Acute appendicitis is the acute inflammation of the appendix, typically due to an obstruction of the appendiceal lumen. It is the most common cause of acute abdomen requiring emergency surgical intervention in both children and adults. The characteristic features of acute appendicitis are periumbilical abdominal pain that migrates to the right lower quadrant (RLQ), anorexia, nausea, fever, and RLQ tenderness. When seen alongside neutrophilic leukocytosis, these features are sufficient to make a clinical diagnosis using appendicitis scoring systems to estimate the likelihood of appendicitis. Imaging (e.g., abdominal CT with IV contrast, abdominal ultrasonography) may be considered if the clinical diagnosis is uncertain. The current standard of management of acute uncomplicated appendicitis is appendectomy within 24 hours of diagnosis (laparoscopic or open) and antibiotics. Emergency appendectomy is indicated for patients with systemic complications. Nonoperative management (NOM), which includes bowel rest, antibiotics, and analgesics, is indicated in patients with an inflammatory appendiceal mass (phlegmon) or an appendiceal abscess, because surgical intervention is associated with a higher risk of complications in these patient groups. Interval appendectomy 6–8 weeks following resolution of the acute episode may be considered in these patients to prevent a recurrence or if there is concern for an underlying appendiceal tumor.
- Appendicitis: acute inflammation of the
- Uncomplicated appendicitis: appendicitis with no evidence of an appendiceal fecalith, an appendiceal tumor, or complications, such as perforation, gangrene, abscess, or mass 
- Complicated appendicitis: appendicitis associated with perforation, gangrene, abscess, an inflammatory mass, an appendiceal fecalith, or an appendiceal tumor 
- Common cause of acute abdomen 
- Lifetime risk: ∼ 8%
- Peak incidence: 10–19 years of age 
- Sex: ♂ > ♀
Epidemiological data refers to the US, unless otherwise specified.
Caused by obstruction of the appendiceal lumen due to:
- Lymphoid tissue hyperplasia; (60% of cases): most common cause in children and young adults
- ; and fecal stasis (35% of cases): most common cause in adults
- Neoplasm; (uncommon): more likely in patients > 50 years of age 
- Parasitic infestation (uncommon): e.g., Enterobius vermicularis, Ascaris lumbricoides, and species of the Taenia and Schistosoma genera 
Obstructed proximal appendiceal lumen (closed-loop obstruction), resulting in:
- Stasis of mucosal secretions → bacterial multiplication and local inflammation → transmural spread of infection → clinical features of appendicitis
- Increased intraluminal pressure → obstruction of veins → edema of the appendiceal walls → obstruction of capillaries → ischemia → gangrenous appendicitis with/without perforation
- Inflammation can spread to serosa, leading to peritonitis
Migrating abdominal pain: most common and specific symptom
- Typically constant and rapidly worsens
- Most patients present within 48 hours of symptom onset.
- Initial diffuse periumbilical pain; : caused by the irritation of the visceral peritoneum (pain is referred to T8–T10 dermatomes) 
- Localizes to the RLQ within ∼ 12–24 hours; : caused by the irritation of the parietal peritoneum
- Associated nonspecific symptoms
Clinical signs of appendicitis
- McBurney point tenderness (RLQ tenderness)
- RLQ guarding and/or rigidity
- (Blumberg sign), especially in the RLQ
- Rovsing sign: RLQ pain elicited on deep palpation of the LLQ 
- Psoas sign: can be performed in two different ways
- Obturator sign: RLQ pain on passive internal rotation of the right hip with the hip and knee flexed
- Hyperesthesia within Sherren triangle: formed by the anterior superior iliac spine, umbilicus, and symphysis pubis
- Lanz point tenderness: at the junction of the right third and left two-thirds of a line connecting both the anterior superior iliac spines
- Pain in the Pouch of Douglas: pain elicited by palpating the rectouterine pouch on rectal examination
- Baldwin sign: pain in the flank when flexing the right hip (suggests an inflamed retrocecal appendix)
The following recommendations apply to adult patients and are consistent with the 2020 World Society of Emergency Surgery (WSES) appendicitis guidelines, the 2018 American Association for the Surgery of Trauma (AAST) appendicitis guidelines, and the 2010 American College of Emergency Physicians (ACEP) clinical policy on acute appendicitis. See “Appendicitis in children” for information about pediatric patients. 
