Acute Abdominal Emergencies — Part 1: Systematic Approach to Acute Abdominal Pain & Appendicitis

1. Systematic Approach to Acute Abdominal Pain

1.1 Overview

Acute abdominal pain is the most common reason for surgical consultation in the emergency department, representing approximately 5% to 10% of all ED visits. The differential diagnosis ranges from benign, self-limited conditions to life-threatening surgical emergencies. A structured, systematic approach that integrates history, physical examination, laboratory evaluation, and targeted imaging is essential for accurate diagnosis and timely intervention.^{1 2}

The primary goals in the initial evaluation of acute abdominal pain are:

1. Identify immediately life-threatening conditions requiring emergent intervention (ruptured AAA, mesenteric ischemia, perforated viscus, ruptured ectopic pregnancy)
2. Determine whether operative intervention is needed and the urgency of that intervention
3. Establish a working diagnosis to guide further management
4. Initiate appropriate resuscitation while the workup proceeds

1.2 History — Key Elements

A thorough history remains the most important diagnostic tool. The following elements should be systematically elicited:

Pain Characterization (OPQRST Framework)

Associated Symptoms

1.3 Physical Examination — Systematic Approach and Pearls

Vital Signs Assessment

Vital signs provide the first indication of hemodynamic stability and systemic compromise:

• Tachycardia (HR > 100): Early sign of hypovolemia, sepsis, or pain
• Hypotension (SBP < 90): Late sign — consider hemorrhagic shock (ruptured AAA, ruptured ectopic), septic shock, or third-spacing
• Fever (>38.0 C): Inflammatory/infectious process
• Tachypnea (RR > 20): Metabolic acidosis (lactate, DKA), diaphragmatic irritation, pain

Abdominal Examination Technique

1. Inspection: Distension (obstruction, ascites), surgical scars (adhesions), visible peristalsis (SBO), ecchymosis (Cullen sign — periumbilical, Grey Turner sign — flank)
2. Auscultation: High-pitched/tinkling (early SBO), absent bowel sounds (ileus, late obstruction, peritonitis)
3. Percussion: Tympany (distension, free air), shifting dullness (ascites), loss of hepatic dullness (pneumoperitoneum)
4. Palpation: Begin in the quadrant farthest from the reported pain location; assess for:
   • Localized vs diffuse tenderness
   • Guarding (voluntary vs involuntary)
   • Rigidity (board-like rigidity = peritonitis)
   • Rebound tenderness
   • Palpable masses (AAA, hernia, abscess)

Classic Physical Exam Signs

1.4 Differential Diagnosis by Pain Location

1.5 Laboratory Evaluation

The following laboratory studies should be considered in the evaluation of acute abdominal pain. Not every test is required for every patient — the clinical scenario guides laboratory selection.^{2 3}

1.6 Imaging Strategy

First-Line Imaging by Clinical Scenario

CT Abdomen/Pelvis — Technical Considerations

• IV contrast: Standard for most acute abdominal pain evaluations. Enhances detection of inflammatory conditions, vascular pathology, and solid organ injury
• Oral contrast: Generally NOT needed in the acute setting — delays imaging and current-generation CT scanners with IV contrast are sufficient. May be considered for suspected leak/fistula
• PO and IV contrast: Consider in thin patients with minimal intra-abdominal fat where IV contrast alone may limit bowel delineation
• CT angiography (CTA): Indicated specifically for suspected mesenteric ischemia and AAA — arterial phase imaging is essential

Plain Radiographs (Abdominal X-ray)

Plain films have limited utility in the era of CT but may be useful for:

• Bowel obstruction: Air-fluid levels, dilated loops (sensitivity ~70% for SBO, but misses early obstruction)
• Pneumoperitoneum: Free air under diaphragm on upright chest X-ray (sensitivity ~80% for perforation; CT is far more sensitive)
• Foreign body: Ingested objects, retained surgical material
• Constipation/fecal loading: When clinical history suggests functional etiology

