Kidney or renal stone CT for flank pain is one of the most common orders I see for CT, especially from the emergency room. This is usually a non contrast CT of the abdomen and pelvis. There is no contrast given through the vein and you don’t have to drink oral contrast either. Usually, this type of CT is done when the patient complains of flank pain, which is on the right or left side below the rib cage and above the hips.
The Kidney stone CT for flank pain is mainly ordered to look for kidney or ureteral stones. Kidney stones are those that are positioned in the kidney while ureteral stones are those passing from the kidney to the bladder through the ureter. Often the ureteral stones are the ones causing the patient to the present to the doctor with flank pain.
Ureteral stones can lodge anywhere from the top near the kidney all the way to where it passes into the bladder. The ureter is a thin tube going from the kidney to bladder and it can become blocked by the stone. Urine then can’t flow from the kidney to bladder. This causes a backup of urine and the kidney collecting system to become big. The kidney collecting system is where the urine forms in the kidney and eventually extends into the ureter. When the kidney collecting system dilates, this is called hydronephrosis.
Sometimes stones in the ureter can pass into the bladder on their own. Other times, they get stuck and need a urology specialist to treat it. The bigger the stone, the tougher it will be for it to pass on its own. Often, patients with stones in their ureters will go to the emergency room because of the pain. The emergency room doctor will determine appropriate treatment.
Infection of an obstructed kidney needs to be treated urgently. Sometimes, a blocked kidney can leak urine around the kidney. The CT scan will identify the urine leak but often not the infection. Your clinical doctors will have to make a diagnosis of infection in most cases.
The good thing about Kidney stone CT for flank pain is that other causes of your flank pain can be made. One of the more common causes is pyelonephritis or infected kidney. On a non contrast CT, the fat around the kidney can be hazy. The ureter may be thicker and a bit dilated. There are many other causes of flank pain which can mimic kidney stone. I have seen appendicitis, diverticulitis and other rarer causes.
Sometimes the scan is negative. In these cases, the pain can be because of the muscular or bony tissues around the flank. Maybe a pulled muscle or injury to the lower rib. Perhaps an infection that isn’t showing up on the CT scan. Your doctors will best be able to make a diagnosis based on the history, physical exam and other testing.