Fluid turnover in renal cysts.

Cystic puncture was performed percutaneously in 18 patients with solitary renal cysts and in 22 with multiple, congenital renal cysts. With the aid of tritiated water it was possible to estimate the fluid turnover in the cysts and compare it with their volume, pressure and potassium and creatinine levels. Fluid turnover was rapid in all the renal cysts. Two to five hours after i.v. injection of tritium, the tritium concentration in cystic fluid averaged 88% of the concentration in plasma fluid in patients with polycystic kidneys and 73 percent in patients with solitary cysts. Fluid turnover was more rapid in small than in large cysts, but there was no such difference between cysts with high and low pressure. It is possible that the fluid turnover was slightly faster in cysts with high potassium and creatinine levels than in those with low levels. The results show that the fluid turnover in a renal cyst of 10 ml is considerable--probably more than 100 ml/24 hours. This indicates that fluid inflow to the cyst comes mainly from cells in the cyst wall and not from a single glomerule. Fluid probably leaves the cyst actively via cells in the cyst wall, since the fluid turnover does not increase with high cyst pressure. The fluid turnover is probably secondary to the active solute transportation, which is performed by the cyst cells. This means that these cells have a tubular cell-like function and should respond to pharmacotherapy.