What is the cause of left flank pain and hematuria in a patient with normal renal ultrasound results?

Causes of Left Flank Pain and Hematuria with Normal Renal Ultrasound

Despite a normal renal ultrasound, patients with left flank pain and hematuria require further evaluation with CT urography as the most appropriate next step to identify potential causes such as small ureteral stones, nutcracker syndrome, or early malignancy.

Differential Diagnosis

When renal ultrasound is normal in a patient with left flank pain and hematuria, several conditions should be considered:

1. Urolithiasis (Small Ureteral Stones)

• Ultrasound has limited sensitivity for detecting ureteral stones, identifying only 38% of stones within the ureter 1
• Small stones may be missed on ultrasound but can still cause significant symptoms
• CT is significantly more sensitive with sensitivity and specificity both well above 90% 1

2. Nutcracker Syndrome

• Compression of the left renal vein between the abdominal aorta and superior mesenteric artery 2, 3
• Classic presentation includes hematuria and left flank pain 2, 4
• May be missed on standard renal ultrasound unless specifically evaluated with Doppler 1, 2
• More common in thin young adults and children 2

3. Page Kidney

• Compression of renal parenchyma by subcapsular hematoma causing hypertension 5
• Can present with flank pain and hematuria similar to nephrolithiasis 5
• May require CT angiography for definitive diagnosis

4. Early Urologic Malignancy

• Small renal cell carcinomas or urothelial tumors may not be visible on standard ultrasound 1
• Risk factors include smoking, obesity, and age >60 years 1, 6

5. Glomerular Diseases

• Various glomerulonephropathies can cause hematuria without visible structural abnormalities
• May coexist with other conditions (e.g., thin basement membrane disease with nutcracker syndrome) 4

Diagnostic Approach

1. Laboratory Evaluation

   • Complete urinalysis with microscopic examination
   • Urine culture to rule out infection
   • Complete blood count, BUN, and creatinine
   • 24-hour urine collection for protein if glomerular disease is suspected 6

2. Imaging

   • CT Urography is the preferred next step with 92% sensitivity and 93% specificity 6
   • For patients with contrast allergy or renal insufficiency, MR Urography is an alternative 6
   • Doppler ultrasound specifically evaluating the left renal vein if nutcracker syndrome is suspected 2, 3

3. Cystoscopy

   • Recommended for all patients ≥35 years with persistent hematuria 6
   • Essential for evaluating lower urinary tract sources of bleeding

Management Based on Diagnosis

• Urolithiasis: Medical expulsive therapy or surgical intervention depending on stone size and location
• Nutcracker Syndrome:
  • Conservative management in children and young adults due to high spontaneous remission rate 2
  • Endovascular stenting for persistent, severe symptoms 7, 3
• Page Kidney:
  • Hypertension management with ACE inhibitors
  • Possible surgical evacuation of hematoma in severe cases 5
• Urologic Malignancy:
  • Treatment depends on type, stage, and grade
  • Options range from surveillance to surgical resection 1

Follow-up Recommendations

For patients with negative initial evaluation but persistent hematuria:

• Low-risk patients: Annual urinalysis
• Intermediate/high-risk patients: Consider urine cytology and repeat urinalysis at 6,12,24, and 36 months 6

Common Pitfalls to Avoid

• Assuming UTI is the cause: Urologic malignancy may be present even with a positive urine culture 6
• Attributing hematuria to anticoagulants: Anticoagulant therapy should not be assumed as the sole cause of hematuria 6
• Relying solely on ultrasound: Ultrasound has limited sensitivity for ureteral stones and small malignancies 1
• Missing multifactorial causes: Hematuria may have more than one cause (e.g., anatomical abnormality plus glomerular disease) 4