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Intraoperative Volume CT Demonstrates Appeal, but Questions Remain
From: ENT Today, August 2008
by Pippa Wysong
ORLANDO - Intraoperative volume CT is showing promise as a tool to help with complex endoscopic sinonasal and skull base procedures. However, it is not needed in every case, and researchers are trying to define just when it is most appropriate to use.
Using it judiciously is the key at this point in time, according to Pete Batra, MD, a rhinologist and Section Head of Nasal and Sinus Disorders at the Cleveland Clinic. As of yet, there are no guidelines for its use, and few centers have the device on hand.
We really have to carefully weigh the risks and the benefits of this technology, and we need to accrue additional data to refine the indications, Dr. Batra told ENT Today in an interview.
CT scans are done on patients with complex disease prior to surgery to use as a map during image-guided surgery (IGS). But what happens is, as you use image guidance and you go through a long case, you're manipulating the anatomy. By doing that, the image guidance becomes less accurate as time goes on, Dr. Batra said. That is why the idea of something such as intraoperative volume CT scanning is appealing, especially in cases where there is uncertainty as to whether the surgical goal has been met, or uncertainty because of altered anatomy.
At the recent annual Combined Otolaryngology Spring Meeting, Dr. Batra described findings from a study using intraoperative volume CT in patients who underwent endoscopic sinonasal and skull base procedures.
Intraoperative Volume CT Study
The study was a retrospective chart review of patients with complex disease and who underwent intraoperative volume CT. The study included a total of 25 patients who were treated at the Cleveland Clinic Head and Neck Institute between May and July 2007. The scanning was done with the portable xCAT (Xoran Technologies) in the operating room.
Patients ranged in age from 20 to 80 years (mean, 56.8 years), and 16 were male. A total of 12 (48%) patients had chronic rhinosinusitis, either with or without polyposis; 6 (24%) had mucoceles; 5 (20%) had neoplasms; one patient (4%) was treated for meningoencephalocele; and one had sphenoid fibrous dysplasia.
In 76% of the patients, volume CT scanning was performed during surgery to help the surgeon view altered anatomy after paranasal sinus dissection. In 24% it was done to confirm complete tumor removal, and in 24% to verify the accuracy of a frontal stent position.
Use of the CT scan led to further surgical intervention in 24% of the patients, which is significant, Dr. Batra said. Two patients underwent additional ethmoid surgery, two patients had additional tumor removal, one had additional bone removal during frontal sinus surgery, and in one case a frontal stent was repositioned more optimally.
If, in a quarter of your patients, you are improving outcome, it seems to suggest this could be a very important technology, he said. However, further study with larger numbers of patients need to be done to confirm its utility and help better define which patients to use it on. At his own institution, Dr. Batra said plans are under way to do prospective studies to further investigate use of the technology.
Pros and Cons of Intraoperative Volume CT
Pros and cons must be carefully weighed when considering use of this technology.
On the pro side, intraoperative volume CT can help with navigation after anatomy has been altered during surgery, and help surgeons confirm that they have reached their surgical objective. On the downside, the technology is costly, and there are risks associated with exposing patients to additional radiation.
Doing a scan during surgery does not take much time. In fact, the entire process takes no more than five to 10 minutes, Dr. Batra said. The actual scan acquisition takes about 40 seconds, so overall it causes very little disruption in the procedure.
When the scan is being performed, only essential personnel should be present in the operating room, and they are shielded behind the machine, he said. All nonessential personnel should be asked to leave the OR at the time of the scan acquisition.
As for patient safety, the amount of radiation use is only about a tenth of what is used prior to surgery in standard image-guided CT, he said. The device used for this study is relatively small and can be stored in the operating suite. The dimensions are 32 inches by 47 inches by 60 inches.
Use of other intraoperative scanning devices for otolaryngologic procedures has been reported in the literature, Dr. Batra said. One is fluoroscopic CT. The main reported limitations of that technology are that it involves a larger piece of equipment, and a radiology technician is needed to operate the C-arm.
Some studies have reported the use of intraoperative MRI. An advantage of this technique is that does not expose patients to further radiation, but the device creates distortion in many types of nearby video monitors, he said.
Overall, intraoperative volume CT scanning could potentially serve as an important adjunct that can facilitate critical decision making in endoscopic sinonasal and skull-based surgery, Dr. Batra said.
How Well Can Residents Use Technology?
In a related study, researchers from Emory University in Atlanta and the Medical University of South Carolina examined how well otolaryngology residents were able to identify anatomical features within and around the paranasal sinuses using various combinations of imaging devices. The study was performed on cadavers.
According to Patrick Sheehan, MD, a rhinology fellow at the Medical University of South Carolina, who presented his results at COSM, endoscopy with IGS registered to intraoperative CT showed the highest accuracy in anatomic identification in the study.
In the study, 11 otolaryngology residents were asked to identify 20 different anatomic sites in partially dissected cadaver heads. They were given one minute at each technology level. The technology levels were endoscopy alone, endoscopy with access to preoperative CT scan, endoscopy plus IGS based on a preoperative scan, and finally endoscopy plus IGS registered to an intraoperative CT scan.
Overall, it was found that use of endoscopy alone was the least accurate, whereas endoscopy plus IGS registered to an intraoperative CT scan was the most accurate in terms of the residents being able to identify sites. For many sites, endoscopy plus IGS registered to preoperative CT came in a close second.
However, while this, and other, studies have shown excellent anatomic accuracy with intraoperative CT and IGS, increased intraoperative safety with these technologies has not been definitively shown, Dr. Sheehan said.
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