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Hydronephrosis describes hydrostatic dilation of the renal pelvis and calyces as a result of obstruction to urine flow downstream. Alternatively, hydroureter describes the dilation of the ureter , and hydronephroureter describes the dilation of the entire upper urinary tract (both the renal pelvicalyceal system and the ureter).
Ureterovesicular junction obstruction (UVJ obstruction) is an obstruction at the level of the ureter and bladder. It accounts for 20% of cases of hydronephrosis detected in utero. It is also most commonly seen in males and involved both sides of the urinary tract in approximately 25% of cases. [1]
The size of the renal pelvis plays a major role in the grading of hydronephrosis. Normally, the anteroposterior diameter of the renal pelvis is less than 4 mm in fetuses up to 32 weeks of gestational age and 7 mm afterwards. [2] In adults, 13% of the normal population have a transverse pelvic diameter of over 10 mm. [3]
Hydronephrosis is seen as an anechoic fluid-filled interconnected space with enhancement within the renal sinus, and normally, the dilated pelvis can be differentiated from the dilated calyces. [1] Figure 13. Hydronephrosis due to ureteropelvic junction obstruction in a pediatric patient. [1] Several conditions can result in urinary obstruction.
Neurogenic bladder can cause hydronephrosis (swelling of a kidney due to a build-up of urine), recurrent urinary tract infections, and recurrent kidney stones which may compromise kidney function. [7] This is especially significant in spastic neurogenic bladder that leads to high bladder pressures.
Features that suggest posterior urethral valves are bilateral hydronephrosis, a thickened bladder wall with thickened smooth muscle trabeculations, and bladder diverticula. [citation needed] Voiding cystourethrogram (VCUG) is more specific for the diagnosis. Normal plicae circularis are variable in appearance and often not seen on normal VCUGs.
Prenatally diagnosed hydronephrosis (fluid-filled kidneys) suggest post-natal follow-up examination. The strongest neo-natal presentation is urinary tract infection.A hydronephrotic kidney may present as a palpable abdominal mass in the newborn, and may suggest an ectopic ureter or ureterocele.
Kidney stones are becoming more common with time, and their incidence is believed to increase recently due to unhealthy diet habits. The passage of kidney stones into ureters might lead to their impaction and the development of local inflammatory process around the stone in addition to the obstruction of the ipsilateral kidney and build up of pressure manifested as hydronephrosis.