多囊性肾脏病变

CYSTIC KIDNEYS,Cystic disease of the kidneys in childhood isa confusing and complicated subject. Also thecomplex and often contradictory nomenclatureused to describe cystic kidneys is not an aid tounderstanding the subject. This section aims toprovide the sonographer with a simpleapproach to cystic kidneys in children., Multicystic kidney or multicystic dysplastic kidneythis refers to many cysts in one kidney often containing some dysplastic elements. Not all multicystic kidneys are dysplastic. The condition is still considered to be non-hereditary. If the multicystic kidney is unilateral, the other kidney may be normal, hydronephrotic or dysplastic. If bilateral, it is incompatible with life, and infants die soon after birth with hypoplastic lungs and/or renal failure.,Terminology, Cystic dysplasiadysplastic kidneys can be unilateral or bilateral, usually contain cysts and are disorganized, containing ectopic tissue such as cartilage and muscle. They may function.Ultrasonically they usually appear small and echogenic with small peripheral cortical cysts. While dysplastic kidneys are often hypoplastic, not all small kidneys are dysplastic. The clinical features are very variable from a normal appearing neonate to a very dysmorphic infant. Dysplastic kidneys are associated with urinary tract obstruction, and many syndromes are associated with cystic dysplastic kidneys. Bilateral renal dysplasia will result in progressive renal failure., Polycystic kidney disease refers to two conditions: autosomal recessive polycystic kidney disease and autosomal dominant renal disease.,Autosomal recessive polycystic kidneys were previously known as infantile polycystic kidneys. Confusingly these kidneys appear highly echogenic on ultrasound. There is generalized dilation of the collecting tubules.Autosomal dominant renal disease was previously known as adult polycystic kidney disease. Cysts develop anywhere along the nephron.,The ultimate diagnosis of the cysticrenal disorder is not dependent on anyone imaging modality and will depend onmany factors. Sources of information whentrying to come to the diagnosis should becollated from many areas, such as:, obstetric history of the mother prenatal history and fetal ultrasonography family history information clinical examination of the child radiology of patient and parents laboratory data, for example DNA pathology if a biopsy is taken or fromany other family members that may havehad a biopsy or nephrectomy in the past.,Ultrasound is still the imaging modalityof choice in children, and the findings onultrasound will direct further imaging asrequired. The ultrasound approach to anycystic renal disease in children mustinclude observations about the following,which should be carefully stated in theultrasound report., unilateral or bilateral renal cysts (bilateralinvolvement is more common in the geneticallyinherited conditions) size of the kidneysare they large or small? localization to one part of the kidney or diffuseinvolvement of the whole kidney. Is there acapsule around the cysts? extrarenal cysts, in particular in the liver orpancreas liver size and hepatic parenchyma appearance presence of a large spleen and portalhypertension.,Renal cysts are common and may behereditary,developmental or acquired. Theclassification of cystic renal disease variesaccording to the perspective from which it iswritten, and despite a vast amount ofliterature on the subject, there is still nogenerally accepted classification in existence.The early Potter classification is of limitedvalue for clinical practice because not all typesrepresent clinical entities.,The following classification is by nomeans all inclusive but aims to emphasizethe important clinical cystic disorders likelyto be encountered by the sonographer.Broadly speaking, cystic disease of thekidneys can be divided into two groupsgenetic disease and non-genetic disease:, Genetic diseaseautosomal recessive polycystic kidneydisease (ARPKD)autosomal dominant polycystic kidneydisease (ADPKD)juvenile nephronophthisis and medullarycystic disease complexglomerulocystic kidney diseasecysts with multiple malformation syndromes;, Non-genetic diseasesimple cystsmulticystic dysplastic kidneymultilocular cystsacquired renal cystic disease (chronicrenal failure)caliceal diverticulummedullary sponge kidney.,Genetic disease,Autosomal recessive polycystic kidney disease(ARPKD) This is a generalized cystic dilation of the renalcollecting tubules so that the kidneys are packedto a greater or lesser degree with tiny little cysts(Fig. 3.31). It is much rarer than the autosomaldominant form and occurs in 1 in 50 000 people.Prenatal diagnosis can be made but there arefalse positive and false negative diagnoses.Congenital hepatic fibrosis is a prerequisite forthe diagnosis of ARPKD.,Figure 3.31 Autosomal recessive polycystic kidney disease (ARPKD).