Diagnosis of Kidney Stones
It has been estimated that 95-98% of all kidney stones can be detected using a special type of CT scan called a non-contrast helical CT. Although it does have a hard time seeing kidney stones caused by the HIV drug indinavir, they are relatively rare and using radiocontrast dye can usually help.The abdominal CT test is also very good at identifying when a kidney stone is causing significant obstruction of the kidney (hydronephrosis).
Other Causes of Flank Pain
The abdominal CT is rapidly becoming the first choice in working up acute flank pain. Although we are often looking primarily for kidney stones, the abdominal CT can help us diagnose conditions that mimic kidney stones:- Kidney Infection: One of the more common conditions mimicking kidney stones is a kidney infection or pyelonephritis. Although mild disease may not show up, a moderate to severe infection often shows some enlargement of the kidney or signs of inflammation around. Using contrast dye can really make the infection obvious on CT.
- Kidney Cancer: This should be suspected in any middle-aged or elderly patient who presents with flank pain and blood in the urine. Findings of cancer may be subtle if there isn’t bleeding or a large mass and may require the use of contrast dye.
- Ovarian Cysts: Gynecologic conditions often present as abdominal or flank pain and most involve an ovarian cyst. However, ectopic pregnancy, fallopian tube abscesses, ovarian cancer, cervical cancer, and uterine fibroids are also seen. Bleeding by an ovarian cyst usually causes the significant pain and is easily seen with the non-contrast helical CT.
- Appendicitis: Doctors always consider appendicitis as a possibility when somebody presents with abdominal pain. The radiologist looks to see if the appendix is enlarged or dilated, if there are signs of inflammation around it, or if there is a pocket of pus suggesting that it ruptured. The abdominal CT is very good at ruling out appendicitis as a possibility.
- Diverticulitis: Diverticulitis is often called the appendicitis of the colon and it can usually be seen well on abdominal CT. Again the radiologist is looking to see if there are signs of inflammation or if there is a pocket of pus.
- Gallstones: Gallstones are frequently found on CT (but they are better seen on ultrasound and MRI) but they may not be the cause of the flank pain. Signs of inflammation from blockage of the gallbladder or bile duct can help identify active gallstone disease.
- Pancreatitis: Although the pain from pancreatitis is not as spasmic as a kidney stone and is usually in the center of the abdomen or back (instead of the flank), it is sometimes mistaken for a stone involving the left kidney. The CT is reasonably good at identifying pancreatitis, especially if contrast dye is used to better identify related complications.
Sources
- Jeong Yeon Cho. “Urolthiasis”. Radiology Illustration: Uroradiology. Ed Seung Hyup Kim. Philadelphia: Saunders, 2003. 371-409.
- Ronald J. Zagoria. “The Lower Urinary Tract”. Genitourinary Radiology: The Requisites. Philadelphia: Mosby, 2004. 201-254.