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Renal malformations account for 30% to 50% of
end-stage renal disease in children. Approximately one half of such
cases are associated with lower urinary tract abnormalities. A spectrum
of phenotypes exists and has been termed CAKUT (congenital abnormalities
of the kidney and urinary tract).
This chapter focuses on the epidemiology of these abnormalities
and their etiologies, clinical manifestations, and aspects of clinical
management.
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Kidney malformation is classified at the clinical level by gross
and microscopic anatomical features. One commonly used classification system
is as follows:
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- Renal agenesis—congenital absence of the kidney
and ureter
- Simple renal hypoplasia—small kidney with a reduced
number of nephrons and normal renal architecture
- Renal dysplasia—presence of malformed kidney tissue
elements
- Renal dysplasia/hypoplasia (hypodysplasia)—small,
dysplastic kidney
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Characteristic microscopic features of the dysplastic kidney
(Fig. 469-1) include abnormal differentiation of
mesenchymal and epithelial elements; a decreased number of nephrons;
loss of corticomedullary differentiation; and the presence of dysplastic
elements, including cartilage and bone. Dysplastic kidneys range
in size from large distended kidneys with multiple large cysts to
small kidneys, with or without cysts. A small dysplastic kidney
without macroscopic cysts is often classified clinically as a hypoplastic/dysplastic
kidney, since pathological examination, which provides a means to
distinguish between simple hypoplasia and dysplasia, is not commonly performed
during life. The multicystic dysplastic kidney (MCDK) is an extreme
form of renal dysplasia.
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The majority of renal malformations are detected during the antenatal
period by fetal ultrasound and account for 20% to 30% of
all anomalies detected. The incidence of renal and urinary tract
malformations is 0.3 to 1.6 per 1000 liveborn and stillborn infants.1 Renal
agenesis and dysplasia is 1.3- to 1.9-fold more common in males
than in females.2 Fifty percent of individuals with a kidney
malformation have a lower urinary tract anomaly. Of these, 25% have
vesicoureteral reflux, 11% have ureteropelvic junction obstruction,
and 11% are affected by ureterovesical junction obstruction.3 Renal
malformations, other than mild antenatal pelviectasis, are associated
with malformation of nonrenal tissues in about 30% of cases.1 There
are over 100 syndromes associated with renal and urinary tract malformations.
The most frequent syndromes are cited in Table
469-1. Bilateral renal agenesis occurs in 1 in 3000 to 10,000
births, while unilateral renal agenesis is estimated to have a prevalence
of 1 in 1000. The incidence of unilateral dysplasia is 1 in 3000
to 5000 births (1:3640 for the MCDK) compared to 1 in 10,000 for
bilateral dysplasia. Nine percent of first-degree relatives of patients ...