Ultrasound versus intravenous urography in the initial evaluation of patients with suspected obstructing urinary calculi.

A consecutive series of 102 patients admitted to the radiology department for emergency intravenous urography (IVP) due to suspected obstructing urinary calculus, had an ultrasound scanning (US) performed immediately prior to the requested IVP. The scannings were performed by US-specialists who had access to all patient data except the IVP result. IVP diagnosed renal outlet obstruction in 53 of the 102 cases. This was correctly diagnosed by US in 50 cases. In three cases where IVP described acute obstruction ("white kidney") no dilatation was visible on US. The false negative rate concerning obstruction was thus 6%. No false positive US investigations occurred. Five cases of uretero-pelvic stenosis were correctly diagnosed at both investigations. 18 kidney stones--two being obstructing--were found at both investigations. IVP diagnosed 40 of 46 ureteral stones. The remaining stones were diagnosed by other means (retrograde pyelography, ureteroscopy). US only visualized 18 ureteral stones. The overlooked stones were all less than 5 mm in size, the major part being situated in the middle and lower ureter. We conclude that US plays a role in the initial evaluation of patients with suspected obstructing urinary calculi. If obstruction is diagnosed emergency IVP may be substituted by an elective investigation or even omitted. If no obstruction is diagnosed IVP must be performed in order to rule out non-dilated obstruction. IVP remains the gold standard for visualization of the urinary tract in patients with suspected acute obstruction.