Contents
Introduction . . . . 201 Image-guidance Systems . . . . 201 Image-guidance for Endonasal Approaches
to the Frontal Sinus . . . . 204 Image-Guidance in External Approaches
to the Frontal Sinus . . . . 206 Conclusion . . . . 208 References . . . . 209
Introduction
The ability of image-guidance systems to provide the surgeon with enhanced anatomic localization during frontal sinus surgery offers the potential for im- proved clinical outcome. Surgery of the frontal sinus is particularly well suited for surgical navigation sys- tems because of the proximity of the sinus to the or- bit and cranial cavities, which demands a high degree of precision and provides little room for misjudg- ments regarding anatomic relationships. The vari- able anatomical development of the frontal sinus and its anterior superior location within the nasal cavity increase the possibility of disorientation during sur- gery. The loss of surgical landmarks can be particu- larly problematic in patients with extensive disease or a history of previous surgery.
Image-guidance Systems
Commercially available image-guidance systems track the position of a surgical instrument relative to the patient’s head using two different types of sig- nals:
쐽 Optical-based (infrared)
쐽 Electromagnetic-based (radiofrequency)
This information is processed by a computer work- station, so the location of the instrument tip can be depicted on a three-dimensional video display of the patient’s preoperative CT scan. Both electromagnetic and optical-based technologies have been found to be highly accurate, providing anatomical localization within 2 mm at the start of surgery [2, 6] and deteri-
Image-Guidance
in Frontal Sinus Surgery
Ralph Metson, Feodor Ung
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Core Messages
쐽 The utilization of image-guidance systems continues to increase for sinus surgery, in general, and frontal sinus surgery in parti- cular
쐽 Image-guidance systems can assist surge- ons with identification and enlargement of the frontal sinus ostium
쐽 Image-guidance systems appear to be most beneficial for revision frontal sinus surgery in which normal anatomic landmarks are obscured
쐽 Image-guidance systems have the potential to reduce complications from frontal sinus surgery
쐽 Technology is no substitute for technique
orating by less than 1 mm at the conclusion of sur- gery [6].
Equipment.Electromagnetic-based systems use a radiofrequency transmitter mounted to a specialized headset, which is worn by the patient during the op- erative procedure. A radiofrequency receiver is in- corporated into the hand-piece of a nonmagnetic in- strument. Cables connect the transmitter and receiv- er to the central workstation, where the data are pro- cessed and displayed on a multiplanar video image of the patient’s preoperative CT scan.
Optical-based image-guidance systems use an in- frared camera array to determine instrument and head position (Fig. 22.1). The camera tracks the coor- dinate position of optical markers that are attached to a straight probe or surgical instrument. A separate set of optical markers is mounted to a reference headset worn by the patient during surgery to moni-
tor head movement (Fig. 22.2). These optical markers further differentiate optical-based systems into ac- tive or passive systems. Active optical-based systems track the position of infrared light-emitting diodes (LEDs), which are powered by cables or individual battery packs. Passive optical-based systems use an infrared emitter in the camera array, which illumi- nates highly reflective spheres (glions) attached to the surgical instrument and patient headset. This technology allows for the use of wireless instrumen- tation and eliminates the problem of multiple cables, which may become tangled and entwined. The came- ra tracks the infrared emissions reflected from the glions, and this spatial information is processed by an optical digitizer and displayed in multiplanar for- mat on a video monitor (Fig. 22.3).
Drawbacks. Although both types of image-guid- ance systems are relatively easy to use, these tracking technologies are associated with different draw- backs. For those systems that use a radiofrequency signal for localization, metallic objects in the surgical field may cause signal distortion. Instrument tables, anesthesia equipment, and other sizable metallic de- vices need to be kept an appropriate distance from the surgical field.
Electromagnetic imaging protocols often require the patient to wear the same headset during both the preoperative CT scan and the operative procedure.
Care must be taken not to allow objects, which could cause distortion, to push against the headset during the scan or procedure. The patient must bring the same headset worn during the CT scan to the hospi- tal to wear during the surgery. The headsets are not interchangeable or reusable per recommendation of the manufacturer, although there is evidence to sug- gest headsets may indeed be reused or interchanged with little effect on accuracy [7]. The electromagnet- ic headset is typically secured at the ear canals and nasal bridge. This configuration necessitates intraop- erative coverage of a portion of the medial orbit and frontal regions. For most sinus surgery this design is not of clinical importance; however, it does preclude use of this headset for procedures that involve exter- nal incisions when operating on the frontal sinus. To allow for an external approach to these areas, the headset would need to be secured in the upside-
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Fig. 22.1.Optical-based image-guidance system. Infrared cam- era is located within the horizontal bar above the video moni- tor
down position, resting on the upper lip instead of the nasion during the preoperative CT scan and opera- tive procedure.
