Congenital Hydronephrosis and Hydroureter

Many infants with hydronephrosis also have renal tubular dysfunction, with renal tubular acidosis being most common. Hydronephrosis is readily diagnosed by most imaging modalities. A congenital urinary tract obstruction evolves while a fetal kidney is still developing. The sequelae of a congenital obstruction thus result in findings that tend to be different from those seen with an obstruction developing later in life.
In newborns with unilateral hydronephrosis, the contralateral kidney ranges from larger than normal, to normal in size, to small, and such findings should be interpreted cautiously. Distinguishing obstructive from nonobstructive hydronephrosis in neonates can be difficult. Without an obvious obstructive site, some of these neonates are followed medically until they grow.
At times with known prenatal hydronephrosis, renal US performed immediately after birth is falsely negative for hydronephrosis, probably due to oliguria. Cystourethrography appears indicated in these children because of an increased risk for vesicoureteral reflux. The term megacystis-megaureter is descriptive and is most often applied to uncorrected vesicoureteral reflux and resultant dilation. In this sense it can be either congenital or acquired. Whether it represents a sequela of uncorrected massive chronic reflux or is a residue of a congenital hydroureter is conjecture. Megacystis-megaureter can be extreme to the point that one or both ureters dilate massively. The bladder also enlarges.
Megacalyces
An infant or adult occasionally has calyceal dilation without concomitant renal pelvis dilation and without underlying obstruction. Whether this condition, also called Puigvert’s disease, is congenital or acquired is conjecture. Medullary pyramids are thinned and as a result the calyces have a straight or even convex outline rather than their usual concave shape. The number of calyces tends to be increased and they have a polygonal shape. The renal pelvis is not dilated and renal function is normal. Megacalyces is associated with increased stone formation. Intravenous urography defines the condition and excludes an obstruction.
Ureteropelvic Junction Obstruction The most common congenital urinary tract obstruction is at the ureteropelvic junction. A ureteropelvic junction stricture in the very young may represent a mild form of multicystic dysplasia. It is not common.
Midureteral Obstruction A congenital midureteral obstruction is rare, with some of these strictures being classified as ureteropelvic junction strictures. A rare association exists between ureteral valves and ureteral strictures. Congenital adynamic midureteral segments are rare. Resection reveals muscular disarray but a patent ureter lumen.
Primary Megaureter
In congenital or primary megaureter a short nonperistaltic distal ureteral segment results in functional obstruction,while the more proximal ureter dilates and does have peristalsis. Etiology for the nonperistaltic segment is unknown but, unlike rectal aganglionosis, ganglion cells are present in this segment. Some authors subdivide primary megaureter into the following categories: (1) obstructive, (2) refluxing, and (3) nonobstructive and nonrefluxing. The degree of obstruction varies, and calyces are not dilated when obstruction is mild. The condition is more
often detected in children than adults and is more common on the left side. In some, ureteral dilation does not progress with age and may even improve. A rare patient first presents with a ureteral stone in a megaureter and an already nonfunctional kidney. Differential diagnosis includes ureteral dilation secondary to reflux (megacystismegaureter) and distal anatomic ureteral obstruction. Generally the distal ureter is not narrowed in a setting of reflux. At times a retrograde study is necessary to exclude anatomic obstruction.
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