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

who are unfamiliar with endoscopic techniques cannot understand how these endoscopic techniques can incorporate fundamental oncological principles so that the endoscopic techniques achieve precision and tissue removal comparable with the more widely accepted, traditional external approaches. Advocates of external approaches are fast to note that facial, cranial, and/or gingival incisions are justifiable in order to attain good exposure and visualization of the surgical field; in this view, such exposure allows for more complete resections. Some surgeons even consider endoscopic treatments to be no more than piecemeal tumor resections. However, for experienced endoscopic surgeons, external incisions are not necessary to attain exposure and visualization. In fact, the visualization of the endoscopic alternative may be even greater than the standard external approaches. In general, most head and neck surgeons who are experienced with endoscopic approaches find few differences between the endoscopic and external procedures for selected lesions in regard to the degree of tissue removal and adequacy of visualization.

Initially advocated for inflammatory disease, endoscopic approaches are increasingly being used for the definitive treatment of nasal and paranasal sinus neoplasms, which previously were resected through more traditional (transfacial or craniofacial) approaches. In the hands of experienced and skilled surgeons, complete endoscopic resection is now attainable in many cases. Endoscopic resection of inverted papillomas, meningoencephaloceles, and a variety of select benign and malignant neoplasms has been advocated as a reasonable alternative to traditional approaches with equivalent efficacy [1–24]. However, large tumor size and uncertainty about the localization of critical neurovascular structures and extranasal tumor margins still limit the use of this approach for a number of other lesions. Today, with the introduction of computer-aided surgery (CAS) and other technological advancements, there are new and exciting surgical possibilities as endoscopic surgeons progressively challenge even these barriers.

16.2APPLICATIONS

CAS devices complement good clinical judgment, thorough preoperative surgical planning, a solid understanding of the endoscopic anatomy, and sound surgical technique, but CAS can never be a substitute for any of these aspects of surgical care. This observation is especially important when performing endoscopic resection of nasal and paranasal sinus neoplasms. When used appropriately, CAS may be useful for preoperative surgical planning, including the identification of critical anatomical landmarks that may be obscured by inflammation, tumor, congenital anomalies, previous surgery, or neoplasms, and for maxillofacial reconstruction.

CAS devices serve as an excellent teaching tool that bears resemblance to an in-flight simulator, which may provide information for the benefit of operating

FIGURE 16.2 This three-dimensional CT reconstruction of a left nasoethmoid neoplasm demonstrates its location relative to the midface craniofacial skeleton.

fication of critical anatomical structures and tumor margins. CAS can be a useful adjunct for the identification of these critical structures. During the surgical procedure, the surgeon can reliably identify and preserve critical structures that are in close proximity to the tumor even if they have been displaced, obscured, or destroyed by the tumor. CAS gives the surgeon the most efficient access to the tumor for endoscopic resections, external resections, and even external resections with endoscopic assistance. Furthermore, CAS also increases the surgeon’s level of confidence and thereby avoids the need for extensive dissection for the sole purpose of identifying a particular structure. This enhanced margin of safety allows experienced surgeons to consider the use of minimal access approaches. With CAS, the extent of surgical exposure may be more limited, since dissection for the confirmation of neurovascular structures may be minimized. Thus, CAS may expedite the entire surgical procedure. Although this observation has not been objectively confirmed, CAS may decrease surgical morbidity during complex surgeries of the maxillofacial skeleton, orbit, and skull base, while facilitating complete tumor resection.

CAS is most accurate and practical when used to identify fixed bony landmarks such as the paranasal sinuses and neurovascular foramina. It is useful to identify and/or preserve an anatomical barrier (such as the ethmoid sinus roof or orbital wall), a vital vessel (such as the internal carotid artery at its petrous portion), and/or an important cranial nerve (such as the optic or vidian nerve at its foramen or canal). CAS may also serve to plan the margins of tumor resection or to plan a craniotomy or sinusotomy (Figures 16.3 and 16.4). The boundaries of resection during medial maxillectomy may be easily identified with CAS. Similarly, the critical landmarks for endoscopic orbital decompression (namely the

FIGURE 16.3 Another three-dimensional CT reconstruction of a left nasoethmoid neoplasm shows involvement of the medial wall of the orbit as well as the orbital apex.

