Renal epithelial cysts, also known as simple renal cysts, are common benign lesions of the renal parenchyma. Since they are uncommon in children and progressively more common with age, they are considered acquired lesions.
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Epidemiology
overall high prevalence
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increasingly common with age 1,2
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uncommon in children
average incidence 0.22% before age 18 3
25% prevalence at 40 years old by autopsy
50% prevalence at 50 years old by autopsy
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Clinical presentation
usually asymptomatic 1,2
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large cysts may be symptomatic 1
pain - related to rupture or hemorrhage
hematuria (rare - more commonly due to associated nephrolithiasis 2)
local urinary obstruction (although not affecting renal function 2)
infected cysts are uncommon, but may present with fever, flank pain, and sympathetic pleural effusion 2
Pathology
Renal epithelial cysts are true cysts derived from isolated segments of the renal tubules, possibly representing excluded diverticula which "detach" from the tubules as they enlarge 2. Once they are larger than several millimeters, they do not communicate with the renal collecting system. They may arise in the renal cortex or medulla.
Epithelial cysts are lined by a single layer of partially dedifferentiated epithelial cells and contain a clear fluid similar to plasma ultrafiltrate 2. They may range in size from a few millimeters up to 30 cm 2. A cyst may rupture into the collecting system, forming a communication and resembling a calyceal diverticulum 1.
The cyst walls can become thickened, fibrotic, and partially calcified in the setting of prior infection or hemorrhage 2.
Radiographic features
Epithelial cysts may manifest along a spectrum from stereotypical "simple" cysts to septated and complicated lesions. Complicated appearance may be due to prior infection or hemorrhage; however, these cysts may be difficult to distinguish from cystic renal cell carcinoma.
Epithelial cysts occur in the renal parenchyma, either within the cortex or medulla. Centrally-located epithelial cysts which efface the collecting system may be indistinguishable from renal sinus cysts.
See renal cyst and Bosniak classification articles for more on the imaging appearance of epithelial cysts.
Treatment and prognosis
Most renal epithelial cysts are clinically inconsequential and are incidental discoveries.
Symptomatic cysts may be treated by percutaneous drainage and sclerosis or laparoscopic resection, depending on their size 2.
Differential diagnosis
Considerations include