From the Guidelines
The workup for flank pain should begin with noncontrast CT (NCCT) as the imaging study of choice for initial evaluation, particularly in patients with suspicion of stone disease (urolithiasis) without known prior stone disease. This approach is supported by the most recent guidelines, including the ACR Appropriateness Criteria published in 2023 1. The use of NCCT allows for reliable characterization of the location and size of an offending ureteral calculus, identification of complications, and diagnosis of alternative etiologies of abdominal pain.
Key components of the workup include:
- Initial evaluation with NCCT for patients with acute onset of flank pain and suspicion of stone disease
- Consideration of ultrasound for evaluating signs of obstruction, although it is less sensitive in the detection of stones
- Potential use of radiography, despite its lower sensitivity compared to NCCT
- For patients with known disease and recurrent symptoms of urolithiasis, NCCT remains the test of choice
It is essential to note that while other diagnostic tools and tests, such as urinalysis, complete blood count, and basic metabolic panel, may provide valuable information, NCCT is the preferred initial imaging study for patients with suspected urolithiasis, as recommended by the ACR Appropriateness Criteria 1. This approach prioritizes the accurate diagnosis and management of flank pain, ultimately impacting morbidity, mortality, and quality of life.
From the Research
Diagnostic Approach
The workup for flank pain (renal colic) typically involves imaging studies to confirm the presence of a urinary stone or other causes of flank pain.
- Unenhanced helical CT scan of the abdomen and pelvis is considered the optimal diagnostic test to confirm a urinary stone in a patient with flank pain 2.
- Point of care ultrasound (PoCUS) can play an important role in the diagnostic algorithm and risk stratification of acute flank pain, but emergency physicians must be aware of its benefits and drawbacks 3.
- Plain abdominal radiographs combined with intravenous urography (IVU) have been used in the past, but have limitations such as poor quality due to lack of bowel preparation, nephrotoxicity of contrast agents, and significant radiation exposure 4.
- Ultrasonography (US) can detect ureteral dilatation with high sensitivity, but may not directly detect small ureteral calculi 4.
- MRI can detect the secondary effects of obstructive urolithiasis and provide quantitative analysis of renal function, but is relatively insensitive for the direct detection of urinary calculi 5.
Imaging Modalities
The choice of imaging modality depends on the clinical presentation and patient factors.
- Unenhanced helical CT (UHCT) is superior for detecting ureteral stones with high sensitivity and specificity, and can identify extraurinary causes of flank pain 4.
- PoCUS can be used for initial evaluation, but may not detect all cases of ureteric stones, especially if they are small or in a location that is difficult to visualize 3.
- MRI may be considered in patients with unusual presentations or when an alternative to CT is warranted, such as in younger patients or those with multiple prior CT exams 5.
Differential Diagnoses
Flank pain and hematuria can have differentials other than nephrolithiasis.
- Page kidney, a condition caused by compression of the renal parenchyma by a hematoma or mass, can present with flank pain and hematuria, and should be considered in the differential diagnosis 6.
- Other causes of flank pain, such as extraurinary abnormalities, should also be considered and evaluated with imaging studies 4.