Diagnosis of Kidney Stones
Most patients with kidney or ureteral stones experience pain (often severe) that is localized on one side of the flank. In very rare cases, pain occurs in the middle of the abdomen. Most kidney stones cause blood in the urine that can only be seen with a microscope (called microscopic hematuria).
It is imortant to diagnose kidney stones as as quickly and as safely as possible. Early diagnosis is important for two reasons. First, once diagnosed, the patient can be treated promptly, often with pain medications and increased fluid intake, which may help the stone to pass through the ureter. Second, it is important to make sure that the pain is not the result of another condition that requires medical treatment (e.g., appendicitis, diverticulitis, ovarian cyst [in women]).
Abdominal x-rays may be used to diagnose kidney stones. Approximately 80 percent of kidney/ureteral stones are calcified and can be seen on x-ray. An x-ray of the abdomen (known as a KUB—kidney, ureter, bladder) may show a small stone overlying one or both of the renal shadows or a stone in one of the ureters. Other types of stones (e.g., phleboliths, which form in the venous structures of the pelvis) also may be visible on abdominal x-ray.
In a diagnostic test called an intravenous pyelogram (IVP) a dye is injected intravenously. This dye, which is relatively dense, is excreted by the kidneys and can be detected by x-rays. Normally, the dye is excreted quickly by both kidneys, appears in the collecting systems, and then moves into the ureters. If there is a blockage, it takes longer for the dye to be excreted. If obstruction is very high grade, it may take hours to see the dye in the obstructed ureter.
IVP is a reliable test for kidney/ureteral stones, but it has a few drawbacks (e.g., exposure to radiation, intravenous dye may cause an adverse reaction). Intravenous pyelogram often is not able to diagnose other conditions that can cause one-sided abdominal pain.
Ultrasound is a noninvasive test that can be used to diagnose kidney stones. This test involves the use of sound waves, and does not require exposure to radiation or to contrast dye. Ureteral stones usually cannot be seen using ultrasound, unless the stone is located at the junction of the ureter and the bladder. In most cases, the effects of the stone (e.g., dilation of the collecting system) are indicated by ultrasound. Movement of the urine from the ureters into the bladder can also be seen using ultrasound. Normally, there are two sprays, or "jets," of urine—one from each ureter. If one spray is missing, there may be an obstructing stone in the ureter.
Ultrasound can be used in women who are or may be pregnant and in patients who are allergic to contrast dye. It can also provide useful information about other conditions that cause abdominal pain, such as gallbladder disease, appendicitis, and gynecological cancers in women.
When a more direct test is needed, CT KUB may be performed. Conventional CT scan (computed tomography) creates one image, slides the patient in a bit, and makes another image. Spiral CT does essentially the same thing, but continuously, and high-speed spiral CT creates images continuously and very fast. In CT KUB, numerous, consecutive images of the abdomen and pelvis are obtained. To diagnose kidney/ureteral stones, the radiologist focuses on a given structure (e.g., the ureter) and follows it along, image by image, in rapid sequence.
This test provides images of the liver, pancreas, gallbladder, and other upper abdominal organs. The radiologist can evaluate the appendix for inflammation, detect diverticulitis, and look for bowel obstruction. In the urinary tract, the kidneys and ureters can be studied in detail, looking for stones, tumors, or other signs of obstruction.
The type of imaging test used to diagnose kidney stones depends on a number of factors, such as the clinical circumstances, the age and sex of the patient, and the availability of the test in a given radiology department. Some departments, for example, may rely more heavily on IVP if spiral CT and ultrasound are not as available.