Simple Kidney Cyst

Definition, Etiology, PathogenesisTop

Simple kidney cysts are found in >10% of adults aged >50 years, more commonly in men, with prevalence increasing with age. Simple kidney 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 kidney cysts include hematuria and infection. Polycystic kidney disease should be considered in those with kidney enlargement, multiple cysts, bilateral cysts, and positive family history.

DiagnosisTop

Simple kidney cysts are often incidental findings on imaging. On ultrasonography, a simple cyst must have smooth round walls, clearly defined back wall, and no solid component or internal vascularity. 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 Bosniak classification should be applied.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.

TreatmentTop

Patients with asymptomatic simple kidney cysts require no further monitoring or imaging. Bosniak IIF cysts should be compared with previous images if available. Contrast-enhanced magnetic resonance imaging (MRI) may be performed in equivocal cases, and if truly IIF, 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 III and IV cysts should be referred to a urologist, who may elect to biopsy a category III cyst or follow it closely. In rare cases where large simple cysts are symptomatic, treatment with cyst drainage and foam sclerotherapy or surgical resection are possible.