Harvard Women's Health Watch

Ask the doctor: What should I do about a kidney cyst?

Q. During a pelvic ultrasound to evaluate uterine fibroids, a radiologist found a cyst in one of my kidneys. Should I be concerned about kidney cancer?

A. Kidney (or renal) cysts are fluid-filled sacs in the kidney that rarely cause symptoms and are usually harmless. They are quite common, and the likelihood of having one or more of them increases as we age. Cysts may be "simple" or "complex." Simple cysts are thin, round sacs with clear fluid, and they are not cancerous. Complex cysts may have thick walls, several lobes, and flecks of calcium or solid components. They are also usually benign, but need further evaluation to be sure they do not contain cancer. Most often a CT scan or MRI will help a urologist or renal expert recommend a strategy of watchful waiting, biopsy, or removal of the cyst. Occasionally, a benign cyst grows large enough to affect the function of the kidney or cause pain. A cyst may also become infected or bleed, causing fever, pain, or blood in the urine (hematuria). In that case, the cyst may need to be removed or drained.

It is not uncommon to have a few simple kidney cysts. This benign condition, which rarely affects kidney function, should not be confused with polycystic kidney disease, a progressive, inherited condition that can severely affect kidney function.

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