Diagnostic Approach for Flank Pain

Initial Diagnostic Evaluation

The American College of Radiology recommends non-contrast CT abdomen and pelvis as the most accurate initial imaging modality for flank pain, with sensitivity and specificity approaching 98-100% for detecting urinary stones regardless of size, location, and chemical composition 1, 2
Ultrasound should be considered as the first-line alternative in specific populations, including pregnant patients, patients with radiation concerns, patients with known renal disease, and when hydronephrosis has already been identified 1, 2, 3

Non-contrast CT detects ureteral stones with highest sensitivity and specificity (98-100%) and identifies extraurinary causes of flank pain in approximately one-third of patients 1

When moderate to severe hydronephrosis is detected on ultrasound in patients with moderate or high risk of ureteric calculi, it can provide sufficient diagnostic information without immediate need for CT 2, 3

In patients with renal colic and moderate to severe hydronephrosis on ultrasound, CT may be reserved for cases where ultrasound is non-diagnostic or when an alternative diagnosis is suspected 2, 3
The American College of Radiology notes that common pitfalls include contrast-enhanced CT obscuring stones within the renal collecting system and delayed development of secondary signs of obstruction leading to false-negative ultrasound findings 1
The absence of hydronephrosis on ultrasound makes the presence of a larger ureteral stone less likely 4

For patients with suspected urolithiasis, a low-dose CT protocol may be sufficient to determine stone size and location for surgical planning 2, 3
In patients with flank pain and negative urinalysis without history of urolithiasis, contrast-enhanced CT may be more appropriate as it better characterizes alternative diagnoses 2