Pediatric polycystic kidney

　　The cause of polycystic kidney disease is gene deletion, among which adult polycystic kidney disease is often due to gene deletion on chromosome 16, occasionally due to gene deletion on chromosome 4, which is an autosomal dominant inheritance with an penetrance of 100%. Therefore, the chromosomal deletion of a single parent will make their children have a 50% chance of inheriting the disease. Infantile polycystic kidney is an autosomal recessive inheritance, and both parents must have the gene mutation of the disease in order to cause their children to develop the disease, with an incidence rate of 25%.

　　1. Pathogenesis

　　Renal cysts originate from the epithelial structure of the kidney, originating from the renal tubules and Bowman's capsule. All renal cysts have certain common structural components, including the upper cortex, expanded cysts containing the filtrate of the glomeruli.

　　(1) Autosomal dominant inheritance type PK: More than 95% of typical patients are caused by abnormal genes on the short arm of chromosome 16, combined with the action of infection and poisoning on the tubules, which stimulates the cyst gene to change the metabolism of tubular cells, directly causing necrosis of the epithelial cells, causing obstruction and promoting cell proliferation to form cysts.

　　(2) Autosomal recessive inheritance type PK: It is caused by DNA mutation, but the chromosomal site of the defective allele is not clear. The parents of the patients do not have the disease, but they carry the gene of the disease, which can cause their children to develop the disease. This disease is rare.

　　2. Pathological changes

　　(1) Infantile polycystic kidney (infantile polycystickidney): It is an autosomal recessive inheritance, usually accompanied by liver lesions. Although it is mainly seen in young children, it can also occur in older children and adults. The kidneys are significantly enlarged, with a normal appearance, smooth surface, but the lobation state of the fetal kidneys is more obvious than that of normal kidneys. Because the renal cortex and medulla are invaded by small cysts, the cross-section shows a spongy or honeycomb-like appearance. Histological examination shows that the renal parenchyma is replaced by a large number of long cysts arranged at right angles to the renal surface. Under the capsule, a few normal glomeruli and convoluted tubes can be seen. Renal function tests show that the cysts are part of the functional part of the renal unit. Microanatomy shows that the cysts are dilated collecting tubules, the ureter and bladder develop normally. In severe cases, due to the lack of fetal urine, the bladder develops abnormally. According to the age at the onset of symptoms, infantile polycystic kidney can be divided into 4 clinical subtypes.

　　① Perinatal (perinatal period) type: Due to the abdominal swelling of infants, the labor process is often long and not smooth, and children with poor circulation and respiratory difficulties can be seen, presenting a typical Potter face. Sometimes, cyanosis, significant respiratory difficulties, and death at birth or soon after birth can occur due to concurrent pulmonary hypoplasia and mediastinal emphysema. Some infants may have large kidneys palpable at birth, with symptoms of uremia, pyuria, hematuria, and hypertension after birth. These infants may survive the perinatal period. Up to 90% or more of the renal tissue in these infants is cystic or dysplastic. Intravenous urography shows no shadowing of the kidneys, and renal ultrasound examination can confirm large and polycystic kidneys. Cystography shows a normal bladder without reflux and no urethral obstruction. If uremia is present at birth, the prognosis is poor, with a high percentage of stillbirths, and the vast majority of uremic infants die within the perinatal period or within 3 months after birth.

　　② Neonatal type: Survivors in the neonatal period often have progressive uremia, hypertension, and bilateral kidney enlargement can be palpated. Renal ultrasound examination shows extensive cystic lesions, about 60% of renal units have developmental abnormalities. Most of them die of uremia within 6 months after birth. Some children can alleviate uremia, improve renal function, and survive into childhood with proper dietary protein restriction, treatment of renal acidosis, hyperphosphatemia, and hypertension. The liver lesions become apparent with age growth.

　　③ Infantile type: 25% to 50% of renal units have cystic renal developmental abnormalities, with clinical manifestations of growth retardation, progressive uremia, and liver dysfunction in childhood. It is difficult to distinguish from neonatal type at birth, but the infantile type does not have progressive uremia in infancy.

　　④ Childhood type: Due to bilateral renal cystic lesions less than 10%, and extensive liver lesions, liver lesions are manifested at the age of 10 to 20 years, and polycystic kidney disease is occasionally found only through post-mortem examination.

　　(2) Adult polycystic kidney disease (adultpolycystickidney): This condition is an autosomal dominant inheritance, about 3% of cases have symptoms in childhood, but it is rare for children to develop renal failure due to this disease. Bilateral kidneys show enlargement with irregular cysts scattered in the cortex and medulla, interspersed with normal renal parenchyma. Cysts can be found at any part of the renal units or collecting tubes. Glomerular cysts are a characteristic of adult polycystic kidney disease in the early stage. Complications (hemorrhage, calculi, and infection) in adults are uncommon in children and are often not severe. Disseminated focal liver cysts account for only 1/3 of adult patients and do not cause dysfunction. Splenic and pancreatic cysts are uncommon.

　　In addition to its clinical manifestations, pediatric polycystic kidney disease can also cause other diseases. This disease often complicates with acute infection, calculi, and in severe cases, chronic renal insufficiency. It can also be accompanied by hypertension, anemia, and eventually lead to uremia.

