Computer-aided surgery of the head and neck

Abstract

Introduction. The advent of minimally invasive surgery of the head and neck has prompted the development of image guidance systems to assist the surgeon with intraoperative anatomical localization. These systems utilize computerized tracking devices to monitor the position of endoscopic instruments relative to the patient's anatomical landmarks. The location of these instruments is depicted on a real-time, three-dimensional video display of the preoperative computerize tomography (CT) or magnetic resonance imaging (MRI) scan. Materials and methods. The study population consisted of 121 patients (49 women, 30 men; mean age 46.2 years, range 15–80 years) who underwent endoscopic surgery of the head and neck at Massachusetts Eye and Ear Infirmary in Boston, MA, between November 1996 and August 1997. Fifty-five patients underwent surgery with an optical-based image guidance system (LandmarX, Xomed, Jacksonville, FL, USA). Twenty-four patients had surgery performed with an electromagnetic-based system (InstaTrak, Visualization Technology, Inc., Woburn, MA, USA). Forty-six (58%) of these image-guided surgeries were revision procedures. The control group consisted of 42 consecutive patients who underwent endoscopic surgery of the head and neck without the use of an image guidance system during the same time period, by the same surgeons, and at the same Institution. Surgical indications included: chronic rhinosinusitis (115 cases); fibrous dysplasia of the ethmoid or sphenoid bone (two cases); optic neuropathy requiring optic nerve decompression (two cases); and cholesterol cysts of the petrous apex requiring trans-sphenoid drainage (two cases). Operating room time was measured as the total number of minutes spent by the patient in the operating room suite. This value reflected anaesthesia and surgery times, as well as time for the setup and operation of the image guidance system, including placement of the patient headsets, calibration and registration of the handheld probes, and use of the system for anatomical localization throughout the procedure. Results. Controlling for CT stage, revision surgeries, and procedures performed, the mean operating room time was greater for the image guidance group (137.3 ± 6.0 min, range 60–375 min) than the control group (119.9 ± 5.7 min, range 70–235 min) (P < 0.05). This value reflects the total number of minutes spent by the patient in the operating room, including time required for anaesthesia, surgery and operation of the image guidance system. Since the image guidance cases averaged 17.4 min longer than controls, the use of an image guidance system was estimated to increase mean hospital charges by $496 per case. Mean estimated blood loss was comparable for the image guidance (178.4 ± 18.0 ml, range 20–750 ml) and control (149.4 ± 20.1 ml, range 25–600 ml) groups. Blood loss correlated with CT stage (P < 0.001), but not revision surgery. Registration of the image guidance system provided anatomical localization to within 2 mm accuracy at the start of surgery in all cases. This degree of accuracy was confirmed with visual verification of known anatomical landmarks by the surgeon at the start of each case. The amount of anatomical drift which occurred during the case ranged from 0.64 mm to 1.37 mm (mean 0.89 ± 0.20 mm) depending on the anatomical reference site selected at the start of surgery. There were no intraoperative complications. Postoperative complications were limited to four cases of epistaxis, two from the image guidance group (2.7%) and two from the control group (4.7%). This difference in complication rates between groups was not statistically significant. Discussion. In this study image guidance systems were found to be accurate and relatively easy to use for surgical procedures of the head and neck; however, the use of such technology was associated with increased operative time and expense. Because of these factors, computer-assisted technology is not currently recommended for use during routine otolaryngological surgery. Image-guided surgery of the head and neck is most appropriate for those cases which present the surgeon with the greatest technical challenge. The enhanced anatomical localization provided by such systems has proved particularly valuable for cases with poor anatomical landmarks, such as revision surgery and those with extensive disease. In this study, the two cases involving endoscopic drainage of cholesterol cysts in the petrous portion of the temporal bone would have been particularly difficult without image guidance technology. Removal of the posterior wall of the sphenoid bone to access these cysts was performed with greater reassurance to the surgeon and safety to the patient because the image guidance system confirmed the anatomical location of the cranial cavity and adjacent carotid artery. In the cases of fibrous dysplasia resection and optic nerve decompression, image guidance technology allowed the surgeon to monitor the depth of bone removal relative to the skull base and optic canal. Intraoperative X-rays or a C-arm could have provided similar information to the operating surgeon, but without the resolution or convenience provided by current image guidance systems. Although the image guidance systems were found to be relatively easy to use, difficulties were encountered during their clinical application related to the tracking technologies. For those systems which used a radiofrequency signal for localization, metallic objects in the surgical field caused signal distortion. When using an optical-based system, it was necessary to maintain a clear line of site between the infrared camera and light emitting diodes (LEDs) mounted on the surgical instrument for the system to function correctly. Conclusions. Image guidance systems are available which can provide the otolaryngologists with precise anatomical localization during head and neck surgery. This information can be particularly valuable for those cases with poor anatomical landmarks from extensive disease or previous surgery; however, the use of this new technology is associated with increased operative time and expense.