Natural History of Renal Angiomyolipoma Favors Surveillance as an Initial Approach

Traditionally, intervention was recommended for angiomyolipomas (AMLs) >4 cm due to the risk of catastrophic hemorrhage.

To delineate the natural history of AMLs, including growth rates and need for intervention.

A retrospective review was performed of an AML series from 2002 to 2013, which have been followed prospectively until 2018. We defined lesion size by maximum axial diameter and categorized lesion size at baseline.

A total of 458 patients with 593 AMLs, with a median follow-up of 65.2 mo, were identified. At diagnosis, 534 (90.1%) lesions were ≤4 cm. Forty-three interventions were required for 34 (5.7%) AMLs: 30 were treated with embolization, seven surgery, two with radiofrequency ablation (RFA), three with mammalian target of rapamycin (mTOR) inhibitors, and one with nivolumab when epithelioid AML was confirmed. The median size at intervention was 4.9 cm (range 1.1-29 cm).

Most (94%) of the lesions grew slowly (growth rate of <0.25 cm/yr) during the period of observation. The number of AMLs <4 cm needed to treat (NNT) prophylactically to prevent one emergent bleed would have been 136 or that to prevent one blood transfusion would have been 205. The NNT (<4 cm) prophylactically to prevent one elective intervention would have been 82. On multivariate analysis, there were significant differences in intervention rates based on tuberous sclerosis complex, size at presentation, and clinical presentation.

This large single-institution updated series of renal AMLs demonstrates that early intervention is not required, regardless of the traditional 4 cm cut-off. The vast majority of AMLs are indolent lesions that are predominantly asymptomatic and slow growing. Follow-up should be no more frequent than annually.

The majority of angiomyolipomas (AMLs) are indolent, slow-growing lesions that do not require intervention, regardless of size at presentation. We suggest that surveillance is a safe initial approach for patients presenting with AMLs.