Sonographic and CT Guidance
Sonographic and CT Guidance
Abstract & Commentary
Synopsis: In comparison to CT guidance for percutaneous hepatic biopsies, sonographic guidance is substantially more cost effective.
Source: Kliewer MA, et al. Percutaneous liver biopsy: A cost-benefit analysis comparing sonographic and CT guidance. AJR Am J Roentgenol 1999;173:1199-1202.
In the united states, most liver biopsies are currently performed using CT, as opposed to ultrasound guidance. Most likely, this is due to a traditionally held belief that ultrasound should be limited to guiding large and/or superficial liver masses. As ultrasound technology, transducers and techniques have evolved and improved; however, sonographic guidance has been shown to be technically effective for guiding biopsies of liver masses smaller than 1.5 cm, as well as for obtaining tissue from deeply located abdominal, pelvic, and retroperitoneal lymph nodes.
The purpose of the current study was to compare the cost of doing a liver biopsy using ultrasound guidance versus its cost using CT guidance. To do this, Kliewer and colleagues from Duke University evaluated 437 liver biopsies performed at their institution during a 31-month period. CT guidance was used for 137 (31%) biopsies, while sonographic guidance was used for 300 (69%) biopsies. Outcomes were considered adequate when sufficient tissue was obtained to characterize a specific abnormality, and inadequate when either insufficient or normal tissue was obtained.
To do their cost analysis, Kliewer et al analyzed two types of variables. Those categorized as probability variables included the probability of obtaining an adequate sample and the probability of a major complication. Cost variables were also analyzed and included the direct and indirect costs, the cost of a major complication, and the "opportunity" cost (i.e., the estimated cost of lost or foregone revenue that could have been generated with the machine had it been used for diagnostic studies, as opposed to the biopsy procedure).
The results of this study revealed that with ultrasound, an adequate sample was obtained in 261 of 300 biopsies (87%), while with CT, an adequate sample was obtained in 107 of 137 biopsies (78%). The mean time requirement to do the biopsies was 80 minutes ± 33 minutes for sonography, and 98 minutes ± 38 minutes for CT. Because actual dollar values could not be disclosed by Kliewer et al, relative values were reported instead. This revealed the overall cost for doing a CT-guided biopsy was 1.89 times greater than an ultrasound-guided biopsy. Further analysis indicated that CT and sonographic guidance costs would be equivalent if the success rate with sonography was only 40%, if the CT "opportunity" cost was 3.13 times less than estimated, or if the sonographic "opportunity" cost was 3.15 times greater than estimated.
Comment by Faye C. Laing, MD
This study is important because it not only confirms that sonography is technically at least as good as CT for guiding liver biopsies but, in addition, it is significantly more cost effective. Another way to understand the comparative "opportunity" costs is that for CT to be cost-equivalent with ultrasound, the CT-guided procedure could not exceed 31 minutes. In contrast, for the sonographically guided procedure to be cost equivalent with CT, the ultrasound-guided procedure could be extended to four hours and nine minutes. Furthermore, based on comparative cost effectiveness, sonography would be preferred if the biopsy success rate was as low as 40%.
Since cost estimates may vary somewhat from one institution to another, the values published in this article should be considered guidelines, and best approximate the cost generated in a large academic center. Nonetheless, the message is clear that with sonographic guidance, there is considerable latitude in both the success rate and in the time required to perform a liver biopsy before a sonographically guided biopsy approaches the cost of a CT-guided biopsy.
This article should prompt radiologists who rely primarily on CT for liver biopsy guidance to rethink their strategy. Obviously, to duplicate the results of Kliewer et al requires sonographic expertise in using this modality for biopsy guidance. Based on the results of this report, however, it seems well worth the effort to acquire this skill. Furthermore, although this article focused on cost effectiveness for percutaneous liver biopsy, it is reasonable to consider extending the use of sonography to guide biopsies of other intra-abdominal organs, and to also consider using this modality for performing biopsies of pelvic and retroperitoneal lymph nodes.
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