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Renal Agenesis

Unilateral Renal Agenesis (Arrow)
Bilateral Renal Agenesis
Bilateral Renal Agenesis (lying down adrenal) (arrowhead)


Absence of the fetal kidney on one side with normal appearance of the: kidney on the other side, urinary bladder and amniotic fluid volume. No evidence of a fetal kidney was seen in an ectopic location. In the other two cases, fetal kidneys were not identified, nor was the urinary bladder or amniotic fluid seen.


This is a case of unilateral renal agenesis. While this is more common than bilateral renal agenesis, it has little significance to the developing fetus if the contralateral kidney is normal. The majority of this discussion will center on bilateral renal agenesis, which is a lethal fetal and neonatal disease.

Bilateral renal agenesis is a rare abnormality of renal development occuring in one to three per 10,000 births. Despite its association with chromosomal, x-linked recessive, autosomal dominant and recessive or non-Mendelian syndromes, it most often occurs without an associated syndrome. Bilateral renal agenesis is 2 to 3 times more common in males than females and is said to carry a recurrence risk of 3% for sporadic cases. A study by Roodhooft et al showed that the frequency of renal malformations in parents and siblings of patients with bilateral or unilateral renal agenesis or renal dysplasia was significantly higher than in a matched control group (9% vs 0.3%) In their review the anomalies often seen were unilateral renal agenesis, double ureters, hydronephrosis, multicystic kidneys and multiple renal cysts. They also noted that approximately 30% of patients with previously affected babies themselves had a "silent" genitourinary malformation.

Induction of the Metanephros by the Ureteric Bud

1 - Ureteric Bud; 2 - Metanephros

From:Trigaux J-P, Van beers B, Delchambre F. Male genital tract malformations associated with ipsilateral renal agenesis: sonographic findings J Clin Ultrasound 19:3-10, 1991

Embryologically renal agenesis results from a failure of the proper development of the metanephros (the future definitive adult kidney) resulting in complete absence of a renal structure. Abnormalities in the mesonephros may result not only in renal agenesis (due to absence of induction of the metanephros by the ureteral bud) but also internal genital malformations (due to failure of the Wolffian and Mullerian duct to develop or to involute [according to sex]). There have been reports of ipsilateral genital abnormalities in 20% to 70% of cases of renal agenesis. in the male, the main abnormalities include: hemitrigone assymtrey, agenesis and cyst of the seminal vesicle, Wolffian paravesical cyst, cystic dilatation of the prostatic utricle and ectopic drainage of the ureter into the seminal vesicle. In the female, the most frequent abnormalities reported are bicornuate or unicornuate uterus and vaginal duplication and atresia. Genital abnormalities associated with renal agenesis develop more frequently in males than females, however in the literature developmental genital abnormalites are more frequently reported in females (25%-70%) than males (10%-45%). This is likely due to the fact that the clinical evidence of internal genital anomalies are much more apparent in females ie vaginal atresia than males ie seminal vesicle cyst. Extra-genital abnormalities associated with renal agenesis include cardiovascular (30%), intestinal 25%) and skeletal (15%) disorders. The most common urinary tract abnormality in the contralateral kidney is vesicoureteral reflux.

Bilateral renal agenesis is often referred to as Potter's syndrome. In fact this eponym describes: bilateral renal agenesis, oligohydramnios, typical facies (low-set ears, prominent epicanthal folds and hypertelorism) and pulmonary hypoplasia. Other commonly seen abnormalites include contractures and fusions of the limbs. Fetuses are often stillborn or die shortly after birth from pulmonary hypoplasia.

Sonographically, the most striking finding in these fetuses is severe oligohydramnios or anhydramnios occuring between the 16th and 28th weeks of gestation. Despite the fact that the primary abnormality is in renal development, the diagnosis is often made by virtue of the absence of filling of the fetal urinary bladder and little to no amniotic fluid. In a retrospective review of over 13,000 cases Bronshtein et al identified the fetal urinary bladder in all but 7 patients. In all 7 patients, an abnormality was present (renal agenesis in 5). While not specific for renal agenesis, failure to identify the urinary bladder after 30 minutes of scanning when seen with oligohydramnios is almost always associated with a severe renal abnormality.While the bladder may be quite small and the amniotic fluid volume reduced in intrauterine growth retardation, the bladder should be identified. Observation of the umbilical arteries as they course around the fetal urinary bladder will assist one in confidently identifying the urinary bladder. As was stated above, observation of renal like structures in a fetus with decreased fluid is often misleading. Bowel may fill the empty renal fossa and simulate the appearance of the kidney. Most cases of false-negative diagnoses of renal agenesis are due to the mistaken identification of paraspinal reniform structures that were thought to be the fetal kidneys, but in fact were the adrenal glands. Remembering the normal appearance of the poorly echogenic renal pyramids may help alleviate this confusion. Studies by Droste et al and others have shown that the adrenal does not become larger in renal agenesis but has a normal weight. Potter and others made the observation that in cases of renal agenesis, the adrenal gland assumed and ovoid or elongated shape. While the appearance of the adrenal gland may simulate the absent kidney, interestingly enought, it may be also be quite useful in confirming the absence of the kidney in the renal fossa. The term lying down adrenal sign as been ascribed to the elongated appearance of the adrenal not normally molded by the adjacent kidney.

