Unenhanced CT is usually the preferred modality for the evaluation of renal and ureteral stone disease because of its ability to resolve between calcified stones, dense non-calcified concretions, and normal renal parenchyma. CT may also detect pathology in other organs that mimics renal colic.

Initial ultrasound rather than CT may be selected for follow-up in patients with known stone disease or in young patients in whom diagnostic testing without ionizing radiation exposure is desired. However, focused ultrasound for nephroureterolithiasis can be technically challenging and is insensitive for small stones, stones at the ureteropelvic junction (UPJ), and stones in the mid ureter. Estimation of stone size may be inaccurate. Ultrasound is more useful in cases of stones >5 mm and cases with hydroureteronephrosis. In most cases with a negative ultrasound and ongoing concern for stone disease, unenhanced CT is performed. Stones are seen as echogenic foci with posterior acoustic shadowing. Absence of a “ureteral jet” in the bladder on the affected side may be seen with Doppler imaging.

The most common cause of calcification/calcium density in the renal parenchyma is nephrolithiasis. Medullary nephrocalcinosis and vascular calcification sometimes confound the diagnosis.

Dual energy CT acquires images with two x-ray tubes set 90 degrees apart that simultaneously scan the patient at higher (140 kVp) and lower (80 kVp) energy levels. Because different types of stones have different chemical composition, and hence k-edges, they absorb photons differently at different energy levels. The composition of different stones can be reliably predicted by calculating a ratio of the attenuation at low and high energy levels.

The distinction between uric acid and non-uric acid stones may be clinically important because some uric acid stones are treated with pharmacologic urine alkalinization rather than invasive procedures.

Special attention should be paid to these areas when evaluating for stones:

A pelvic venous phlebolith may be differentiated from a ureteral calculus by the “soft tissue rim” sign, which represents the thickened, inflamed ureteral wall around the calcification. If this is present, it is more likely that the calcification represents a ureteral calculus.

Ureteral stents or percutaneous nephrostomy tubes temporize until the patient has clinically stabilized.

Yoshimura et al. published that the strongest risk factors for requiring emergent surgical drainage with obstructive calculi were poor performance status (e.g., spinal cord injury), female sex, and age >75.