1.What is a kidney cyst? What are the types of kidney cysts? Answer:Renal cyst is a cystic lesion that appears on the surface or inside of the kidney and does not communicate with the outside world. According to the classification of etiology, there are two kinds of renal cysts: congenital and acquired. Congenital, also known as hereditary renal cysts, commonly include polycystic kidney, medullary spongy kidney and polycystic renal dysplasia. Acquired ones are simple renal cyst, parapelvic cyst and acquired cystic nephropathy, the latter is mostly seen in uremic and long-term dialysis patients. Simple renal cysts are the most common in clinical practice. 2.What causes renal cysts? A: The causes of congenital renal cysts are as follows: (1) congenital dysplasia. Congenital dysplasia can produce a variety of diseases, the common ones are medullary spongy kidney and dysplastic polycystic kidney disease. The genes of congenital dysplasia are usually not abnormal, so it is different from genetic inheritance or genetic mutation. (2) Hereditary factors. Commonly there are polycystic kidney, mostly inherited through parents’ genes, divided into autosomal dominant and autosomal recessive inheritance, but there are also patients with polycystic kidney who neither inherit from parents nor belong to congenital dysplastic polycystic kidney disease, but genetic mutation at the time of embryo formation. This condition is less common. Therefore, some polycystic kidney patients can have no parental genetic history. (3) Various infections. Infections can cause abnormal changes in the body’s internal environment thus creating environmental conditions favorable for cystic gene changes and increasing the activity of internal factors of cysts, which can promote the generation and growth of cysts. The causes of acquired renal cysts are relatively simple, mainly due to various causes of renal tubular obstruction, local ischemia and congenital developmental disorders. Due to the obstruction of renal tubules, the local expansion forms simple renal cysts. 3.What is the danger of renal cyst to human body? A: Smaller renal cysts are not felt by human body normally, while larger cysts (more than 5cm in diameter) will compress normal kidney tissues and lead to damage of kidney function. There is also a part of cysts located in the renal pelvis, which will cause fluid accumulation in the kidneys of patients, causing back pain, waist distension and other discomfort. When kidney cysts become infected, bleed, or rupture under the action of external force, they will cause pain in the back of the patient’s back and endanger their health. So you need to pay attention to kidney cysts, especially the larger ones, which need to be reviewed in hospital regularly. 4.How to distinguish renal multiple cysts and polycystic kidney? What is the difference of their harmfulness? A: Renal multiple cysts are cystic blisters of one or several different sizes that are not accessible to the outside world in one or both kidneys. Unilateral is more common and the kidney function is usually normal. on ultrasound examination, the renal parenchyma of polycystic kidney cyst has normal echogenicity and its echogenicity is lower than the internal echogenicity of liver or spleen, and the patient has no family history of the disease. Polycystic kidney is a congenital genetic disorder of numerous cysts of varying sizes in the renal parenchyma. The large cysts can be very large, while the small ones are only visible to the naked eye. The cysts increase the size of the kidney and have an uneven cystic surface with yellowish plasma, sometimes dark brown or reddish brown due to bleeding. Ultrasound images of adult type polycystic kidney show: the kidney is significantly enlarged, typically with a distorted morphology and an extremely irregular, often lobulated surface. There are numerous cysts of different sizes in the kidney, with neat cavities and enhanced echogenicity of the renal parenchyma outside the cysts. The echogenicity of the renal sinus region is often compressed and distorted by the majority of cyst-like echogenicity. The main risk of multiple cysts in the kidney is the compression of normal renal tissues, causing impairment of renal function. It usually appears when the cysts are large in size (cysts more than 5 cm in diameter). Polycystic kidney then causes severe impairment of kidney function with hypertension. As the disease progresses, it eventually leads to chronic kidney failure. There is a difference between the two, and polycystic kidney is far more harmful than simple kidney cyst.