Image-guided ENT doesn't take the place of anatomical knowledge and it isn't yet the standard of care, but you can bet surgeons performing sinus surgery appreciate having extra assurance when maneuvering instruments millimeters from the orbital cavity or skull base. With a quick check of the image-guided system, they know for certain if they should stop to avoid devastating complications or safely continue as planned.
How does it work?
Image guidance operates off CT scans or MRI images brought to the OR on CD-ROM disk, USB drive or via a facility's in-house imaging network. Two basic types of image-guided technology exist: electromagnetic and infrared.
- Electromagnetic systems do not require a direct line of sight between the reference array and the image processor, meaning images will continue to be transmitted and displayed even if someone walks between the surgeon and the system's unit. A few potential drawbacks: Surgeons must use proprietary instruments and surgical teams must keep metal items (towel clips, for example) away from the patient in order to avoid interfering with the system's electromagnetic field. Electromagnetic systems allow for a less cluttered OR but, despite that benefit, these systems aren't commonly used.
- Infrared systems demand a clear line of sight between instruments and the system's imaging unit. Fiducial markers are placed on the patient's forehead and instruments, which transmit images to the system's transmitter.
This technology has improved dramatically in recent years. Earlier systems experienced lag time between where an instrument was actually located and where it would show up on the screen. Now the movements are fluid and very close to real time. The newer systems also let surgeons register almost all of their own instruments instead of relying on a single registered pointer to track their progress.
Plenty of applications
Image-guided surgery is not the standard of care, but it has widespread application. Almost all training programs use it, and most private practice surgeons are becoming well-versed in the technology. Its use is becoming widespread in the ENT field.
One common indication for the technology is revision sinus surgery, because the normal anatomy has been altered. I might not use image guidance for revision surgery if I did the primary procedure, but will certainly rely on the technology any time I'm following up on another surgeon's work. I'll also use it for patients who present with abnormal sinus anatomy related to developmental, traumatic or post-operative issues.
Additionally, the American Academy of Otolaryngology Head and Neck Surgery endorses use of the technology for extensive sino-nasal polyposis; pathology involving the frontal, posterior ethmoid and sphenoid sinuses; disease abutting the skull base, orbit, optic nerve or carotid artery; cerebrospinal fluid or conditions involving a skull-base defect; and benign and malignant sino-nasal neoplasms.
Traditionally, image-guided ENT works off MRI or CT scan images. Newer systems, however, can fuse the images, which is extremely useful when removing tumors from the skull base.
Differentiating between tumor and sinus disease is difficult on a CT scan, but bone structure is clearly defined. On the other hand, an MRI will clearly show a tumor, but won't display bone structure. Combining the images lets surgeons identify the tumor via the MRI and the bone structure via the CT scan.
Newer systems also let surgeons plan trajectories for certain procedures. For example, surgeons can use image-guidance to pre-operatively plan a targeted approach to tumors in the skull base. During surgery, the system guides surgeons along the pre-planned path, letting them track the correct trajectory.
The footprint and flexibility of units have become increasingly important to facility administrators and surgical teams. Newer units are more compact, which is important, especially when using infrared systems that demand a line of sight between instruments and the imaging unit. On older units, the infrared cameras were attached to the system's monitors. Now, the cameras are able to be moved around the OR, providing more flexibility in the overall setup while still maintaining the required direct line of sight.