Kidney Cancer Institute explains simple kidney cysts do not pose a cancer risk to patients, whereas complex kidney cysts have different characteristics that may make them cancerous. A simple kidney cyst is spherical, is filled with liquid and contains a thin outer membrane. A complex kidney cyst is usually irregular, contains calcified material and has a thick outer membrane.
KCI states simple kidney cysts appear on radiographic scans done for another purpose. These cysts hardly ever pose a risk to patients. Rare, larger cysts may interfere with the function of other organs, such as the lungs or stomach. A thin needle aspirates, or sucks out the fluid, of larger, benign cysts. This minimally invasive surgery involves the help of CT scans and ultrasounds. Kidney cysts are classified from Category I to Category IV, with Category IV as the most likely to be cancerous.
Complex kidney cysts may have walls within themselves that separate parts of cysts, according to KCI. Calcium deposits may form inside these structures, making complex cysts harder than simple ones. Tissue inside complex cysts may be enhanced, meaning part of the structure receives a blood supply. This enhancement indicates the possibility of kidney cancer within the cyst.
Complex kidney cysts have a 13 to 90 percent chance of having cancer. Larger, more irregular cysts have greater chances of becoming cancerous. A urologist surgically removes complex cysts upon their diagnosis.