Initial management 
- Perform rapid clinical evaluation using .
- Screen for (e.g., due to ) or .
- Establish IV access and obtain blood samples for laboratory studies.
- Provide if necessary.
- Keep patients NPO and initiate supportive care: e.g., IV fluids, analgesia, antiemetics
- Determine the likelihood of diagnosis based on a combination of:
- Patient demographics (e.g., age, sex)
- Initial laboratory studies (see “Diagnostics”)
- , e.g., 
- Proceed with subsequent management based on the likelihood of diagnosis.
Subsequent management 
Diagnostic imaging is often performed for most patients. A selective and individualized approach is generally recommended to minimize patient exposure to radiation and expedite care. 
Low likelihood of appendicitis
- Associated scores: ≤ 4, ≤ 2–4
Management: Additional testing for appendicitis may not be required. 
- Consider other .
- Perform further as needed.
Next steps: Determine disposition. 
- Consider discharge home with follow-up within 24 hours in select patients (e.g., motivated adults < 40 years old with clinical stability and no ) 
- Consider observation, reassessment (e.g., every 6–8 hours), and/or diagnostic imaging for:
- Suspected early appendicitis
- Unclear underlying cause of symptoms
- Older adults (e.g., > 60 years old) 
Moderate likelihood of appendicitis
- Associated scores: ≤ 5–8, ≤ 5–6
- Management: confirmatory imaging required, e.g., ultrasound abdomen, CT abdomen (See “Diagnostics.”)
- Imaging confirms appendicitis: See “High likelihood of appendicitis”.
- Imaging is inconclusive or negative for appendicitis 
- Low index of suspicion: See “Low likelihood of appendicitis.”
- High index of suspicion: Consult surgery.
High likelihood of appendicitis 
- Associated scores: ≥ 9, ≥ 7–9
Management: Urgent surgical consult for admission and definitive treatment required
- Begin .
- Arrange preoperative CT abdomen as needed (e.g., for patients > 40 years old). 
- Laparoscopic appendectomy within 24 hours for uncomplicated appendicitis (no signs of sepsis or complicated appendicitis)
- for with systemic manifestations (e.g., generalized peritonitis or sepsis)
Appendicitis inflammatory response score (AIR Score) 
- A relatively new scoring system that emphasizes laboratory parameters and graded clinical findings to provide a more objective clinical evaluation
- Provides a more accurate estimated likelihood of acute appendicitis than the Alvarado scoring system 
|Appendicitis inflammatory response score |
|Physical examination||Rebound tenderness||Mild||1|
|Temperature ≥ 38.5°C (101.3°F)||1|
|≥ 50 mg/L||2|
| Likelihood of appendicitis |
Alvarado score (MANTRELS) 
- A 10-point scoring system that uses eight parameters to estimate the likelihood of appendicitis
- Accuracy is higher in young to middle-aged adults than in children < 10 years of age and adults > 60 years of age.  
|Alvarado score (MANTRELS) |
|Symptoms||Migration of pain to RLQ||1|
|Nausea and/or vomiting||1|
|Physical examination||Tenderness in RLQ||2|
|Elevated temperature > 37.3°C (99.1°F)||1|
|Laboratory parameters||Leukocytosis (> 10,000/mm3)||2|
|Shift to the left (≥ 75% neutrophils)||1|
| Likelihood of appendicitis |
Laboratory studies 
- Routine studies
- Tests to evaluate differential diagnoses
A normal WBC count does not rule out acute appendicitis.
