Definition, Etiology, PathogenesisTop
Simple renal cysts are found in >10% of adults aged >50 years, more commonly in men, with increasing prevalence with age. Simple renal cysts may increase in size with age and are usually asymptomatic; however, large cysts (>5 cm) may cause abdominal distention, flank or lower back pain, or nonspecific gastrointestinal symptoms. Possible complications of simple renal cysts include hematuria and infection. Polycystic kidney disease should be considered in those with renal enlargement, multiple cysts, bilateral involvement and positive family history.
Simple renal cysts are often incidental findings on imaging. On ultrasonography, a simple cyst must have smooth round walls, no solid component or internal vascularity, and clearly defined back wall. Cysts with these characteristics or small cysts with <1 mm thin septations do not require further imaging.Evidence 1Strong recommendation (downsides clearly outweigh benefits; right action for all or almost all patients). Moderate Quality of Evidence (moderate confidence that we know true effects of intervention). Quality of Evidence lowered due to the relatively small number of observations (imprecision). van Oostenbrugge TJ, Fütterer JJ, Mulders PFA. Diagnostic Imaging for Solid Renal Tumors: A Pictorial Review. Kidney Cancer. 2018 Aug 1;2(2):79-93. doi: 10.3233/KCA-180028. PMID: 30740580; PMCID: PMC6364093. Cysts that do not meet these criteria should be investigated with computed tomography (CT) scanning and classified with the Bosniak renal cyst classification system.Evidence 2Moderate Quality of Evidence (moderate confidence that we know true effects of the intervention). Quality of Evidence lowered due to indirectness. Silverman SG, Pedrosa I, Ellis JH, et al. Bosniak Classification of Cystic Renal Masses, Version 2019: An Update Proposal and Needs Assessment. Radiology. 2019 Aug;292(2):475-488. doi: 10.1148/radiol.2019182646. Epub 2019 Jun 18. PMID: 31210616; PMCID: PMC6677285.
Patients with asymptomatic simple renal cysts require no further monitoring or imaging. Bosniak 2F cysts should be compared with previous images if available. Contrast-enhanced magnetic resonance imaging (MRI) may be performed in equivocal cases, and if truly 2F, the cyst should be followed with yearly ultrasonography. Changes in the cyst should be reinvestigated with CT.Evidence 3Strong recommendation (benefits clearly outweigh downsides; right action for all or almost all patients). Moderate Quality of Evidence (moderate confidence that we know true effects of intervention). Quality of Evidence lowered due to the relatively small number of cases (imprecision). Shaish H, Ahmed F, Schreiber J, Hindman NM. Active Surveillance of Small (< 4 cm) Bosniak Category 2F, 3, and 4 Renal Lesions: What Happens on Imaging Follow-Up? AJR Am J Roentgenol. 2019 Mar 12;212(6):1215-1222. doi: 10.2214/AJR.18.20758. PMID: 30860891. Bosniak 3 and 4 cysts should be referred to a urologist, who may elect to biopsy a category 3 cyst or follow it closely. In rare cases where large simple cysts are symptomatic, treatment with cyst drainage and foam sclerotherapy or surgical resection of the cyst are possible.