A 49 year old man presents with severe colicky pain from his right flank radiating to his groin associated with nausea and vomiting. He subsequently develops rigors and a tender abdomen. His urinalysis reveals trace blood. What is the SINGLE next best investigation?
A. Ultrasound abdomen
B. Kidneys, ureters, and bladder X-ray
C. Colonoscopy
D. Intravenous pyelogram
E. Laparoscopy
This is a typical presentation of a ureteric calculus. The pain is severe and associated with nausea and vomiting. Urinalysis or microscopy would reveal blood. X-ray is the answer here. X-rays are still the most commonly used first diagnostic step in diagnosing renal stones. It may not be the best method as it does still misses 20% of stones which are not radio-opaque however it is still cost-effective. In certain UK hospitals, Urologist are moving towards ordering a CT KUB without even having an X-ray performed. The reason behind this is that it is much more accurate than an X-ray and CT scans are now so readily available. For that reason, if the question had an option of Non-enhanced CT scan and asked for “the SINGLE most appropriate diagnostic test” or “the SINGLE most definitive test”, pick the CT scan.
Plain X-rays of the kidney, ureter and bladder (KUB) are useful in watching the passage of radio-opaque stones (around 80% of stones are of calcium and so will be radioopaque).
Renal Ultrasound scan is sensitivity for detecting renal calculi but is variable depending on the series. Some series suggest close to 95% sensitivity for detecting stones, others just 50%. Ultrasound scanning may be helpful to differentiate radio-opaque from radiolucent stones and in detecting evidence of obstruction by looking for hydronephrosis or hydroureter. A combination of plain abdominal radiography and renal ultrasonography is a useful screening test for renal calculi.
Non-enhanced CT scanning (spiral non-contrast CT) is now the imaging modality of choice and has replaced intravenous pyelogram (IVP). It is a very accurate method of diagnosing renal and ureteric stones (99% visible). Allows accurate determination of stone size and location and good definition of pelvicalyceal anatomy. It also helps exclude differential causes of an acute abdomen (e.g. A ruptured abdominal aortic aneurysm which may present similarly).