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 appendicitis is emergency appendectomy (laparoscopic or open) and antibiotics. 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 initial approach to management should be guided by the likelihood of acute appendicitis based on clinical features and laboratory parameters (see Risk stratification tools for acute appendicitis).
Low likelihood of appendicitis: Consider alternative diagnoses (see differential diagnoses of acute abdomen).
- Perform further diagnostic tests if needed (see diagnostic workup of acute abdomen).
- Consider discharging the patient with advice to follow up after 12–24 hours (or earlier if symptoms worsen).
- Consider hospitalization for observation if the index of suspicion is high or the underlying cause is unclear.
- Reassess scores after 12–24 hours (every 6–8 hours in hospitalized patients).
Moderate likelihood of appendicitis: Confirm diagnosis with imaging.
- Imaging confirms appendicitis: Initiate treatment.
- Imaging rules out appendicitis: Follow steps for low likelihood of appendicitis.
- Imaging is inconclusive 
- Low index of suspicion: Follow steps for low likelihood of appendicitis.
- High index of suspicion
High likelihood of appendicitis: Initiate treatment.
- Empiric antibiotic therapy is recommended in all patients.
- Emergency appendectomy
- Nonoperative management (NOM) with antibiotic therapy may be considered in the setting of a clinical trial in patients who present with early uncomplicated appendicitis.
- NOM is recommended for the management of appendiceal mass or appendiceal abscess; recurrences may require interval appendectomy.
Acute appendicitis is usually a clinical diagnosis based on history, physical examination, and laboratory studies. The appendicitis scoring systems should be used to guide management decisions. Imaging is recommended if the clinical diagnosis is uncertain.
Laboratory studies 
- CBC: mild leukocytosis with left shift ; normal WBC count does not rule out acute appendicitis
- CRP: elevated (> 10 mg/L) 
- BMP: ↑ creatinine, electrolyte abnormalities may be present in patients with severe vomiting; and diarrhea
- Urinalysis: typically normal in appendicitis; possible findings of mild pyuria and/or hematuria
- Tests to rule out differential diagnoses
Risk stratification tools for acute appendicitis
There are several scoring systems to estimate the likelihood of acute appendicitis in a patient with RLQ pain. The following three scoring systems are most frequently used in clinical practice and are based on clinical features and laboratory studies. These scores guide management decisions, including determining when imaging may be unnecessary.
Alvarado score (MANTRELS) 
- A 10-point scoring system that uses eight parameters to estimate the likelihood of appendicitis
- Leukocytosis and RLQ tenderness carry the greatest weight.
- 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 |
The Alvarado score may not provide a reliable estimated likelihood of acute appendicitis in patients who are either very young or very old. 
Pediatric appendicitis score 
- A scoring system to estimate the likelihood of appendicitis in patients 3–18 years of age
- The parameters that carry the greatest scores are RLQ tenderness and RLQ pain elicited on coughing, jumping, and percussion.
|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 
- A relatively new scoring system that places emphasis on laboratory parameters and the gradation of clinical features 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 |
Indications for imaging and preferred initial imaging modality (CT scan, ultrasound) are controversial and vary depending on institution and location. Some sources recommend imaging regardless of the likelihood of appendicitis, while other sources recommend the use of risk stratification tools to make these decisions. 
Recommended indications 
- Moderate likelihood of appendicitis
- Patients > 60 years of age, regardless of the likelihood scores 
- To rule out suspected differential diagnoses
- Relative indications 
- Imaging likely unnecessary: This is somewhat controversial; some sources recommend imaging regardless of the likelihood and the use of CT has made imaging commonplace even in patients with very low and very high likelihood of acute appendicitis. 
CT abdomen with IV contrast
- Indications: preferred initial imaging modality in adults (except for pregnant women) 
- Supportive findings 
- Additional considerations
- Preferred initial imaging modality in children or pregnant patients 
- As an alternative to CT scan if CT findings are inconclusive 
- Supportive findings  
Abdominal ultrasound is more reliable for confirming acute appendicitis than ruling it out. 
- 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
Antibiotic therapy 
- Indication: all patients with acute appendicitis
- Required coverage: : against gram-negative and anaerobic organisms 
Empiric antibiotic therapy for acute appendicitis 
|Parameters to consider||Recommended antibiotic regimens||Duration|
|Uncomplicated appendicitis||Managed with appendectomy || || |
|Non-operative management (NOM) || |
(managed with appendectomy or NOM) 
Operative management with appendectomy 
- Definition: surgical removal of the appendix
- Timing of surgery 
- Indications: Emergency appendectomy is the current standard of care for acute appendicitis (without periappendiceal mass or abscess). 
- Contraindications 
- Approach 
Appendectomy in patients with an appendiceal abscess or an inflammatory appendiceal mass is associated with an increased risk of intraoperative hemorrhage, postoperative wound infection, and fecal fistula formation. 
Nonoperative management of acute appendicitis (NOM; conservative management) 
- Inflammatory appendiceal mass 
- Appendiceal abscess 
- Patient refusal of surgery
- High surgical risk due to comorbidities
- History of previous surgical/anesthesia complications
- Septic shock
- Generalized peritonitis
- Inability to percutaneously drain an appendiceal abscess
- Appendiceal fecalith 
The use of NOM in early uncomplicated appendicitis is an area of ongoing research. 
- Advantages: avoids operative risks and costs in approx. 80% of patients 
- Disadvantages 
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 intra-abdominal 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. 
Interval appendectomy 
- Definition: appendectomy performed 6–8 weeks following the resolution of an acute episode of appendiceal mass or appendiceal abscess to minimize surgical complications 
- Currently not routinely recommended 
- Consider in persistent or recurrent symptoms of appendicitis in a patient with an appendiceal mass or appendiceal abscess treated conservatively. 
- Consider in patients > 40 years of age if there is concern for an underlying appendiceal tumor. 
- Advantages of routine interval appendectomy
Disadvantages of routine interval appendectomy
- Operative risks and costs
- Postoperative complications 
- Unnecessary surgery in 70–80% of patients 
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.
- Empiric IV antibiotic therapy for acute appendicitis
- Transfer to OR or admit to surgical ward for specific 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 intra-abdominal 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 
- The reliability of signs and symptoms in children is lower.
- Ultrasound is the diagnostic procedure of choice.
Appendicitis in pregnancy 
- Atypical (higher) pain localization
- Perforated appendix is associated with a higher risk of fetal loss.
- Ultrasound is the diagnostic procedure of choice.
Appendicitis in patients > 60 years of age 
- Clinical presentation
- Older patients are more likely to develop complications, especially perforated appendix. 
- Imaging should be considered regardless of the scores. 
- Consider diagnostic laparoscopy if imaging findings are inconclusive. 
- Consider colonoscopy after treatment of acute appendicitis to rule out early colonic malignancy. 
Patients > 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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