Investigation of urolitiases is mainly conducted using ultrasound or CT scan (urology scan).
Despite the fact that 90% of urinary litiases are radiopaque, their detection using a single plate on the abdomen is relatively insensitive (in the order of 45%), given the multiple stacking present. Sensitivity to ultrasound can vary from 60 to 80%, depending on whether or not obstructive phenomena are also present, as well as on the size of the urolitiasis and its location. In fact, its sensitivity will be greater if the litiasis is located at the pyelo-ureteral or uretero-vesical junction rather than on the average trajectory of the ureter. The litiases missed during the ultrasound are generally ≤ 5 mm in size (most between 2-3 mm), and thus show good probability of spontaneous passage.
Spiral CT scan, using a dedicated protocol for urolitiasis detection without oral or intraveinous contrast medium and a low radiation technique, has a sensitivity and specificity rate of about 96% for the detection of urolitiases. This excellent rate of screening can be explained by the fact that it is possible to follow the ureter over its entire trajectory and that 90% of urolitiases are radiopaque.
However, radiation has to be taken into account in the decision algorithm. Also, a patient known to suffer from recurrent nephritic colics could be investigated using ultrasound first. A patient with negative ultrasound results, but with persistent symptoms despite conservative treatment, could then be re-evaluated clinically using a urology scan, if needed. It should be noted that the urology scan is performed using a low radiation dose protocol.
With a view to limiting radiation, investigation of a first episode of nephritic colic can be conducted using ultrasound first, and based on the findings, completed using a urology scan. It can also be done by urology scan from the outset, especially if the patient is over 30 years of age or if there is a clinical possibility of another etiology such as diverticulitis, or other.