The value of CBCT during AVS has long been investigated, and most studies have suggested that CBCT is a useful tool for identifying RAV, thereby improving the success rate of AVS [11–17]. However, the present study showed contrasting results, in which a similar success rate was noted in patients with or without the assistance of CBCT (88.4% vs. 82.3%, P = 0.347).
Based on this contrary finding, the following questions were raised regarding the AVS procedure: In what situations should CBCT be performed? In what situations is CBCT not needed? In the present study, CBCT was mostly performed in the learning stage to confirm the catheterization of the RAV, and the results showed that CBCT could improve the success rate of AVS from 62.5–96.4% in this stage (P = 0.028). Therefore, it is hypothesized that CBCT may be helpful for interventional radiologists who are in the initial stages of learning to perform AVS. In addition, the present study also showed that CBCT could not improve the success rate of AVS when performed by an experienced interventional radiologist, suggesting that CBCT may not be needed in this situation.
However, the learning curve for AVS was based on personality traits. Some individuals may learn faster, whereas others may require more practice. In addition to the learning curve, the present study showed that the success rate could be improved from 71.0–88.7% with the assistance of CBCT in patients with atypical RAV imaging patterns. However, in patients with typical RAV imaging patterns, the success rate did not increase despite the assistance of CBCT. Thus, it is hypothesized that CBCT may be helpful in patients with atypical RAV imaging patterns and may not be needed in patients with typical RAV imaging patterns.
A previous study described various imaging appearances of RAV on venography . According to the imaging appearance described, a classification criterion was established in the present study to divide the RAV imaging pattern into typical or atypical categories . With this classification, RAV on venography can be accurately identified even without the help of CBCT. To the best of our knowledge, this is the first study to clarify that patients with atypical RAV imaging patterns will benefit from CBCT when performing AVS. RAV has various shapes and variations in venography, which is the main difficulty in performing AVS. As it is occasionally improperly identified, the shape of right-side venous injection may not be a reliable feature for recognizing the RAV [8, 9, 17]. In addition to the venous shape, the presence of communications with the IVC, right renal vein, intercostal vein, and right phrenic vein through superficial or emissary veins is one of the most important imaging features for the identification of RAV . In the present study, there was a high confidence level for the identification of RAV when venous injection showed the typical type of RAV accompanied by communication. In addition, the results showed that the radiation dose (P = 0.018) and sampling time (P = 0.001) were significantly higher in patients with CBCT than in patients without CBCT in the overall study population. Radiation dose is also a significant concern when performing AVS. Due to the additional exposure, the radiation dose is increased in a single patient, suggesting that CBCT should be performed cautiously .
Furthermore, one patient experienced RAV rupture during CBCT in the present study, which led to the failure of AVS. Because the RAV is usually small, the injection pressure may be too high when using a power injector, which may burst the RAV. Therefore, when performing CBCT, a manual injection technique is preferred over a power injector.
There are several limitations to the present study. First, this was a retrospective study with a relatively small number of patients included, and thus may be subject to selection and statistical bias. Second, the on-site quick cortisol assay (QCA) was not used in the present study, despite its use in improving the success rate, as reported in a previous study . However, QCA is not available in many centers; therefore, it has limited use in clinical practice. Finally, this study was performed in a single center, and the imaging classification criteria for identifying RAV should be validated in other centers.
In conclusion, CBCT is not a mandatory and should be cautiously used procedure for experienced operators during AVS, unless there are uncertainties about definite catheterization of the RAV or the venous anatomy is very atypical. However, less experienced operators may benefit from CBCT, since they are naturally less confident and need confirmation by CBCT before proceeding to sampling.
Cone-beam computed tomography is helpful for an interventional radiologist in the beginning stages of learning how to perform adrenal venous sampling
Cone-beam computed tomography is helpful in patients with atypical imaging pattern of right adrenal vein
Cone-beam computed tomography may increase the additional radiation dose and sampling time when performing adrenal venous sampling