A kidney nodule, also referred to as a kidney cyst, is a formation in the kidneys that consists of a round pouch of fluid, according to Mayo Clinic. Typically, kidney cysts or nodules are noncancerous, but they may be a symptom of a disorder that could impair kidney function.
Although smaller cysts don't typically produce signs or symptoms, common symptoms of a larger kidney nodule or cyst include fever, upper abdominal pain or dull pain on the back or side of the body, according to Mayo Clinic.
As people age, they become more at risk for kidney cysts, states Mayo Clinic. Although kidney nodules or cysts can cause only minor discomfort, in extreme cases, complications such as an infected cyst, a burst cyst or urine obstruction may occur. When kidney cysts become infected or burst, they may cause fever or pain in the back and side of the body. If a urine obstruction occurs, a blockage in the flow of urine may result in swelling of one or both kidneys.
As of 2014, a specific cause of kidney nodules or cysts is unknown, but theories suggest that these cysts develop when a pouch is formed on the surface layer of a weakened kidney, according to Mayo Clinic.