Renal cyst (renal cyst, cyst of kidney) is a general term for cystic masses of varying sizes that do not communicate with the outside world that appear in the kidneys. Common renal cysts can be divided into adult-type polycystic kidneys, simple renal cysts and acquired renal cysts. Adult-type renal cyst is a congenital hereditary disease in which the kidney parenchyma is filled with countless cysts of varying sizes that are not connected to the outside world. Kidney cysts contain fluid inside the cysts, small ones are invisible to the naked eye and large ones can be several centimeters, so they are called polycystic kidneys. Manifestations include increased nocturia, low back pain, and high blood pressure. Urinalysis has hematuria, a small amount of proteinuria, often slowly develop into chronic renal failure. 10% of people have kidney stones and 30% have polycystic liver. Experienced doctors can confirm the diagnosis with the help of ultrasound and intravenous pyelogram. Simple renal cysts may be a congenital anomaly, which are unilateral or bilateral kidneys and have one or several round cystic cavities of varying sizes that do not communicate with the outside world, most of which are unilateral, so they are called simple renal cysts. Its incidence may increase with age, and 50% of people over 50 years old can find this kind of cyst when they do ultrasound. The diagnosis can be confirmed with the help of ultrasound and CT. Unique characteristics of simple renal cyst: Simple renal cyst is the most common type of cystic kidney disease in clinic, unlike polycystic cyst, this disease is not congenital but formed later, in the past it was thought to be caused by local ischemia, in recent years it is thought that it may be developed by renal tubular diverticulum. The incidence of simple renal cysts increases with age as the distal tubules and collecting and diverticula increase. Mainly seen in adults, the incidence increases with age, and about half of people over 50 years of age have at least one cyst. Cysts can be either one or two-sided, with one or a few cysts per kidney. Cysts are usually isolated and spherical, located in the superficial renal cortex can change the shape of the kidney, can also be located in the deep cortex or medulla, the diameter of 0.5 ~ 1M, can also be 3 ~ 8M, the cyst wall is thin and transparent, containing straw-yellow fluid, viscous, if there has been inflammation, the wall of the capsule can be thickened, fibrosis or even calcification. The cyst is not connected to the renal pelvis, and the wall is lined with a single layer of flat epithelial cells. The disease is usually asymptomatic and is often detected unintentionally for other purposes or during a physical examination. Occasionally, hematuria and localized pain, renal obstruction and secondary infection may occur. Individuals with hypertension due to compression of adjacent blood vessels by the cysts, resulting in local ischemia and increased renin, in which case aspiration of the cyst fluid or removal of the cysts reduces the blood pressure to normal, and may occasionally result in erythrocytosis. The disease does not lead to renal hypoplasia. The natural changes of simple renal cysts are slow. Acquired renal cysts occur mainly as a result of uremia or after dialysis treatment. It is not related to age but to the duration of hemodialysis. The kidneys originally did not have renal cysts, and according to the literature, most patients on dialysis for more than 3 years develop cysts. It has at least 4 cysts in one kidney, mostly 2 to 3 centimeters in diameter. Some cysts can be infected or even cancerous, and the diagnosis can be confirmed by ultrasound or CT examination.