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

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Complete description of the numerous reports devoted to CAS in sinus surgery is beyond the scope of this brief discussion. Other authors have presented similar experiences and have described similar conclusions.

13.4DESCRIPTION OF TECHNIQUE

After the diagnosis of refractory rhinosinusitis, which has persisted despite aggressive medical treatment and previous surgery, has been confirmed, revision FESS may be necessary. Informed consent for the procedure should include an explicit discussion of the surgical risks, including bleeding, scar tissue formation, persistent or new infection, blurred vision, double vision, blindness, cerebrospinal fluid leak, meningitis, brain abscess, brain injury, and death. In addition, the use of CAS should also be discussed with the patient. Since CAS is a new and exciting technology, there is some tendency to overstate its potential benefits. Care should be taken to avoid this problem.

Before surgery, an appropriate CT scan should be obtained. For CAS, direct axial images, from which the CAS workstation can reconstruct coronal and sagittal images and three-dimensional models, are necessary. Preoperative image data may be transferred to the CAS workstation via local networks or on digital media (such as optical disks). In general, the quality of the reconstructed images will be better with thinner axial slice thickness. Software algorithms within the CAS workstation help avoid the stair-stepped appearance of the reconstructed images. One must realize, however, that these reconstructed coronal and sagittal images contain computer-generated data and may not accurately represent the patient’s anatomy.

It is helpful to study the multiplanar images (axial, coronal, and sagittal) as part of presurgical planning. Residual ethmoid air cell walls and/or areas of new bone formation can be seen, and their relationships to the ethmoid roof, lamina papyracea, and sphenoid sinus can be appreciated. Structures such as the optic nerve and the cavernous sinus portion of the internal carotid artery can be followed by ‘‘scrolling’’ through images in one plane while following them in the other two planes. This maneuver can provide invaluable information as to areas at risk for catastrophic complications. With current CAS workstations, utilizing a variety of headsets, reference frames, and registration techniques, there is virtually no need to obtain additional CT’s immediately prior to performing CAS; that is, the CT scan may be completed days, weeks, or even months prior to the surgery. Of course, long delays between the CT scan and actual surgery are not advisable for other reasons, but at least the newer systems avoid the need for CT scans on the day of surgery.

Computer-aided revision sinus surgery can be performed under local anesthesia with intravenous sedation or general anesthesia. The choice of anesthetic may be based on the surgeon’s preference. The specific details of the set-up of

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the CAS equipment reflects the design and technology of the CAS platform chosen for the procedure. For sinus surgery, essentially all systems employ a headset that provides a reference frame for surgical navigation. Before surgical navigation can be used, registration, a calibration process through which the computer correlates corresponding points in the surgical volume and CT scan data set volume, must be completed. Each CAS system has its own registration protocol. (For a complete discussion of these issues, please refer to Chapters 3, 4, 11, and 12). Then the CAS surgical instruments, which may include straight and curved aspirators, the microdebrider, and through-biting forceps, may be calibrated.

After registration is completed, the accuracy of surgical navigation should be confirmed. An estimate of accuracy is made by comparing known endoscopic anatomical landmarks with the corresponding CAS localizations displayed on the computer monitor. It is helpful to utilize anatomical structures that are not likely to be altered during the revision surgical procedure. Such landmarks include the posterior choana, the vomer of the nasal septum, and the maxillary crest. These anatomical verification points must be utilized throughout the surgical procedure whenever a question regarding localization accuracy arises. Confidence in the reliability of the localization during the surgical procedure is enhanced if the initial correlation between anatomical landmarks and corresponding localizations is estimated to be within 1–2 mm.

After the surgery has begun, it is important to reassess the accuracy of the system against known points. If surgical navigation accuracy does not appear to correlate well with these anatomical landmarks, the initial anatomical verification points—which had indicated acceptable accuracy at the beginning of the case— should be reexamined with the localizing probe. Any inaccuracies should be reconciled. The reference frame position and/or headset should be inspected for proper placement. Repeat registration should be performed if necessary. If the inaccuracies cannot be reconciled, the CAS workstation should not be utilized during the procedure.

After an acceptable registration has been achieved, diagnostic nasal endoscopy is performed with a CAS localizing probe, such as a straight aspirator. This allows the surgeon to correlate endoscopic images and the preoperative CT scan data as a step in the revision sinus operation. In particular, determining the relationship of the middle turbinate or its remnant to the lateral nasal wall provides reliable orientation early in the revision surgical procedure. If the middle and superior turbinates have been completely resected, identification of the sphenoid face and posterior ethmoid roof are early goals. Finally, if the maxillary sinus natural ostium or an accessory ostium can be found, the posterior maxillary sinus wall and its roof can be visualized with an angled telescope. By correlating these maxillary sinus landmarks with its medial wall, the lamina papyracea can be located and established as the lateral boundary of the ethmoid dissection. Any of the above-mentioned techniques can be used, depending on the specific clinical situation.

