Kidney Stone Imaging
Kidney stones are commonly identified on imaging tests like X-ray ultrasound and CT. Kidney stones can vary in size, composition and shape. They often cause symptoms when they pass into the ureter. Kidney stones that block the kidney and ureter will be painful and require invasive treatment in some cases.
What are kidney stones?
They are hard deposits of minerals and salts that form in the kidneys. They often occur when the urine becomes concentrated.
Symptoms of kidney stones
Kidney stones which are in the kidney often do not cause symptoms. Kidney stones cause symptoms when they move around especially to the ureter (tube which carries urine from the kidney to the bladder).
Symptoms will include severe flank pain that comes in waves. Pain or burning when urinating. Nausea and vomiting. Fever and chills if there is infection. The urine can be a blood tinged color.
How is a kidney stone diagnosed?
A kidney stone is diagnosed with imaging studies like X-ray, ultrasound and CT. CT will identify most stones. They can also show us where the stone is and if the kidney and ureter is blocked.
What causes kidney stones?
Urine which is concentrated with salts and minerals can form stones. Foods you eat, certain medications and a genetic predisposition can all influence stone formation.
What do kidney stones look like on imaging?
Kidney Stones On X-ray
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.
On X-rays, stones can 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 than 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.
Kidney Stones On CT Scan
CT is often a definitive test for imaging stones. 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 arising from the urinary tract.
Kidney Stones On Ultrasound
Ultrasound may identify some stones. We can also see if the kidney is blocked or has hydronephrosis. Ultrasound does not image the ureters as well as CT so we may not see the stone causing obstruction.
Ultrasound may however also diagnose stones when they are not really there. Certain artifacts can look like small stones. Ultrasound is more dependent on the skill of the technologist performing the test.
What are risk factors for stones?
Risk factors for stones are many and include urinary tract malformations, infections, metabolic abnormalities, low fluid intake, obesity and prior surgery on the urinary tract.
What else can look like kidney stones in radiology?
X-rays done for diagnosing stones can have many mimickers. Many abdominal and pelvic calcifications can look like kidney stones.
Phleboliths can be mistaken for a urinary tract stone on X-ray. These are small calcifications in pelvic veins. Atherosclerotic calcifications in blood vessels can look like stones sometimes.
There are also kidney stones which we do not see on X-ray.
CT scans are more definitive for the diagnosis of kidney stones. Sometimes pelvic phleboliths can look like a stone in the ureter.
Ureteral stone
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. CT is often definitive.
Bladder stones
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 on X-ray. Calcifications related to the prostate in men and fibroids in women can also sometimes mimic bladder stones. CT is often definitive for diagnosing these.
Are kidney stones dangerous?
Kidney stones can be dangerous because they can block the kidney and urinary tract. This can result in loss of kidney function if not treated.
Infections that occur when kidney stones are passing are dangerous and need to be treated promptly.
A portion of the urinary tract can rupture and urine can spill out of the urinary tract.
What type of doctor treats kidney stones?
Urologists are often involved in the diagnosis and treatment of kidney stones. They are specialists in diagnosing and treating diseases of the urinary tract. Many other types of doctors like primary care and emergency medicine are involved in the diagnosis and medical treatment of stones.
Kidney stones treatment
Surgical management of stones is most likely when:
Stones that are larger than 5 mm are less likely to pass.
Location of the stone is closer to the kidney.
Having one kidney
Infection associated with the stone
Failed medical treatment
Surgical management often involves placing a stent in the ureter to relieve the obstruction. A lithotripsy is done at a later time. Emergent options for patients not suitable for stent placement include a percutaneous nephrostomy where a catheter is placed into the kidney through the skin to allow urine to pass.
Kidney stones: summary
Kidney stones are commonly diagnosed on imaging studies like X-ray, ultrasound and CT. Kidney stones often cause symptoms when they pass into the ureter and cause a blockage. Kidney stones are best assessed on CT scans. Treatment can be both medical and surgical. Urology doctors are often involved in the treatment of kidney stones.