Decisions regarding the optimal timing and initial imaging modality should be based on individual patient factors (e.g., demographics, likelihood of appendicitis, risk of alternate diagnoses of concern, comorbidities), available resources, and local specialist preferences and hospital policy. 
Options for first-line imaging in nonpregnant adults 
- CT abdomen 
Ultrasound abdomen (typically performed in conjunction with an ) 
- Advantages: can limit the exposure to radiation and contrast, potentially reduce cost and length of stay (LOS) associated with CT use
- Limitations: lower accuracy and reliability , can increase cost and LOS if CT abdomen is still required 
- First-line imaging for pregnant adults and children: ultrasound abdomen 
The combined use of ultrasound abdomen can reduce the need for CT abdomen in certain patients with suspected appendicitis, however, this should be balanced with the risk of missing the diagnosis.  and an initial
- POCUS 
- Supportive findings  
CT abdomen with IV contrast
CT abdomen is the most accurate initial imaging modality for appendicitis. 
- Supportive findings 
- Additional considerations
- Findings: similar to CT scan findings
Indications: Consider in the following groups of patients with inconclusive findings on imaging. 
- Women of reproductive age
- Patients with obesity
- Patients > 65 years of age
- Findings 
- Additional steps based on findings 
- Bowel rest (NPO)
- (see “IV fluid therapy”)
- Electrolyte repletion as needed
- IV analgesics (see “Pain management”) 
- IV antiemetics as needed
- Antipyretic therapy
Empiric antibiotic therapy for acute appendicitis 
- Indication: all patients with acute appendicitis
- Required coverage: : against gram-negative and anaerobic organisms 
Preoperative antibiotics for uncomplicated appendicitis: Administer one of the following agents as prophylaxis against surgical site infection (can be discontinued after surgery or within 24 hours) 
- A cephalosporin with anaerobic coverage: Cefoxitin OR Cefotetan
- Combination therapy with a first-generation cephalosporin (e.g., cefazolin; ) PLUS metronidazole 
- In patients allergic to penicillin/cephalosporin, administer clindamycin OR metronidazole PLUS one of the following: 
Nonoperative management for appendicitis (with or without interval appendectomy)
- Agents: See ''Mild or moderate infection'' in “ .” 
- Duration for early uncomplicated appendicitis (not yet standardized): Consider initial parenteral antibiotics for at least 2–3 days then switch to oral antibiotics for 7 days. 
- Duration for complicated appendicitis ( or ): 3–5 days 
- Definition: surgical removal of the appendix, usually within 24 hours of the diagnosis 
- Emergency appendectomy 
- Relative contraindications 
- Approach 
Surgery for acute uncomplicated appendicitis can safely be delayed for up to 24 hours from diagnosis.
Interval appendectomy 
Typically performed after a trial of.
- Definition: appendectomy performed 6–8 weeks following the resolution of an acute episode of appendiceal mass or appendiceal abscess to minimize surgical complications 
- Indications: currently not routinely recommended 
Nonoperative management (NOM; conservative management) is typically preferred for patients at high risk of surgical morbidity if operated on immediately. It is sometimes followed by an interval appendectomy. NOM can also be offered to select patients with early uncomplicated appendicitis in consultation with an experienced surgeon, however, this remains an area of ongoing research. 
- Inflammatory appendiceal mass 
- Appendiceal abscess 
- Patient refusal of surgery
- High surgical risk due to comorbidities
- History of previous surgical/anesthesia complications
- Consider in select patients with early uncomplicated appendicitis 
- Septic shock
- Generalized peritonitis
- Inability to percutaneously drain an appendiceal abscess
- Appendiceal fecalith 
Steps of nonoperative management 
- Empiric parenteral antibiotic therapy for 2–3 days: See ''Mild or moderate infection'' under ''Community-acquired infections'' in empiric antibiotic therapy for intraabdominal infections. 
- Supportive care (see above)
- Periappendiceal abscess > 4 cm: image-guided percutaneous drainage; send aspirate for cultures
- Monitor vitals and serial abdominal examinations every 6–12 hours.
