J. M. Prince1, E. M. Bultman2, A. Drewry1, J. L. Hinshaw2, E. J. Abel1 1University Of Wisconsin,Department Of Urology,Madison, WI, USA 2University Of Wisconsin,Department Of Radiology,Madison, WI, USA
Introduction: Percutaneous biopsy may provide important information for patients with small renal masses (SRM) prior to treatment. However, 15-20% of patients undergoing biopsy receive indeterminate results, and thus do not benefit from the procedure. The objective of this study was to evaluate clinical and anatomical factors that are predictive of obtaining indeterminate results from percutaneous SRM biopsy.
Methods: Comprehensive clinical and anatomical factors were reviewed for consecutive SRM (≤4cm) patients treated with renal mass biopsy at the University of Wisconsin Hospital from 2000 to 2014. Univariable and multivariable logistic regression analysis was performed to determine which factors were associated with indeterminacy.
Results: A total of 413 SRM biopsies were performed in 386 patients. The median tumor size was 2.35 cm (IQR 1.90-2.95). 15.5% of the masses were cystic and 84.5% were solid. Enhancement (>20 HU ) was seen in 84.0%, while 5.3% were pseudo-enhancing (10-20 HU), and 1.9% were non-enhancing. A skin-to-tumor distance of ≥14 cm was observed in 4.1% of the masses. Similar to previous studies, we observed an indeterminate rate of 17.4% in the entire cohort and among cystic lesions, the indeterminate rate was 43.8%.
After multivariable analysis, independent predictors of indeterminate biopsy included: cystic features (OR 4.91, 95% CI 2.46-9.83, p < 0.0001), tumor diameter (OR 0.59, 95% CI 0.39-0.90, p = 0.015), skin-to-tumor distance ≥14cm (OR 4.29, 95% CI 1.50-12.25, p = 0.0065), and radiographic enhancement (OR 3.61, 95% CI 1.52-8.56, p = 0.0036).
Other factors evaluated but not significant to predict indeterminate biopsy included: exophytic shape, hemorrhage, necrosis, fat content, calcifications, type of imaging modality used prior to and for guidance during biopsy, biopsy type (i.e. core or fine needle aspiration), patient BMI, proximity to adjacent organs, anteroposterior and polar positioning within the kidney and laterality of the mass.
Conclusion: Four independent predictors for indeterminate biopsy are described including: cystic features, mean mass size, enhancement ≤20 HU, and skin-to-tumor distance ≥14cm. These factors can be used to identify patients with a significant risk for a non-diagnostic biopsy result and facilitate better patient selection for this procedure.
