Extrarenal pelvis refers to the presence of the renal pelvis outside the confines of the renal hilum; it is a normal anatomic variant.
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Epidemiology
It is found in ~10% of the population 2.
Radiographic features
Ultrasound
An extrarenal pelvis usually appears dilated, erroneously suggesting obstructive pathology. Subsequent investigation with CT usually clarifies a false interpretation on ultrasound.
CT/MRI
- a normal extrarenal pelvis will demonstrate normal renal cortical thickness, bilateral symmetrical contrast excretion, and normal-appearing calyces 3
Differential diagnosis
- hydronephrosis, from whatever cause
- PUJ obstruction
Practical points
After evaluation with ultrasound and/or CT/MRI, if there is still confusion about whether a dilated renal pelvis is obstructed or not, renal scintigraphy can clarify
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