Kevin C. Welch, MD
Rhinologists (Ear nose and throat surgeons who have further specialized in surgery of the sinuses and skull base) perform procedures with the aid of small rigid telescopes (called endoscopes) and cameras to magnify and illuminate the nasal and sinus tissue. Surrounding the sinuses are organs that are vital to a person's health and wellbeing. The most important structures surrounding the sinuses are the eyes, the tear ducts, the optic nerves (nerves of vision), the brain, and carotid arteries (the vessels carrying the main blood supply to the brain). While years of training, knowledge of anatomy, and skill are vital to an understanding of anatomy, a tool known as image-guidance allows surgeons to know almost precisely where any given structure is within and surrounding the nose and sinuses, compared to where the instrument is, at any given point during surgery.
The term "image-guidance" refers to the use of a probe or instrument, which is generally placed within the nose, that is tracked by a machine as that probe moves through the nose and sinuses. A computer, which is either physically or remotely attached to that probe, provides the surgeon with a map of the nose and sinuses. This map is provided by a CT scan or an MRI, which is performed prior to your surgery. This CT scan or MRI is commonly referred to as an "image-guidance scan."
In some respects, image-guidance is similar to a GPS system, constantly calculating the position of the probe within a patient's nose and sinuses and displaying that location on a "3-dimensional" layout of the sinuses provided by the patient's own CT scan or MRI. Unlike GPS systems in your car, image-guidance tools don't tell surgeons where they can go; rather, it gives them a very precise knowledge of where they are.
This is most helpful when surgeons are operating very close to those very important structures surrounding the sinuses mentioned above, when patients have had surgery in the past which has changed their normal anatomy and thus taken away some of the usual landmarks surgeons use to know where they are in the sinuses, or when tumors or infections have changed the normal anatomy so as to remove those landmarks as well.
There are two types of image-guidance systems commonly used today. Both systems perform the same functions; however, the technology they use to provide the information to the surgeon is very different. In all cases, a device is attached to the patient. This device is known as a head frame or mask.
These systems use infrared sensors in combination with light-emitting structures or light reflectors that are fixed to the patients head (e.g., via a headband strap or sticker) and fixed to a handheld probe. Both the headband and the instrument must be simultaneously "seen" by the computer in order to track where the surgeon's instrument is within the sinuses.
These systems use electromagnetic fields that use reference points on a device attached to the patient's head (a plastic mask with metallic beads or headband) and a wired instrument that the surgeon uses within the nose and sinuses. Unlike optical systems, electromagnetic systems do not have be "seen" by the computer (meaning that it doesn’t matter if other devices or equipment in the operating room are placed in between the computer and the patient). However, unlike optical systems, too much metal within the electromagnetic field can cause inaccuracies.
Image-guidance in action
Image-guided systems are used for a number of surgeries. The following is a list of some surgeries that might benefit from image-guided surgery
- Primary sinus surgery
- Revision sinus surgery
- Sinus surgery when polyps are present
- The removal of sinus tumors
- CSF (brain fluid) leaks
- Optic nerve decompression
- Surgery on the pituitary gland
- Surgery within the orbit
- Surgery on other tumors or infections at the skull base
The advantages of such systems are obvious: they can help surgeons know the precise anatomy of each patient's nose and sinuses (even if prior surgery or tumors/infections/inflammation have changed the normal anatomy) and help them identify important landmarks during surgery.
All patients must undergo a CT scan or an MRI in order to use image-guided surgery. For some, this can mean an extra dose of radiation or for patients who are claustrophobic, time spent in a long tube (MRI only). Additionally, like any other technology we use, these computer systems can be subject to human error in use.
Image-guided surgery has been a tremendous advance in the field of endoscopic sinus and tumor surgery. The overwhelming agreement among experts in the field is that image-guidance makes some surgical procedures safer and more complete. You will have to discuss with your surgeon whether you would be a candidate for image-guided surgery during your surgical procedure, as not all endoscopic procedures require this technology.
©American Rhinologic Society