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Unilateral Renal Agenesis
Introduction
Unilateral renal agenesis, also called solitary kidney, is a common congenital anomaly. Affected individuals are usually asymptomatic, and if a diagnosis is not made prenatally, they may not receive medical attention until complications arise. If unilateral renal agenesis is diagnosed in childhood, nearly 50% of affected children have an associated renal abnormality, including 30% with vesicoureteral reflux (VUR). Being born with one kidney is not equivalent to reaching adulthood with two kidneys and subsequently undergoing a nephrectomy. Individuals with unilateral renal agenesis, even in the absence of reflux, have an increased risk of hypertension, renal insufficiency, and progression to end-stage renal disease requiring transplant. Earlier identification of unilateral renal agenesis may forestall the development of these complications. Improvements in ultrasound (US) technology have made it easier to identify unilateral renal agenesis with prenatal US.
Disorder
Definition
Unilateral renal agenesis is the congenital absence of one kidney and ureter.
Prevalence and Epidemiology
Unilateral renal agenesis occurs in approximately 1 : 1000 to 1 : 2000 births, but it often goes undetected prenatally. In a systematic review, unilateral renal agenesis was diagnosed prenatally in 1 : 8000 pregnancies, and in a population-based registry of European countries with routine sonography, unilateral renal agenesis was identified prenatally in only 1 : 20,000 pregnancies. This is in contrast to the excellent detection of bilateral renal agenesis, and it highlights the importance of maintaining an index of suspicion. Male predominance of unilateral renal agenesis has been reported in some studies but not others. The left kidney is absent more often than the right. Unilateral renal agenesis is also more common in the setting of pregestational diabetes.
Associated renal anomalies, including VUR, ureteropelvic junction (UPJ) obstruction, and ureterovesical junction obstruction, have been reported in 30% to 50% of children referred for evaluation. In females, müllerian anomalies are common, particularly bicornuate uterus, uterus didelphys, and unicornuate uterus. Occasionally, these associated anomalies are first identified in the setting of Herlyn-Werner-Wunderlich syndrome (uterus didelphys, obstructed hemivagina, and ipsilateral renal agenesis) because of hematocolpos at the time of initiation of menstruation during puberty. In males, there is an increased incidence of congenital absence of the vas deferens and cysts of the seminal vesicles. Other associations include caudal dysgenesis, skeletal anomalies, and malformations of the central nervous system. Unilateral renal agenesis is a component of several syndromes, including branchiootorenal syndrome, 22q11.2 deletion syndrome (see Chapter 154 ), and Fraser syndrome (see Chapter 128 ), and it is one of several renal anomalies encountered in the VACTERL ( v ertebral, a nal, c ardiac, t racheal, e sophageal, r enal, and l imb anomalies) association (see Chapter 146 ). The aneuploidy risk is increased in the setting of other anomalies.
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