From the Guidelines
For suspected gallstones or ureteric stones causing right upper quadrant (RUQ) pain, a non-contrast CT scan is the preferred initial imaging study. This recommendation is based on the most recent and highest quality study available, which emphasizes the importance of non-contrast CT in diagnosing stone disease, including ureteric stones and gallstones 1. Non-contrast CT is highly sensitive and specific for detecting both ureteric stones and gallstones, with the advantage of avoiding potential contrast-related complications such as allergic reactions or kidney injury.
For ureteric stones specifically, non-contrast CT is considered the gold standard, as it can identify stones as small as 1mm, determine their exact location, and assess for hydronephrosis or other complications. The American College of Radiology (ACR) Appropriateness Criteria for acute onset flank pain-suspicion of stone disease (urolithiasis) also supports the use of non-contrast CT as the initial imaging study of choice 1.
While ultrasound is often the first-line imaging modality for gallstones due to its high sensitivity and lack of radiation, non-contrast CT can still effectively visualize gallstones and evaluate for complications like cholecystitis or pancreatitis. Contrast-enhanced CT would only be indicated if there are concerns for complications such as cholecystitis with perforation, abscess formation, or if malignancy is suspected, as it helps better delineate tissue planes and vascular structures 1. The radiation dose from a single non-contrast CT is generally considered acceptable given the diagnostic benefit in these acute presentations.
Some key points to consider when choosing between non-contrast and contrast-enhanced CT include:
- The ability of non-contrast CT to detect ureteric stones and gallstones without the need for contrast
- The potential for contrast-related complications, such as allergic reactions or kidney injury
- The importance of evaluating for complications such as cholecystitis or pancreatitis
- The role of ultrasound as a first-line imaging modality for gallstones, but also the effectiveness of non-contrast CT in visualizing gallstones and evaluating for complications.
Overall, the use of non-contrast CT as the initial imaging study for suspected gallstones or ureteric stones causing RUQ pain is supported by the most recent and highest quality evidence available.
From the Research
Determining the Etiology of RUQ Pain
To determine if the etiology of right upper quadrant (RUQ) pain is a gallstone or a ureteric stone, the choice of imaging modality is crucial.
- The primary imaging modality for assessing acute RUQ pain is ultrasound (US), as it is both sensitive and specific in demonstrating gallstones, biliary dilatation, and features that suggest acute inflammatory disease 2, 3.
- However, when it comes to detecting ureteric stones, non-contrast enhanced computed tomography (CT) is more effective than intravenous urography (IVU) in precisely identifying ureteric stones and is equally effective as IVU in determining the presence or absence of ureteric obstruction 4.
- Non-contrast enhanced spiral CT has been shown to be accurate and reliable in detecting obstructing ureteral calculi in patients with flank pain, with a sensitivity of 98%, specificity of 100%, and positive and negative predictive values of 100% and 97%, respectively 5.
- Noncontrast spiral CT can detect up to 95% of renal, ureteric, and bladder stones, especially those with calcium composition 6.
Choice of CT Scan
Given the high accuracy of non-contrast enhanced CT in detecting ureteric stones, a CT scan without contrast is likely the better choice for determining the etiology of RUQ pain when a ureteric stone is suspected.
- A non-contrast CT scan can help identify ureteric stones and other causes of RUQ pain, such as kidney stones or other abdominal pathologies.
- The use of contrast is not necessary for detecting ureteric stones, and non-contrast CT scans are generally faster and less expensive than contrast-enhanced CT scans.