What is a kidney cyst? What are the types of kidney cysts?
Renal cysts are cystic lesions that appear on the surface or inside the kidney that are not connected to the outside world. According to the etiology, there are two types 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.
What causes renal cysts?
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 gene for congenital dysplasia is usually not abnormal, so it is distinct 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 internal environment of the body thus creating environmental conditions favorable to the change of cyst genes, which increases the activity of internal factors of cysts, and this 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.
What are the risks of renal cysts to human body?
Smaller renal cysts are not felt by human body normally, while larger cysts (more than 5cm in diameter) will compress normal kidney tissues and cause damage to kidney function, requiring laparoscopic decompression surgery or puncture to aspirate cystic fluid. There are also some cysts located in the parapelvic area of the kidney, which can cause fluid accumulation in the kidney of patients and cause discomfort such as back pain and distension. When kidney cysts become infected, bleed, or rupture under external force, they can cause pain in the patient’s lower back and endanger health. So you need to pay attention to kidney cysts, especially the larger ones, which need to be reviewed regularly at the hospital.
Do kidney cysts have any symptoms?
Simple kidney cysts usually have no symptoms. However, larger cysts can cause the following uncomfortable symptoms.
(1) Discomfort or pain in the waist and abdomen. The pain is characterized by vague, dull pain, fixed on one or both sides, radiating to the lower part and lower back. If the cyst is combined with infection and bleeding, the patient may feel severe pain and experience an increase in body temperature.
(2) Hematuria. It may manifest as microscopic hematuria or flesh-eye hematuria.
(3) Abdominal mass. Sometimes it is the main reason for patients to visit the clinic. 60~80% of the enlarged kidneys can be palpated, and the larger the kidneys are, the worse the kidney function is.
(4) Proteinuria. Usually the amount is not much, not more than 2 grams in 24 hours urine, so nephrotic syndrome will not occur.
(5) Hypertension. The cyst compresses the kidney and causes renal ischemia, which increases renin secretion and causes hypertension.
(6) Hydronephrosis. If it is a parapelvic cyst, it will cause hydronephrosis in the kidney and cause swelling and pain in the patient’s back.
What are the general methods to detect and follow up renal cysts?
The following tests can be done to diagnose renal cysts.
(1) Urine examination. Urine routine is usually normal, if the cyst presses the kidney parenchyma or combined with intracapsular infection, a small amount of red blood cells and white blood cells may appear in the urine.
(2) Ultrasound. It can understand the number, size and wall of the cyst, and can be distinguished from the renal parenchymal mass, which is the preferred examination method for renal cysts. Typical
B ultrasound shows no echo in the lesion area, smooth cyst wall and clear boundary. When the cyst wall shows irregular echogenicity or limited echogenicity enhancement, malignant transformation should be alerted. In case of secondary infection, the cyst wall is thickened and there is fine echogenicity in the lesion area, and the echogenicity is enhanced when there is bleeding in the cyst. When the imaging suggests multiple cysts, it should be distinguished from polycystic cysts and polycystic kidneys.
(3) Intravenous urography (IVU). It can show the degree of cyst compression of renal parenchyma and can be distinguished from hydronephrosis.
(4) CT examination of the kidney. It is valuable for those who cannot be identified by B-ultrasound. When the cyst is accompanied by bleeding, infection or malignancy, it shows heterogeneity and increased CT value. When
CT shows cystic features, cyst puncture can be unnecessary. To distinguish between cysts and hydronephrosis CT urography (CTU) can be done.
(5) Magnetic resonance imaging (MRI). If further examination of the nature of the cysts is needed, MRI enhancement of both kidneys can also be performed.