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Unilateral renal agenesis


Unilateral renal agenesis (URA) is absence of one kidney and usually the unilateral ureter. It occurs more commonly on the left than the right side and there is a male predominance of 1.8 to 1. It is usually asymptomatic since the other kidney frequently becomes hypertrophic and compensates for the missing one. The condition is usually detected only coincidentally during a routine ultrasound examination or examination related to other congenital anomalies. It can occur at the 5th week of embryonic development when the ureteric bud arises from the mesonephric duct. It may be due to unilateral absence of the nephrogenic ridge, abnormal differentiation of the distal mesonephric or ureteric buds or failure of the ureteric bud to stimulate development of the metanephric blastema unilaterally.


Unilateral renal agenesis should be suspected when a single umbilical artery is found. A unilateral cystic or dysplastic kidney together with oligohydramnios should raise the suspicion of URA on the contralateral side. A family history of renal malformations should also raise the suspicion for URA and URA is seen in 4.5% of first degree relatives affected with bilateral renal agenesis. The diagnosis is made by seeing only one kidney. It is important to search for a second kidney in an ectopic location including the pelvis and rarely even the thorax. Normal fetal bladder filling and normal amniotic fluid volume is usually seen unless the single kidney is abnormal. Associated findings include single umbilical artery, genital abnormalities (females, 25 to 50%, males, 10 to 15%). In males there is a high incidence of absent or malformed proximal mesonephric duct structures (including vas deferens, seminal vesicle and ejaculatory duct). There are absent or malformed Mullerian duct structures (uterus and fallopian tube) in the female. Other organ system abnormalities including cardiovascular (30%) gastrointestinal (25%) and musculoskeletal (14%).

Differential Diagnosis:

An ectopic kidney must be ruled out including pelvic and rarely thoracic. The adrenal gland or bowel in the renal fossa may simulate the kidney.

Sonographic Features:

Single fetal kidney More commonly absent kidney on left and in males (1.8:1) Normal amniotic fluid usually Single umbilical artery associated finding Multicystic kidney is associated with contralateral renal agenesis (10%) If single kidney is abnormal, oligohydramnios may be present May be able to demonstrate absence of renal artery on color flow Doppler Other associated genital, cardiovascular, gastrointestinal and musculoskeletal anomalies may be present


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Associated Syndromes

10p partial duplication
13 ring
6q partial duplication
Cerebro-renal -digital (Kouseff type)
Klippel-Feil anomaly
Oculo-renal syndrome (Karcher type)
Oculo-renal syndrome (Sommer type)
Partial lower limb duplication - renal agenesis
Smith-Lemli -Opitz, type II
Ulnar- mammary (Schinzel - Pallister)


Accuracy of prenatal diagnosis of renal agenesis with colourflow imaging in severe 2nd trimester oligohydramnios
Sepulveda W, Stagiannis KD, Fiack NJ, Fisk NM
Am J Obstet Gynecol 173:1788-92

The early prenatal sonographic diagnosis of renal agenesis: techniques and possible pitfalls
Bronshtein M, Amit A, Achiron R, Noy I, and Blumfeld Z
Prenatal Diagnosis 14: 291-7

In: Ultrasound in Obstetrics and Gynecology, Vol. I
Chervenak F, Isaacson G, Campbell S
Little, Brown & Co: Boston, MA, p969-970

In: Diagnostic Ultrasound of Fetal Anomalies Vol II
Nyberg D, Mahony B, Pretorius D
Mosby Year Book: St. Louis, p969-970

The significance of early 2nd trimester sonographic detection of minor fetal renal anomalies
Bronshtein M,Bar-Hawa I, Lightman A
Prenatal Diag 15:627-632

In: The Principles and Practice of Ultrasonography and Obstetrics and Gynecology, 4th Edition
Fleischer A, Romero R, Manning F, Jeanty P, James Jr. A
Appleton & Lange: Norwalk, p253-254

In: Human Malformations and Related Anomalies, Vol I
Stevenson R, Hall T, Goodman R
Oxford U Press: Oxford, New York, p501-550