Kidney (renal) cysts are fluid-filled sacs that form on one or both of the kidneys. Usually, these cysts do not cause symptoms or kidney damage, in which case they are referred to as simple kidney cysts.
Simple kidney cysts are very different from the type of cysts that develop when a person has the genetic condition polycystic kidney disease (PKD), which causes scarring of the kidney tissue that can eventually damage the kidney and lead to kidney failure.
Simple cysts sometimes cause symptoms if they have become large enough or have started to press on other organs. They can also become infected, leading to pain and fever.
Diagnosing Simple Kidney Cysts
Since these cysts do not generally cause symptoms, they are usually only discovered when a test or scan is performed for some other condition. When a cyst is found, imaging tests are performed to determine whether it is a simple cyst or a sign of a more serious condition. The imaging tests that may be employed are described below.
Ultrasound employs a device called a transducer to bounce sound waves off organs and generate an image of their structure. Images of the whole urinary tract can be created and used to distinguish between cysts that are harmless and those that signal more serious conditions.
In a computerized tomography (CT) scan, a combination of X-rays and computer technology is used to generate 3D images. This may involve a dye being injected, which is referred to as a contrast medium. For these scans, patients are required to lie down on a table, which is moved into a device shaped like a tunnel where the X-rays are obtained. These scans can reveal tumors and cysts present in the kidneys.
Magnetic resonance imaging
Magnetic resonance imaging (MRI) scans use magnets and radiation to create very detailed images of soft tissue and organs. This process may also involve the use of a contrast medium. Here again, a person lies on a table that is moved into a tunnel-like machine. These scans also reveal the presence of any cysts or tumors.
PKD is usually diagnosed using ultrasound, which is the most non-invasive and cost-effective way of diagnosing the condition. If a person is at risk of PKD, but is aged older than 40 years and has an ultrasound scan that shows the kidneys are normal, then they are unlikely to have PKD. Occasionally, a CT scan or MRI scan may be used to find cysts that are too small to be detected by ultrasound. When cysts are found, MRI is the technique used to monitor the growth and volume of both the kidneys and the cysts.
Sometimes, genetic testing is performed, which involves a sample of blood being taken and checked for gene mutations known to cause PKD. This is not always recommended because it is expensive and not always reliable. Genetic testing fails to detect PKD in around 15% of patients who undergo the test. Situations where genetic testing may be recommended include the following:
- Where there is uncertainty in diagnosis after imaging techniques have been used
- Where a person is younger than 30 years of age and has a family history of PKD, a negative ultrasound, and intends to have a children
- Where a person with a family history of the condition wishes to donate a kidney