Introduction:

Renal angiomyolipoma (AML) is one of the most common solid benign renal tumors. Although most of these tumors are often discovered incidentally during radiological imaging, symptomatic presentations such as flank pain, gross hematuria, or retroperitoneal hemorrhage may also exist. AMLs are often imaged intensively and treated empirically when they reach between the sizes 4-6cm. When to intervene remains controversial. Our aim was to investigate the growth rate, examine radiographic features, and evaluate trends in clinical presentation.

Methods:

This is multicenter single institution retrospective study. We reviewed all patients diagnosed with renal AML between three Mayo Clinic sites (Rochester, Arizona, Jacksonville) between 1997-2021. Only patients with 3 or more abdominal scans with at least 2 years between first and last scans and at least 36 months follow-up were selected.  A thorough review was performed of radiologic reports, images, and charts. Patient demographics, tumor characteristics, and type of imaging modalities were recorded. We also looked at intervention rates, tumor size, and growth rates. A t-test and chi-square test were used to compare differences between renal AML < 4 and > 4 cm. 

Results:

960 patients were initially identified. Following exclusion criteria 863 patients were identified. The majority of patients were female (81.6%). 723 presented with an initial mass < 4 cm and 136 >4 cm. 63 patients had tuberous sclerosis. 197 (22.8%) required intervention and 52 (6.1%) patients bled. When comparing the two groups (initial size < 4cm and >4 cm) patients with an initial mass >4cm were more likely to bleed, have tuberous sclerosis, or receive intervention. Percent growth changes between the two groups over 6, 12, 24, 36, and 48 months were not significantly different. 

Conclusion:

To our knowledge this is the largest series on AMLs. Our single-institution multicenter series on AMLs confirms that the majority of AMLs are small (<4 cm), and grow at a slow pace. Our study also shows that larger AMLs (>4 cm) do not grow at a faster rate. However, larger AMLs are more likely to bleed and require intervention. We believe further studies focusing on radiographic characteristics may help guide which lesions need earlier intervention. 

Funding: none