What are the causes of right flank pain?

Causes of Right Flank Pain

Right flank pain has multiple etiologies, with urolithiasis being the most common cause, but clinicians must systematically evaluate for gastrointestinal, gynecologic, infectious, and vascular pathologies that frequently present with similar symptoms.

Urologic Causes (Most Common)

Nephrolithiasis/Urolithiasis

• 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, 2.
• Stones can occur anywhere in the urinary tract—renal pelvis, ureter, or bladder—with ureteral stones causing the most severe symptoms due to obstruction 3, 2.
• Pain from uncomplicated stones typically does NOT worsen with external flank pressure, as it results from internal distension rather than external compression 4, 5.
• Microscopic or gross hematuria is present in most cases and significantly increases the probability of stone disease 1.

Acute Pyelonephritis

• Presents with flank pain that DOES worsen with external pressure (positive costovertebral angle tenderness), distinguishing it from uncomplicated stones 5, 6.
• Associated with fever, chills, dysuria, and systemic signs of infection 1, 6.
• Ultrasound may show enlarged kidneys with hypoechoic parenchyma and loss of normal corticomedullary junction 6.

Perinephric Abscess

• Pain significantly worsens with external flank pressure, similar to pyelonephritis 5.
• Requires contrast-enhanced CT for diagnosis rather than non-contrast imaging 5.

Polycystic Kidney Disease

• Can present with right flank pain due to cyst expansion, hemorrhage into cysts, or associated stone formation 7.
• Ultrasound reveals symmetrically enlarged kidneys with multiple cysts 7.

Page Kidney

• Rare cause presenting with flank pain and hematuria mimicking nephrolithiasis 8.
• Results from subcapsular hematoma compressing renal parenchyma, causing secondary hypertension through renin-angiotensin-aldosterone activation 8.
• May occur without recent trauma history 8.

Gastrointestinal Causes

Right Colonic Diverticulitis

• Seen in 8% of patients presenting with right lower quadrant/flank pain on CT imaging 9, 1.
• Can closely mimic appendicitis or urologic pathology 9.

Inflammatory Bowel Disease

• Crohn's disease with terminal ileitis can present with right-sided flank/lower quadrant pain 9, 1.
• CT frequently identifies this as an alternative diagnosis when appendicitis is excluded 9.

Gastroenteritis and Colitis

• Common non-appendiceal diagnoses on CT in patients with right-sided abdominal/flank pain 9, 1.
• Includes infectious enterocolitis such as typhlitis 9.

Bowel Obstruction

• Seen in 3% of patients with right lower quadrant pain on CT 9.
• Can cause referred pain to the flank region 9.

Appendicitis (Retrocecal)

• Retrocecal appendix location can present with predominant flank pain rather than classic right lower quadrant pain 9.
• CT has 95% sensitivity and 94% specificity for diagnosis 9.

Hepatobiliary Causes

Acute Cholecystitis

• Can present with right upper quadrant pain radiating to the right flank 9.
• Ultrasound is first-line imaging, showing gallbladder wall thickening, pericholecystic fluid, and sonographic Murphy's sign 9.

Chronic Cholecystitis/Biliary Dyskinesia

• Presents with recurrent right upper quadrant/flank pain 9.
• May require cholecystokinin-augmented hepatobiliary scintigraphy for diagnosis 9.

Ascending Cholangitis

• Can mimic acute cholecystitis with right-sided pain, but typically presents with Charcot's triad (fever, jaundice, right upper quadrant pain) 9.

Gynecologic Causes (Women)

Ovarian/Adnexal Pathology

• Benign adnexal masses are among the most common CT diagnoses in women with right lower quadrant/flank pain when appendicitis is excluded 9, 1.
• Includes ovarian cysts, torsion, and tubo-ovarian abscess 9.

Pelvic Congestion Syndrome

• Identified on CT as a cause of chronic right-sided pelvic/flank pain 9, 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.
• Requires immediate evaluation with ultrasound and β-hCG 1.

Musculoskeletal Causes

Paraspinal Muscle Strain

• Pain that occurs after prolonged static positioning and worsens with movement or palpation suggests musculoskeletal origin 1.
• Involves paraspinal muscles, facet joints, or referred pain from lumbar spine pathology 1.
• Pain is typically positional, unlike the position-independent pain of renal colic 1.

Vascular Causes

Renal Infarction

• Rare but important cause, often from embolic phenomena in patients with atrial fibrillation 2.

Key Diagnostic Approach

Imaging Selection Based on Clinical Scenario

For suspected urolithiasis:

• Non-contrast CT abdomen/pelvis is the gold standard, with 98-100% sensitivity and specificity regardless of stone size, location, or composition 1, 5, 2.
• Identifies alternative extraurinary diagnoses in approximately one-third of patients 1, 2.

For pregnant patients:

• Ultrasound is first-line to avoid radiation exposure, with up to 100% sensitivity for hydronephrosis 9, 1.
• Low-dose non-contrast CT may be used in second/third trimesters if ultrasound is non-diagnostic 9.

For suspected infection:

• Contrast-enhanced CT is preferred over non-contrast to evaluate for pyelonephritis or abscess 5.
• Pain worsening with external flank pressure is the key clinical clue 5.

For recurrent stone formers:

• Low-dose non-contrast CT or ultrasound to minimize cumulative radiation exposure 9, 1.
• Plain radiography has limited utility (only 29% sensitive overall, 72% for large proximal stones) 1.

Critical Red Flags Requiring Urgent Evaluation

• Fever, chills, or signs of systemic infection (suggests pyelonephritis or sepsis) 1.
• Inability to urinate or decreased urine output (suggests complete obstruction) 1.
• Hemodynamic instability or shock (suggests ruptured ectopic, hemorrhage, or sepsis) 1.
• Delayed menses in women of reproductive age (ectopic pregnancy until proven otherwise) 1.

Common Pitfalls to Avoid

• Do not assume all flank pain is kidney-related—the positional nature of symptoms distinguishes musculoskeletal from visceral causes 1.
• Do not miss ectopic pregnancy in young women—always consider gynecologic causes requiring urgent intervention 1.
• Do not use contrast-enhanced CT as first-line for suspected stones—contrast may obscure stones within the collecting system 5.
• Do not rely on plain radiography alone—it misses 71% of stones and provides no information about alternative diagnoses 1.

Management Implications Based on Etiology

For confirmed urolithiasis:

• Stones <5 mm typically pass spontaneously with conservative management 9, 1.
• Larger stones or complete obstruction may require endoscopic intervention 1.
• When no CT diagnosis is made, only 14% require hospitalization and 4% need intervention 9.
• When non-appendiceal CT diagnosis is established, 41% require hospitalization and 22% need surgical or image-guided intervention 9.