FIGURE 16.4 (A) This three-dimensional CT model shows the volume of the frontal sinus as well as its relative position. With this information, it is possible to plan the location of the bone cuts for elevation of the anterior table of the frontal sinus. (B) This intraoperative photo shows the outline of frontal sinus pneumatization as determined by a traditional 6-foot Caldwell plain film template (temp) and intraoperative surgical navigation (ISG). CAS provided a more accurate estimation of the size of the frontal sinus; therefore, CAS serves as a better guide for the placement of the bone cuts for osteoplastic sinusotomy.

medial and/or inferior orbital wall) and dacryocystorhinostomy (namely the lacrimal sac and duct) can be recognized. CAS can also be useful for identification of the optic canal or foramen when decompressing the nerve as part of a tumor resection or for posttraumatic neuropathy, especially in the absence of the traditional landmarks. Although CAS cannot provide information about soft-tissue composition and position intraoperatively (since surgery will alter those soft tissues), CAS can identify bony landmarks, which in turn provide important cues about the adjacent soft tissues. For example, intraorbital dissection of the orbital soft tissue during resection of the periorbita as part of an en bloc resection is greatly facilitated by identifying the frontoethmoidal suture and the ethmoidal and/or optic neurovascular foramina. These structures are not as readily visible as when dissecting in a subperiorbital plane, since the periorbita covers the frontoethmoid suture and neurovascular foramina.

16.2.3 Maxillofacial Reconstruction

CAS may facilitate the reconstruction of maxillofacial skeleton after the oncological resection is complete. At the CAS workstation, the surgeon can create a virtual mirror image reconstruction to achieve a symmetrical reconstruction by using the image of the contralateral side as a guide (Figure 16.5). Alternatively, the preoperative image can be used as a virtual moulage or mold to recreate the

FIGURE 16.5 (A) This patient had right enophthalmos after an orbital trauma. Formal orbital reconstruction was necessary. (B) Preoperative CAS-based surgical planning and intraoperative CAS surgical navigation was used to determine the appropriate level of the orbital floor relative to the contralateral side. The crosshairs indicate the desired relative height for the orbital floor reconstruction.

TABLE 16.1 The Ideal Computer-Aided Surgery Device

Good correlation between actual surgical anatomy and CAS images (including reconstructions)

Surgical navigation accuracy of 2 mm or better to minimize the risk of complications Dynamic registration (which compensates for inadvertent head movement) Specialized CAS CT or MRI not required

Minimal training for it use Cost-effective alternative

Easy user interface which does not require the presence of a technician

Real-time update of imaging (compensation for intraoperative tissue manipulation/ distortion)

preoperative image. Of course, this option may only be useful if the disease process has not altered that contour. Thus, the surgeon can reconstruct a supraorbital bar, frontal bone, or orbital floor using titanium mesh or other material of preference and then CAS may confirm the adequacy of the profile using CAS.

16.3ADVANTAGES AND DISADVANTAGES

Table 16.1 outlines the desired qualities of the ideal CAS system. Current CAS devices have inherent properties that may be an advantage or disadvantage, depending on its user (Tables 16.2 and 16.3).

The need for adequate experience, training, and clinical judgment to use these devices effectively and safely cannot be overemphasized. CAS has a learning curve that initially lengthens—rather than shortens—the length of surgery. On the other hand, the learning curve also dictates that with experience, the time associated with CAS set-up decreases. In fact, CAS may even reduce the time required for surgery. Experienced surgeons, who are endoscopically resecting sinonasal neoplasms, may actually find that CAS may reduce or even eliminate

TABLE 16.2 CAS Advantages

Accelerates the learning curve

Facilitates minimal access approaches

Identifies neurovascular foramina

Identifies altered anatomy

Localizes precise osteotomy/craniotomy/sinusotomy

Reduces operative time

Reduces morbidity

TABLE 16.3 CAS Disadvantages

Limited accuracy

No real-time update of intraoperative tissue manipulations

Limits access to the surgical field

Costly:

The device

Additional CT or MRI imaging

Technician

Time necessary for registration

False sense of confidence

the time required for the identification of important structures by minimizing the need for extensive dissection throughout the surgery.

The accuracy of intraoperative CAS surgical navigation must be monitored throughout the procedure. Even in the CAS systems that support dynamic registration (so that the system compensates for inadvertent movement of the patient’s head by tracking the head’s position), reference frames can slip. When this occurs, the accuracy of surgical navigation will be compromised. Surgical navigation accuracy can be checked by localizing recognizable fixed structures; then the surgeon can compare the calculated position shown by the CAS computer with the known position in the operating field volume. It should be remembered that under the best circumstances, CAS surgical navigation accuracy is still 1– 2 mm; therefore, knowledge of anatomy is still critical.

