Martin J. Citardi, MD
Professor & Chair
Over the past 12-15 years, rhinologists and general otolaryngologists have increasingly embraced the use of intraoperative surgical navigation in more complex endoscopic procedures of the paranasal sinuses. The lack of real-time imaging updates that reflect the impact of surgical removal of and disruption of tissue has been commonly cited as a major shortcoming for surgical navigation. In the theory, the intraoperative acquisition of new images would represent a major advance. Two recent publications discuss intraoperative imaging in endoscopic sinus surgery and thus begin to elucidate a technological solution to this key shortcoming for surgical navigation.
Both reports feature initial clinical impressions of the Xoran xCAT ENT portable intraoperative volume CT scanner. This device is easily adaptable for relatively easy use in the typical OR set-up for sinus surgery. The machine can provide reformatted images axial, coronal, and sagittal images at a slice thickness as thin as 0.4 mm. The image quality for soft-tissues is poor, but the bony detail in these images is quite good.
In the first report, Jackman and co-authors1 present a preliminary description of intraoperative CT scanning in endoscopic sinus surgery. In this cases series, 20 patients underwent intraoperative imaging after completion of the planned surgical procedure. In 6 patients, or 30%, additional surgical intervention was performed after review of the intraoperative imaging. The findings that triggered additional surgical intervention included residual uncinate process, mixed midline frontal sinus compartment, incomplete frontal cell type 3 dissection, residual sphenoethmoidal cell and residual posterior ethmoid partition.
In the next report, Batra and co-authors2 describe their initial experiences with intraoperative xCAT in a series of 25 patients. The initial indications for sinus surgery was more heterogenous and included 5 patients with sinonasal neoplasms, 1 patient with a fibro-osseous lesion, and 1 patient with a meningoencephalocele. Among these 25 patients, 6 patients, or 24%, required additional surgical intervention based upon the intraoperative imaging. Reasons for additional surgical intervention included residual tumor (2 patients), retained ethmoid partitions (2 patients), thick bone at the so-called frontal beak region (1 patient), and malposition of a frontal sinus stent (1 patient).
Admittedly, both series represent impressions obtained in tertiary settings. Thus, extrapolation to a general ENT practice may be problematic. Nonetheless, both studies suggest that approximately 25-30% of patients may benefit from intraoperative imaging—at least in tertiary practice settings.
Other technologies,such as fluoroscopic CT with C-arm and intraoperative MRI (iMRI), have all received some attention as potential intraoperative imaging modalities, but all carry significant limitations. C-arm-based technologies are quite cumbersome, and their images provide adequate, but not ideal bony detail, which is a primary concern in most sinus surgeries. In general, iMRI machines are prohibitively expensive in that they require dedicated OR rooms; obviously, MRI provides great soft tissue information, which probably has its greatest utility for tumor cases, not procedures performed for inflammatory diseases of the paranasal sinuses. In contrast, a platform such as the xCAT ENT system may be better option for most sinus surgeries, since it offers a small, practical footprint and good images optimized for bony detail.
Of course, intraoperative CT imaging carries the risk of radiation. The miniCAT scanner, a device that operates much as the xCAT ENT scanner does, is a volume CT scanner that gives an effective radiation dose of 0.17 mSv, compared with 0.07 mSv for a conventional skull x-ray and with 2 mSv for a standard head CT.3 This radiation risk seems small compared to potential advantages in those situations where intraoperative imaging would be considered.
Intraoperative CT scanning is expensive. The initial capital outlay for an intraoperative CT scanner is approximately $300,000-400,000. The exact incremental cost per case has not been determined. One may assume that the introduction of this technology would entail additional OR time (and thus cost) from its usage. But, those costs would need to be weighed against potential savings from lower rates for revision surgery and better outcomes. It is also possible that effective use of intraoperative imaging would increase the efficiency of the surgeon, who may be able to perform a surgery faster with intraoperative imaging. Nonetheless, cost remains a major obstacle to widespread adoption.
In sum, intraoperative CT scanning may represent another technological advance that will shape rhinologic surgery over the next several years. The initial reports appear promising, but the ultimate acceptance of this technology will require further experiences that validate the initial impressions in a favorable cost-benefit analysis.