Renal cysts are sacs of fluid that form in the kidneys, either as a single cyst or multiple cysts. They are categorized as simple or complex. Simple cysts are the most common renal masses, consisting of a thin wall surrounding water-like fluid, and are usually asymptomatic. Complex cysts are septated and/or enhanced on imaging, with solid material inside. They may manifest with pain, fever, and hematuria, and should raise suspicion of malignancy. Cysts can be diagnosed via imaging such as ultrasound, CT scan, or MRI, and are usually incidental findings. In most cases, treatment is unnecessary. Indications for surgery include symptomatic cysts or cysts that carry a risk of complications. Complex cysts require follow-up and must be removed if renal cell carcinoma is suspected. Possible complications include cyst rupture, infection, and compression of an adjacent structure (e.g., the ureter).
- Sacs of fluid that form in the kidneys
- Solitary or multiple renal cysts
|Overview of renal cysts|
|Simple cysts||Complex cysts|
|Description|| || |
|Clinical features|| |
|Diagnostics|| || |
|Bosniak classification of renal cysts |
|Class||Findings on contrast-enhanced CT scan||Likelihood of malignancy||Management|
|I|| || |
|II|| || |
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- Not indicated in most cases
- Indication for surgery: symptomatic cysts (e.g., impaired urinary flow, pain, bleeding) or risk of further complications (e.g., infection, malignancy)
- Complex cysts require follow-up and must be removed if renal cell carcinoma is suspected (e.g., due to changes in echogenicity or shape).
Complications are rare.
- Cyst rupture
- Cyst infection
- Compression of adjacent tissue (e.g., of the ureter causing impaired urinary flow)
We list the most important complications. The selection is not exhaustive.