쐽 When using an optical-based system, it is necessary to maintain a clear line of sight between the infrared camera and the optical markers mounted on the surgical instrument and patient headset for the system to function properly.
The instrument must be held with LEDs or glions un- covered and pointed in the direction of the infrared
camera. Furthermore, operating room personnel and equipment cannot be positioned between the patient headset and the camera lens, which is generally locat- ed six feet above the head of the table.
Instrumentation. Since the introduction of im- age-guidance technology in the mid-1990s, the num- ber and variety of surgical instruments that may be used with surgical navigation systems has grown rapidly. From the initial straight pointers and suc- tions, a variety of instruments with multiple angles and configurations have been specifically developed to support frontal sinus surgery applications. Many of the optical systems now offer universal instru-
Fig. 22.2.Headset and hand-held probe used for the optical-based image-guidance system. The mirrored spheres reflect the in- frared signal, enabling the camera to track the position of the patient’s head and the probe tip
ment registration. With this process almost any rigid surgical instrument can be digitized during surgery and used for anatomical localization. Even micro- debriders may be tracked with this technology. For external surgical approaches that would be obstruct- ed by the presence of a headset, such as frontal sinus obliteration, skull reference arrays have been devel- oped. These glion-equipped posts can be percutane- ously affixed to the skull at an unobtrusive location and used to monitor patient head position.
Image-guidance for Endonasal Approaches to the Frontal Sinus
Frontal Sinusotomy. Image-guidance technology greatly facilitates preoperative understanding of in- tricate anatomy of the frontal sinus outflow tract. By depicting three-dimensional information in a multi- planar format, synchronized viewing of all three or- thogonal planes is possible.
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Fig. 22.3.Video display of axial, coronal, sagittal, and 3D views of patient’s preoperative CT scan. The location of the cross-hairs corresponds to the position of the tip of the surgical instrument within the nasal and sinus cavities during endoscopic surgery
The advantages of using image-guidance technology in frontal sinusotomy are:
쐽 The ability to rapidly and simultaneously scroll through all three planes promotes a bet- ter sense of the three-dimensional relation- ships of the frontal sinus in regard to impor- tant surrounding structures
쐽 It is often possible to follow the entire course of the frontal drainage pathway and examine it for areas of pathology. In this way, surgical navigation systems are exceedingly helpful for preoperative planning
쐽 Intraoperatively, image-guidance technology is used to help identify the frontal ostium in an atraumatic manner during frontal sinusotomy
In those patients with disease limited to the frontal recess, an anterior ethmoidectomy is performed and obstructing tissue removed from the recess with an angled Blakesley forceps. An image-guidance- equipped instrument such as a ball-tipped probe or curved suction cannula is then passed to confirm os- tial location and patency (Fig. 22.4). The proximity to the adjacent skull base and orbit can also be assessed.
Surgical navigation systems can also assist in dis- tinguishing the frontal sinus ostium from an adja- cent supraorbital ethmoid cell. When a supraorbital ethmoid cell is present, its opening is typically found posterolateral to the more anteromedial location of the true frontal sinus ostium. However, within the narrow confines of the frontal recess, these two open- ings can be easily confused if image-guidance is not employed.
By providing anatomical localization and prevent- ing surgical disorientation, image-guidance technol- ogy has been shown to increase surgeon confidence [3]. In a review of 800 sinus procedures done at a community hospital, Reardon [4] noted a significant increase in the number of frontal sinuses entered af- ter the introduction of a surgical navigation system.
The incidence of maxillary, ethmoid, and sphenoid sinus entry did not change with image-guidance ap- plication.
Frontal Sinus Drillout.Surgery on the frontal si- nus remains a clinical challenge because of the high
rate of ostial restenosis after frontal sinusotomy. In the past, patients who failed frontal sinusotomy pro- ceeded to frontal sinus obliteration. More recently, the frontal sinus drillout procedure, also known as the Modified Lothrop or Draf 3 procedure, has been described.
