Extrarenal pelvis mimicking hydronephrosis: a case for caution.

Extrarenal pelvis is an anatomical variant that appears as a large hypoechoic mass just outside the renal sinus and can be confused with hydronephrosis, especially on a point-of-care renal ultrasound. Unlike hydronephrosis, it is not associated with dilated calyces, parenchymal thinning, hydroureter, or enlarged kidney per se.