2. Acute Appendicitis

2.1 Epidemiology and Pathophysiology

Acute appendicitis is the most common surgical emergency worldwide, with a lifetime risk of approximately 7% to 8%. Peak incidence occurs in the second and third decades of life. The classic pathophysiological model involves luminal obstruction (by fecalith, lymphoid hyperplasia, or rarely tumor) leading to increased intraluminal pressure, bacterial overgrowth, venous congestion, ischemia, and ultimately perforation if untreated.¹

The classic symptom progression — periumbilical visceral pain migrating to the right lower quadrant as localized parietal peritoneal inflammation develops — occurs in approximately 50% to 60% of patients. Atypical presentations are common, particularly in:

• Retrocecal appendix (30% of cases): Flank or back pain; less pronounced RLQ findings
• Pelvic appendix: Suprapubic pain, urinary symptoms, diarrhea
• Elderly patients: Blunted inflammatory response; often present late with perforation
• Pregnant patients: Appendix displaced cephalad by the gravid uterus; RUQ pain in third trimester
• Immunocompromised patients: Diminished leukocytosis and peritoneal signs

2.2 Clinical Scoring Systems

Alvarado Score (MANTRELS)

The Alvarado score, first described in 1986, remains one of the most widely used clinical prediction tools for appendicitis. It assigns points based on symptoms, signs, and laboratory findings.^{1 4}

Interpretation:

Appendicitis Inflammatory Response (AIR) Score

The AIR score was developed to improve upon the Alvarado score by incorporating CRP and refining the weighting of inflammatory markers. It has demonstrated superior discrimination compared to the Alvarado score in validation studies.^{1 5}

Interpretation:

2.3 Imaging for Appendicitis

CT Abdomen/Pelvis with IV Contrast

CT is the imaging modality of choice for suspected appendicitis in adults.^{1 6}

CT Findings of Appendicitis:

• Dilated appendix (diameter >6 mm, measured outer wall to outer wall)
• Appendiceal wall thickening and enhancement
• Periappendiceal fat stranding (most sensitive CT sign)
• Appendicolith (present in approximately 25% of cases; associated with increased perforation risk)
• Periappendiceal fluid
• Abscess (indicates complicated appendicitis)
• Extraluminal air (indicates perforation)
• Phlegmon (inflammatory mass without drainable fluid collection)

Ultrasound

Ultrasound is the preferred first-line imaging modality in children and pregnant patients.^{1 7}

Ultrasound Findings of Appendicitis:

• Non-compressible appendix with diameter >6 mm (graded compression technique)
• Target sign (concentric rings on transverse view)
• Appendicolith with posterior acoustic shadowing
• Periappendiceal fluid
• Increased periappendiceal echogenicity (fat stranding equivalent)
• Loss of the normal wall layer structure

Important: A non-visualized appendix on ultrasound does NOT exclude appendicitis. If clinical suspicion remains, proceed to CT (adults) or MRI (pregnant patients).

MRI in Pregnancy

MRI without gadolinium is the second-line imaging modality when ultrasound is inconclusive in pregnant patients.⁷

2.4 Classification: Uncomplicated vs Complicated Appendicitis

2.5 Management of Acute Appendicitis

Uncomplicated Appendicitis — Surgical Management

Appendectomy remains the standard of care for uncomplicated appendicitis in most practice settings. Both laparoscopic and open approaches are acceptable, with laparoscopic appendectomy preferred in most patients due to:^{1 6}

• Reduced wound infection rates
• Shorter hospital stay
• Faster return to normal activity
• Improved cosmesis
• Better visualization (especially in obese patients and women of reproductive age where the diagnosis may be uncertain)

Timing: Surgery should be performed within 24 hours of diagnosis. Evidence from multiple systematic reviews and randomized controlled trials demonstrates that delaying appendectomy beyond 24 hours is associated with increased complication rates, though delay up to 24 hours from presentation (for nighttime cases to be performed the following morning) is safe and does not increase perforation risk.¹

Uncomplicated Appendicitis — Antibiotic-Only (Non-operative) Management

The concept of managing uncomplicated appendicitis with antibiotics alone has been the subject of multiple randomized controlled trials. The landmark CODA trial (Comparison of Outcomes of Antibiotic Drugs and Appendectomy) provided the most definitive evidence to date.⁸

