What is the best initial imaging choice for a patient presenting with abdominal distention and left lower quadrant pain, considering a KUB (Kidney, Ureter, Bladder) X-ray?

Imaging for Abdominal Distention and Left Lower Quadrant Pain

A KUB (plain abdominal radiograph) is not appropriate as the initial imaging test for abdominal distention with left lower quadrant pain—you should order a CT abdomen and pelvis with IV contrast instead. 1

Why KUB is Inadequate

Plain abdominal radiography has extremely limited diagnostic value for evaluating left lower quadrant pain and suspected diverticulitis. 2 While a KUB can demonstrate large amounts of free intraperitoneal or retroperitoneal air, it is significantly less sensitive than CT for detecting small amounts of air and provides no information about the underlying cause of symptoms. 2 The American College of Radiology explicitly states that plain radiography is not useful as an initial test for left lower quadrant pain due to limited sensitivity. 1

The Preferred Imaging Choice

CT abdomen and pelvis with IV contrast is the gold standard initial imaging test, with 98% diagnostic accuracy. 3 The American College of Radiology rates this modality as 8/9 (usually appropriate) for evaluating left lower quadrant pain. 3

Key Advantages of CT with IV Contrast:

• Identifies the underlying diagnosis including diverticulitis (the most common cause in adults), appendicitis, bowel obstruction, perforation, abscess, and malignancy 2, 1, 3
• Detects complications such as perforation, abscess formation, fistula, and bowel obstruction that require immediate intervention 1, 3
• Reveals alternative diagnoses that present with similar symptoms, with sensitivity ranging from 50-100% compared to only 33-78% for ultrasound 2
• Guides treatment decisions by determining disease severity and whether outpatient management, antibiotics, percutaneous drainage, or surgery is needed 3
• Reduces hospital admissions by more than 50% through accurate risk stratification 3

Special Population Considerations

For premenopausal women with suspected gynecologic pathology (ectopic pregnancy, pelvic inflammatory disease, ovarian torsion), transvaginal/pelvic ultrasound is the preferred initial test. 2, 1 However, if gynecologic causes are excluded clinically or sonographically, proceed directly to CT. 3

What to Look for on CT

The radiologist should specifically evaluate for:

• Bowel wall thickening with pericolonic fat stranding (suggests diverticulitis) 3
• Extraluminal air or free fluid (indicates perforation requiring emergency surgery) 3
• Abscess size and location (determines whether percutaneous drainage is needed: <4 cm = antibiotics alone; ≥4 cm = drainage + antibiotics) 3
• Pericolonic lymphadenopathy >1 cm (strongly suggests perforated colon cancer rather than diverticulitis and mandates colonoscopy) 3, 4
• Degree of bowel distention and transition points (evaluates for obstruction) 3

Critical Red Flags Requiring Emergency Evaluation

Proceed immediately to CT if the patient has any of these features:

• Fever with inability to pass gas or stool (suggests obstruction or complicated diverticulitis) 3
• Severe abdominal tenderness with guarding or rebound (indicates peritonitis from perforation) 3
• Signs of shock (tachycardia, hypotension, altered mental status suggesting sepsis) 3
• Progressively worsening pain over several days 3

Alternative Imaging Modalities (When CT is Not Available)

• CT without IV contrast is acceptable when IV contrast is contraindicated (renal failure, severe contrast allergy), though it is less accurate for detecting abscesses. 3 The American College of Radiology rates this as 6/9. 3
• Ultrasound with graded compression has variable sensitivity (77-98%) and specificity (80-99%) for diverticulitis but is operator-dependent, limited in obese patients, and misses many alternative diagnoses. 2 It is not widely used in the United States for this indication. 2
• MRI has sensitivity of 86-94% and specificity of 88-92% for diverticulitis but has longer scan times, greater susceptibility to motion artifact, higher cost, decreased availability, and difficulty detecting extraluminal air. 2

Common Pitfalls to Avoid

• Do not rely on clinical diagnosis alone—misdiagnosis rates are 34-68% without imaging. 3
• Do not assume diverticulitis without imaging—perforated colon cancer can present identically, and the only reliable distinguishing feature is pericolonic lymphadenopathy >1 cm on CT. 4
• Do not order a KUB thinking it will provide useful diagnostic information—it will only delay definitive diagnosis and appropriate treatment. 2, 1
• Do not skip imaging in elderly patients with atypical presentations—they may have serious pathology without classic symptoms. 5