Lying Down Adrenal Sign (Flattened Adrenal) - Renal Agenesis

Normal adrenal gland (red arrow) in neonate being formed by adjacent kidney (yellow arrow)
Case of unilateral renal agenesis with lying down adrenal (arrow)
Renal agenesis in a fetus with lying down adrenal (arrow)

It is important to differentiate between renal agenesis and a small atrophic kidney, if possible. A small kidney may produce arterial hypertension or chronic urinary tract infection or even possibly result in a renal neoplasm. Two other points should be remembered in assisting one in making the correct diagnosis. One, although the fetal kidneys normally begin to produce urine after the 10th week of gestation, they do not become a major source of urine and thus amniotic fluid until the 14th to 16th week of gestation. Thus a normal amount of amniotic fluid at 13 to 14 weeks gestation does not exclude the diagnosis. Two, as the renal arteries are not formed in renal agenesis, color Doppler sonography may be useful in the identification of these patients. Sepulveda et al found 8 patients referred with oligohydramnios to have no renal artery signal at sonography. In all patients, renal agenesis was seen in at least one kidney.

While the incidence of unilateral renal agenesis is not known it is likely 4 to 20 times more common than bilateral renal agenesis. The contralateral kidney tends to be abnormally large due to compensatory hypertrophy.


Sangal PR, Feinstein SJ, Chandra PC, Spence MR. Recurrent bilateral renal agenesis. Am J Obstet Gynecol155:1078-9, 1986

Roodhooft AM, Birnholz JC, Holmes LB. Familial nature of congenital absence and severe dysgenesis of both kidneys. N Engl J Med 310:1341, 1984

Dubbns PA, Kurtz AB, Wapner RJ, Goldberg BB. Renal agenesis: spectrum of in utero findings. J Clin Ultrasound 9:189-193, 1981

Droste S, Fitzsimmons J, Pascoe-Mason J, Shepard TH, Mack LA. Size of the fetal adrenal in bilateral renal agenesis. Obstet Gynecol 76:206, 1990

Trigaux J-P, Van Beers BV, Delchambre F. Male genital tract malformations associated with ipsilateral renal agenesis: sonographic findings. J Clin Ultrasound 19:3-10, 1991

Gruenwald P. The relation of the growing Mullerian duct to the Wolffian duct and its importance for the genesis of malformations. Anat Rec 81:1-19, 1941

Thompson DP, Lynn HB. Genital anomalies associated with solitary kidney. Mayo Clin Proc 41:538-548, 1966

Wiersma AF, Peterson LF, Justema EJ. Uterine anomalies associated with unilateral renal agenesis. Obstet Gynecol 47:654-657, 1976

Hoffman CK, Filly RA, Callen PW. The "lying down" adrenal sign: a sonographic indicator of renal agenesis or ectopia in fetuses and neonates. J Ultrasound Med 11:533-536, 1992

Mahony BS. Ultrasound evaluation of the fetal genitourinary tract In Ultrasonography in Obstetrics and Gynecology Ed by Peter W. Callen, 3rd Ed., 1994, WB Saunders and Co., Philiadelphia

Bronshtein M, Bar-Hava I, Blumenfeld Z. Differential diagnosis of the nonvisualized fetal urinary bladder by transvaginal sonography in the early second trimester. Obstet Gynecol 82:490-3, 1993

Jeanty P, Romero T, Kepple D, Stoney D et al. Prenatal diagnosis of unilateral empty renal fossa. J Ultrasound Med 9:651-654, 1990

Robson WL, Leung AK, Rogers RC. Unilateral renal agenesis. Advances in Pediatrics 42(3):575-592, 1995

Sepulveda W, Stagiannis KD, Flack NJ, Fisk NM. Accuracy of prenatal diagnosis of renal agenesis with color flow imaging in severe second-trimester oligohydramnios. Am J Obstet Gynecol 173(6):1788-92, 1995

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Peter W. Callen, M.D.
Professor of Radiology, Obstetrics, Gynecology and Reproductive Science
University of California Medical Center, San Francisco, California