Diagnosis and evaluation of urolithiasis
The most appropriate imaging modality will be determined by the clinical situation, which will differ depending on if a ureteral or a renal stone is suspected.
Standard evaluation includes a detailed medical history and physical examination. Patients with ureteral stones usually present with loin pain, vomiting, and sometimes fever, but may also be asymptomatic. Immediate evaluation is indicated in patients with solitary kidney, fever or when there is doubt regarding a diagnosis of renal colic.
Ultrasound (US) should be used as the primary diagnostic imaging tool, although pain relief, or any other emergency measures, should not be delayed by imaging assessments. Ultrasound is safe (no risk of radiation), reproducible and inexpensive. It can identify stones located in the calyces, pelvis, and pyeloureteric and vesico-ureteral junctions (US with filled bladder), as well as in patients with upper urinary tract (UUT) dilatation.
Ultrasound has a sensitivity of 45% and specificity of 94% for ureteral stones and a sensitivity of 45% and specificity of 88% for renal stones.
The sensitivity and specificity of KUB is 44-77%]. Kidney-ureter-bladder radiography should not be performed if NCCT is being considered; however, it is helpful in differentiating between radiolucent and radiopaque stones and should be used for comparison during follow-up.
Evaluation of patients with acute flank pain/suspected ureteral stones
Non-contrast-enhanced computed tomography has become the standard for diagnosing acute flank pain, and has replaced intravenous urography (IVU). Non-contrast-enhanced CT can determine stone diameter and density. When stones are absent, the cause of abdominal pain should be identified. In evaluating patients with suspected acute urolithiasis, NCCT is significantly more accurate than IVU.
Non-contrast-enhanced CT can detect uric acid and xanthine stones, which are radiolucent on plain films, but not indinavir stones. Non-contrast-enhanced CT can determine stone density,inner structure of the stone, skin-to-stone distance and surrounding anatomy; all of which affect selection of treatment modality. The advantage of non-contrast imaging must be balanced against loss of information on renal function and urinary collecting system anatomy, as well as higher radiation dose.
Radiation risk can be reduced by low-dose CT, which may, however, be difficult to introduce in standard clinical practice. In patients with a body mass index (BMI) < 30, low-dose CT has been shown to have a sensitivity of 86% for detecting ureteral stones < 3 mm and 100% for calculi > 3 mm. A MA of prospective studies has shown that low-dose CT diagnosed urolithiasis with a pooled sensitivity of 93.1% (95% CI: 91.5-94.4), and a specificity of 96.6% (95% CI: 95.1-97.7%). Dual-energy CT can differentiate uric acid containing stones from calcium-containing stones.
Radiological evaluation of patients with renal stones
Intravenous urography (IVU) can provide information about renal function, the anatomy of the collecting system and the level of an obstruction, while CT allows for rapid 3D data acquisition including information on stone size and density, skin-to-stone distance and surrounding anatomy, but at the cost of increased radiation exposure. Low-dose and ultra-low-dose protocols seem to yield comparable results to standard-dose protocols with the exception of detection of very small stones or stones in obese patients.
A small randomised study showed that in supine percutaneous antegrade ureteroscopy (PNL), pre-operative planning using CT, compared to IVU, resulted in easier access and shorter operating times.
In case stone removal is planned and the renal collecting system needs to be assessed, a contrast study should be performed.