What is the recommended imaging for a patient with left flank pain?

Imaging for Left Flank Pain

CT abdomen and pelvis with IV contrast is the recommended first-line imaging modality for patients presenting with left flank pain, due to its high sensitivity and specificity for diagnosing the most common causes including diverticulitis and urolithiasis. 1

Diagnostic Algorithm for Left Flank Pain

First-Line Imaging

• CT Abdomen and Pelvis with IV contrast:
  • Gold standard for evaluating left flank pain
  • Reported overall accuracy of 98% 1
  • Provides comprehensive assessment of potential causes
  • Helps stratify patients for appropriate therapy
  • Can detect subtle bowel wall abnormalities and complications such as diverticular abscess 1
  • Identifies extraurinary causes of flank pain in about one-third of patients 2

Special Populations and Considerations

For suspected urolithiasis:

• Non-contrast CT is preferred:
  • Sensitivity and specificity near 100% for urinary tract calculi 1
  • Avoids contrast-related risks
  • Can be performed quickly (within 5 minutes) 2

For pregnant patients or young patients requiring radiation avoidance:

• Ultrasound (transabdominal):
  • First-line for pregnant patients
  • Can detect hydronephrosis, which is an indirect sign of obstruction
  • Less sensitive than CT but avoids radiation exposure
  • Can be directed to the area of maximal pain 1

For premenopausal women with possible gynecologic pathology:

• Transvaginal ultrasound:
  • Consider as initial imaging if gynecologic cause is suspected 1
  • May help avoid unnecessary CT scans

Strengths and Limitations of Different Modalities

CT Advantages

• Detects both urinary and extraurinary causes of pain
• Identifies complications requiring surgical intervention
• Guides appropriate management decisions
• Low-dose CT techniques can reduce radiation by 75-90% while maintaining diagnostic accuracy 1

MRI

• Not recommended as first-line for acute flank pain
• Less sensitive for extraluminal air and urinary tract calculi
• More time-consuming and subject to motion artifacts in symptomatic patients 1
• May have a role in differentiating diverticulitis from colon cancer in select cases 1

Plain Radiography

• Limited utility in evaluation of suspected diverticulitis or urolithiasis
• Can only demonstrate large amounts of retroperitoneal or intraperitoneal air
• Significantly less sensitive than CT 1
• Not recommended as initial imaging test 1

Contrast Enema

• Historically used but now supplanted by CT
• Will not show extraluminal abnormalities such as abscesses
• More invasive and less sensitive than CT
• Increases risk of colonic perforation in acute diverticulitis 1
• Not recommended for initial evaluation 1

Common Pitfalls to Avoid

1. Assuming all left flank pain is renal colic:

   • Left flank pain may be caused by diverticulitis, bowel obstruction, vascular conditions, or gynecological issues 3

2. Relying solely on clinical presentation:

   • Misdiagnosis based on clinical assessment alone occurs in 34-68% of cases 1
   • The classic triad of pain, fever, and leukocytosis for diverticulitis is present in only 25% of cases 1

3. Stopping at non-contrast CT when findings are equivocal:

   • While non-contrast CT is excellent for urolithiasis, IV contrast improves detection of other pathologies
   • However, adding contrast after initial non-contrast CT changes management in only 1.9% of cases 4

4. Overlooking alternative diagnoses:

   • Conditions like Page kidney, renal infarction, or appendicitis can present similarly to renal colic 3

In summary, CT abdomen and pelvis with IV contrast remains the imaging modality of choice for evaluating left flank pain, with modifications to the protocol based on specific clinical scenarios such as suspected urolithiasis (non-contrast CT) or pregnancy (ultrasound).