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The goal of revision ethmoid surgery is the wide marsupialization of the ethmoid labyrinth. This involves removal of all remaining ethmoid air cell walls by dissecting along the lamina papyracea and ethmoid roof while preserving surgical landmarks, such as the middle turbinate basal lamella and its anterior vertical attachment. Of course, maximum mucosal preservation should be attempted. Through-biting instruments are helpful when removing bone from the ethmoid roof and lamina papyracea since they reduce the torque placed on these bony cell wall remnants when compared with curettes and standard grasping forceps.

13.5SPECIFIC SURGICAL SCENARIOS

One of the most common diagnoses of patients undergoing revision endoscopic sinus surgery is sinonasal polyposis. It is also common for these patients to have had more extensive surgery than nonpolyposis patients. Frequently the middle and superior turbinates have been partially resected. Figure 13.3 depicts a coronal CT image of a patient with recurrent symptomatic nasal polyposis, refractory to medical therapy. Partial resection of inferior, middle, and superior turbinates had

FIGURE 13.3 This coronal CT depicts prior middle turbinate resection and associated ethmoid sinus opacification. The left posterior ethmoid cavity is aerated and represents a key early landmark in this patient’s revision ethmoid surgery. The uncinate process is intact bilaterally.

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FIGURE 13.4 At the beginning of a revision FESS procedure, diagnostic nasal endoscopy coupled with CAS defines the relevant anatomy. In addition, the accuracy of surgical navigation can be confirmed. In this example, the endoscopic image shows the position of the localizing aspirator. The multiplanar CT images (namely the coronal, sagittal, and axial images in the orthogonal planes through a specific point) show the calculated position of the instrument tip. The middle turbinate is lateralized and there is polypoid mucosa in the middle meatus. The lateral nasal wall (LNW) can be seen. In this way, navigation accuracy is confirmed and key structures may be appropriately localized.

been performed during the patient’s initial surgery. A superior nasal septal perforation is present, and both uncinate processes are intact.

During the revision CAS procedure, the first step is to establish the accuracy of surgical navigation by localizing to a known landmark. In Figure 13.4, the multiplanar CT images shows a representative localization that confirms system accuracy; that is, the tip of the probe is seen at the inferior portion of the middle turbinate basal lamella. The sagittal image depicts this information well. Figure 13.4 also demonstrates that the left middle turbinate remnant is scarred to the lateral nasal wall and the mucosa is polypoid. Penetration of the basal lamella allowed the surgeon to enter the posterior ethmoid cavity and readily identify the posterior ethmoid skull base. This can be seen in the next set of multiplanar CT and endoscopic images (Figure 13.5).

Figure 13.6 shows the right nasal cavity in the same patient. The middle turbinate has been partially resected. The multiplanar CT and endoscopic images

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FIGURE 13.5 After penetration of the left middle turbinate basal lamella, the position of the ethmoid roof must be determined. In this instance, the skull base is clearly seen, and the CT scan images obtained via surgical navigation confirm this landmark.

FIGURE 13.6 This intraoperative CAS screen capture shows the precise location of the localizing aspirator in the anterior middle meatus. The right middle turbinate (MT) has been partially resected, and its inferior border is superior to the maxillary sinus natural ostium in the axial plane.

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FIGURE 13.7 Another intraoperative CAS screen capture depicts localization through a point in the right posterior ethmoid. The right middle turbinate basal lamella has been penetrated for access to the posterior ethmoid, and the skull base has been identified in the posterior ethmoid cavity. The probe tip is at the junction of the lateral skull base and the superior aspect of the lamina papyracea. The optic nerve is not at immediate risk, as seen on the axial image.

depict the inferomedial boundary of the lamina papyracea and the inferior edge of the middle turbinate remnant. In this anatomical situation, the inferior border of the middle turbinate can mislead the surgeon in regard to the proper location of the maxillary sinus natural ostium. If a ‘‘blind’’ maxillary antrostomy were created in this location, the orbit could be easily penetrated. Instead, careful search for the uncinate process and its complete removal resulted in the proper and safe identification of the natural ostium of the maxillary sinus. Then the middle turbinate basal lamella was penetrated under CAS guidance, and the posterior skull base position was verified (Figure 13.7). After precise identification of the lamina papyracea and the skull base in the posterior ethmoid cavity, the ethmoid cavity was then marsupialized by removing cell wall remnants. In this situation, through-biting forceps are helpful by reducing unnecessary torque and aiding in mucosal preservation (Figures 13.8 and 13.9).

