Acute appendicitis

Deputy Editor-in-Chief: Raul S. Gonzalez, M.D.
Editor-in-Chief: Debra L. Zynger, M.D.
Elliot Weisenberg, M.D.

Topic Completed: 1 July 2018

Minor changes: 31 August 2021

Copyright: 2003-2021,, Inc.

PubMed Search: Acute appendicitis (Review[ptyp] "loattrfree full text"[sb])

Elliot Weisenberg, M.D.
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Cite this page: Weisenberg E. Acute appendicitis. website. Accessed September 20th, 2021.
Definition / general
  • Acute inflammation of the appendix not attributable to distinct inflammatory disorders such as idiopathic inflammatory bowel disease
Essential features
  • Acute inflammation of the appendix not attributable to distinct inflammatory disorders
  • Occurs in 7% of Americans; more common in children and young adults and in those with a Western diet
  • Most common symptom is periumbilical pain radiating to the right lower quadrant
  • Acute appendicitis has myriads of clinical mimics
  • Grossly normal appendix must be studied histologically as a gross exam may miss acute appendicitis
  • Histologic diagnosis: neutrophils within the wall of the appendix in correct clinical context
ICD coding
  • ICD-10: K35 - acute appendicitis
  • ICD-10: K35.2 - acute appendicitis with generalized peritonitis
  • ICD-10: K35.3 - acute appendicitis with localized peritonitis
  • ICD-10: K35.8 - other and unspecified acute appendicitis
  • ICD-10: K35.80 - unspecified acute appendicitis
  • ICD-10: K35.89 - other acute appendicitis
  • Lifetime risk for Americans is estimated at 7%
  • Over 300,000 appendectomies occur annually in the United States
  • M:F about 1.4:1 (BMJ 2006;333:530, Rosai: Rosai and Ackerman's Surgical Pathology, 11th Edition, 2017)
  • More frequent in children and young adults, most commonly occurring between early teens and 25 but may occur at any age; higher incidence in younger subjects likely related to increased lymphoid tissue
  • More common with a low bulk Western diet, less common in Africa and Asia
  • Putative pathogenesis of most cases involves
  • Luminal obstruction by a fecalith, lymphoid hyperplasia, fecal debris (including seeds or parts of bone), true calculus or tumor
    • Subsequent increased intraluminal pressure and impaired venous outflow with mucosal damage
    • Bacterial infection that spreads to the wall of the appendix with possible mural necrosis, peritonitis or abscess formation; microbiologic studies usually yield 10 - 14 separate microorganisms
    • Evidence of obstruction is lacking in some cases and other mechanisms such as ischemia, infection or hypersensitivity may have a role
Clinical features
  • Stereotypic presentation is well known to most clinicians
    • Initial periumbilical pain radiates to the right lower quadrant within a day; most marked at McBurney's point: located 3.8 - 5.7 cm (2 to 3 fingerbreadths) over the right anterior iliac spine, in line with the umbilicus
    • Accompanied by fever, anorexia, nausea, vomiting, guarding and rebound tenderness of the right lower quadrant upon palpation of the left lower quadrant (Rovsing's sign), pain with extension of the right hip (psoas sign) and internal rotation of the right hip (obturator sign)
  • Possible signs of perforation include rigidity and high fever
  • Possible signs of an atypical presentation include right upper quadrant pain, right flank pain, nonlocalizing abdominal pain and generalized abdominal pain of longer duration
  • Clinical signs may be subtle in the elderly and in infants
  • Incidence of normal appendices after emergent surgery for acute appendicitis
  • Mimics of acute appendicitis are numerous (biliary colic, cystic fibrosis, deciduosis, diverticular disease including Meckel diverticulum, ectopic pregnancy, endometriosis, gastroenteritis, gynecologic infections, idiopathic granulomatous appendicitis, intussusception, mesenteric lymphadenitis, mittelschmerz, obstruction, pancreatitis, parasites, peptic ulcer disease, sarcoidosis, spirochetosis, tuberculosis, tumors, typhlitis, urinary tract infection)
  • Complications include abscesses (liver and elsewhere), peritonitis, pylephlebitis (including possible portal vein involvement), death in neglected cases
  • Fibrous luminal obliteration may be sequelae of acute appendicitis
  • Mucosal or luminal neutrophils within the wall of the appendix in the correct clinical context
  • Most cases are associated with granulocytosis, elevated CRP and elevated ESR
  • HIV positive patients may lack or have minimal granulocytosis
Radiology description
  • Mural thickening and enhancement, appendiceal dilation, periappendiceal fat stranding, cecal thickening, fecalith presence, free peritoneal fluid or mass effect on the cecum
Prognostic factors
  • Elderly, immunocompromised and patients with significant comorbidities may have a more aggressive course
Case reports
  • Surgical excision with antibiotic therapy is the standard of care
  • Laparoscopic resection is possible in the vast majority of cases
  • Severe disease may necessitate more extensive surgery
  • Patients with perforation may require antibiotics followed by appendectomy (interval or delayed appendectomy)
  • Antibiotic treatment without appendectomy is controversial but appears to be gaining support (JAMA 2018;320:1259)
Gross description
  • Appearance varies from grossly normal to hemorrhagic and necrotic with a fibrinopurulent coating
  • Serosa often congested
  • Rupture may be evident
  • Mucosa shows ulceration and hyperemia
  • Lumen may contain pus and blood
  • Fecalith may be present
Gross images

