Hydronephrosis

Diagnosis

Hydronephrosis can be unilateral or bilateral, mild, moderate, or severe. It may be transient and regress or progress as the pregnancy continues. The severity remains consistent in approximately 70%. Significant hydronephrosis should fit at least one of the following ultrasound findings: anteroposterior renal pelvic diameter of 10 mm. or more; a ratio of anteroposterior diameter of the renal pelves to the anteroposterior diameter of the kidney measured at the same level greater than 50%; the presence of calyceal dilatation; pelviectasis together with cystic change in the kidneys. Longstanding severe hydronephrosis results in permanent kidney damage; duration of the hydronephrosis is related to the degree of renal damage after birth. If bilateral hydronephrosis is present, oligohydramnios will often result; in unilateral cases amniotic fluid volume is expected to be normal. In some severe cases, rupture of the collecting system will result in paranephric urinoma or urinary ascites. Although urinomas may resolve spontaneously, the prognosis for kidney function is still poor. Unilateral cases of hydronephrosis, even severe ones, require only ultrasound follow-up if the contralateral kidney appears normal. In bilateral cases, follow-up scans should be initiated every 2-6 weeks to evaluate amniotic fluid volume as a measurement of renal function. Impairment of kidney function may require preterm delivery and surgical management in the newborn period.