Congenital & Cystic Kidney Disease

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Congenital & cystic kidney diseases are a diverse group of disorders affecting renal structure and function. These conditions often present with symptoms like hematuria, flank pain, recurrent UTIs, & kidney stones.

Horseshoe kidney, the most common congenital renal malformation, results from an interruption in the embryologic ascent of the kidney and has a higher incidence in chromosomal aneuploidy (e.g. Turner syndrome). Horseshoe kidneys are often asymptomatic, but increase the risk for nephroblastoma (Wilms tumor), hydronephrosis, infections, & renal cancer.

Renal dysplasia, featuring abnormal mesenchymal tissue like cartilage and bone, is the most common cystic disease in children. Renal agenesis signifies the congenital absence of renal parenchyma, and its bilateral form presents with oligohydramnios & Potter sequence, which manifests as flattened nose, clubfeet, and lung hypoplasia.

Autosomal recessive polycystic kidney disease (ARPKD) is symptomatic in early childhood and results from mutations in the PKHD1 gene, coding for fibrocystin. In ARPKD, cysts lined by cuboidal epithelium form in the collecting ducts. Clinical features include bilaterally enlarged kidneys, oligohydramnios leading to Potter sequence, bilateral flank masses, and hypertension. ARPKD is also associated with hepatic abnormalities such as cystic dilation of intrahepatic bile ducts, hepatomegaly, & hepatic fibrosis.

Autosomal dominant polycystic kidney disease (ADPKD) usually presents in adulthood, and is caused by mutations in either the PKD1 (polycystin-1) or PKD2 (polycystin-2) gene. Cysts in ADPKD develop throughout the nephron and grow progressively larger over time. Clinical manifestations include hypertension, berry aneurysms in the circle of Willis leading to subarachnoid hemorrhage, liver & pancreatic cysts, and diverticulosis.

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What is a horseshoe kidney and what complications can it cause?

A horseshoe kidney is the most prevalent congenital renal malformation, characterized by the fusion of the lower parts of the two kidneys. During embryological development, the horseshoe kidney can become obstructed by the inferior mesenteric artery, preventing it from ascending to its normal position. This condition is often associated with chromosomal aneuploidy, such as Turner syndrome (XO). Complications include an increased risk of Wilms tumor, infections, renal stones, and hydronephrosis.

What is renal agenesis and what complications can it lead to?

Renal agenesis refers to the congenital absence of renal parenchyma, essentially meaning one or both kidneys fail to develop. Bilateral renal agenesis is particularly severe and leads to oligohydramnios, a condition characterized by low levels of amniotic fluid. This, in turn, can result in Potter sequence, a series of physical abnormalities including a flattened nose, clubfeet, and lung hypoplasia.

What are the clinical features associated with autosomal recessive polycystic kidney disease (ARPKD)?

ARPKD typically manifests in early childhood and can be detected on fetal ultrasound as bilaterally enlarged kidneys filled with diffuse small cysts. These cysts originate in the collecting ducts and are lined by cuboidal epithelium. The condition often leads to hypertension within the first months of life. Additional complications include oligohydramnios, resulting in Potter sequence (facial abnormalities, extremity abnormalities, pulmonary hypoplasia). Liver complications like cystic dilation of intrahepatic bile ducts, hepatomegaly, and hepatic fibrosis can also occur.

How does autosomal dominant polycystic kidney disease (ADPKD) differ from autosomal recessive polycystic kidney disease (ARPKD)?

Unlike ARPKD, which manifests in early childhood, ADPKD usually becomes symptomatic in adulthood. It is caused by mutations in either the PKD1 or PKD2 genes. The cysts in ADPKD form throughout the nephron and tend to grow larger over time. Common clinical features include hypertension and the development of berry aneurysms in the circle of Willis, which can result in subarachnoid hemorrhage. ADPKD may also present with extra-renal manifestations such as hepatic cysts, pancreatic cysts, and diverticulosis.

What is medullary sponge kidney and how does it differ from other renal cystic diseases?

Medullary sponge kidney is a condition characterized by the presence of multiple cysts in the renal medulla. These cysts specifically develop along the terminal collecting duct. Unlike other cystic kidney diseases like autosomal dominant polycystic kidney disease (ADPKD) where cysts can form throughout the nephron, the cysts in medullary sponge kidney are localized to the medulla.