We often see patients with incidentally found simple renal cysts on ultrasounds done for urinary symptoms/abdominal pain. Once a cyst is found, I feel obligated to continue to monitor it with serial ultrasounds. But why follow up on a simple renal cyst? And for how long?
I will be discussing the article by Rediger et al, from Canada, which addresses both these questions.
Why follow up a renal cyst?
The 2 main reasons for follow-up are:
- Early detection of polycystic renal disease (PKD).
- To detect malignant degeneration.
The article by Rediger et al found that only a small proportion of patients eventually developed PKD (12%). In these patients, the diagnosis of ADPKD was made relatively early during follow-up (in the first 1-3 years).
No patient developed a malignancy in their study.
More details on the study
These researchers from Ontario retrospectively looked at charts of patients diagnosed with simple renal cysts. They included patients with 1-3 simple cysts as patients with more than 3 cysts are already cataloged as having PKD.
Forty percent of the cysts were found incidentally and the rest during the evaluation of abdominal pain (16%) or other symptoms. The median diameter of the larger cyst at the first ultrasound was 0.8 cm (IQR 0.5, 1.2). Median follow up was 4.1 years and the median number of follow up ultrasounds was 3.
Eleven of the 87 patients in the study were diagnosed with PKD. Five of the eleven had a family history of PKD.
Ten patients had complete resolution of the cysts.
3 patients underwent surgical intervention to remove the cysts due to suspected malignancy or change.
About 10% of patients with simple renal cysts can eventually meet criteria for the diagnosis of PKD. Because the diagnosis of PKD is established early during follow-up of simple cysts in most patients, I would suggest a 1,3 and 5 year follow up to diagnose PKD — since a 2-year delay in diagnosis is unlikely to affect clinical outcomes in the early asymptomatic stages of the disease.
Following simple renal cysts for the purpose of early detection of malignancy does not seem to be supported by current literature.
Patients with 4 cysts or more should be referred to Nephrology since they meet the definition of PKD.