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Acute appendicitis

Last updated: February 10, 2021

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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.

References:[2][3]

Epidemiological data refers to the US, unless otherwise specified.

Caused by obstruction of the appendiceal lumen due to: [4]

References:[7][8]

  • Obstructed proximal appendiceal lumen (closed-loop obstruction), resulting in: [8]
    • 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

References:[9]

The location of the pain may be variable as the appendix's location varies, especially in pregnant women. [11]

References:[3][7][8]

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).

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 [11][16]

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) [11][13][17][18][19]

  • 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. [16] [18]
Alvarado score (MANTRELS) [20]
Characteristics Score
Symptoms Migration of pain to RLQ 1
Anorexia 1
Nausea and/or vomiting 1
Physical examination Tenderness in RLQ 2
Rebound pain 1
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
  • ≤ 4: Low [17]
  • 5–6: Moderate
  • ≥ 7: High [17]


The Alvarado score may not provide a reliable estimated likelihood of acute appendicitis in patients who are either very young or very old. [16]

Pediatric appendicitis score [21][22]

  • 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 [21]
Characteristics Score
Symptoms Migration of pain to RLQ 1
Anorexia 1
Nausea/vomiting 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 [23]

  • ≤ 3: Low
  • 4–6: Moderate
  • ≥ 7: High

Appendicitis inflammatory response score [11]

  • 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 [24]
Appendicitis inflammatory response score [25]
Characteristics Score
Symptoms Vomiting 1
RLQ pain 1
Physical examination Rebound tenderness Mild 1
Moderate 2
Strong 3
Temperature ≥ 38.5°C (101.3°F) 1
Laboratory parameters Leukocytosis 10,000/mm3–14,999/mm3 1
≥ 15,000/mm3 2
PMN 70–84% 1
≥ 85% 2
CRP 10–49 mg/L 1
≥ 50 mg/L 2
Likelihood of appendicitis
  • ≤ 4: Low
  • 5–8: Moderate
  • ≥ 9: High

Imaging [11][12][16][26][27]

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. [16][17]

  • Recommended indications [13][16][17][23][27]
    • Moderate likelihood of appendicitis
    • Patients > 60 years of age, regardless of the likelihood scores [13][28]
    • To rule out suspected differential diagnoses
  • Relative indications [17]
  • 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. [17]

CT abdomen with IV contrast

  • Indications: preferred initial imaging modality in adults (except for pregnant women) [26]
  • Supportive findings [26]
  • Additional considerations
    • Consider low-dose CT scan (with IV contrast) to minimize radiation exposure. [29]
    • Consider CT without contrast in patients with contrast allergy.

Abdominal ultrasound

  • Indications
    • Preferred initial imaging modality in children or pregnant patients [26]
    • As an alternative to CT scan if CT findings are inconclusive [27]
  • Supportive findings [16] [30]

Abdominal ultrasound is more reliable for confirming acute appendicitis than ruling it out. [16]

MRI abdomen and pelvis [13][26][31]

  • Indications
    • MRI without IV contrast: pregnant patients with inconclusive ultrasound findings [26][31]
    • MRI with IV contrast: nonpregnant patients with inconclusive ultrasound findings and contraindications for CT scan
  • Findings: similar to CT scan findings

Diagnostic laparoscopy

Supportive care

Antibiotic therapy [12][27][34][35]

  • Indication: all patients with acute appendicitis
  • Required coverage: : against gram-negative and anaerobic organisms [12]

Empiric antibiotic therapy for acute appendicitis [12][35]

Parameters to consider Recommended antibiotic regimens Duration
Uncomplicated appendicitis Managed with appendectomy [12][13][35]
  • Discontinue after surgery or within 24 hours [12][13]
Non-operative management (NOM) [12][31][36]
  • Not yet standardized
  • Initial parenteral antibiotics for at least 2–3 days then switch to oral antibiotics for 7 days.
  • See ''Nonoperative management'' below for further details. [31][36]

Complicated appendicitis

(managed with appendectomy or NOM) [13][31][37][38]

  • 3–5 days [13][31][37][38]

Operative management with appendectomy [12][13][27][31][39]

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. [42]

Nonoperative management of acute appendicitis (NOM; conservative management) [13][31][36][43][44]

Indications [12][31][36][41][44]

Contraindications [31][36]

Early uncomplicated appendicitis

The use of NOM in early uncomplicated appendicitis is an area of ongoing research. [12][36]

  • Advantages: avoids operative risks and costs in approx. 80% of patients [31][44]
  • Disadvantages [31][36][44][47]
    • Approx. 20% chance of recurrence requiring an appendectomy [31]
    • Recurrent need for outpatient visits and antibiotic use
    • Risk of missing an appendiceal tumor
    • Patient anxiety about recurrent episodes [36]

Steps of nonoperative management [12][36]

Think of PAIN to remember the conservative management of appendicitis: Pain management, Antibiotics, Intravenous fluid therapy, NPO!

Interval appendectomy [13][31][44][49][50]

  • Definition: appendectomy performed 6–8 weeks following the resolution of an acute episode of appendiceal mass or appendiceal abscess to minimize surgical complications [50]
  • Indications
    • Currently not routinely recommended [13][44]
    • Consider in persistent or recurrent symptoms of appendicitis in a patient with an appendiceal mass or appendiceal abscess treated conservatively. [13][31][41]
    • Consider in patients > 40 years of age if there is concern for an underlying appendiceal tumor. [51][52]
  • Advantages of routine interval appendectomy
    • Decreased risk of recurrences [31][43][50]
    • Decreased risk of missing an underlying appendiceal tumor [31][52]
    • Decreases need for recurrent outpatient visits
    • Decreases patient anxiety related to potential recurrence [36]
  • Disadvantages of routine interval appendectomy

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.

Right-sided carcinoma of the colon may manifest with clinical features similar to those of acute appendicitis! [55]

References:[54][55]

The differential diagnoses listed here are not exhaustive.

Inflammatory appendiceal mass (appendiceal phlegmon) [31][41]

Appendiceal abscess [12][31][41]

Gangrenous appendicitis

Perforated appendix [31]

Pylephlebitis [57]

We list the most important complications. The selection is not exhaustive.

References:[8][9]

Appendicitis in children [11][58]

  • The reliability of signs and symptoms in children is lower.
    • Most reliable symptoms: emesis and duration of pain
    • Most reliable signs: abdominal tenderness and pain with walking, jumping, or coughing
  • Ultrasound is the diagnostic procedure of choice.

Appendicitis in pregnancy [11][59]

Appendicitis in patients > 60 years of age [13][14][28][48][60]

Patients > 60 years of age have a higher risk of perforation! [13]

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