Passing a kidney stone means the kidney stone has gone from the kidney and passed into the ureter or tube that carries urine from the kidney to the bladder. This is commonly associated with pain and blood in the urine. This often brings patients to seek care, particularly in emergency settings. The symptoms can overlap with other conditions and CT is commonly ordered.
CT will exclude other dangerous conditions which can mimic the symptoms of passing a kidney stone such as appendicitis or diverticulitis. Additionally, the CT will show how big the stone causing the blockage is, how much hydronephrosis is present and any associated complications.
Stones that are passing in the ureter will almost always be visible on CT scan. CT without contrast placed into your vein are more commonly done when stones are suspected. Stones are white against a black and gray background of the fat, bowel and blood vessels. The radiologist who interprets the scan will follow the course of the ureter looking for a stone. Often, there is a blockage of the kidney which will alert the radiologist to a passing stone.
In some cases, it can be difficult to distinguish a stone from a calcification in the pelvis called a phlebolith. A phlebolith is a common finding of a calcification in a pelvic vein. This can mimic a stone in the ureter, particularly in patients who are thin and have little pelvic fat or when the ureter isn’t dilated and tough to distinguish from the surrounding structures. Sometimes atherosclerotic calcifications or hardening of arteries can also mimic a stone. In these cases, a CT with contrast called a urogram can be done.
Most patients with passing kidney stones are treated conservatively with pain medicine and fluids. Admission to the hospital may be indicated when pain control is inadequate, in those with limited kidney function or superimposed infection. The odds of passage of the stone without treatment are dependent on the size of the stone. Those stones smaller than 4 mm pass most of the time on their own. In cases where the stone doesn’t pass, a urology doctor may intervene to relieve the blockage and break the stone up.