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    Evaluation and management of isolated renal pelviectasis diagnosed on second-trimester ultrasound


    Q. A 32-year-old gravida 1 para 0 presents for a routine ultrasound at 21 weeks' gestation. Ultrasound examination demonstrates unilateral pelviectasis (Figure 1). What is the definition of fetal pelviectasis and how frequently is it present during midtrimester?

    A. Fetal pelviectasis (also called pyelectasis or renal pelvis dilation) is a common finding on midtrimester ultrasound, occurring in 0.5% to 4.5% of fetuses.1-3 It can be unilateral or bilateral, and is more common in male fetuses. Carbone and colleagues recently reported the frequency of fetal pelviectasis in 62,103 women undergoing midtrimester ultrasound.2 There were 1,248 cases of pelviectasis (2% incidence) and in 84.5% of these cases (n=1,055) it was an isolated finding.

    Figure 1: Ultrasound demonstrating measurement of AP diameter of fetal kidneys at 21 weeks’ gestation.
    The most commonly used criteria for diagnosis of pelviectasis are an anteroposterior measurement in a transverse scanning plane of 4 mm or larger in the second trimester (up to 27.9 weeks) and/or 7 mm or larger in the third trimester. Pelviectasis is defined as a renal pelvic diameter 4 mm to 9.9 mm, and hydronephrosis as 10 mm or larger.4

    Pelviectasis in a midtrimester fetus is usually self-limited, and most commonly represents a transient, physiologic state. However, in some cases pelviectasis can occur because of true renal pathology and may be associated with other fetal anomalies.

    What other ultrasound findings are important to assess?

    Table 1: Postnatal pathology reported after prenatally detected pelviectasis
    When fetal pelviectasis is identified, careful ultrasound examination should be performed to rule out other associated malformations (Table 1).5,6 Ultrasound evaluation of the genitourinary system should include determination of bilateral versus unilateral involvement, presence of dilated ureter(s), appearance of the renal parenchyma and calyces, size and thickness of the bladder and bladder wall, and volume of amniotic fluid (Figure 2).

    Figure 2: Coronal image demonstrating mild pelviectasis with dilation of the major calyces.
    Structural defects, such as duplicated kidneys, are a relatively common cause of pelviectasis and should be considered.5 When there is a duplicated collecting system, insertion of the ureters into the bladder often is accompanied by an ureterocele with resultant obstruction of the ureter(s). It is never normal to visualize the ureters prenatally, and this finding may imply obstruction at the vesicoureteral junction, bladder outlet obstruction, or reflux. Megaureter can also result from an intrinsic ureteral problem. Gender should be assessed by ultrasound because pelviectasis is more common in males1 and the differential diagnosis is somewhat different in male and female fetuses. In addition, internal and external genital tract anomalies can accompany urinary tract malformations, so this should be assessed.