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

needle biopsies were diagnostic and accurate. This is especially notable because none of these lesions were palpable or located in easily accessible regions. No complications were encountered.

An example of an interactive MR-guided needle biopsy is shown in Figure 5.4. A 57-year-old male noted left upper neck swelling for 1 month without a palpable mass. Further evaluation disclosed the lesion on MRI, and an MRguided FNA was performed as demonstrated. The cytological findings were consistent with a pleomorphic adenoma, which was subsequently excised.

In a recent study by Davis and associates [6], a series of 21 patients were submitted for MR-guided biopsies of head and neck lesions. Of these, 9 were nonpalpable lesions, and 8 lesions involved deeps tissue spaces within the head and neck not conventionally accessible by standard FNAB techniques. Two patients had previously unsuccessful needle biopsies of their lesion. The authors found a concurrence rate of 92% between the MR-guided needle biopsy technique and subsequent open biopsy or surgical therapy. No complications were encountered within this patient series. The authors concluded that the use of MR-guided needle biopsy added to the accuracy and safety of the needle biopsy procedure. Furthermore, several patients were able to avoid potentially morbid and disfiguring surgeries based on the MR-guided needle biopsy results. Similar findings were noted in a series of 24 patients reported by Wang and associates [18].

Further work needs to the established to verify the accuracy and safety of MR-guided needle biopsy in the head and neck. The intuitive advantages of MR imaging coupled with the ability to perform scans track the biopsy needle trajectory may potentially offer the most reliable integrated needle biopsy technique in the head and neck. Further work is currently being conducted to develop active real-time tracking systems for the needle biopsy instrument and to develop alternative trajectory approaches for difficult to reach lesions [12].

5.3.2 MRI-Guided Endoscopic Sinus Surgery

Image guidance during endoscopic sinus surgery (ESS) has been a major focus in otolaryngology-head and neck surgery [2,19,20]. The impetus for image guidance during ESS comes from the ‘‘key hole’’ nature of the surgery and the two-dimen- sional view provided by the nasal endoscope, as well as the complex surrounding anatomy. ESS can be technically challenging because of the proximity of the central nervous system and orbital structures and because of the anatomical variations that may be encountered [2]. Furthermore, extensive disease, such as sinonasal polyposis, as well as the relatively frequent need to perform revision surgery in a field that has been previously altered may add to the surgical complexity and risk of the procedure.

Although ESS is an ideal situation for the application of intraoperative MRguided surgery, it has not been yet studied extensively. Fried and associates [10]

(C)

FIGURE 5.4 (A) Axial MR image demonstrating a left upper neck lesion just posterior to parotid gland. This lesion was not palpable on physical exam. (B) Similar axial MR view with fast image sequence for image-guided biopsy. The needle is seen as the dark linear artifact entering the lesion from the patient’s left. (C) Coronal MR image showing the needle in the tumor, confirming that the center of the lesion is being sampled.

reported on an initial patient experience in the open magnet system with MRguided ESS. In this series, 12 patients underwent MR-guided surgery: 11 for chronic rhinosinusitis and one for an inflammatory tumor. Four of these cases were revision procedures. The authors reported no complications for the procedures performed in the MRI operating suite. Image acquisition time approximated 14 sec per image and was found to be helpful during the procedure to delineate changes within the soft tissues. Although these procedures took longer than standard surgical times, subsequent cases have been able to be performed in a streamlined fashion after clinical familiarity with the MR-guided surgery unit has been acquired. The major limitation encountered with MR-guided ESS was found to be the relative unavailability of specialized ESS instrumentation compatible with the MR unit. Specifically, MR-compatible light cables, endoscopes, and sinus instruments were available, but the lack of an MR-compatible microdebrider and drill did influence the completeness of the surgical procedures in certain cases. A representative image sequence from interactive MR-guided ESS is presented (Figure 5.5). As indicated, the ability to image in real time in three orthogonal planes is ideal for image-guided sinus surgery.

