American Board of Internal Medicine (ABIM) Certification Practice Exam

What is the recommended imaging technique for evaluating suspected nephrolithiasis if the initial ultrasound is negative?

1. Ultrasonography

2. Noncontrast helical CT of the abdomen

3. Magnetic resonance imaging

4. Plain abdominal X-ray

The correct answer is: Noncontrast helical CT of the abdomen

The recommended imaging technique for evaluating suspected nephrolithiasis after a negative initial ultrasound is noncontrast helical CT of the abdomen. This method is favored due to its high sensitivity and specificity for detecting kidney stones, as it can effectively visualize even small calculi that may not be evident on ultrasound. Unlike ultrasound, which may miss stones especially if they are located in certain parts of the urinary tract, noncontrast CT can provide a comprehensive view of the entire urinary system without the need for contrast agents, making it both efficient and safe for patients. Given that kidney stones can lead to significant complications, prompt and accurate diagnosis is crucial. Noncontrast CT is particularly useful because it can also identify other potential causes of renal colic or other abdominal pain that might mimic nephrolithiasis. Other imaging techniques such as magnetic resonance imaging, while useful in specific circumstances (such as in patients who cannot have a CT scan due to allergies to contrast or concerns about radiation), are generally not used as first-line imaging for kidney stones. Plain abdominal X-ray has limited utility in this context because many stones are not radiopaque and may therefore go undetected.