What is the preferred imaging modality, Ultrasound (US) or Computed Tomography (CT) of the abdomen, for a 70-year-old female (YOF) with flank pain and a history of urolithiasis requiring lithotripsy?

From the Guidelines

For a 70-year-old female with flank pain and history of urolithiasis requiring lithotripsy, CT abdomen is the better imaging choice. This recommendation is based on the most recent and highest quality study, which suggests that Noncontrast CT (NCCT) is the imaging study of choice for initial evaluation of patients with acute onset of flank pain and suspicion of stone disease, even in those with known prior stone disease 1. The study, published in the Journal of the American College of Radiology in 2023, highlights the superiority of NCCT in characterizing the location and size of an offending ureteral calculus, identifying complications, and diagnosing alternative etiologies of abdominal pain.

While ultrasound may have a role in evaluating for signs of obstruction, its sensitivity in detecting stones is significantly lower than NCCT, making it a less preferred initial imaging modality for this patient 1. Key advantages of CT abdomen include:

• Superior sensitivity and specificity in detecting urinary stones
• Ability to accurately identify stone size, location, and density
• Better detection of complications like obstruction or infection
• Ability to identify alternative diagnoses if stones aren't present

In contrast, ultrasound has advantages including no radiation exposure, lower cost, and bedside availability, but its lower sensitivity for detecting stones, particularly smaller ones and those in the ureter, makes it less suitable as the initial imaging modality for this patient 1. However, ultrasound may be considered if radiation exposure is a significant concern or for follow-up imaging after initial diagnosis.

From the Research

Imaging Modalities for Urolithiasis

• Ultrasound (US) and Computed Tomography (CT) abdomen are two common imaging modalities used to diagnose and manage urolithiasis.
• According to 2, unenhanced CT can rapidly, accurately, and safely determine the presence or absence of ureteral obstruction, making it a valuable tool in the diagnosis of urolithiasis.
• CT abdomen is considered the gold standard examination in both the diagnosis and follow-up of patients with urolithiasis, as stated in 3.

Comparison of US and CT Abdomen

• While ultrasound is a useful tool in the follow-up of patients with urolithiasis, especially in pregnant patients and children, CT abdomen is more sensitive and specific in diagnosing urolithiasis, as mentioned in 4 and 5.
• The use of low-dose CT protocols and newer iterative reconstruction algorithms has resulted in a substantial decrease in ionizing radiation exposure, making CT abdomen a safer option, as discussed in 5.
• In patients with a history of urolithiasis requiring lithotripsy, CT abdomen may be preferred over US due to its high sensitivity and specificity in detecting ureteral obstruction and stone size and location, as stated in 6 and 2.

Clinical Considerations

• The choice of imaging modality may depend on the individual patient's characteristics, such as pregnancy or radiation exposure concerns, as mentioned in 4 and 5.
• In patients with acute flank pain, unenhanced CT abdomen can help diagnose or exclude other abnormalities that may cause similar symptoms, as discussed in 2.