Unilateral renal agenesis

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

Associated Syndromes

  • 10p partial duplication
  • 13 ring
  • 21q-
  • 6q partial duplication
  • Cerebro-renal -digital (Kouseff type)
  • Kallmann’s,
  • Klippel-Feil anomaly
  • Kousseff
  • Neuro-facio-digital-renal
  • Oculo-renal syndrome (Karcher type)
  • Oculo-renal syndrome (Sommer type)
  • Partial lower limb duplication – renal agenesis
  • Rubella
  • Smith-Lemli -Opitz, type II
  • Ulnar- mammary (Schinzel – Pallister)
  • 18q-


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