BERKELEY, CA (UroToday.com) - The role of radiology in patient management has evolved over the years. We have seen the progression from detection-only based techniques to those that allow not only high detection rates (i.e., high sensitivity), but also a very good correlation to histology findings (i.e., high specificity). In this regard, the possibility of being able to non-invasively characterize histologic subtypes of tumors is a necessary trend, such as in patients with renal cell carcinoma (RCC) where clinical management may be dependent on the tumor histologic subtype. Invasively attempting (percutaneous or surgical) histologic characterization of RCCs for subtyping is not always desirable. Despite its high accuracy, RCCs can be difficult to biopsy percutaneously, particularly small lesions, carrying an important rate of technical failure and false-negative results. As an example, the usually less aggressive papillary tumors may be amenable to watchful waiting management, especially in unwilling or poor surgical candidates.
RCC diagnosis rates have shown a steady increase, mainly due to the incidental diagnosis during imaging for other purposes (up to 61% of new cases). Very often, these imaging studies are in the form of routine computed tomography (CT) examinations, which frequently are performed after the administration of intravenous iodinated contrast. Because renal abnormalities are unsuspected, unenhanced images are not acquired. This practice is in accordance to the efforts to reduce the hazard of the radiation doses given to patients undergoing imaging.
Several reports have demonstrated the feasibility of RCC subtype differentiation employing dynamic multiphasic imaging CT studies, using the unenhanced images for the baseline CT attenuation measurements of renal masses. In our experience, recommendations for additional CT imaging studies for incidentally found renal lesions in patients without baseline unenhanced phase are not always followed, and such additional imaging is burdensome both for the patient (subjected to a incremental amounts of radiation exposure) and to radiology departments (further loading the usually busy working schedules). For such reasons, RCC subtype differentiation in incidentally found renal masses, with no available unenhanced phase, would be of clinical benefit.
In our paper we tried to differentiate the three most common RCC histologic subtypes using images provided by single-phase post-contrast CT examinations of histologic-proven RCCs. We sought to intra-individually compare the ability to differentiate RCC subtypes between multiphasic and arterial single-phase contrast enhanced CT based on both previously described and novel indices, using the psoas muscle as a surrogate. We quantitatively evaluated tumor enhancement, calculating the tumor enhancement (TE) and tumor-to-cortex index (TCI).
Our results showed that it was possible to distinguish papillary tumors from clear cell and cromophobe simultaneously with high accuracy using TE (sensitivity and specificity of 100% and 90%, respectively) and TCI (sensitivity and specificity of 100% and 84%, respectively) thresholds of < 23% and < 0.22, (AUC 0.978 and 0.971), respectively. Comparison of receiver operating characteristic curve analyses between single-phase and multi-phase evaluation methods did not show significant differences. Unfortunately, we were not able to find significant differences in the distinction of clear cell from cromophobe tumors for both evaluated methods (single-phase and multi-phase), but only between clear cell and non-clear cell tumors. Nevertheless, we believe that this can be clinically more useful.
In conclusion, our study provided evidence to support that RCC subtype differentiation can be assessed with high accuracy on an arterial single-phase contrast-enhanced-CT study, similar to multi-phase evaluation when unenhanced images are unavailable.
António P. Matos and Miguel Ramalho as part of Beyond the Abstract on UroToday.com. This initiative offers a method of publishing for the professional urology community. Authors are given an opportunity to expand on the circumstances, limitations etc... of their research by referencing the published abstract.
Hospital Garcia de Orta, Almada, Portugal
Renal cell carcinoma subtype differentiation using single-phase corticomedullary contrast-enhanced CT - Abstract