Unilateral renal agenesis is a congenital disease characterized by the lack of development of a kidney. It is either inherited or results from spontaneous gene mutations, sometimes occurring as part of a syndrome. When renal agenesis is bilateral, it is not compatible with life.
Prenatally, unilateral renal agenesis (URA) follows the course of an uneventful pregnancy. It can be diagnosed via ultrasound during antenatal care, but this is difficult and often the ipsilateral adrenal gland is mistaken for a kidney. A good number of cases are thus diagnosed after birth. When the condition occurs in isolation, infants are normally well during the postnatal period.
The detection of URA is often coincidental. In childhood, it may be discovered in the context of genitourinary complaints, such as urinary tract infections (UTIs), which have an amplified frequency when vesicoureteral reflux, seen in over 30% of children with URA, is present . Obstruction of the urinary tract is yet another possible source of illness . If the existing kidney is healthy, sufferers can lead normal lives. Notably, the contralateral kidney is usually significantly larger than normal, and harbors a higher number of nephrons; an adaptive measure that allows it to carry out twice the filtration of a normal kidney . At length, this increases the risk of renal failure and hypertension in adults.
A number of anomalies have been known to coexist with URA, and these are often more apparent and more readily detected. The main developmental errors seen are Mullerian and Wolffian duct malformations in females and males respectively. Mullerian duct abnormalities include a malformed uterus or vagina. These may present later in life, with symptoms such as an abdominal mass, dysmenorrhea, recurrent pregnancy loss, and infertility. In men, the epididymis, ductus deferens, and the seminal vesicles can be involved . Moreover, the above disorders range from complete absence of vital structures to minor deviations that are asymptomatic.
As mentioned earlier, URA is associated with a number of syndromes, for instance, Mayer-Rokitansky-Küster-Hauser syndrome, DiGeorge syndrome, and a combination of vertebral defects, anal atresia, cardiac defects, tracheoesophageal fistula, renal anomalies, and limb abnormalities that typify the VACTERL association. Cardiac and musculoskeletal defects have also been described.
Ultrasound is the preferred technique in the detection URA because of its noninvasive nature. In addition, Doppler ultrasound further enhances correct diagnosis by minimizing inaccuracies discussed above, concerning the ipsilateral adrenal gland . It is essential to gauge the performance of the existing kidney through the approximation of the glomerular filtration rate (GFR). Magnetic resonance imaging (MRI) scanning can prove instrumental when detailing other non-urinary defects.
Those with URA need life long medical follow ups to monitor their blood pressure and renal function. Investigations include urinalysis to perceive proteinuria and signs of UTIs, measurement of urea and electrolytes, as well as the GFR. Furthermore, sub-clinical urinary tract malformations have been reported in first degree relatives of individuals with URA . Hence the latter may benefit from genetic counseling, as their abnormalities may be the consequence of an autosomal dominant gene  .