[Management of isolated fetal dilatations of the kidney pelvis]

Abstract

The most common sonographic abnormality found in the fetal urinary tract is collecting system dilatation, accounting for 4.5% of examinations. Numerous renal pelvis measurements and various gestational age cut-off points have been recommended in the assessment of obstructive fetal uropathy. As a result, renal pelvic measurements are not well standardized. The first measurements of the renal pelvis diameter in the 80's suggested that a threshold value of 10 mm was significant in order to distinguish between physiologic and pathologic dilatations. The routine use of prenatal ultrasound and the improving resolution of ultrasound equipment allow the detection of smaller dilatations. The third-trimester threshold value for the antero-posterior renal pelvis diameter of 7 mm is the best ultrasound criterion to predict postnatal renal abnormalities with a positive predictive value of 69%. A renal pelvis dilatation during the second trimester of pregnancy can be used as a warning sign for urinary tract malformation, and should not be ignored even if there is no further progression in the third trimester, because this finding may reveal a significant urologic abnormality in 12% of cases. Isolated pyelectasis can signal the presence of vesico-ureteral reflux. Normal appearing urinary tract on 2 successive neonatal ultrasound rarely coexist with significant abnormal findings on voiding cysto-urethrography. Therefore, in such cases, invasive investigations are not justified.