- Schedule interval colonoscopy in patients > 40 years of age following NOM of acute appendicitis to rule out early colonic malignancy. 
This checklist is applicable to patients with confirmed acute appendicitis and those with a high likelihood of appendicitis according to any of the risk stratification tools for acute appendicitis.
- Urgent general surgery consult for consideration of appendectomy or nonoperative management (NOM)
- IV fluid therapy
- Parenteral analgesics (see “Pain management”) 
- Parenteral antiemetics as needed (see “Antiemetics”)
- Consider nasogastric tube insertion.
- Transfer to OR or admit to surgical ward for definitive management.
- The appendix is composed of the same four histological layers of the alimentary canal.
- See “Microscopic anatomy” in “appendix. ” for the histological features of a healthy
- Transmural neutrophilic infiltration is the characteristic histological feature of acute appendicitis.
- Blood vessel thrombosis, mucosal ulceration, and/or gangrene of the appendiceal wall may also be present.
- (especially in elderly patients)
- and renal colic
- psoas sign) (in patients with a positive
- Gynecological diseases (e.g., pelvic inflammatory disease, )
- See “.”
The differential diagnoses listed here are not exhaustive.
Inflammatory appendiceal mass (appendiceal phlegmon) 
- Description: an ill-defined mass of inflammatory periappendiceal tissue
- Clinical features: manifests as a tender mass in the RLQ
Appendiceal abscess 
- Description: a localized collection of pus and necrotic tissue that forms around an inflamed appendix, which typically follows an untreated perforated appendix
- Clinical features: manifests as a tender mass in the RLQ in an acutely ill patient (i.e., high-grade fever, possible paralytic ileus, leukocytosis, signs of sepsis)
- Description: irreversible necrosis of the appendiceal wall
- Clinical features
- Treatment: emergency appendectomy and IV antibiotics
Perforated appendix 
- Description: rupture of the appendix
- Clinical features
- Description: septic thrombosis of the portal vein or its branches
- Etiology: : a complication of intraabdominal sepsis (e.g., due to perforated appendicitis, diverticulitis, or necrotizing pancreatitis)
- Clinical features: fever, abdominal pain
- Treatment: broad-spectrum antibiotics
- Prognosis: Thrombosis of the portal circulation can result in bowel infarction and death.
We list the most important complications. The selection is not exhaustive.
- Uncomplicated appendicitis with adequate management (surgical intervention) has an excellent prognosis.
- Perforation and peritonitis: ∼ 1% mortality rate
- Up to 20% of patients are found to have a normal appendix following surgery.
- The mortality rate is higher (∼ 5%) in elderly patients with complicated appendicitis.
Special patient groups
Appendicitis in children 
- Clinical features
- Routinely obtain laboratory studies; intial CRP ≥ 10 mg/mL and WBC count > 16,000/mL strongly predict appendicitis.
- Consider either of the following clinical risk scores:
- Ultrasound is the diagnostic procedure of choice.
|Pediatric appendicitis score |
|Symptoms||Migration of pain to RLQ||1|
|Physical examination||RLQ tenderness||2|
|RLQ pain elicited on coughing/jumping/percussion||2|
|Temperature ≥ 38°C (100.4°F)||1|
|Laboratory parameters||Leukocytosis (≥ 10,000/mm3)||1|
|PMN ≥ 75%||1|
Likelihood of appendicitis 
The diagnosis should not be based solely on the clinical score in children. 
Appendicitis in pregnant individuals 
- Clinical features
- Complications: A perforated appendix is associated with a higher risk of fetal loss.
Appendicitis in patients > 60 years of age 
- Clinical features
- Diagnostics: Imaging should be considered regardless of the scores. 
- Complications: Older patients are more likely to develop complications, especially perforated appendix. 
Individuals > 60 years of age have a higher risk of perforation! 
- One-Minute Telegram 14-2020-1/3: Pills vs. scalpels: appendicitis treatment revisited
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