Anomalies of the Urinary System: Anomalies of Kidney Number

Congenital anomalies of the urinary system represent structural and functional developmental abnormalities that arise during embryogenesis as a result of genetic, environmental, or multifactorial influences. Disorders of the urinary tract are among the most common congenital malformations in humans and account for more than 30% of all congenital anomalies, while in pediatric populations their prevalence may reach 35–40%. These abnormalities are of major clinical importance because they may lead to impaired renal function, recurrent urinary tract infections, obstructive uropathy, hypertension, chronic kidney disease, and other long-term complications. This article reviews congenital anomalies associated with abnormalities in the number of kidneys and analyzes their clinical significance, diagnostic approaches, and possible complications. Kidney number anomalies include unilateral and bilateral renal agenesis, renal aplasia, congenital absence of one kidney, hypoplastic nonfunctioning kidney, and supernumerary (third) kidney. In some cases, these abnormalities may remain asymptomatic for many years and are detected incidentally during ultrasonographic or radiological examination. However, severe forms, particularly bilateral renal agenesis, may be incompatible with life and are associated with high perinatal mortality.