By Hossein Aliabadi, M.D., F.A.A.P., F.A.C.S

Figure 1  (Click to Enlarge)







Evaluation of Fetal Hydonephrosis

The detection of congenital uropathies in the fetus has been made possible by recent technologic advancements in the field of maternal fetal ultrasonography. The discovery of in utero hydronephrosis, in turn, has had a major influence on the practice of pediatric urology. With increasing frequency in recent years, we as pediatric urologists have been called upon to evaluate fetal ultrasonographic findings and to advise prospective parents of expected outcomes in the unborn with hydronephrosis. With increasing regularity we see anxious to-be-parents in our waiting rooms alongside our pediatric patients with reports and ultrasound imaging studies in hand, eager to discuss the findings. Most commonly, fetal sonography has been obtained to assess fetal maturity (Table 1), but other indications have included persistent breech presentation, smaller or larger than expected uterine size, history of hydronephrosis or other developmental anomalies in a sibling, and elevated maternal alpha-fetal protein. While prenatal ultrasound screening is routine in some countries, it is not a uniform practice in our society; its use, however, is becoming more wide spread.

Fetal hydronephrosis, or dilatation of the urinary collecting system, is the most commonly detected abnormality identified in the developing fetus (Table 2). Currently, the main benefit of neonatal detection of hydronephrosis is early post-natal diagnosis and the prevention of post-natal infection and possible future renal damage (Table 3). Continuously, criteria are being developed and refined for predicting the need for post-natal surgery to correct prenatally diagnosed hydronephrosis. This task is especially challenging in cases where no specific indications for maternal fetal ultrasonography existed, and where the newborn appears perfectly healthy with no other indications to suggest benefit in surgical treatment.

Rarely, prenatal intervention may be appropriate in highly selective cases to bypass the obstructed urinary tract in-utero with the hope of preventing progressive renal and pulmonary impairment. While technical feasibility of in-utero surgery has been demonstrated, limited human experience provides insufficient information to advocate such treatment with great enthusiasm (Figure 1).

Analysis of several unselected series shows the overall incidence of congenital fetal hydronephrosis detected by routine maternal fetal ultrasonography to be about 0.15 percent. Nearly 50 percent of detected sonographic lesions represent anomalies involving the genitourinary tract, and it is reasonable to conclude that this incidence would be higher in series including high-risk pregnancies. Unilateral hydronephrosis is more frequent than bilateral. Supravesicle obstruction (e.g. Ureteral Pelvic Junction [UPJ] obstruction) is more common than infravesicle obstruction (e.g. posterior urethral valves) (Figure 2).  The incidence of false positive and negative rates continue to decrease with experience and technical refinements, ranging from 10-25 percent in the past. It is extremely important to recognize that the detection of hydronephrosis in-utero is not synonymous with urinary tract obstruction (Table 4). Dilation may be detected with such conditions as high-grade unilateral or bilateral vesicoureteral reflux, prune belly syndrome, or "physiologic" hydronephrosis, to name a few, without necessarily signifying the presence of any significant renal functional abnormalities One must, therefore, assess several features together to arrive at the most reasonable etiology for hydronephrosis.

Currently, the majority of pediatric urologists feel very strongly that prenatal intervention for congenital hydronephrosis is necessary or advisable only in a very select group of patients. The reports from centers with the most experience with in-utero intervention are constantly being refined. As the body of evidence accumulates, the long-term results in morbidity, survival, and the risks to mother and the fetus, are further defined. This experience should serve as a benchmark for the development of guidelines to be followed in the future.

The collection and dissemination of such important information has served as the impetus for the development of organizations such as the Society for Fetal Urology (SFU). By sharing data and maintaining dialogue among pediatric urologists, perinatologists, pediatric radiologists, and neonatologists, we hope to better define the indications for a successful outcome (Table 5). While institutional variations exist, we find a methodical approach such as our algorithm can provide a guide in this difficult arena. In general, we consider prenatal intervention in a setting of an otherwise "healthy" fetus with progressive, bilateral hydronephrosis or in a solitary kidney, with adequate renal function (as measured by many indices), presence of oligohydramnious but without overt evidence for renal dysplasia, normal karyotype, and without other severe anomalies. Such decisions are made giving due consideration to the social, moral, ethical and legal issues that surround each case.

The most common situation we face is that of unilateral hydronephrosis which seldom causes pulmonary or systemic complications. Bilateral hydronephrosis without oligohydramnious, pulmonary dysfunction or other associated congenital anomalies are seen less frequently. In such situations, we advise periodic ultrasonic examinations in-utero while allowing pregnancy to progress without intervention. In addition to increasing hydronephrosis, if oligohydramnious develops under observation and favorable renal function is present, following thorough assessment of all parameters, consideration for early delivery may be given as a means to protect the kidneys and, possibly, the lungs. Otherwise, following the delivery, low-dose prophylactic antibiotics should be prescribed if there is significant dilatation of the collecting systems, in uncircumcised males, and in females to avert the possibility of infection. Sonographic examination may be carried out prior to discharge from the hospital or, electively, after the first few days of life. We obtain voiding cystourethrogram and a follow-up ultrasound a few weeks later. If warranted, a lasix, augmented Mag-Ill renogram is obtained at about 4 weeks of age (in a full-term baby) to complete the evaluation for obstruction or refluxing lesions (Table 6). The decision to continue prophylactic therapy, obtain follow-up studies, or recommend surgical treatment rests upon the findings of these anatomic and functional studies. When obstructive uropathy is present, early relief optimizes the chance for renal recuperation, maturation, and growth. Equivocal findings demand reasonable periodic re-evaluation tailored to each individual, to avoid the development of renal damage.

In summary, perinatal urology has become an important aspect of pediatric urologic practice. In-utero ultrasonography has made possible the early detection and evaluation of fetal hydronephrosis. It is most important to recognize that fetal hydronephrosis is not synonymous with congenital obstructive uropathy. Therefore, all efforts should be made to differentiate the many facets of fetal hydronephrosis with the goal of preventing on-going renal damage with minimal morbidity and risks to the mother and the fetus.


Direct inquiries to: Drs. Aliabadi, Wolpert and Reinberg, Pediatric Surgical Associates, Section of Urology, 2545 Chicago Avenue South, Suite 104, Minneapolis, MN 55404; telephone 612/813-8000 or 800/992-6983. Or Childrens Center for Pediatric Urology, 612/813-6262 or 800/CPU-6262.



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