How do you know if a cyst in the kidney is malignant?

To know if a kidney cyst is malignant, it is important to perform a series of studies and medical evaluations. The most common steps to determine the nature of a kidney cyst are:

Renal ultrasound: Ultrasound can show the shape and size of the cyst, as well as the presence of any suspicious features, such as irregular walls or inhomogeneous fluid.

Computed tomography (CT): If the cyst has suspicious features on ultrasound, a CT scan may be done to obtain more detailed images. This helps to identify if there are solid masses within the cyst or changes in the cyst walls that suggest malignancy.

Magnetic resonance imaging (MRI): is useful to better characterize the cyst and may provide additional information about its composition. This is particularly useful if there is doubt after the CT scan.

Bosniak classification: The Bosniak classification system is used to categorize renal cysts based on their appearance on imaging and help determine the risk of malignancy.

Biopsy: In some cases, if the cyst is suspected to be malignant or if imaging tests are inconclusive, a renal biopsy may be performed to obtain a sample of the tissue and examine it under a microscope.

In general, benign kidney cysts do not cause symptoms. However, if a cyst becomes large, it may cause pain in the back or abdomen. If the cyst is malignant, there may be additional symptoms such as blood in the urine, unexplained weight loss, or fatigue.