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

To investigate the natural history and rationalize follow-up of renal angiomyolipomas (AMLs).

A 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.

A 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).

This 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.