Although this study and other accruing patient series have demonstrated the safety of MR-guided ESS, its efficacy and advantages are yet to be determined. Significant advances are yet to be realized in terms of ESS instrumentation compatibility and availability. In addition, although image quality is satisfactory for ESS purposes, further refinements in image quality will be necessary to fully apply MR-guided ESS to the expected patient population. Those patients requiring revision procedures and patients with anatomical variations that make standard surgical approaches more risky could prove to be the patient population in whom MR-guided ESS has greatest applicability and efficacy. Furthermore, patients with sinonasal tumors that can be approached endoscopically would also be ideal candidates for MR-guided ESS, since the amount of tumor resected could be followed with real-time imaging. Similar advantages of real-time intraoperative imaging would be helpful in cases of extensive sinonasal polyposis. As further patient experience is gathered with MR-guided ESS, it will likely have a role in selected cases.

5.3.3 Additional Surgical Horizons

Image-guided surgery with MRI has been espoused by other surgical disciplines including neurosurgery [21]. With the recent advances in MR-guided surgical technology and the already present experience in the neurosurgical literature, it is logical that MR-guided surgery for skull base lesions will be an area of increasing interest. MRI has the ability to distinguish several tissue types within the skull base region, offering the surgeon valuable anatomical localization for the procedure, as well as information regarding the extent of resection for a given tumor

FIGURE 5.5 Images from MR-guided endoscopic sinus surgery. Upper left view demonstrates the interactive pointer approaching the right ethmoid sinus from the bottom of the screen. The pointer position (crosshair) is confirmed within the right ethmoid sinus complex on intraoperative MR images in the sagittal, coronal, and axial planes. (From Ref. 10.)

[22]. Similarly, MR-guided pituitary surgery may prove to be advantageous. Often the extent of the pituitary resection is determined by both visualization and intraoperative imaging confirmation. Intraoperative MR-guided surgery may significantly facilitate these procedures.

5.4 ADVANTAGES OF MRI-GUIDED SURGERY

As with any novel technology, acceptance in the surgical arena proceeds relatively slowly and cautiously. However, from the initial patient studies accumulated thus far, MR-guided surgery will offer significant advantages over current tracking techniques. These advantages can be related to the MRI as an imaging modality. In addition, specially designed MRI units have the ability to perform near real-time images during surgery.

Because MR is more sensitive to soft tissue morphology, it will likely have

an increasing role in the diagnosis and treatment of head and neck lesions. As otolaryngologists become more familiar with MR as an imaging tool, they are more likely to consider it as an adjunctive tool in surgery. The MR image has the ability to demonstrate anatomy in true three-dimensional planes rather than a reconstructed sagittal plane. This will prove to be a significant advantage in the complex three-dimensional anatomy of the head and neck. Because MRI does not involve radiation exposure, it is better suited for intraoperative image guidance than intraoperative CT.

Although intraoperative real-time imaging would be the most advantageous system for image-guided surgery within the head and neck, this has yet to be realized. The image scan times currently available for MR-guided surgery in otolaryngology are acceptable and provide a surgeon with discrete information about the progress of the surgical procedure. This is not possible with the currently available electromagnetic or optical tracking systems. With such systems, judgments on instrument localization and extent of surgery need to be based on the real-time endoscopic image that guides the surgeon and the static preoperative CT image. Intraoperative real-time MR imaging may present a distinct advantage in this regard. Such intraoperative imaging will allow the surgeon to follow the procedure and determine what anatomical changes have been rendered by the surgery. For example, as the surgeon proceeds with the intranasal polypectomy in ESS, use of intraoperative imaging may assist in determining how much of the polypoid disease has been resected and how much remains. Because MR can also document heat-related tissue changes, intraoperative MR guided laser or thermal ablation of tumors has recently been explored [23]. This ability to track the progress of the surgical procedure as it is being undertaken also may have applicability in surgery for tumors of the head and neck, when the lesion cannot be removed from surrounding attached surfaces.