　　Patients with symptoms before the age of 50 have a longer survival time, often have a family history, and symptoms are divided into two aspects. On one hand, they are related to cysts, and on the other hand, they are related to impaired renal function. Symptoms related to cysts include discomfort, back pain, lumbar mass, hematuria, acute infection, and colic when hematuria or concomitant stones pass through the ureter. As the lesion progresses, renal tissue is compressed, renal function is impaired, leading to chronic renal insufficiency, and ultimately, uremia. Before renal failure occurs, there is often a decrease in urine concentrating ability, more than 70% of patients have hypertension, and physical examination can feel the enlargement of the kidneys, which are nodular in surface.

　　1. The autosomal dominant genetic type PK can have symptoms for decades without symptoms, until the cysts grow to a large size and symptoms appear. Early symptoms and signs include back pain, abdominal mass, gross hematuria, urinary tract infection, and hypertension. Renal calculi are more common than in the general population, and intracranial hemorrhage secondary to ruptured aneurysms is rare. Enlarged liver is common, and about half of the patients have renal insufficiency.

　　2. The autosomal recessive genetic type PK has obviously swollen kidneys with pulmonary hypoplasia, Potter's special facial features, and renal insufficiency, mainly seen in newborns. In older children, hypertension, edema, urinary tract infection, and portal hypertension can be serious signals.

　　Genetic counseling helps prevent the occurrence of polycystic kidney disease. In recent years, due to the in-depth study of genetics, it has been found that there are genes for hemoglobin α-chain and phosphoglycollate phosphatase (phosphoglycollatephosphatase) on the short arm of chromosome 16. By collecting villous samples from the chorionic villus through the vagina and performing DNA analysis with special DNA probes (DNA probe), a prenatal diagnosis of adult polycystic kidney disease can be made correctly, and early termination of pregnancy can be considered. In the past, early diagnosis mainly relied on ultrasound, but ultrasound was also unable to detect renal cysts in the fetus. Now, using DNA probes, not only can adult polycystic kidney disease be detected before birth, but it can also be distinguished from other renal cystic diseases after birth or in adults.

　　In children with polycystic kidney disease, in addition to mild proteinuria and low urine specific gravity, routine urinalysis often does not show any abnormalities. When there is hematuria and infection, red and white blood cells are present in the urine, peripheral blood white blood cell count increases, creatinine levels rise when renal function is impaired, uremia appears, electrolyte disturbance occurs, and metabolic acidosis may develop. Ultrasound, intravenous urography, and CT scans are the main diagnostic methods. The kidney shape is enlarged and irregular, the renal pelvis and calyces are deformed due to compression by cysts, the calyces can be elongated and curved like a spider's leg or crescent-shaped. The X-ray image is similar to that of renal tumors, but the lesions of this disease are widespread and bilateral. The above X-ray findings are rare before the age of 10, but B-ultrasound can detect cysts at an early stage. Retrograde pyelography has the risk of infection, and renal biopsy has the possibility of bleeding. About 1/3 of cases are associated with liver cysts, but they do not cause liver dysfunction. Cysts can also occur in other organs such as the bladder, epididymis, lung, ovary, testis, pancreas, spleen, thyroid, and uterus. 6% of patients have cerebrovascular accidents.

　　Patients with infantile polycystic kidney disease should maintain regular and reasonable dietary habits, that is, focus on high-protein, high-vitamin foods. Choose high-nutrient plant or animal proteins such as milk, eggs, fish, lean meat, and various bean products. Various fresh vegetables and fruits are rich in vitamins and have high nutritional value.

　　There is no specific treatment for infantile polycystic kidney disease. Controlling blood pressure and infection can effectively delay the progression of renal failure. The following are symptomatic and supportive treatment measures:

　　1. Antihypertensive drugs are used to control hypertension, etc.

　　2. Antibiotics are mainly used to treat complications of acute pyelonephritis, control urinary tract infections, and a few for preventive purposes.

　　3. Treatment of intracystic hemorrhage is the most effective for intracystic hemorrhage in polycystic kidney disease. In the absence of antiproteinase, barium thrombin (Liqiuzhi) can be used for intravenous or intramuscular injection, as well as the use of hemostatic drugs acting on the vascular wall. Large-volume intravenous infusion of protamine sulfate is also effective.

　　4. Surgery may be considered for perinephric abscess, subarachnoid hemorrhage from an aneurysm, or a large kidney.

　　5. Renal replacement therapy is used to treat renal insufficiency, including dialysis and kidney transplantation when necessary. Currently, the sufficiency and individualization of modern dialysis technology have made the prognosis of patients with polycystic kidney disease quite good internationally. With the promotion and popularization of modern dialysis technologies such as HDF and Biofiltration in China, an increasing number of patients with polycystic kidney disease are expected to survive for a long time.

　　6. Cyst puncture Cyst puncture treatment for this disease was initially widely used to delay the progression of renal failure, but the efficacy has not been confirmed. It has basically not been used in recent years, but some authors have recently used it for individual larger cysts. The author of this chapter often punctures and aspirates fluid from single or multiple large cysts, then injects 2 to 5ml of anhydrous alcohol according to the size of the cyst, and observes for several months. The cyst has not returned to its original size, but the long-term delaying effect on the progression of renal function is unknown.

　　In patients with polycystic kidney disease, renal function often shows a linear decline. Without antihypertensive treatment, patients from the same family enter end-stage renal failure (ESRF) at similar ages, but in 30% of polycystic kidney families, they may not enter ESRF until the ages of 80 to 90.