From the Guidelines
CT stonogram (non-contrast CT) should be ordered as the first-line imaging test for patients presenting with acute flank pain, hematuria, and symptoms suggestive of urolithiasis, especially when rapid diagnosis is needed, as it has high sensitivity (95-98%) and specificity for detecting stones of all compositions except pure matrix stones 1.
Indications for CT Stonogram and KUB Ultrasound
The choice between CT stonogram and KUB ultrasound depends on various factors, including clinical urgency, patient characteristics, and radiation exposure concerns.
- CT stonogram is preferred for patients with acute onset flank pain and suspicion of stone disease, as it provides superior stone detection, size measurement, and location determination 1.
- KUB ultrasound is appropriate for initial evaluation in pregnant women, children, young patients requiring repeated imaging, and those with known stone disease needing follow-up, as it offers radiation-free imaging with good sensitivity for stones >5mm and hydronephrosis 1.
- Ultrasound is also preferred for patients with renal insufficiency to avoid contrast exposure and radiation concerns 1.
Special Considerations
- For patients with symptomatic hydronephrosis with unknown cause, CT abdomen and pelvis without IV contrast may be useful, especially when obstructive urolithiasis is a primary concern 1.
- Radiography of the abdomen and pelvis (KUB) may be used in combination with ultrasound to improve stone detection rates, especially for stones in the mid and distal ureters 1.
- Low-dose CT examinations and dual-energy CT can be used to minimize patient radiation dose and characterize stone composition 1.
- MR urography (MRU) and digital tomosynthesis (DT) are alternative imaging modalities that can be used in specific situations, such as evaluating the urinary system and detecting intrarenal stones 1.
From the Research
Indications for CT Stonogram and KUB Ultrasound
- The decision to order a CT stonogram or a KUB ultrasound depends on various factors, including the clinical presentation, patient population, and availability of imaging modalities 2, 3, 4, 5.
- For patients with acute onset of flank pain and suspicion of stone disease, low-dose noncontrast CT (NCCT) is the imaging study of choice, with a sensitivity of 97% and specificity of 95% 4.
- Ultrasound is recommended as the initial imaging modality for suspected renal colic in pregnant women and children, but recent literature suggests that a low-dose CT scan may be safe in pregnancy 4, 5.
- For patients with known stone disease whose stones are visible on radiographs, radiographs are a good tool for post-treatment follow-up 4.
- KUB ultrasound can be used for follow-up in 63% of cases, and all stones seen on CT scout were also visible on KUB 3.
- The addition of x-ray KUB abdomen increases the sensitivity for ureteric stones to 77% 2.
Specific Scenarios
- In patients with renal failure, ultrasound (US) kidney, ureter, and bladder (KUB) has a sensitivity of 81% for renal stones, but its sensitivity for ureteric stones is low (46%) 2.
- For patients with asymptomatic calyceal stones who prefer an observational approach, a yearly KUB is recommended to monitor progression of stone burden 5.
- Intraoperative imaging by fluoroscopy or US plays a large part in assisting the urologist with the surgical intervention chosen for the individual stone patient 5.
Imaging Modalities
- Unenhanced spiral CT scans are considered the gold standard for diagnosing renal calculi, replacing intravenous urography (IVU) at most centers 5.
- Magnetic resonance urography and computed tomography (CT) scans are also available, each with its advantages and limitations 5.
- Plain radiography is suggested for the follow-up of radiopaque stones, with ultrasound and limited IVU reserved for the follow-up of radiolucent stones to minimize cumulative radiation exposure from repeated CT scans 5.