Endoscopic frontal sinus drillout can be a techni- cally demanding procedure because of the narrow anatomy of the frontal recess, the angled field of view at which the surgeon operates, and the paucity of landmarks from previous surgery. These factors in- crease the likelihood of surgical disorientation even for the experienced sinus surgeon. When an image- guidance system is utilized for drillout surgery, a cal- ibrated curved probe can be used to assist in identifi- cation of the frontal ostium and to ensure that drill- ing is performed in the direction of the frontal sinus floor. Without an image-guidance system, initial drilling is “blind” until the frontal sinus is entered.
Once the frontal sinus has been entered, bone remov- al continues under direct endoscopic visualization.
The advantages of using image-guidance in drillout surgery are:
쐽 The surgical navigation system is used during bone removal to alert the surgeon to the prox- imity of the skull base, orbit, and anterior na- sal skin (Fig. 22.5)
쐽 At the conclusion of surgery, the image-guid- ance system is used to verify that all compart- ments of the frontal sinus, including supraor- bital ethmoid cells, have been completely opened
Success rates for frontal drillout surgery with and without image-guidance are comparable, although there appears to be a trend toward a higher surgical success rate when surgical navigation systems are employed [8]. Even though image-guidance may not alter the overall long-term outcome of drillout sur- gery, the extent to which image-guidance systems en- hances surgeon confidence, particularly when drill- ing in the vicinity of the orbit and skull base, cannot be overstated.
Image-Guidance in External Approaches to the Frontal Sinus
Frontal Sinus Obliteration.When endoscopic ap- proaches to the frontal sinus fail to control frontal si- nusitis, frontal sinus obliteration must be consid- ered. Although frontal sinus obliteration is highly successful, its rate of major intraoperative complica- tions remains high, occurring in over 20% of pa- tients [9]. These complications include dural expo- sure, dural injury with cerebrospinal fluid leak, and exposure of orbital fat [9].
쐽 Most complications during frontal sinus oblit- eration are due to misdirected osteotomies that extend beyond the confines of the frontal sinus and result in an the osteoplastic flap which is too large
Underestimation of the size of the frontal sinus can result in a bony flap that is too small, making com- plete removal of mucosa from the sinus interior diffi- cult and increasing the risk of postoperative muco- cele formation
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Fig. 22.4.Intraoperative view of image-guided frontal sinusotomy
To utilize image-guidance in frontal sinus obliter- ation, a skull reference array is anchored percutane- ously near the vertex of the cranium at the start of surgery. This positioning affords unencumbered ac- cess to the frontal region throughout the procedure.
Once the frontal bone is exposed through a coronal or mid-forehead incision, a hand-held probe is used to demarcate the perimeter of the frontal sinus. This information, in conjunction with the x-ray template, is used to direct bony cuts through the anterior table with a sagittal saw and expose the sinus interior (Fig. 22.6). Anatomic accuracy of the image-guidance system is verified once the frontal sinus has been
opened. The mucosa is then stripped from the interi- or of the frontal sinus, and the entire surface is drilled with diamond burrs to obliterate mucosal remnants and promote neovascularization. Oxidized cellulose is used to seal the frontal sinus ostia, and the sinus is then filled with abdominal fat. A closed suction drain is placed and the incision is closed in layers.
Carrau et al. [5] were the first to report the use of image-guidance technology for the localization of the osteoplastic flap during frontal sinus obliteration surgery. Measuring the difference between the fron- tal sinus perimeter outlined by an image-guidance
Fig. 22.5.Intraoperative view of image-guided endoscopic frontal sinus drillout (modified Lothrop or Draf 3 procedure)
probe and that obtained with a traditional radio- graphic template in six cases, the authors suggested that the surgical navigation system was more accu- rate. A later study [10] compared four frontal sinus mapping methods: 6-foot Caldwell radiography, sinus transillumination, sinus trephination with probing, and image-guidance technology. The authors con- cluded that image-guided mapping of the frontal si- nus was the most accurate method of delineating the limits of the frontal sinus and least likely to overshoot the real sinus margins. Since successful frontal sinus obliteration surgery is predicated upon the precise lo- calization of osseous anatomy, the utilization of a sur- gical navigation system may enhance the safety of this procedure. A recent study demonstrated a significant reduction in the rate of intraoperative complications during frontal sinus obliteration when this method of image-guided surgery was utilized [11].
Endoscopic Frontal Sinus Obliteration.The endo- scopic approach to frontal sinus obliteration pro- vides a minimally invasive alternative to traditional frontal sinus obliteration. This technique combines a supraorbital incision, similar to that used for frontal sinus trephination, with endoscopic instrumenta- tion. Standard image-guidance headsets that do not conceal the medial canthal region may be employed.
