Simple renal cysts

　　Simple renal cysts can be caused by congenital glomerular and tubular structural variations, or can be caused by postnatal injury, infection, and other factors.
　　The pathogenesis of simple renal cysts has not been fully elucidated. Although it belongs to a non-hereditary congenital disease, Schnlzinger (1994) and others found two families with simple renal cysts and performed gene linkage analysis on them, but did not find any association with autosomal dominant polycystic kidney disease (ADPKD). It is believed that there may be autosomal dominant simple renal cysts. Lesions are more common in the lower pole of the kidney. Cysts originate from renal tubules and protrude from the renal cortical surface, appearing blue, and can also be located in the deep cortex or medulla. Generally, the diameter is less than 1cm, but can also be 3-4cm, and some can reach 10cm or more. The cyst contains sterile clear amber-colored fluid, 5% of which is bloody fluid. About 1/3 to 1/2 of the cases have malignant changes in the cyst wall. The cyst wall is thin, lined with a single layer of flat epithelium, and can also be fibrotic and calcified, resembling an eggshell. Lower pole cysts can compress the ureter, causing obstructive hydronephrosis and infection.

　　Complications caused by simple renal cysts:
　　The cyst located at the renal hilum compresses the renal artery, causing an increase in plasma renin, which can lead to hypertension; or it can cause obstructive hydronephrosis and secondary infection, as follows:
　　1. In the absence of antihypertensive medication, systolic blood pressure ≥139mmHg and/or diastolic blood pressure ≥89mmHg, hypertension is classified into stages 1, 2, and 3 according to blood pressure levels. Systolic blood pressure ≥140mmHg and diastolic blood pressure 2. Obstructive nephropathy refers to the obstruction of urine flow in the urinary tract, which produces backward pressure and affects the normal physiological function of the renal parenchyma, leading to renal lesions. The degree of obstruction can be complete or partial; the scope can be bilateral or unilateral; the onset can be acute or gradual; the location can be upper urinary tract or lower urinary tract; the upper urinary tract is above the ureterovesical junction (ureter, renal pelvis, ureterorenal junction); the lower urinary tract is below the ureterovesical junction (urethra, bladder neck, bladder ureteral junction). The impact on the kidney is related to the degree of obstruction and the duration. Early removal of obstruction can make the lesions disappear, while late removal can lead to permanent loss of renal function that cannot be reversed. Therefore, it is very important to recognize obstructive nephropathy and remove the obstruction in a timely manner.

　　Simple renal cysts usually occur in adulthood, generally without clinical symptoms, do not affect renal function, and occasionally cause hematuria leading to medical consultation. The vast majority of patients are discovered incidentally during B-ultrasound or CT scans. Urinalysis is normal, hematuria is rare, but renal cysts can cause abdominal pain and the discovery of abdominal masses, hypertension, and other symptoms. If the cyst bursts into the renal pelvis and calyces, hematuria may occur, and the cyst can also lead to symptoms of renal pelvis and calyces obstruction.

　　Since there is no effective treatment, the main preventive goal is to prevent kidney complications and maintain renal function.
　　Patients with this disease should avoid close contact activities, especially collisions and compressions, to prevent the rupture of the cyst. Patients with this disease are prone to urinary tract infections, especially women, and must receive active symptomatic and supportive treatment.

