What are the next steps for a 20-60 year old patient with ongoing right flank pain and a negative computed tomography (CT) scan result, with no significant past medical history?

Right Flank Pain with Negative CT: Next Steps

Proceed with ultrasound to evaluate for gynecologic pathology in women or consider MRI for hepatobiliary/pancreatic causes, while simultaneously reassessing for musculoskeletal origins and ensuring adequate follow-up imaging if symptoms persist, as alternative diagnoses are identified in approximately one-third of patients with negative initial imaging. 1

Immediate Reassessment Priorities

Verify CT Protocol and Timing

• Confirm the CT was performed with IV contrast, as non-contrast CT has very limited diagnostic value for many abdominal pathologies beyond stone disease 2
• Consider that timing matters: early imaging may miss evolving pathology like appendicitis or diverticulitis 2
• Review the CT report specifically for extraurinary findings, as CT identifies alternative diagnoses in 23-45% of cases even when the primary suspected diagnosis is excluded 3

Distinguish Pain Characteristics

• Position-dependent pain suggests musculoskeletal origin (paraspinal muscles, facet joints, lumbar spine pathology), particularly if occurring after prolonged static positioning 1
• Colicky, wave-like pain independent of position radiating to groin/genitals suggests renal colic, even with negative CT 1, 4
• Pain that resolved and recurred may indicate intermittent ovarian torsion in women or spontaneous stone passage 5

Gender-Specific Evaluation

For Women (Age 20-60)

• Pelvic ultrasound (transabdominal + transvaginal) is the next appropriate step to evaluate gynecologic causes including ovarian torsion, adnexal masses, pelvic congestion syndrome, or ectopic pregnancy 2, 1, 3
• Combined ultrasound achieves 97.3% sensitivity and 91% specificity for gynecologic pathology in adult women 3
• Consider delayed menses history to rule out ectopic pregnancy, which can present as flank pain 1

For All Patients

• Urinalysis may be negative in over 20% of confirmed urinary stones, so absence of hematuria does not exclude stone disease 1
• Ultrasound can detect hydronephrosis with up to 100% sensitivity, making larger stones (>5 mm) less likely if absent 1

Alternative Diagnoses to Pursue

Gastrointestinal Causes

• Right colonic diverticulitis can precisely mimic renal colic and is increasingly common with age 1, 3
• Gastroenteritis, colitis, inflammatory bowel disease are common CT diagnoses in patients with flank pain 2, 1
• Consider constipation as a benign but common cause 2

Hepatobiliary/Pancreatic Pathology

• If right upper quadrant component exists, MRI with MRCP is superior to CT for biliary sources of pain, with 85-100% sensitivity for cholelithiasis/choledocholithiasis 2
• MRI can distinguish acute from chronic cholecystitis based on T2 signal characteristics 2

Rare but Critical Diagnoses

• Retroperitoneal fibrosis can present with flank pain and may not be apparent on initial CT; consider if bilateral hydronephrosis develops 6
• Page kidney (subcapsular hematoma causing secondary hypertension) presents identically to nephrolithiasis with flank pain and hematuria 7
• Check blood pressure: new hypertension with flank pain warrants contrast-enhanced CT or CTA 7

Imaging Algorithm for Persistent Pain

If CT Was Non-Contrast Only

• Repeat CT with IV contrast to evaluate for inflammatory conditions, vascular pathology, and soft tissue abnormalities 2
• IV contrast is essential for optimal diagnostic accuracy in non-stone etiologies 3

If CT Was Contrast-Enhanced and Negative

• Ultrasound for gynecologic (women) or simple renal cysts 1, 3
• MRI abdomen with MRCP if hepatobiliary source suspected or CT findings equivocal 2
• Low-dose repeat CT in 7 days if symptoms persist and initial imaging was early in disease course 1, 8

Management Based on Clinical Context

Red Flags Requiring Urgent Re-evaluation

• Fever, chills, or signs of systemic infection mandate immediate hospital admission regardless of imaging 1
• Hemodynamic instability requires urgent evaluation for vascular emergency 1, 7
• Inability to urinate or decreased urine output needs urgent assessment 1
• Recurrence within 72 hours warrants repeat imaging 5

Outpatient Management with Close Follow-Up

• Maintain high fluid intake and strain urine to catch potential stones 1
• Rapid analgesia (NSAIDs preferred) with reassessment within 1 hour 1
• Telephone follow-up at 1 hour after initial analgesia 1
• Fast-track repeat imaging within 7 days if managed outpatient with persistent symptoms 1
• Only 14% require hospitalization and 4% need intervention when CT shows no diagnosis, compared to 41% and 22% respectively when alternative diagnosis is identified 1

Common Pitfalls to Avoid

• Do not assume negative CT excludes all pathology: CT sensitivity for stones is 95-100%, but rare lucent stones exist 4, 9
• Do not delay imaging in young females: consider gynecologic causes requiring urgent intervention like ovarian torsion 1, 5
• Do not miss ectopic pregnancy in women with delayed menses 1
• Do not ignore positional characteristics: this distinguishes musculoskeletal from visceral pain 1
• Normal urinalysis does not exclude stone disease: over 20% of confirmed stones have negative urinalysis 1
• In obese patients (BMI >31), standard-dose CT may be needed as low-dose protocols have inadequate image quality 8