RENAL DILATATION DIAGNOSTIC RADIOLOGY

Renal dilatation
Hydronephrosis is frequently detected antenatally, although the cause may be difficult to demonstrate. Dilatation is due either to obstructive uropathy, for example vesico- or pelviureteric junction obstruction, posterior urethral valves or obstructed upper moiety of a duplex kidney, or it may be nonobstructive, for example due to reflux. Postnatal ultrasound scans should be performed when the infant is more than 4 days old, because there is commonly a period of dehydration immediately after birth. This may cause an obstructed or otherwise dilated kidney to appear normal for the first few days of life. If normal a follow-up scan is generally recommended at about the age of 6 weeks.

The presence of any calyceal dilatation or ureteric dilatation, as opposed to dilatation confined to the renal pelvis, is an important factor to note, indicating a greater degree of severity. A measurement of the anteroposterior diameter of the dilated intrarenal pelvis is a useful baseline from which to compare subsequent follow-up scans. It should be noted that slight separation of the renal pelvis is a normal finding in the newborn: an anteroposterior renal pelvis of 5 mm is the upper limit of normal.

The presence of a baggy, extrarenal pelvis, less than 10 mm, without pelvicalyceal system (PCS) dilatation is usually managed conservatively using ultrasound monitoring to demonstrate any increasing dilatation. PCS dilatation with a renal pelvic diameter of between 10 and 20 mm is more serious and likely to require an assessment of renal function with a MAG3 renogram. Conservative treatment is possible, but surgery may be required for very poor function.

The dilated renal tract is predisposed to infection due to ascending infection in reflux or haematogenous infection in an obstructed system, where a pyonephrosis requiring percutaneous nephrostomy may develop. As a consequence antibiotic prophylaxis is frequently advised in the neonate with significant renal tract dilatation.

Bilateral renal tract dilatation in boys may be due to posterior urethral valves with secondary dilatation of the upper tracts due to the urethral obstruction. The diagnosis is confirmed by fluoroscopic micturating cystography. This diagnosis may be suspected sonographically by the association of bilateral hydronephrosis with a distended and thick-walled bladder.