What is the recommended evaluation and first‑line treatment for a patient with suspected acute appendicitis?

Evaluation and First-Line Treatment of Suspected Acute Appendicitis

Appendectomy—either laparoscopic or open—remains the gold-standard first-line treatment for acute appendicitis, offering definitive cure with lower recurrence rates and superior long-term outcomes compared to antibiotics alone. 1

Initial Clinical Evaluation

Obtain a focused history and physical examination targeting specific high-yield findings:

• Classic symptom progression: Vague periumbilical pain migrating to the right lower quadrant, followed by anorexia, nausea, and low-grade fever makes appendicitis highly likely 2, 3
• Physical examination findings that rule in appendicitis in adults: Right lower quadrant pain, abdominal rigidity, and periumbilical pain radiating to the right lower quadrant 3
• Additional predictive signs: Positive psoas sign, positive obturator sign, positive Rovsing sign, rebound tenderness, and guarding 1, 4, 3
• In children specifically: Absent or decreased bowel sounds, positive psoas sign, positive obturator sign, and positive Rovsing sign are most reliable 4, 3

Laboratory testing should include:

• Complete blood count with differential looking for WBC >10,000/mm³ and left shift 1, 4
• C-reactive protein (CRP), with CRP ≥8-10 mg/L being highly predictive 4
• The combination of WBC >10,000/mm³ AND CRP ≥8 mg/L has a positive likelihood ratio of 23.32 4

Risk Stratification Using Clinical Scores

Apply validated scoring systems to guide imaging decisions:

• For adults: Use the AIR (Appendicitis Inflammatory Response) score or Adult Appendicitis Score, which have the highest discriminating power 4
• For children: Use the Pediatric Appendicitis Score or Alvarado score 4, 3
• Do NOT use the Alvarado score alone to confirm appendicitis in adults due to insufficient specificity, though it helps exclude the diagnosis 4

Risk-stratified management pathway:

• Low-risk patients: Discharge with 24-hour follow-up, minimal or no imaging required 4
• Intermediate-risk patients: Proceed to imaging (see below) 4
• High-risk patients (AIR 9-12, Alvarado 9-10, or strong clinical suspicion): Refer directly to surgeon; in patients <40 years old, may proceed to surgery without imaging 4

Imaging Strategy

Non-Pregnant Adults

CT abdomen and pelvis with IV contrast is the recommended initial imaging modality for intermediate-to-high risk patients, with sensitivity 96-100% and specificity 93-95%. 1, 4, 2

• IV contrast is essential—it increases sensitivity to 96% compared to unenhanced CT 4
• Oral contrast is unnecessary and delays diagnosis without improving accuracy 4
• For adolescents and young adults, use low-dose CT with contrast to reduce radiation exposure 4

Children and Adolescents

Ultrasound is the first-line imaging modality to avoid radiation, with sensitivity 76% and specificity 95%. 4, 5

• If ultrasound is equivocal or non-diagnostic and clinical suspicion persists, proceed directly to CT with IV contrast (sensitivity 96-100%, specificity 93-95%) or MRI without IV contrast (sensitivity 94%, specificity 96%) 4, 5
• Do not repeat ultrasound after an initial non-diagnostic study 4
• Point-of-care ultrasound by emergency physicians or surgeons shows higher accuracy (sensitivity 91%, specificity 97%) 4

Pregnant Patients

Ultrasound is the initial imaging choice. 4

• If ultrasound is inconclusive, MRI without IV contrast is preferred over CT (sensitivity 94%, specificity 96%) to avoid fetal radiation 1, 4
• A negative or inconclusive MRI does not rule out appendicitis; surgery should be considered if clinical suspicion remains high 4

Elderly Patients

CT with IV contrast is strongly recommended due to higher rates of complicated appendicitis and mortality (case fatality rate >16% in nonagenarians). 1, 4

First-Line Treatment

Uncomplicated Appendicitis

Appendectomy (laparoscopic or open) is the treatment of choice and should be performed as soon as reasonably feasible once diagnosis is established. 1, 5

• Laparoscopic appendectomy is preferred in children and offers better outcomes in most patients 5
• Surgery should be performed within 24 hours of admission for uncomplicated appendicitis 5
• Initiate broad-spectrum antibiotics immediately upon diagnosis, covering aerobic gram-negative organisms and anaerobes 1, 6

Recommended antibiotic regimens:

• Piperacillin-tazobactam monotherapy 2
• Ceftriaxone 2g daily + metronidazole 500mg every 6 hours 6
• Amoxicillin/clavulanate 1.2-2.2g every 6 hours 6
• For beta-lactam allergy: Ciprofloxacin 400mg every 8 hours + metronidazole 500mg every 6 hours 6

Non-operative management (NOM) with antibiotics alone may be considered in highly selected patients:

• Only for CT-confirmed uncomplicated appendicitis without appendicolith 1, 6, 2
• Patients must accept a 27% recurrence rate within 1 year 1, 6
• CT findings that predict NOM failure (≈40% failure rate): appendicolith, mass effect, or dilated appendix >13 mm 2
• Male patients with sustained improvement within 24 hours of antibiotics and symptom duration >24 hours before admission may have better NOM success 6
• NOM protocol: IV antibiotics for at least 48 hours, then oral antibiotics for total 7-10 days; hospitalize for at least 48 hours for observation 6

Complicated Appendicitis

Early appendectomy within 8 hours is recommended for perforated appendicitis. 5

• Patients with free perforation and diffuse peritonitis require urgent appendectomy due to significantly higher mortality (11.9-15% vs 1.5-2.3% for non-perforated) 1
• For well-circumscribed appendiceal abscess: Percutaneous drainage plus antibiotics is the most appropriate first-line treatment 1, 6
• Interval appendectomy may be considered after successful drainage, though this remains controversial 6

Critical Pitfalls to Avoid

• Do not delay imaging in intermediate-risk patients to proceed directly to surgery—this risks unnecessary operations and missed alternative diagnoses 4
• Do not rely on clinical scores alone to confirm appendicitis; they must be combined with imaging 4
• Ultrasound has low sensitivity (33.9-51.5%) for detecting perforation; if perforation is suspected, proceed to CT 4
• Non-visualization of the appendix on ultrasound does not exclude appendicitis—26% of patients with equivocal ultrasound ultimately have appendicitis 4
• In elderly patients, atypical presentations are common; maintain high suspicion and low threshold for CT imaging 1
• Pregnant and immunosuppressed patients should undergo timely surgical intervention to decrease risk of complications 7
• If imaging is negative but clinical suspicion remains high: Observe with supportive care and ensure 24-hour follow-up, or consider exploratory laparoscopy if pain progresses 4