How should an adult with central lower abdominal pain be evaluated and managed?

Evaluation and Management of Central Lower Abdominal Pain in Adults

For an adult presenting with central lower abdominal pain, obtain a beta-hCG test in all women of reproductive age, assess vital signs for tachycardia (the most sensitive early warning sign of surgical complications), and proceed directly to CT of the abdomen and pelvis with IV contrast as the optimal initial imaging study. 1, 2, 3

Immediate Clinical Assessment

Critical Vital Signs and Red Flags

• Tachycardia is your most important early warning sign—it predicts serious complications including anastomotic leak, perforation, or sepsis even before other symptoms develop 1, 2, 3
• The combination of fever, tachycardia, and tachypnea together strongly predicts surgical complications 1, 2
• Severe pain out of proportion to physical examination findings should be assumed to be acute mesenteric ischemia until proven otherwise 1, 2
• Signs of peritonitis (rigid abdomen, rebound tenderness) require urgent surgical evaluation 1, 2

Essential History Elements

• Document the last bowel movement and passage of gas—this has 85% sensitivity and 78% specificity for predicting adhesive small bowel obstruction in patients with prior abdominal surgery 1
• Abrupt or instantaneous onset of severe pain suggests vascular catastrophe, particularly aortic dissection or mesenteric ischemia 1
• Colicky pain indicates bowel obstruction as the bowel attempts to overcome occlusion 1
• The triad of abdominal pain, constipation, and vomiting suggests sigmoid volvulus 1
• Any prior laparotomy makes adhesive obstruction the leading diagnosis, accounting for 55-75% of small bowel obstructions 1

Mandatory Laboratory Testing

Before any imaging, obtain: 1, 2, 3

• Beta-hCG in all women of reproductive age—this is mandatory before proceeding with CT to rule out ectopic pregnancy 1, 2, 3
• Complete blood count to evaluate for leukocytosis 1, 2, 3
• Comprehensive metabolic panel including liver function tests 3
• Serum lipase (more specific than amylase) for suspected pancreatitis 3
• Urinalysis to evaluate for urinary tract infection or nephrolithiasis 3

Laboratory Interpretation Nuances

• High C-reactive protein has superior sensitivity and specificity compared to white blood cell count for ruling in surgical disease, though normal CRP does not exclude complications 1, 2
• Elevated lactate suggests ischemia or sepsis, but normal lactate does not exclude internal herniation or early ischemia 1, 2
• In elderly patients, many laboratory tests may be normal despite serious infection—do not over-rely on normal laboratory values early in disease 1, 2

Imaging Strategy

Primary Recommendation

CT of the abdomen and pelvis with IV contrast is the optimal initial imaging choice for acute central lower abdominal pain, particularly when fever is present or serious pathology is suspected 1, 2, 3

Specific Imaging Protocols

• Use IV contrast whenever possible for optimal evaluation of vascular structures, bowel wall enhancement, and soft tissue pathology 3
• Scan the entire abdomen and pelvis rather than limiting coverage based on symptoms—limited scanning visualized all acute pathology in only 33% of abnormal cases 3
• If IV contrast is contraindicated, non-contrast CT is still appropriate but has reduced sensitivity 3

Alternative Imaging in Special Populations

• In pregnant patients with negative or equivocal ultrasound findings, MRI is the preferred next step to avoid radiation exposure 3
• Conventional radiography has limited diagnostic value and should not be routinely ordered 1

Differential Diagnosis by Clinical Presentation

Most Common Causes in Central Lower Abdomen

• Acute appendicitis accounts for 15.9-28.1% of cases requiring surgery 1, 4, 5
• Small bowel obstruction accounts for 15% of acute abdominal pain admissions, most commonly caused by adhesions, hernias, and neoplasms 1
• Diverticulitis (can be right-sided or left-sided) 4, 5
• Sigmoid volvulus—classic patient is elderly, institutionalized, and on psychotropic medications 1

Critical Diagnoses Not to Miss

• Mesenteric ischemia—the triad of abdominal pain, fever, and hemocult-positive stools occurs in approximately one-third of patients 1
• Bowel perforation or anastomotic leak 1, 2
• Internal herniation (especially in post-bariatric surgery patients) 1, 2

Special Population Considerations

Elderly Patients

• Have a higher likelihood of malignancy, diverticulitis, and vascular causes 1, 2
• May present with atypical symptoms requiring more thorough evaluation even with normal laboratory tests 1, 2

Post-Bariatric Surgery Patients

• Often present with atypical symptoms, and classic peritoneal signs are frequently absent 1, 2
• Internal herniation should be considered even with normal lactate 1, 2

Women of Reproductive Age

• Always consider gynecologic conditions including ectopic pregnancy, ovarian torsion, and pelvic inflammatory disease 1, 2, 3

Management Based on Diagnosis

Surgical Conditions

• Appendicitis patients should be admitted 4
• Bowel obstruction, perforation, and mesenteric ischemia require urgent surgical consultation 1, 4

Medical Management

• Diverticulitis can frequently be managed on an outpatient basis with antibiotics, but may require admission and surgical consultation 4
• Inflammatory bowel disease may be managed outpatient or require admission depending on severity 4

Critical Pitfalls to Avoid

• The absence of peritonitis on examination does not exclude bowel ischemia—patients with sigmoid volvulus often lack peritoneal signs despite established ischemia due to chronic distension masking the examination 1, 2
• Do not over-rely on normal laboratory values, especially in elderly patients 1, 2
• Avoid overuse of repeat CT scans—diagnostic yield drops from 22% on initial presentation to 5.9% on the fourth CT or greater 3
• In patients with abdominal pain plus diarrhea, CT changed management in only 11% versus 53% in patients with pain alone—use a thoughtful approach in this setting 3