Is the follow-up of small renal angiomyolipomas a necessary precaution?

•This is the first study with a primary purpose to investigate growth of small Angiomyolipomas (AMLs) (≤20 mm).•Small AMLs are less likely and slower to change than larger AMLs.•Multiple AMLs or AMLs due to genetic conditions are associated with a faster AML growth rate.•AMLs with a large extra-renal component are less reliably measured by ultrasound and may require CT to confirm size.

AimTo investigate the natural history and rationalize follow-up of renal angiomyolipomas (AMLs).Materials and methodsA prospectively gathered radiology database was scrutinized to identify patients with renal AMLs over a 3 year period (January 2006 to December 2008). Radiological investigations were examined to identify those AMLs exhibiting change during surveillance.ResultsA total of 135 patients were identified. Mean age at first detection was 49.6 years and patients were followed up for a median 21.8 months (6–85.3 months). Small AMLs (≤20 mm) were less likely to grow than their larger counterparts [odds ratio 13.3, confidence interval (95% CI) 1.4–123.9, p = 0.02] and exhibited a slower growth rate (0.7 versus 9.2 mm/year). Patients with AMLs that increased in size were significantly younger (median age 43 versus 52 years, p < 0.001). Multiple AMLs or those associated with genetic conditions grew at a significantly greater rate (3 versus 0.1 mm/year, p < 0.001). AMLs with a large extra-renal component are less reliably measured on ultrasound (median error 7 versus 1 mm, p < 0.001).ConclusionThis is the first study with the primary purpose to investigate growth of small AMLs (≤20 mm). Small, solitary AMLs (≤20 mm) do not require follow-up due to their low probability of growth. Patients with multiple AMLs and younger patients require closer monitoring due to their comparatively greater AML growth rate. Ultrasound-detected AMLs with an extra-renal component may require computed tomography (CT) to confirm their size.