Introduction
This topic covers the normal imaging anatomy of the kidneys, ureters, bladder and urethra as seen on ultrasound, excretory urography, CT urography and MRI, together with the common congenital anomalies and normal variants that an examiner must recognise so they are not mistaken for disease.
Normal imaging anatomy
The kidneys lie retroperitoneally, the right usually slightly lower than the left. Each kidney has a cortex, medullary pyramids and a central renal sinus containing the calyces, the renal pelvis and the vessels. Key landmarks:
- Adult length on ultrasound is about 9 to 12 cm; the long axis is tilted so the lower poles lie closer to the midline than the upper poles.
- The renal sinus fat is normally echogenic; the pelvicalyceal system is seen as anechoic or excretory-contrast-filled structures.
- The ureters run retroperitoneally on the psoas muscle and the pelvic side wall. They have three physiological narrowings: the ureteropelvic junction, the crossing of the iliac vessels at the pelvic brim, and the intramural segment at the ureterovesical junction.
- The bladder wall is thin and smooth when distended; the ureteral jets into the bladder can be shown with colour Doppler ultrasound.