More than 37 million Americans experience at least one episode of acute sinusitis each year, making it one of the most common health conditions, according to the American Academy of Otolaryngology. First-line treatments include antibiotics and decongestants, but for chronic or recurrent sinusitis, endoscopic sinus surgery can clear the diseased tissue and open the nasal passages.

Image guidance was first used for neurosurgery, but the technology has gained a solid foothold for use in endoscopic sinus surgery. The bony framework of the sinuses limits the shifting of soft tissue; therefore, the pre-operative scans remain useful when they're used intraoperatively.

Experts say, however, that image guidance should be used with caution. The AAO endorses it for certain cases, including revision sinus surgery and situations where the sinus anatomy is distorted (see "Indications for Image-guided Sinus Surgery"). Even proponents of image guidance say it's vitally important that surgeons don't use the technology as a crutch.

"When these systems first came out, some experts felt that they might actually increase complications if surgeons used them to attempt complex procedures without having a good understanding of the sinus anatomy," says Raj Sindwani, MD, an ENT surgeon at Saint Louis University School of Medicine and Director of the SLU Comprehensive Sinus Clinic. "Technology is no substitute for technique."

If you're considering investing in an image guidance system, which cost between $100,000 to $200,000, here are a few things to keep in mind.

The basics
At least four companies (BrainLAB, GE Medical Systems, Medtronic and Stryker) have released image-guidance systems, which operate using four basic components:

• a data set, which is usually a CT scan (but may also be another imaging modality, such as MRI)
• a computer to process the CT data and enable it to be used intraoperatively and interactively;
• a way of matching or "registering" the CT scans to the patient in the operating room (this is usually done with a headset worn over the patient's forehead) and
• a way of calibrating and tracking instruments so that when they're moved in the surgical field, they can be localized with respect to the CT scans.

In the hands of an experienced surgeon, image guidance can provide an extra margin of safety during the procedure by providing a comprehensive view of the sinus anatomy and helping the surgeon avoid inadvertent damage to the eyes or brain. Also, surgeons can load the CT scans into the image guidance system ahead of time and pre-plan the surgery. "It's like taking a virtual tour of the anatomy before you start," says Noam Cohen, MD, an ENT surgeon at the University of Pennsylvania School of Medicine.

Differentiating factors
Image guidance systems use either infrared light or electromagnetic navigation to calibrate and track instruments in the surgical field. With the infrared systems, the surgeon has to maintain a direct line of sight between the instruments and the central unit. If he inadvertently blocks the signal by bending over the patient, or another member of the team walks between the central unit and the surgical field, the images on the monitor will "freeze." "Eventually, surgeons learn to manipulate their hands in the surgical field so that they don't interfere with the line of sight," says Dr. Cohen.

With electromagnetic systems, the instruments must be connected to the central unit with cords. "This creates more 'spaghetti' on the surgical field," notes Dr. Sindwani. He adds that the headset that the patient wears during the procedure is a little bulkier than the ones used in optical systems. "The headset tends to cover up most of the patient's forehead, so you're restricted from making incisions above the patient's eyebrow." Also, any metallic object near the surgical site could interfere with the electromagnetic field.

According to James Palmer, MD, an ENT surgeon at the University of Pennsylvania School of Medicine, the systems have been compared and contrasted in numerous studies, and they're all accurate and easy to use once the surgeon becomes accustomed to them. "Surgeons just need to trial each system and choose the one they think is best," he says. "And they need to remember that all systems reach for the ideal, but none is perfect."

Jason Newman, MD, a fellow ENT surgeon at the University of Pennsylvania School of Medicine, agrees. "Nobody has ever conclusively shown one system to be better than the others," he says. "Surgeons tend to develop their own preferences based on what system they were trained on."

Dr. Cohen notes that switching from one system to another is fairly simple. He'd trained with the GE and BrainLAB systems, but now he primarily uses the Medtronic system. "The learning curve to switch from one system to another was about five minutes," he says.

Other factors to consider
Consider the availability of technical support when choosing your system, says Dr. Cohen. "You want a rep who will be available 24 hours a day, and ideally be on site for your first 10 cases, as well as any particularly complex cases." Dr. Cohen's rep comes in before procedures to make sure the scans are done properly, and she's often in the OR during a procedure to help make minor adjustments to the system. Dr. Newman adds that it's important to have a staff that is familiar with the system and knows how to set everything up.

Although many surgeons are performing endoscopic sinus surgery without image guidance, Dr. Cohen believes that the technology might eventually become standard of care. "Any surgeon who is coming out of a training program will know how to use this technology," he says. "But the real test of whether image guidance should be standard of care will occur when we look at long-term results and see if patients undergo fewer revision surgeries and end up taking fewer steroids and medications when this technology is used. Right now, it's too early to tell."