Kidney or renal cysts are fluid-filled collections that form on or in the kidneys. Kidney cysts are very common. Up to 50% of people over the age of 50 have kidney cysts. 

Types of Kidney Cysts

The vast majority are an incidental finding on a scan. Most of these are classified as ‘simple’ renal cysts which means that they are benign and the chance of cancer is almost zero. Most cysts are simple cysts. Occasionally a cyst will be classified as a ‘complex’ renal cyst. In this case further scans are required to establish what treatment or follow up is required.

Symptoms

Most kidney cysts actually do not cause any symptoms, and are identified incidentally. Symptoms may include:

• Dull pain in your flank or back

• Fevers or chills

Causes

The exact cause of kidney cysts is not known. One theory is that kidney cysts develop when the kidney surface weakens and forms a pouch (diverticulum). The pouch then fills with fluid, detaches and develops into a cyst. Rarely, genetic conditions can also cause kidney cysts.

Complications

 Kidney cysts can occasionally lead to complications. These include:

• Infection. A kidney cyst may become infected, causing present as loin pain, fever and chills

• Ruptured cyst. A kidney cyst that bursts may cause pain in your back or side.

• Urine obstruction. A kidney cyst may block the drainage of urine from the kidney leading to kidney swelling (hydronephrosis) and pain. 

• Risk of cancer. Some complex cysts may have cancerous involvement and need to be surgically removed.

Diagnosis

Tests to evaluate kidney cysts include:

• Imaging tests.  Ultrasound, CT and MRI imaging test can be used to investigate kidney cysts. These tests will help us determine the type of kidney cyst and whether it needs further treatment. 

• Blood tests. Blood tests will check your your overall kidney function. 

Bozniak Classification of Kidney Cysts

You may see a term called Bozniak classification on your CT scan report.  The summary of the classification system is provided below.

• Bosniak 1 cyst

  • Risk of cancer <1% 

  • Treatment: does not require follow-up

• Bosniak 2 cyst

  • Risk of cancer <5% 

  • Treatment: does not require follow-up

• Bosniak 2F cyst

  • Risk of cancer 5%

  • Treatment: requires follow-up imaging to assess progress

• Bosniak 3 cyst

  • Risk of cancer 50%

  • Treatment: should be surgically removed or closely monitored

• Bosniak 4 cyst

  • Risk of cancer 80-95% 

  • Treatment: should be surgically removed

Treatment

Treatment may not be necessary

If the kidney cysts is simple and causes you no bother and no symptoms, and it does not interfere with your kidney function, then you you may not need any treatment at all. 

Treatments for cysts that cause symptoms

If a kidney cyst causes symptoms or its complex in nature, then you may need surgery to remove the cyst. At Adelaide Urology Care, we offer robotic surgery to remove the cystic lesion through small incisions to offer quicker recovery and healing.

Contact

At Adelaide Urology Care, we are dedicated to giving you the personalized care you need. Please do not hesitate to contact us for more information. 

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Kidney Cyst on CT Scan

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Bozniak Classification of Kidney Cysts