A curvilinear incision is made along the inferior edge of the medial eyebrow and carried down through the subcutaneous tissue and periosteum.
The location of the frontal sinus is then verified with the surgical navigation system and the medial floor of the sinus opened. This bony opening is enlarged to permit passage of both a nasal endoscope and surgi- cal instruments. Using the 0° and 30° endoscopes, the frontal sinus mucosa is elevated and removed. The entire interior of the frontal sinus is then drilled with diamond burrs under endoscopic visualization to re- move any mucosal remnants. The surgical navigation system is used to assist with orientation while drill- ing within the sinus. It is particularly helpful when exenterating frontal cells or removing septations within the frontal sinus. Once drilling is complete, the frontal sinus ostium is plugged with oxidized cel- lulose and the sinus is completely filled with abdom- inal fat. The incision is then closed in layers.
Thus far, the use of image-guidance technology in endoscopic frontal sinus obliteration has avoided complications associated with conventional frontal sinus obliteration such as dural exposure, dural tear with cerebrospinal fluid leak, and orbital entry. In ad- dition, early results indicate that operative time, blood loss, and length of hospital stay were all signif- icantly reduced for those undergoing endoscopic obliteration compared with conventional osteoplas- tic techniques [12]. However, these results should be interpreted with caution, as the long-term outcome of endoscopic frontal sinus obliteration has yet to be determined.
Conclusion
Image-guidance systems appear to be particularly well-suited to frontal sinus surgery. They can assist the surgeon with localization of the frontal sinus os- tium during endonasal procedures and the sinus pe- rimeter during external procedures. Navigation technology has the potential to improve the efficacy and safety of frontal sinus surgery; however, its use is no substitute for proper surgical training and tech- nique.
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Fig. 22.6.Intraoperative view during image-guided frontal si- nus obliteration surgery. The image-guidance probe is used to verify the proper location of the x-ray template and to direct bony cuts through the anterior table of the frontal sinus
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References
1. Kennedy D, Shaman P, Han W, et al (1994) Complications of ethmoidectomy: A survey of the American Academy of Otolaryngology-Head and Neck Surgery. Otolaryngol Head Neck Surg 111 : 589–599
2. Metson R, Gliklich RE, Cosenza M (1998) A comparison of image-guidance systems for sinus surgery. Laryngoscope 108 : 1164–1170
3. Metson R, Cosenza MJ, Cunningham MJ, et al (2000) Physician experience with an optical image-guidance sys- tem for sinus surgery. Laryngoscope 110 : 972–976 4. Reardon EJ (2002) Navigational risks associated with
sinus surgery and the clinical effects of implementing a navigational system for sinus surgery. Laryngoscope 112(suppl) : 1–19
5. Carrau RL, Snyderman CH, Curtin HB, et al (1994) Computer-assisted frontal sinusotomy. Otolaryngol Head Neck Surg 111 : 727–732
6. Metson R, Cosenza M, Gliklich RE, et al (1999) The role of image-guidance systems for head and neck surgery. Arch Otolaryngol Head Neck Surg 125 : 1100–1104
7. Javer AR, Kuhn FA (2000) Stereotactic computer-assisted navigational (SCAN) sinus surgery: Accuracy of an elec- tromagnetic tracking system with the tissue debrider and when utilizing different headsets for the same patient. Am J Rhinol 14 : 361–365
8. Samaha M, Cosenza MJ, Metson R (2003) Endoscopic frontal sinus drillout in 100 patients. Arch Otolaryngol Head Neck Surg 129 : 854–858
9. Weber R, Draf W, Keerl R, et al (2000) Osteoplastic frontal sinus surgery with fat obliteration: technique and long term results using MRI in 82 operations. Laryngoscope 110(6) : 1037–1044
10. Ansari K, Seikaly H, Elford G (2003) Assessment of the accuracy and safety of the different methods used in map- ping the frontal sinus. J Otolaryngol 32 : 254–258
11. Sindwani R, Metson R (2004) Impact of image-guidance on complications during osteoplastic frontal sinus sur- gery. Otolaryngol Head Neck Surg 131 : 150–155
12. Ung F, Sindwani R, Metson R (2004) Endoscopic frontal sinus obliteration: A new technique for the treatment of chronic frontal sinusitis.Annual Meeting of the American Academy of Otolaryngology-Head and Neck Surgery. New York, NY. September 19, 2004
