Diagnostic Approach to Right Flank Pain

Urologic Causes

The American College of Radiology recommends non-contrast CT abdomen/pelvis as the gold standard for suspected urolithiasis, with 98-100% sensitivity and specificity regardless of stone size, location, or composition 1, 3.
Kidney stones are the leading cause of acute flank pain, presenting with colicky, wave-like severe pain that radiates to the groin and is independent of body position 1.
Pain from uncomplicated stones typically does NOT worsen with external flank pressure, as it results from internal distension rather than external compression 2, 3.
Microscopic or gross hematuria is present in most cases and significantly increases the probability of stone disease 1.

Right colonic diverticulitis is seen in 8% of patients presenting with right lower quadrant/flank pain on CT imaging, and can closely mimic appendicitis or urologic pathology 4, 1.
Inflammatory bowel disease, such as Crohn's disease with terminal ileitis, can present with right-sided flank/lower quadrant pain 4, 1.
Bowel obstruction is seen in 3% of patients with right lower quadrant pain on CT, and can cause referred pain to the flank region 4, 5.
Appendicitis (retrocecal) can present with predominant flank pain rather than classic right lower quadrant pain, and CT has 95% sensitivity and 94% specificity for diagnosis 6, 4.

Benign adnexal masses are among the most common CT diagnoses in women with right lower quadrant/flank pain when appendicitis is excluded, and includes ovarian cysts, torsion, and tubo-ovarian abscess 4, 1.
Ectopic pregnancy must be considered in any woman of reproductive age with delayed menses and flank pain, as this is a life-threatening emergency 1.

Ultrasound is first-line imaging for suspected infection, and can show gallbladder wall thickening, pericholecystic fluid, and sonographic Murphy's sign in acute cholecystitis 5.
Contrast-enhanced CT is preferred over non-contrast to evaluate for pyelonephritis or abscess, and pain worsening with external flank pressure is the key clinical clue 3.
Low-dose non-contrast CT or ultrasound can be used to minimize cumulative radiation exposure in recurrent stone formers 7, 1.

Stones <5 mm typically pass spontaneously with conservative management, while larger stones or complete obstruction may require endoscopic intervention 7, 1.
When no CT diagnosis is made, only 14% require hospitalization and 4% need intervention, while 41% require hospitalization and 22% need surgical or image-guided intervention when a non-appendiceal CT diagnosis is established 4.