELOPMENT OF COMPUTER-AIDED TRANSSPHENOIDAL HYPOPHYSECTOMY
In 1969 Hardy published an excellent description of his transsphenoidal technique, which included the use of the operating microscope and televised radiofluoroscopy [7]. In this article he details the benefit of real-time fluoroscopy for identification of surrounding anatomical landmarks. By the time of its publication in 1969, he had performed over 200 cases using fluoroscopic guidance. His work represents the birth of surgical navigation for pituitary surgeons.
Recent advances have included the use of preoperative radiology, along with computer software, to create a navigational data set, which can be used during the surgery. This is usually performed with CT or MRI scans. Specialized software programs also support the simultaneous use of multiple imaging data sets. Ideally, imaging for hypophysectomy should include a CT scan of the bone boundaries, an angiogram of the surrounding vessels and a MRI of the sellar region. For this reason, the use of multiple preoperative images offers significant appeal.
MRI scans obtained before and after transsphenoidal hypophysectomies have demonstrated a fair amount of residual disease. Kremer et al. studied 22 patients with macroadenomas and found 11 cases with residual pituitary tissue [17]. Such residual tissue suggests that more thorough dissection in the sella may reduce disease persistence or progression. CAS has been shown to provide for more thorough dissection in sinus surgery and may prove to do the same in pituitary surgery.
Most CAS systems use a preoperative data set. Recently, both MRI and CT technology have been used for real-time scanning and surgical guidance during hypophysectomies [15,16]. MRI scans, which are a familiar imaging modality for neurosurgeons, offers the advantage of better soft tissue enhancement. MRI also avoids radiation exposure for both patient and staff. Unfortunately, intraoperative MRI systems require special, nonferromagnetic instrumentation, because the MRI scanner generates strong magnetic fields. In contrast with MRI, CT offers better bone margin enhancement. Standard surgical instruments and anesthesia are more easily utilized with an intraoperative CT scanner, but special accommodations for the CT scanner still must be made.
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Schwarz et al. utilized intraoperative MRI guidance in 200 intracranial cases [16]. They found that MRI guidance using an open-bore system provided continuous visual feedback and did not affect the complication rate or time of surgery. This series included five cases of transsphenoidal pituitary resections. (For more information about intraoperative MRI, see Chapter 5.)
Real-time CT guidance has also been reported during hypophysectomy. Kitazawa et al. described nine cases in which a mobile CT scanner was used [18]. They felt that the system provided ‘‘accurate information about the location and volume of residual tumor as well as . . . surrounding deeper structures.’’ Mattox and Mirvis used real-time CT scanning during sinus surgeries [15]. They stated that in selected cases, the added radiation exposure was justified due to the improved surgical safety for the patient.
Most CAS systems rely upon a preoperative CT or MRI scan. Since these scans are obtained in advance of surgery, surgeons can readily review the images for surgical planning and patient counseling. These systems are also less cumbersome in the operating room, since they do not require the significant modifications that intraoperative MRI scanners and CT scanners require.
CAS in transsphenoidal hypophysectomy carries an important caveat. Since hypophysectomy involves soft tissue manipulation and removal, intraoperative findings that reflect these soft tissue changes cannot be demonstrated on a preoperative imaging data set. For this reason, the incorporation of intraoperative imaging into standard CAS systems would be very helpful.
15.5SURGICAL TECHNIQUE FOR TRANSSPHENOIDAL HYPOPHYSECTOMY
The otorhinolaryngologist usually provides access and closure during transsphenoidal hypophysectomy. The amount of dissection performed for such access depends on the anatomy and surgeon preferences [19]. Different approaches, including sublabial, open rhinoplasty, transethmoidal, transseptal, and direct transnasal routes, may be performed under the visualization afforded by the operating microscope and/or surgical telescope [20]. Even headlight illumination may be used. The common element in all of these techniques is access to the sphenoid sinus. For this reason, the sphenoid sinuses themselves and the anatomical structures that surround the sphenoid sinus should be carefully reviewed in coronal, axial, and sagittal CT images before surgery. Knowledge of the anatomy in this area provides the otorhinolaryngologist with the information necessary for the choice of the appropriate approach or combination of approaches [21–23].
During the surgical approach to the pituitary fossa, the otorhinolaryngologist must avoid the sphenopalatine artery (Figure 15.1), the internal carotid artery (Figure 15.2), and the optic nerve (Figure 15.3). Furthermore, the bone of the lateral wall of sphenoid sinus may be dehiscent (Figure 15.4). In addition, sphe-