　　Laboratory tests for simple renal cysts include:
　　1. Imaging examination
　　1. B-ultrasound is the preferred examination method. The typical B-ultrasound findings are anechoic areas, smooth cyst walls, and clear boundaries. When the cyst wall shows irregular echoes or localized echo enhancement, malignant lesions should be suspected; when secondary infection occurs, the cyst wall thickens, and there are fine echoes within the lesion area; when accompanied by bloody fluid, the echo is enhanced.
　　2. CT is valuable for cases that cannot be determined by B-ultrasound, especially when the cyst is accompanied by bleeding or infection, showing heterogeneity, increased CT values. When CT shows cystic features, it is not necessary to perform diagnostic puncture.
　　3. IVU can show the degree of compression of the renal parenchyma or ureter by the cyst.
　　4. MRI can help determine the nature of the cyst fluid.
　　2. Cyst puncture and cyst fluid examination
　　When B-ultrasound, CT, etc., cannot make a definitive diagnosis or there is a suspicion of malignant lesions, cyst puncture can be performed under B-ultrasound guidance, and the cyst fluid can be extracted for examination. When the cyst is secondary to a tumor, the cyst fluid is bloody or dark brown, with a significant increase in fat and other components, positive cytology, elevated CA-50 tumor markers, and moderate increase in fat and protein content when complicated with infection. The cyst fluid is dark and turbid, with a significant increase in amylase and LDH. Cytological examination shows inflammatory cells, and the culture of the cyst fluid can determine the pathogen. After extracting the cyst fluid,造影剂 and/or gas can be injected to show the condition of the cyst wall. If the cyst wall is smooth, it indicates the absence of a tumor.

　　Dietary注意事项 for patients with simple renal cysts:
　　1. Foods to eat
　　Patients with simple renal cysts should eat light, easy-to-digest foods, fresh vegetables, and moderate amounts of fruit, and drink water appropriately. Pay attention to a balanced diet and nutrition.
　　2. Foods to avoid
　　The diet for renal cysts should avoid spicy and irritating foods such as chili; avoid alcohol; smoking (including passive smoking); avoid chocolate; coffee, sea fish, shrimp, crabs, and other 'inducing' foods; avoid salty foods, especially preserved foods; avoid contaminated foods such as unhygienic foods, rotten and deteriorated foods, leftover meals, etc.; avoid grilled foods.
　　3. Limit the intake of certain foods
　　1. Protein control: Modern medicine believes that both low and excessive protein intake are harmful to the kidneys. Particularly after a large intake of protein, excessive metabolic products can be produced, such as urea, creatinine, guanines, polyamines, and certain middle-molecular substances in uremic toxins, which are basically metabolic products of nitrogen (protein). Controlling protein intake (low-protein diet during renal failure) plays an important role in reducing the burden on the kidneys, reducing the production of uremic toxins, and alleviating the condition.
　　2. Salt intake restriction: When controlling salt, adjustments should be made according to the patient's condition and the degree of renal function, but not all patients with chronic renal insufficiency need to be strictly salt-restricted.
　　3. Water intake: In simple renal cysts, due to the decreased renal concentrating function, more water is needed to excrete metabolic products from the kidneys. Therefore, simple renal cyst patients should not be water-restricted blindly if there is no obvious edema, heart failure, or hypertension.

　　Simple renal cysts develop slowly, may not damage the kidney, and most patients are of advanced age when discovered, so the treatment tends to be conservative.
　　1. If there is no kidney parenchyma or obvious compression of the renal pelvis and calyces without infection, malignancy, hypertension, or the above symptoms are not obvious, even if the cyst is large, surgery is not recommended, and close follow-up with B-ultrasound should be adopted.
　　2. When secondary infection occurs, considering that antibiotics can penetrate the cyst wall and enter the cyst cavity, antibiotic treatment and puncture drainage under ultrasound guidance can be used first. If this fails, consider open surgery.
　　3. If it is confirmed that the cyst has cancer or is accompanied by renal cancer, early surgical treatment should be performed.
　　4. When the diameter of the cyst is greater than 4cm, puncture and sclerosing agent treatment can be performed, and the choice of sclerosing agent should be cautious. Tetracycline has both hardening and infection prevention effects, with an efficacy of 96%, and few side effects. Bismuth phosphate also has good efficacy, with 44% of the cysts completely disappearing, 52% shrinking, and no serious complications.
　　5. When the above treatment is ineffective and the symptoms or cyst infection are obvious, cyst decortication or partial nephrectomy can be performed.
　　6. If the kidney is severely infected due to the cyst and the renal function is severely damaged on one side while the renal function on the other side is normal, nephrectomy can be performed.
　　In summary, the treatment of simple renal cysts must comprehensively consider the impact of the cyst on the kidney and the whole body, and determine according to the development of the cyst. If the above conditions are not obvious, it is advisable to follow up closely and observe without急于 treating.