Multicystic dysplastic kidney (MCDK)
The pathology results from abnormal fusion of the ureteric bud and the metanephric mesenchyme. The affected kidney is completely non-functional, and the ureter is atretic. The disease is sporadic and diagnosed twice as frequently in males.
Clinical features and diagnosis:
- Bilateral involvement is incompatible with life.
- It is often accompanied by contralateral abnormalities: vesicoureteral reflux (VUR) or ureteropelvic junction (UPJ) obstruction.
- There is a high risk of associated genital malformations in females, making pelvic ultrasound mandatory.
- Sonograms reveal multiple anechoic cysts with centrally located echogenic parenchyma lacking corticomedullary differentiation.
- If small (up to 5 cm), cysts tend to undergo involution. 99mTc-DMSA scintigraphy is used to confirm the absence of function.
Genetic polycystic kidney diseases
These disorders belong to the group of ciliopathies—defects in cellular cilia function, which explains the involvement of other organs (liver, pancreas, blood vessels).
| Sign | ADPKD (ADPKD) | ARPKD (ARPKD) |
|---|---|---|
| Inheritance | Autosomal dominant | Autosomal recessive |
| Age of onset | Usually the 3rd decade of life (rarely in childhood) | Neonatal period or early childhood |
| Kidney size | Normal or enlarged | Markedly enlarged (>90th percentile) |
| Ultrasound findings | Large cysts, asymmetric involvement | Microcysts (1–2 mm) — "salt and pepper" appearance |
| Extrarenal manifestations | Liver cysts, cerebral vascular aneurysms | Congenital hepatic fibrosis, portal hypertension |
In ADPKD, normal parenchyma is preserved between cysts. In children under 5 years of age, the presentation must be differentiated from tuberous sclerosis. In ARPKD, there is an inverse relationship: the earlier renal failure manifests, the less pronounced the hepatic pathology is in early childhood, whereas hepatomegaly and splenomegaly come to the forefront in older children.
Other cystic lesions
- Simple cysts. While a common and often benign finding in adults, they require close attention in pediatrics. Prior chemotherapy or radiation therapy may be a risk factor. It is important not to confuse a cyst with a caliceal diverticulum—magnetic resonance urography (MRU) is used for precise differentiation.
- Localized cystic disease. Characterized by involvement of only a single renal segment. Unlike multilocular cystic nephroma or Wilms tumor, this lesion lacks a connective tissue capsule and does not progress.
- Acquired cystic kidney disease. Develops in the vast majority (up to 90%) of patients on hemodialysis for more than 10 years. The main danger of such cysts is the risk of renal cell carcinoma (RCC) and intracystic hemorrhage. Following successful kidney transplantation, the native cystic kidneys usually decrease in size.
Nephronophthisis and medullary cystic disease
These two conditions share a similar morphological and radiological picture, but fundamentally different genetics and clinical features. On ultrasound, the kidneys appear echogenic, and corticomedullary cysts form only in late stages.
- Juvenile nephronophthisis (JN): an autosomal recessive disorder. It leads to chronic kidney disease (CKD) in childhood or adolescence. It is accompanied by growth retardation, anemia, and extrarenal anomalies (skeletal, hepatic, cognitive).
- Medullary cystic disease (MCD): an autosomal dominant disorder. It presents in adults (up to age 40) and occurs in an isolated manner, without involvement of other organ systems.
Briefly: answers to topical questions
What extrarenal manifestations occur in autosomal dominant polycystic kidney disease (ADPKD)?
Autosomal dominant polycystic kidney disease (ADPKD) features cystic lesions in other organs and vascular anomalies. The main extrarenal manifestations include:
- Cysts — localized in the liver, pancreas, and spleen (rare in children, frequency increases with age). Liver failure develops rarely.
- Aneurysms — cerebral (of the arteries of the circle of Willis), leading to subarachnoid hemorrhage, as well as aortic aneurysms.
- Congenital hepatic fibrosis — rarely associated with this disease.
Which specific extrarenal syndromes and anomalies accompany juvenile nephronophthisis?
Juvenile nephronophthisis (Juvenile nephronophthisis) is associated with a number of specific extrarenal manifestations. These include:
- Skeletal anomalies — various developmental disorders of the skeletal system.
- Congenital hepatic fibrosis — a pathology accompanied by the proliferation of connective tissue.
- Intellectual disability — developmental delay.
These manifestations accompany the chronic kidney disease, growth retardation, and anemia typical of this disease.
What clinical forms of autosomal recessive polycystic kidney disease (ARPKD) are distinguished based on age?
Depending on the age of onset, autosomal recessive polycystic kidney disease (ARPKD) is divided into several clinical types, in which the severity of liver fibrosis is inversely proportional to the severity of renal involvement:
- Perinatal and neonatal types (early onset) — characterized by more severe renal involvement.
- Infantile and juvenile types (in older children) — liver pathology predominates in the clinical picture.
Congenital hepatic fibrosis is present to some degree in all patients.
Mutations in which genes lead to the development of autosomal recessive polycystic kidney disease (ARPKD)?
The development of autosomal recessive polycystic kidney disease (ARPKD) is caused by specific genetic defects. The disease results from a recessively inherited mutation in the PKHD1 gene located on chromosome 6. This condition is a rare genetic disorder (occurring with an incidence of 1:55,000 live births), while the patients' parents always remain phenotypically healthy.
For quick memorization of the two main polycystic diseases: ADPKD — Dominant, in Adults (large cysts). ARPKD — Recessive, in Children (microcysts with "salt and pepper" appearance and liver fibrosis).
Class and exam questions
How to Differentiate Multicystic Dysplastic Kidney from Ureteropelvic Junction Obstruction?
The key criterion is the location of the residual parenchyma. In multicystic dysplasia, it is located centrally, whereas in obstruction (hydronephrosis), it is displaced to the periphery as a thin rim.
Which examination will confirm that a cystic lesion is a caliceal diverticulum?
Magnetic resonance urography (MRU) in the delayed excretory phase. If it is a diverticulum, contrast medium from the renal collecting system will enter it.
What is the specific feature of radioisotope diagnostics in early stages of nephronophthisis?
Since the tubules are primarily affected, DMSA scintigraphy (which is taken up by the tubules) may fail to visualize the kidneys at all. Meanwhile, the DTPA study (which is filtered by the glomeruli) remains within normal limits.
What else to study on this topic
- Tuberous Sclerosis: Differential Diagnosis of Angiomyolipomas and Cysts
- Magnetic Resonance Urography (MRU) Protocols in Pediatrics
- Specifics of Diagnostic Imaging for Kidney Stones in Children
- Nephrocalcinosis: Assessment of Severity via Ultrasound
- Radioisotope Methods: DMSA, MAG3, and DTPA in Nephrology
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