CT Detects More Kidney Stones Than Ultrasound, But Rarely Changes Treatment

A patient lies on an ultrasound table four to six weeks after surgery to remove kidney stones. The radiologist scans methodically, looking for fragments left behind. The images look clear. But what if something small was missed? What if a CT scan, more sensitive and more thorough, would have caught it? These questions have haunted urologists for years, driving a wedge between what imaging can detect and what imaging should detect.

Researchers at Shaare Zedek Medical Center in Jerusalem set out to answer a deceptively simple question: Does finding more stones actually change how doctors treat patients? Between January 2024 and May 2025, they enrolled 60 patients who underwent both ultrasound and CT scans within 72 hours of their routine postoperative follow-up visits. The patients had all undergone either ureteroscopy or percutaneous nephrolithotomy—minimally invasive procedures designed to eliminate kidney stones completely. The study was designed not merely to measure which imaging method was more accurate, but whether superior accuracy translated into better care.

The results revealed a striking disconnect. CT scans identified residual stone fragments in 10 percent of patients where ultrasound found nothing. By the numbers, ultrasound detected 20 of 27 residual stones that CT identified, yielding a sensitivity of 79 percent. CT, as expected, was more thorough. But here is where the story pivots: only two patients out of 60—just 3.3 percent—required any intervention beyond routine surveillance based on what CT alone revealed. Both of those patients presented with symptoms: one had a five-millimeter ureteral stone causing obstruction and flank pain; the other had a four-millimeter fragment associated with persistent pain and swelling of the kidney. In both cases, the patients underwent repeat surgery. All other CT-detected fragments were small, measuring four millimeters or less, and posed no immediate threat. They were watched, not treated.

The study exposed a fundamental tension in modern medicine: the gap between what we can detect and what we should act upon. Ultrasound, despite its limitations, correctly identified whether patients were stone-free in the vast majority of cases. It tended to overestimate stone size—by an average of 1.2 millimeters—and this overestimation worsened in patients with higher body mass index. Yet this imprecision rarely led to unnecessary surgery. The researchers found that body mass index was the only significant predictor of false-positive ultrasound findings, suggesting that in heavier patients, clinicians might reasonably request CT confirmation when ultrasound results were ambiguous.

The implications ripple outward. CT scans expose patients to ionizing radiation, a concern that compounds over a lifetime, particularly for younger patients with recurrent stone disease who may need repeated imaging. Even modern low-dose CT protocols deliver radiation doses that, while modest, accumulate across years. Ultrasound carries no such burden. It is cheaper, universally available, and can be performed in community settings without specialized equipment. The question, then, is not whether CT can detect more—it clearly can—but whether that additional detection justifies the cost and radiation exposure when it so rarely changes what doctors actually do.

Current guidelines from the American Urological Association and the European Association of Urology already recommend individualized imaging strategies, leaving room for clinical judgment. This study provides the evidence to support that flexibility. The authors propose a risk-adapted approach: ultrasound as the first line of surveillance for routine follow-up, with CT reserved for patients with equivocal ultrasound findings, higher clinical risk, or persistent symptoms. For the patient on the ultrasound table, this means a safer, simpler path forward—unless something suggests otherwise. The lesson extends beyond kidney stones. It is a reminder that in medicine, the ability to see more does not always mean seeing better, and that the best imaging strategy is one aligned not with technological capability but with what actually matters: keeping patients well.