The KUB x-ray shows a linear radiopaque density measuring about 6mm in the right lower pelvic region at the level of S5. This is likely to be a right distal ureteric calculus.

The course of the ureter on a KUB x-ray is as follows:

• Begins at the pelvi-ureteric junction which lies at the level of second lumbar vertebra, with the right PUJ being marginally lower.
• Runs along the tips of the transverse processes of the lumbar vertebrae.
• Then, medial to the sacroiliac joint.
• At the level of the ischial spines, turns medially and forward to join the lower part of the urinary bladder, roughly at the level of coccyx.

Three points of ureteral narrowing, where calculi are likely to become impacted are,

• Pelviureteric junction
• The site where ureter crosses the pelvic brim
• Vesicoureteric junction