Identification of the anterior vertical attachment of the middle turbinate can be a helpful landmark in the presence of residual and/or recurrent anterior eth-

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FIGURE 13.8 This endoscopic image shows the appearance of the left nasal cavity at the completion of computer-aided revision FESS. The middle turbinate remnant has been preserved and remaining ethmoid cell walls have been removed.

FIGURE 13.9 This endoscopic image shows the appearance of the right nasal cavity at the completion of computer-aided revision FESS. The middle turbinate remnant has been preserved and the natural ostium of the maxillary sinus can be seen. Ethmoid cell wall remnants have been removed from the skull base and lamina papyracea.

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FIGURE 13.10 This coronal CT image demonstrates left middle turbinate lateralization that mimics the endoscopic appearance of a shortened ethmoid.

moid and frontal recess disease; however, in revision FESS cases, careful examination of the preoperative CT may show that this endoscopic landmark has become distorted. In a primary case, ethmoid air cells are located posterior and lateral to the vertical attachment of the middle turbinate. In a revision case, the vertical attachment of the middle turbinate may become lateralized and scarred to the lamina papyracea, resulting in an anterior ethmoid sinus mucocele (Figures 13.10 and 13.11). This creates a misrepresentation of the position of the anterior ethmoid roof and residual ethmoid cell wall remnants from a purely endoscopic viewpoint. Endoscopic dissection in this scarred middle meatus may lead to an inadvertent orbital injury and/or unsuccessful drainage of the mucocele. Appropriate marsupialization of the mucocele in this situation should be performed anterior to the middle turbinate vertical attachment. Increased confidence in choosing the proper location for drainage is improved with CAS by correlating these structures endoscopically with the multiplanar CT images.

Patients who have undergone orbital decompression for Graves’ ophthalmopathy may develop symptoms of chronic rhinosinusitis. This is likely to be

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FIGURE 13.11 This coronal CT image is slightly anterior to the image in Figure 13.10. An anterior ethmoid sinus mucocele, resulting from middle turbinate lateralization, is seen.

worse in patients who have undergone prior radiotherapy, which may lead to secondary damage of mucociliary clearance mechanisms. Surprisingly, Mann found that in his series of 23 patients no patient required revision sinus surgery and rather aggressive medical therapy and extended follow-up were sufficient [28]. Of course, some Graves’ patients may have concomitant paranasal sinus disease and require eventual surgery. Figure 13.12 depicts anterior ethmoid opacification in a patient who has already received orbital decompression. Under CAS guidance, the inferior and superior margins of lamina papyracea resection could be identified as well as intact lamina papyracea posteriorly. A plane between the orbital fat and the anterior ethmoid polyps was identified by endoscopic criteria; in this way, the careful removal of the polyps proceeded without injury to the orbital contents (Figure 13.13). A similar situation may occur in patients who have undergone a previous external ethmoidectomy approach. In the absence of a true bony wall separating the ethmoid sinus from orbital contents, powered instrumentation should be used with extreme caution. Orbital fat and/or the me-

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FIGURE 13.12 This coronal CT image shows left anterior ethmoid sinus opacification after prior external orbital decompression. Note the absence of the lamina papyracea.

dial rectus muscle can be pulled into the oscillating blade, which can injure soft tissues quickly and easily.

In extreme cases of prior surgical alteration of landmarks, CAS is invaluable in identifying even the most basic landmarks. Figure 13.14 depicts a patient in whom both traditional surgical approaches (namely Caldwell-Luc procedures) and intranasal endoscopic techniques have been utilized for the treatment of nasal polyposis. One can appreciate the absence of reliable landmarks. In these patients, CAS perhaps offers the most assistance. In this case, the left posterior ethmoid roof and lamina papyracea was identified endoscopically and verified through surgical navigation early during the surgical procedure. Similarly, the right posterior ethmoid roof and lamina papyracea was identified after penetration of the remnant of the middle turbinate basal lamella.

In patients with diffuse sinonasal polyposis, which may be associated with tissue hyperemia and significant intraoperative blood loss, CAS is a useful adjunct. Patients with extensive disease are likely to have more bleeding when compared to patients with less extensive disease. While this blood loss is not