Extrarenal pelvis

Extrarenal pelvis refers to the presence of the renal pelvis outside the confines of the renal hilum; it is a normal anatomic variant.

Epidemiology

It is found in ~10% of the population .

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

Differential diagnosis

• hydronephrosis, from whatever cause
• PUJ obstruction

Practical points

After evaluation with ultrasound and/or CT/MRI, if there is still confusion whether a dilated renal pelvis is obstructed or not, renal scintigraphy can clarify