What is the differential diagnosis for a patient with right flank pain radiating down to the right buttocks and leg for one month?

Differential Diagnosis for Right Flank Pain Radiating to Right Buttocks and Leg for One Month

The most likely diagnoses include urolithiasis (kidney stone), lumbar radiculopathy, iliopsoas pathology (abscess or hematoma), iliac artery occlusive disease, and less commonly retroperitoneal pathology or referred pain from intra-abdominal sources.

Primary Urologic Considerations

Urolithiasis (Kidney Stone Disease)

• Ureterolithiasis is the most common cause of acute flank pain, though the one-month duration suggests either recurrent episodes or chronic partial obstruction 1.
• Classic presentation includes colicky, wave-like severe pain radiating to the groin or genitals, though radiation to the buttock can occur with proximal ureteral stones 2.
• Importantly, over 20% of patients with confirmed urinary stones may have negative urinalysis, so absence of hematuria does not exclude stone disease 2.
• Non-contrast CT abdomen/pelvis demonstrates 98-100% sensitivity and specificity for detecting stones regardless of size, location, or composition 1, 3.

Other Renal Pathology

• Page kidney (subcapsular hematoma causing renal compression) can present with flank pain and hematuria, mimicking nephrolithiasis 4.
• Hydronephrosis from any cause of ureteral obstruction should be considered 5.

Musculoskeletal and Neurologic Causes

Lumbar Radiculopathy

• Pain radiating from the spine into the buttock and leg lasting one month strongly suggests radicular pain or painful radiculopathy involving L2-L4 nerve roots 6.
• The one-month duration and radiation pattern are more consistent with nerve root pathology than acute visceral causes 2.
• Pain occurring after prolonged static positioning favors musculoskeletal origin involving paraspinal muscles, facet joints, or referred pain from lumbar spine pathology 2.

Iliopsoas Muscle Pathology

• Right flank pain combined with buttock/leg symptoms requires urgent evaluation for psoas abscess or retroperitoneal pathology, as this combination suggests iliopsoas muscle involvement 7.
• Psoas involvement causes hip flexion weakness and pain with hip extension; retroperitoneal pathology can affect the lumbar plexus (L2-L4 nerve roots) 7.
• Femoral neuropathy from compression or inflammation is possible 7.

Vascular Considerations

Iliac Artery Occlusive Disease

• Claudication involving the right buttock with gradually increasing symptoms over months suggests iliac artery stenosis or occlusion 8.
• This typically presents in patients with diabetes, hypertension, and smoking history 8.
• CTA pelvis with runoff can reveal common iliac artery stenosis or occlusion 8.

Intra-Abdominal and Gastrointestinal Causes

Right-Sided Colonic and Appendiceal Pathology

• Right colonic diverticulitis, appendicitis (especially retrocecal), and inflammatory bowel disease can present as right-sided flank pain 2.
• However, the one-month duration and radiation to buttock/leg make these less likely unless there is chronic inflammation or abscess formation 8.
• If appendicitis is suspected with atypical presentation, CT abdomen and pelvis with IV contrast is usually appropriate 8.

Hepatobiliary Causes

• Hepatic and biliary abnormalities can cause right flank pain but typically do not radiate to the buttock and leg 9.

Gynecologic Causes (if applicable)

• Benign adnexal masses and pelvic congestion syndrome can cause flank pain in women 2.

Recommended Diagnostic Approach

Initial Imaging

• Contrast-enhanced CT abdomen and pelvis with IV contrast is the imaging modality of choice for this presentation, with sensitivities ranging from 85.7% to 100% for acute abdominal pathology 7.
• CT can identify retroperitoneal collections, psoas abscesses, stones, and alternative diagnoses beyond typical urologic causes 7.
• Non-contrast CT is preferred if urolithiasis is the primary concern, as it avoids contrast nephrotoxicity while maintaining excellent stone detection 1, 3.

Alternative Imaging

• MRI may be appropriate when CT is contraindicated and is useful for visualizing soft tissue pathology including nerve root compression 9.
• Ultrasound has 96% sensitivity when combining findings of pyeloureteral dilation, direct stone visualization, and absence of ureteral ejaculation, but is less comprehensive for alternative diagnoses 9, 1.

Critical Red Flags Requiring Urgent Evaluation

• Fever, chills, or signs of systemic infection suggest infected hydronephrosis or psoas abscess requiring immediate intervention 2, 7.
• Hip flexion weakness or neurologic deficits indicate possible psoas abscess or severe nerve root compression 7.
• Hemodynamic instability or shock requires urgent evaluation 2.
• Inability to urinate or decreased urine output mandates urgent assessment 2.

Common Pitfalls to Avoid

• Do not assume all flank pain is kidney-related—the radiation to buttock and leg is a key distinguishing feature suggesting alternative pathology 2.
• Do not assume appendicitis based solely on right-sided pain—the buttock/leg radiation is a red flag for alternative pathology 7.
• Do not delay imaging based on negative urinalysis, as significant pathology can exist without hematuria 2.
• Do not miss psoas abscesses, as they can lead to sepsis and require prompt drainage 7.