In addition, soft tissue shifts caused by surgical dissection or tumor removal cannot be tracked by any of the currently available CAS devices. The intraoperative monitor display is based on the patient’s preoperative CT scan data set. This limitation is particularly important if the surgeon plans to operate beyond the bony confines of the paranasal sinuses. For instance, during endoscopic resection of skull base or orbital lesions, surgically induced distortion of the intracranial, skull base, or orbital soft tissues is a possibility. Intraoperative MRI, CT, or ultrasound have been advocated to circumvent this problem, but these devices are even more costly, are time-consuming, require special surgical instrumentation and operative suites, and/or are not currently widely available.

There are also some limitations with the 3D reconstruction. To truly simulate a surgical procedure in the 3D reconstruction requires intense work in order to delineate every structure that will be encountered in the proposed surgical procedure. In other words, to simulate an infratemporal fossa approach, the surgeon, radiologist, or radiology technician has to delineate the boundaries of the structures that will be manipulated (e.g., temporalis muscle, masseter muscle, parotid, scalp, orbitozygomatic complex, and any structures of interest within the

infratemporal fossa). This requires a thorough knowledge of CT or MR anatomy. New CAS software may facilitate these simulations, but these upgrades have not been introduced. In the near future there should be anatomical recognition programs for neural structures to facilitate these tasks.

One of the greatest limitations of CAS devices is their cost. The devices range from $150,000 to $400,000, depending on their capabilities and applications. Adding to the cost is the need for a fine-cut CT scan or MRI, which provides the raw data for the CAS system. Most patients will have already undergone a scan for diagnostic purposes; therefore, the CT or MRI scan for CAS is an additional added cost. Often the device requires a dedicated technician or nurse during the registration process or even throughout the entire surgery. These costs can be amortized by sharing the CAS devices among different surgical services and using fine-cut imaging protocols when the need for CAS is anticipated. Nonetheless, the costs are still considerable and will be passed to the patient or thirdparty payers and/or absorbed by the buying institution.

16.4ENDOSCOPIC RESECTION OF SPECIFIC NEOPLASMS AND EROSIVE LESIONS

When compared to other neoplasms of the head and neck, tumors originating in the nose or the paranasal sinuses present with a relatively low incidence in the general population. The most common of the malignant neoplasms is squamous cell carcinoma, occurring in less than 1 in 200,000 inhabitants per year [27]. Benign neoplasms are found even more infrequently. The most frequent benign tumors arising from this region are inverted papillomas, osteomas, hemangiomas, and juvenile nasopharyngeal angiofibroma (JNA). Although they are not true neoplasms, sinus mucoceles, meningoceles, and encephaloceles may present as intranasal or sinus masses and can be equally destructive to neighboring orbital and skull base structures. Three-dimensional reconstruction utilizing CAS can be utilized to guide the limits of resection by outlining the margins of the tumor resection margin or point of entry during a mucocele decompression.

Many lesions of the skull base are not easily accessible for biopsy. Frequently a seemingly minor biopsy requires a fairly extensive surgical approach to obtain an adequate specimen. This is especially true for lesions in the pterygopalatine, clival, and parasellar regions. The use of endoscopic approaches, assisted by CAS, can avoid the morbidity of a transfacial or transbasilar approach (Figures 16.6).

Some patients may have unresectable lesions threatening vital structures such as the optic nerve and other orbital structures. In these cases, tumor debulking and decompression of vital structures may be indicated. Benign lesions, such as fibrous dysplasia, can safely be debulked. In these procedures, the optic nerve, orbit, or secondary mucoceles in the dependent sinuses can be decompressed

FIGURE 16.6 The crosshairs on this sagittal CT reconstruction show posterior tumor boundary, which guided planning for an intracranial osteotomy.

without extensive dissection. CAS is helpful in identifying the nasofrontal recess, orbital apex, carotid canal, ethmoid roof, optic canal, and the margins of the disease process.

16.4.1Endoscopic Resection of Common Benign Lesions of the Sinonasal Region

and Anterior Skull Base

16.4.1.1Inverted Papilloma (Schneiderian Papilloma)

Inverted papilloma is one of the most common benign tumors of the paranasal sinuses. This locally aggressive tumor derives its name from the microscopic features that characterize it; its histology reveals the digitiform proliferation of squamous epithelium into the underlying stroma. Patients present with this entity in the fifth to sixth decades of life, with a clearly marked male predominance of 2–4:1 [1–5,28–32]. Classically, the tumor originates from the lateral nasal wall and subsequently involves the contiguous paranasal sinuses. Although no specific symptoms are unique to this entity, unilateral nasal obstruction constitutes the most consistent initially presenting symptom in 71–87% of cases. The potential for malignant transformation is one of the features that characterizes this tumor, with reports ranging from 5 to 13% in some of the studies with larger series of patients [30,31].