Kidney stones are commonly identified on X-rays done for a variety of reasons. While it is more common these days to image kidney stones with CT, I still see plenty of X-rays being done to either diagnose stones or to follow them once they have passed into the ureter. Some patients will present with pain and blood in the urine while others will be asymptomatic.
Not all kidney stones are seen on X-rays. Those stones that contain calcium will be seen while others will not. Stones related to medications, matrix stones, stones composed of cysteine and uric acid may not be visualized. Risk factors for stones are many and include urinary tract malformations, infections, metabolic abnormalities, low fluid intake and prior surgery on the urinary tract.
On X-rays, stones will be located anywhere along the urinary tract to include the kidneys, ureters and bladder. While these structures are not seen on the X-ray directly, it is possible to know their approximate location. Those stones that are visible will be focal and white, greater then the background tissues of the abdomen. You can have one tiny stone, multiple large stones or a stone filling the entire collecting system in the kidney.
When a patient is passing a stone from the kidney into the ureter, then the stone may be seen anywhere along the course of the ureter. The ureter normally goes from the kidney all the way to the bladder. Diagnosing a ureteral stone on X-ray can be challenging as it is difficult to see and there are other calcifications like those related to blood vessels which can mimic stone.
Stones can also form in the bladder. These will be calcifications which we see in the pelvis along the midline. These can also be confused with other calcifications such as phleboliths or those related to veins in the pelvis. Calcifications related to the prostate in men and fibroids in women can also sometimes mimic bladder stones.
A CT can be done in confusing cases or for confirmation. The CT will also show what degree of urinary obstruction is present and shows stones which are not visible on X-rays. CT may also identify other diagnosis which may be responsible for symptoms that are thought to be from the urinary tract.