CODA Trial Key Findings (2020):

Key Takeaways from Antibiotic-Only Management:

1. Antibiotics are a reasonable first-line option for selected patients with uncomplicated appendicitis without an appendicolith who are informed of the risks
2. Patients with an appendicolith have significantly higher failure rates (29% crossover to surgery within 90 days) and antibiotic-only management is not recommended for this subgroup
3. Overall complication rates are higher with antibiotic-only management, primarily driven by the appendicolith subgroup
4. Approximately 40% of patients who initially respond to antibiotics will experience recurrence within 5 years
5. Appendicitis recurrence after antibiotic treatment is not associated with increased perforation rates

Antibiotic regimens for non-operative management (typically 10 days total):

• IV phase (minimum 24–48h if admitted): Ertapenem 1g IV daily OR ceftriaxone 2g IV daily + metronidazole 500mg IV q8h
• Oral transition: Amoxicillin-clavulanate 875/125mg PO BID OR ciprofloxacin 500mg PO BID + metronidazole 500mg PO TID

Complicated Appendicitis — Management

Perforation with diffuse peritonitis: Emergent appendectomy (laparoscopic preferred if technically feasible).¹

Periappendiceal abscess (>3–5 cm):

• Initial management: IV antibiotics + CT-guided percutaneous drainage
• Interval appendectomy: Considered 6–8 weeks after resolution; however, recent evidence suggests interval appendectomy may not be necessary in all adults. The risk of underlying malignancy increases with age (>5% in patients >40 years), supporting interval appendectomy or at minimum, follow-up colonoscopy in older patients
• Indications for interval appendectomy: Recurrent symptoms, patient preference, concern for underlying neoplasm (especially age >40)

Phlegmon (inflammatory mass without drainable collection):

• IV antibiotics and close monitoring
• Surgery only if clinical deterioration
• Consider interval appendectomy as above

2.6 Special Populations

Pediatric Appendicitis

• Diagnosis: Ultrasound is the preferred first-line imaging modality; CT only if US is inconclusive and clinical suspicion remains high
• Pediatric Appendicitis Score (Samuel): Validated clinical scoring system specifically for children (includes right iliac fossa tenderness, cough/hopping/percussion tenderness, migration, anorexia, nausea/vomiting, fever, leukocytosis, neutrophilia)
• Management: Appendectomy remains the standard; antibiotic-only management is under active investigation in pediatric populations and may be considered in selected cases based on shared decision-making
• Perforation rates: Higher in younger children (<5 years) due to delayed diagnosis and rapid progression; omentum is less developed and provides less containment⁷

Appendicitis in Pregnancy

• Incidence: Most common non-obstetric surgical emergency in pregnancy (approximately 1 in 1,000–2,000 pregnancies)
• Diagnostic challenges: Appendix displacement by gravid uterus; physiologic leukocytosis of pregnancy (WBC up to 15,000/mcL is normal in pregnancy, up to 29,000/mcL in labor); nausea is common in early pregnancy
• Imaging: Ultrasound first; MRI without gadolinium if US is inconclusive. CT should be reserved for cases where MRI is unavailable and clinical suspicion is high — the risk of missed appendicitis (perforation, fetal loss) outweighs radiation risk
• Management: Prompt appendectomy (laparoscopic approach is safe in all trimesters). Delay increases perforation risk, which is associated with fetal loss rates of 20–35% (vs <2% with uncomplicated appendicitis in pregnancy)
• Positioning: Left lateral tilt to avoid aortocaval compression after 20 weeks gestation^{1 7}

Elderly Patients

• Presentation: Often atypical — less pronounced pain, minimal fever, blunted leukocytosis
• Perforation rate: Significantly higher (40–70%) due to delayed presentation and diagnosis
• Mortality: 10-fold higher than younger adults
• Recommendation: Low threshold for CT imaging; high index of suspicion even with mild symptoms. Evaluate for underlying cecal malignancy (colonoscopy or CT colonography should be considered in patients >40 years if not recently performed)¹

References