5.5 DISADVANTAGES OF MR-GUIDED SURGERY

Although intraoperative MR-guided surgery has several intuitive but yet realized advantages, it is not without attendant disadvantages. Probably the most important disadvantage of MR-guided surgery is the initial start-up expense and capitalization costs encountered in developing an I-MRI surgical suite. Such development takes an extraordinary amount of planning and economic resources for given institution. Presently, we are aware of only three actively employed MRguided surgery suites used for head and neck surgical procedures. In addition to the tremendous capitalization costs, additional economic resources need to be devoted to the purchase and development of MR-compatible instrumentation [8]. In a specialty field such as otolaryngology–head and neck surgery, with the multiple types of instrumentation required, these secondary costs can be prohibitive as well.

MR-guided surgery within the head and neck may also suffer from other problems, including imaging artifact from instruments that are only partially compatible with the MR suite and a relatively low signal-to-noise ratio based on current technology. There is an inherent trade-off in the time required to produce a real-time scan (both image acquisition time and image processing time) and the quality of the image. In addition, if the surgeon desires imaging with several sequences (i.e., both T1- and T2-weighted images), significant additional scanning time will be required, which will in turn slow the operative procedure. As MR technology improves, these time factor issues should have a diminishing impact.

5.6 FUTURE DIRECTION

Although the experience with MR-guided surgery within otolaryngology/head and neck surgery has been somewhat limited, its exploration has been sparked by an increasing interest in image-guided surgery among otolaryngologists. The current technology is somewhat limited, since it is bounded by expense as well as imaging and technical constraints. As further technological developments are incorporated into the I-MRI suite, we anticipate that this technology will become more widely available. This will subsequently lead to more experience with the unit and adaptation for certain clinical applications, which will in turn lead to greater efficacy. Planning for future work continues in several areas. Aside from the continuing accrual of clinical experience with the current unit, further work on the adaptation of specialized otolaryngology surgical instruments is being undertaken. Newer generations of scanners that require less space and may provide more vertical access to the patient undergoing an MR-guided procedure. Further study is being conducted on mobile MR-guided units. With such anticipated advantages, MR-guided surgery within the head and neck is an entirely realizable possibility.

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posed on the physician. Some information has a life shorter than the time required to disseminate it through traditional methods of professional communication (medical charts, textbooks, print journals, continuing medical education, and face-to-face conversation). Additionally, many traditional forms of clinical information (radiographs, endoscopic examinations) are rapidly being converted into digital information (bits) that can easily be stored, manipulated, duplicated, and disseminated.

Fortunately, decreasing costs per computational unit and advances in information technology will make this information more manageable and more accessible. Several technological trends are going to affect this transformation significantly:

Widespread broadband access. Broadband access will allow physicians to have instant access to information-intensive resources, such as large databases, radiographs, intraoperative video, video from patient encounters, and video conferencing from remote locations. Broadband will also facilitate information sharing and consultation with colleagues regardless of location.

The emergence of application service providers. Through subscription fees, application service providers will give practitioners access to computational capabilities over the Internet, without the need to maintain expensive hardware or develop or purchase expensive software.

The proliferation of wireless Internet technologies. The wireless Internet will allow physicians to access and manage information from any location using handheld devices, freeing them from traditional computers. These wireless devices will allow physicians to refill medications with the touch of a button, answer queries from the office without having to call on the phone and wait on hold, and provide access to patient information and other medical databases.

The increasing complexity of health care delivery. Socioeconomic factors and regulatory issues, as well as the greater sophistication of even routine diagnostic modalities and therapeutics, are driving a greater complexity in almost all healthcare delivery settings.

Expansion of the medical knowledge base. Medical research has greatly expanded the entire medical knowledge base. This expansion will likely accelerate, as the pace of the acquisition of additional information about human genomics accelerates. The technological revolution that facilitates the field of genomics and its related disciplines will ultimately impact healthcare.

As the Internet and information technology will transform the practice of surgery, it also creates several new responsibilities for physicians. Prior to the Internet, physicians were the main source of medical information because access