Genitourinary Radiology > Embryology > Metanephros > UPJ Obstruction

UPJ Obstruction


Ureteropelvic junction obstruction is caused by an overabundance of collagen tissue in the ureter, leading to thickening and stricture formation, resulting in obstruction of the urinary tract. The etiology is unclear, and has been attributed to various disturbances in ureteral bud development, in utero ischemia, aberrant crossing vessels, and fibrous bands that compress the ureteric bud. Early diagnosis is important to prevent hydronephrosis and renal pelvis distension that, in severe, cases, can proceed to loss of renal cortex and decreased renal function. The abnormality may be seen at prenatal ultrasound as a dilated renal pelvis or hydronephrosis. Postnatal diagnosis is made by urography, sonography, CT, MRI, and scintigraphy, all of which show hydronephrosis. Retrograde pyelography and IV urography show focal narrowing at the ureteropelvic junction.

Gray scale ultrasound of left kidney in a newborn shows dilated calyces (c) and renal pelvis (p) down to the level of the UPJ. The right kidney showed multicystic dysplastic kidney (MCDK). (Click here to see the contralateral MCDK. Click the BACK button to return to this page).

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