What are the possible causes of right flank pain in a patient without kidney stones?

Right Flank Pain Without Kidney Stones: Differential Diagnosis

When kidney stones are excluded, right flank pain most commonly arises from gastrointestinal causes (particularly right colonic diverticulitis and appendicitis), gynecologic pathology in women, or infectious/inflammatory renal conditions like pyelonephritis. 1

Key Diagnostic Distinctions

Pain Characteristics That Guide Diagnosis

• Pain worsening with external flank pressure strongly suggests pyelonephritis or perinephric abscess rather than stone disease, as uncomplicated stones cause pain from internal distension, not external compression 1, 2
• Pain occurring after prolonged static positioning points toward musculoskeletal origin involving paraspinal muscles, facet joints, or referred pain from lumbar spine pathology 2
• Classic renal colic (colicky, wave-like severe pain independent of body position radiating to groin) is characteristic of stones, so absence of this pattern broadens the differential 1, 2

Major Non-Stone Causes of Right Flank Pain

Gastrointestinal Etiologies

• Right colonic diverticulitis accounts for 8% of patients presenting with right lower quadrant/flank pain on CT imaging and closely mimics appendicitis or urologic pathology 1
• Retrocecal appendicitis can present with predominant flank pain rather than classic right lower quadrant pain, with CT demonstrating 95% sensitivity and 94% specificity for diagnosis 1
• Inflammatory bowel disease (particularly Crohn's disease with terminal ileitis) presents with right-sided flank/lower quadrant pain 1
• Bowel obstruction is identified in 3% of patients with right lower quadrant pain on CT and can cause referred pain to the flank region 1

Infectious/Inflammatory Renal Causes

• Acute pyelonephritis presents with fever >38°C, chills, flank pain, nausea, vomiting, or costovertebral angle tenderness, with or without cystitis symptoms 3
• Perinephric abscess should be suspected when fever and systemic signs accompany flank pain that worsens with external pressure 1, 3
• On ultrasonography, kidneys may be enlarged with hypoechoic parenchyma and loss of normal corticomedullary junction in acute pyelonephritis 4

Gynecologic Causes in Women

• Benign adnexal masses (including ovarian cysts, torsion, and tubo-ovarian abscess) are among the most common CT diagnoses in women with right lower quadrant/flank pain when appendicitis is excluded 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, 2

Other Renal Pathology

• Polycystic kidney disease with cyst hemorrhage or infection can cause flank pain; nephrolithiasis occurs in approximately 20% of ADPKD patients and should enter the differential diagnosis 5
• Nonobstructing calyceal stones may still cause pain despite lack of obstruction, though this is less common 6

Optimal Imaging Strategy

When Infection Is Suspected

• Contrast-enhanced CT is preferred over non-contrast to evaluate for pyelonephritis or abscess 1
• Ultrasound is first-line for suspected cholecystitis, showing gallbladder wall thickening, pericholecystic fluid, and sonographic Murphy's sign 1

When Non-Urologic Pathology Is Suspected

• CT abdomen/pelvis with IV contrast allows evaluation of other etiologies of flank pain and is 81% sensitive overall for detecting renal stones ≥1 mm (95% sensitivity for stones ≥3 mm), so it can still identify larger stones if present 7
• Non-contrast CT identifies alternative diagnoses in approximately one-third of patients presenting with acute flank pain 2, 8

Critical Clinical Pitfalls to Avoid

• Do not assume all flank pain is kidney-related; the positional nature of symptoms and response to external pressure are key distinguishing features 2
• Do not delay imaging in young females—consider gynecologic causes that may require urgent intervention, particularly ectopic pregnancy in women with delayed menses 2, 3
• Do not miss signs of systemic infection (fever, chills, hemodynamic instability) that mandate immediate hospitalization regardless of imaging results 2, 3
• Absence of hematuria does not exclude significant pathology; over 20% of patients with confirmed urinary stones may have negative urinalysis, and infectious/inflammatory conditions often lack hematuria 2, 9

Management Implications

• When no CT diagnosis is made, only 14% require hospitalization and 4% need intervention 1, 2
• When a non-appendiceal CT diagnosis is established, 41% require hospitalization and 22% need surgical or image-guided intervention 1, 2
• Fever, hemodynamic instability, or signs of sepsis require immediate hospital admission regardless of imaging results 2, 3