Contributed by Elliot Weisenberg, M.D. and Andrey Bychkov, M.D., Ph.D.

Fibrinopurulent exudate

Mucosal ulceration

Severe disease

Dark mucosa

Images hosted on other servers:

Yellow-tan exudate

Microscopic (histologic) description
  • Hallmark of acute appendicitis is neutrophilic infiltrates of the wall of the appendix
    • Acute mucosal inflammation is usually present
    • Often neutrophilic infiltrates within the lumen
    • Histologic findings alone are not sufficient to diagnose acute appendicitis
    • Depending on the severity of the inflammation, variable necrosis of the appendiceal wall is present with mucosal sloughing
  • Process may be divided into
    • Acute focal
    • Acute suppurative
    • Gangrenous
    • Perforative
  • Vessels may show thrombosis or contain lymphocytes resembling chronic lymphocytic leukemia
  • Granulation tissue response or cicatricial fibrosis may be apparent in some cases
  • Minority of cases show a lymphohistiocytic response containing foamy histiocytes termed xanthogranulomatous appendicitis
Microscopic (histologic) images

Contributed by Raul S. Gonzalez, M.D. and Elliot Weisenberg, M.D.

Marked neutrophilic infiltration

Transmural inflammation

Intraluminal neutrophils

Periappendiceal abscess

Neutrophils in muscularis propria


High power

Images hosted on other servers:

Neutrophils within muscularis propria

Differential diagnosis
  • Idiopathic inflammatory bowel disease is the most important pathologic differential diagnosis
    • Ulcerative colitis acutely involving the appendix (ulcerative appendicitis) shows changes seen in ulcerative colitis (cryptitis, crypt abscesses, exudates), usually pancolitis is present
    • Chronic ulcerative colitis demonstrates increased lymphocytes and plasma cells in the lamina propria, architectural distortion and Paneth cells hyperplasia
    • Crohn's disease involving the appendix shows similar feature to those in the colon (cryptitis, crypt abscesses, lymphoid aggregates, transmural inflammation, fibrosis and often granulomata) and usually occurs with severe ileocolonic disease
  • Other specific infective agents associated with acute inflammation of the appendix, of academic concern but in the differential diagnosis of typical acute appendicitis
Board review style question #1
What group is most prone to the development of acute appendicitis?

  1. Elderly in the United States
  2. Infants in Japan
  3. Infants in the United States
  4. Middle age women in sub-Saharan Africa
  5. Teenagers in the United States
Board review style answer #1
E. Teenagers in the United States. Any age group may be affected by acute appendicitis but it is most common in patients age 5 to 15 likely related to increased density of lymphoid tissue. It is more common in populations with a low bulk western diet.

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Reference: Acute appendicitis
Board review style question #2
What is most likely to be in the clinical differential diagnosis of acute appendicitis?

  1. Gastric carcinoma
  2. Gastric extranodal marginal zone lymphoma
  3. Hepatocellular carcinoma
  4. Pancreatic carcinoma
  5. Pelvic inflammatory disease
Board review style answer #2
E. Pelvic inflammatory disease. The clinical diagnosis of acute appendicitis is broad and includes pelvic inflammatory disease, inflammatory bowel disease, pancreatitis, peptic ulcer disease, Meckel diverticulum and many other entities. Malignant disease only rarely enters into the differential diagnosis of acute appendicitis.

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Reference: Acute appendicitis
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