Kidney Cyst: What It Is, Types, and Whether It Is Dangerous

A kidney cyst is a fluid-filled formation that can form in one or both kidneys. Most often it is a simple cyst that does not change the structure of the organ and does not impair its function. The reason for this breakdown is a typical situation: a cyst is found on ultrasound, and one needs to understand what the wording in the report means.

What a kidney cyst is

A simple kidney cyst, also known as a simple renal cyst, is an abnormal hollow sac filled with fluid. The shape is usually round or oval; there may be one cyst or several, in one kidney or both. Each kidney is about the size of a fist and contains about a million nephrons that filter the blood. A simple cyst does not enlarge the organ, does not replace its normal structure, and does not reduce filtration.

Polycystic kidney disease is structured differently. It is a genetic disease with cystic degeneration of the parenchyma: multiple cysts form in both kidneys, the volume of the organ increases significantly, neighboring nephrons are compressed, and the kidney gradually loses its filtering function. The autosomal dominant form occurs with a frequency of 1 in 400–1000 people and most often manifests at the age of 30–50 years. A simple cyst has nothing to do with this disease.

Types of cysts: what the doctor clarifies

In imaging descriptions, the same cyst may be called different things. The doctor clarifies the type and significance of the formation based on ultrasound, CT, or MRI data. Polycystic kidney disease is not a variant of a simple cyst but a separate genetic disease with multiple cysts in both kidneys.

Why kidney cysts appear, including in older adults

The cause of simple cysts has not been fully studied; it is known that they occur more often with age. In one large study, about 1 in 10 people had simple cysts, and among people aged 50 and older — almost 1 in 5. Cysts develop more often in men than in women: in one study, twice as often. With age, cysts tend to increase in size and appear in greater numbers. There is no prevention for simple cysts.

Symptoms: when a cyst manifests itself

Usually simple cysts do not cause symptoms and do not create additional health problems, so they are found incidentally, on imaging performed for another reason. In rare cases, a cyst reaches a size at which it presses on bones or neighboring organs, and then pain or discomfort occurs. Other rare variants: impaired blood flow or urine outflow through the kidneys and ureters, infection with fever, pain and tenderness, rupture with pain and blood in the urine (hematuria), increased blood pressure. With such symptoms, one should consult a doctor.

How a cyst is detected and what the size may be

Diagnosis relies on imaging and laboratory tests that help rule out more serious problems, including some types of kidney cancer. The size of a simple cyst ranges from a pea to a golf ball. If more information is needed to confirm the diagnosis, the doctor may order a CT or MRI.

• Abdominal ultrasound — creates an image of the kidneys and detects cysts.
• CT — shows cysts and tumors; a contrast-enhanced variant is possible.
• MRI — provides a more detailed picture without X-ray radiation.
• Blood and urine tests — assess kidney function.
• Repeat ultrasounds — are used to monitor changes.

Whether a cyst is dangerous

A simple cyst is usually harmless, and complications are rare. If a cyst causes symptoms or impairs blood and urine flow, a doctor evaluates it and decides whether intervention is needed. For cysts without symptoms, doctors usually do not intervene but may order regular ultrasound for monitoring.

A kidney cyst by itself is not a reason to call an ambulance. The numbers 103 and 112 are needed for a life-threatening condition — for example, loss of consciousness or severe pain that cannot be tolerated.

This material is for reference and does not replace a doctor's consultation.

This content is for reference and does not replace a doctor's consultation. Medical disclaimer