(A) Cut section of a postmortem specimen in a patient with ARPKD. There are multiple small cysts throughout the whole of the renal substance. It is these multiple cysts with their posterior acoustic enhancement which give the hyperechogenic appearances on ultrasound. (BD)Sonograms of the kidney in three patients with ARPKD to demonstrate the wide variation in appearance. The kidneys are all large, over the 95th centile, and are globally hyperechoic. The visible cysts are generally small, rarely exceeding 2 cm. Sometimes the increase in echogenicity is primarily medullary.,A,B,C,D,There are two types of presentation of ARPKDdepending on the age of the patient and the dominance of the renal or the hepatic disease. In those children who present at birth or during the neonatal period the renal disease dominates, while in those who present later in childhood or adolescence the liver disease dominates, with much milder renal manifestations. The hepatic disease in these children is called congenital hepatic fibrosis with renal tubular ectasia and comes to medical attention because of theproblems associated with hepatic fibrosis, such as splenomegaly, portal hypertension, varices and bleeding.,Gross cystic dilation of the intrahepaticbiliary tree is usually called Caroli syndrome.The original description was purely of thehepatic disease, but dilation of the bile ductsis seen in early presenting ARPKD and in themilder end of the renal spectrum of renal tubularectasia. The risk for a sibling of having thiscondition is 25%, and the parents kidneysshould be normal.,Sonographic Appearances There is a wide spectrum of appearances frombirth and with increasing age throughout childhood. There is bilateral equal involvement of the kidneys,and the reniform shape is usually maintained. The kidneys must be big and are generally overthe 90th centile for age in the young. With increasingage and progression of the renal disease,fibrosis mayresult in stabilization and comparative decrease inthe renal size., The inhomogeneous global increase inecho texture is due to the myriad ofmicrocysts presenting multiple acousticinterfaces. In some a subcapsular rim of normalhypoechoic cortex is diagnostic. Medullary pyramids may be hypoechoic atbirth in some less severely affected but overtime become hyperechoic. In older childrenthe corticomedullary differentiation is usuallylost., Visible macrocysts are uncommon butcan be seen, and they are generally nomore than 12 cm in diameter. Theybecome more common with age. Hepatic fibrosis is always present. Thehepatic echo texture may be normalbut,with increasing fibrosis, will becomecoarse and increased particularly in theperiportal region.,Figure 3.32 Dilated bile ducts in autosomal recessive polycystic kidney disease (ARPKD). Longitudinal sonogram of the liver showing the dilated cystic spaces.These are not cysts but dilations of the bile ducts. The liver should always be carefully examined in all children suspected of having ARPKD., The liver must be carefully examined for lesions which are cystic dilations of the biliary tree. The hepatic cystic lesions are not true cysts but rather out-pouchings of the bile ducts (Fig.3.32)., In older children, because of the hepaticfibrosis and liver disease, portalhypertension may be present. Evidence ofportal hypertension with an enlargedspleen and varices must be sought. Doppler examination of the liver, spleenand portal system is an essential part ofthe examination in these children.,Further imaging When the child is older and over theneonatal period,an IVU is performed.This willdemonstrate the streaky radiating pattern ofcontrast which is almost pathognomonic ofARPKD (Fig. 3.33). The importance of doingthis examination is that in showing thecaliceal pattern it will help exclude othercauses of large echogenic kidneys in theneonatal period, such as dysplasia.,A,B,Figure 3.33 Intravenous urogram (IVU) in autosomal recessive polycystic kidney disease (ARPKD). (A) & (B) Two examples of the IVU appearances of ARPKD. The urogram should always be performed to demonstrate the caliceal pattern. This will demonstrate the typical radiating appearance of the contrast as it passes through the collecting system and help differentiate