Natural History of Renal Angiomyolipoma (AML): Most Patients with Large AMLs >4 cm Can Be Offered Active Surveillance as an Initial Management Strategy

Abstract Background The natural history of renal angiomyolipoma (AML) is unknown. Treatment recommendations are based on smaller case series, with selection bias towards symptomatic patients. Objective To define the natural history of renal AML, including growth rates, size, and clinical presentation. Design, setting, and participants We used a unique radiology data-mining system (Montage; Montage Healthcare Systems, Philadelphia, PA, USA) to retrospectively review the radiology database in an academic health centre between 2002 and 2013 to identify all renal AMLs. Of 2741 patients identified, 447 with 582 AMLs had three or more imaging studies suitable for analysis. Intervention Angioembolisation, surgery, radiofrequency ablation, and mammalian target of rapamycin inhibitors. Outcome measurements and statistical analysis The primary end point was the growth rate of untreated AMLs. We used a linear mixed-effects model to determine change in growth rate over time. We evaluated the association among growth rate, size, and patient factors as well as interventions. Results and limitations The majority of untreated AMLs (>92%) had not grown at a median follow-up of 43 mo, with no difference in growth rates between AMLs ≤4 and >4 cm. Most AMLs occurred in female participants (80%) and were asymptomatic (91%). Tuberous sclerosis complex (TSC) was confirmed in 3.8% ( n = 17) and presented at an earlier age. Median size was 1 cm but was significantly larger for TSC (5.5 cm; p < 0.001). Interventions were performed in 5.6% of patients. Limitations of our study include the retrospective design, selection against fat-poor AMLs, and lack of histology. Conclusions This large, single-institution series on AMLs confirms that lesions >4 cm do not require early intervention based on size alone. The vast majority are sporadic, asymptomatic, and initially harmless, with a negligible growth rate. Our findings support a policy of initial active surveillance for all asymptomatic AMLs. Patient summary We evaluated the natural history and growth rates of renal AMLs. We found no difference in growth rates between AMLs >4 and ≤4 cm. Initial AS appears to be a safe management option.