A simple kidney cyst is a thin-walled, fluid-filled sac in the kidney. Cysts are very common, found in up to half of people over 50, and are usually noticed by chance on a scan done for another reason.
Simple cysts are benign, do not turn into cancer and rarely affect kidney function. The task is to distinguish them from complex cysts, which have thick walls, internal divisions or solid parts and carry a risk of malignancy, and from polycystic kidney disease, an inherited disorder with many cysts in both kidneys.
Symptoms
- Usually no symptoms at all
- A dull ache in the flank or back with a large cyst
- Blood in the urine, uncommonly
- Fever and flank pain if a cyst becomes infected
- Sudden sharp pain if a cyst bleeds or ruptures
- Raised blood pressure or obstruction of urine flow, rarely, with very large cysts
Causes and risk factors
Why simple cysts form is not fully understood. They are thought to arise from weakened segments of the kidney tubules that balloon out and seal off. They become more frequent and larger with age, and are more common in men, smokers and people with high blood pressure or reduced kidney function. People on long-term dialysis often develop multiple acquired cysts, which carry a small cancer risk. Simple cysts are not inherited, unlike polycystic kidney disease.
How it is diagnosed
- Ultrasound: A round, echo-free structure with a thin smooth wall is diagnostic of a simple cyst and needs no further testing.
- CT or MRI with contrast: Used when the ultrasound is not typical. Cysts are graded with the Bosniak classification from I to IV.
- Bosniak I and II: Benign; no follow-up required.
- Bosniak IIF: Probably benign; repeat imaging at 6 to 12 months and then yearly for about 5 years.
- Bosniak III and IV: Malignancy risk of roughly 50 percent and 90 percent respectively; surgical assessment is advised.
- Kidney function and urine test: Expected to be normal with simple cysts; abnormalities point to another problem.
Treatment options
- No treatment: Correct for the great majority. A cyst that causes no symptoms needs no intervention, whatever its size.
- Surveillance imaging: For Bosniak IIF cysts only.
- Aspiration with sclerotherapy: A needle drains a symptomatic cyst under ultrasound guidance and alcohol is instilled to reduce refilling. Recurrence is still fairly common.
- Laparoscopic cyst decortication: Keyhole removal of the cyst roof for large, painful or recurrent cysts, with 1 to 2 nights in hospital.
- Partial nephrectomy: Removal of a suspicious complex cyst with a rim of normal tissue, often robot-assisted, preserving the rest of the kidney.
- Antibiotics and drainage: For the uncommon infected cyst.
When it is urgent
Seek local emergency care for sudden severe flank pain, fever with shaking chills, heavy or clotted blood in the urine, or dizziness and a fast pulse after an injury to the flank.
Travelling to Türkiye for treatment
A simple cyst does not justify a trip, and you should be wary of anyone offering to operate on one that causes no symptoms. Travel is reasonable for a second reading of scans when a cyst has been labelled complex, or for planned laparoscopic or robotic surgery on a symptomatic or Bosniak III to IV cyst, which typically means 5 to 8 days in Istanbul. Send the actual CT or MRI images in advance, not only the report.
Send your reports, scans and a short history and a Clinic-Y coordinator replies within 24 hours with suitable teams and written, all-inclusive proposals side by side. Reviewing your case is free.
Frequently Asked Questions
Can a simple cyst become cancer?
No. Cancers that look cystic were complex from the beginning, which is why accurate imaging classification matters.
My cyst is 6 centimetres. Must it come out?
Size alone is not a reason. Treatment is for pain, obstruction, infection or suspicious features.
Do I have polycystic kidney disease?
A few cysts with normal sized kidneys and no family history is not PKD. Age-specific cyst counts on imaging are used when there is doubt.
Will diet or medicine shrink it?
No diet, supplement or medicine shrinks simple cysts.