Acute Appendicitis

How to Cite This Chapter: Lysecki P, Kahnamoui K, Ciećkiewicz J. Acute Appendicitis. McMaster Textbook of Internal Medicine. Kraków: Medycyna Praktyczna. Accessed May 20, 2024.
Last Updated: April 20, 2021
Last Reviewed: April 20, 2021
Chapter Information

Etiology and Pathogenesis Top

Acute appendicitis is one of the most common causes of abdominal pain and peritonitis. It most frequently results from obstruction of the appendiceal lumen by a fecalith. The obstruction allows bacterial stasis and overgrowth while also causing intramural and intraluminal fluid accumulation and edema. The resultant increase in local pressure may compromise vascular flow, leading to appendiceal ischemia and possibly necrosis and/or perforation. Bacteria may be able to translocate through an inflamed/ischemic appendiceal wall or may freely enter the peritoneal cavity through a perforation. If the infectious process is able to be contained by the body’s immune or inflammatory response, a localized phenomenon such as abscess or phlegmon may develop. However, if free perforation occurs, diffuse peritonitis may result.

Clinical Features Top

1. Symptoms:

1) Abdominal pain is the most common presenting symptom. In early appendicitis the patient typically has poorly localized discomfort in the periumbilical region. As peritonitis develops, the pain may localize, most frequently to the right iliac fossa. In advanced pregnancy the pain may be located in the right upper quadrant due to superior displacement of the abdominal viscera by the gravid uterus. In patients with an extraperitoneal or retrocecal appendix, the pain may also occur elsewhere.

2) Anorexia is a frequent symptom. Nausea and vomiting may also occur.

2. Signs: Common vital sign abnormalities include tachycardia and fever. Local abdominal guarding (on palpation or percussion), local pain when attempting to cough, and rebound tenderness may be observed. Special signs that have been described in appendicitis include McBurney point tenderness (a point two-thirds of the distance from the umbilicus to the anterior superior iliac spine), Rovsing sign (tenderness in the right lower quadrant elicited by palpation in the left lower quadrant), obturator sign (pain when the right hip is internally rotated passively with the hip and knee flexed), and psoas sign (pain when the right hip is actively flexed with the knee extended). Pain on coughing and rebound tenderness are indicative of the development of peritonitis, which may be localized or generalized. Digital rectal examination most often shows no specific abnormalities but should be performed, as it may reveal other causes of pain.


The diagnosis of appendicitis should be considered in all patients with abdominal pain and should be established promptly to minimize the risk of progression to perforation. In the setting of clinical uncertainty it may be appropriate to admit the patient for observation and monitoring with serial assessments.

Diagnostic Tests

1. Blood tests: In 80% to 85% of cases elevated white blood cell (WBC) and neutrophil counts are observed. Other blood tests such as liver function tests and creatinine should be considered to evaluate for a different underlying cause.

2. Urinalysis: Results may be suggestive of another underlying cause of symptoms. However, microscopic hematuria and pyuria may accompany appendicitis adjacent to the ureter or bladder, and these findings should not be used to discredit the diagnosis of appendicitis.

3. Imaging studies: Computed tomography (CT) is considered the study of choice for the diagnosis of appendicitis, given its high accuracy and low rate of nondiagnostic studies. However, ultrasonography is often used as the initial diagnostic modality because of its availability and lack of radiation exposure or use of IV contrast. Compression ultrasonography (CUS) confirms diagnosis with high specificity if results reveal a tubular structure >6 mm in diameter that cannot be compressed, shows no peristalsis, and is surrounded by a layer of fluid (a normal appendix is often not visualized by ultrasonography). A fecalith may also be visualized on ultrasonography. Only positive results of the study are of diagnostic value. This is the preferred test in pregnant women and children. Magnetic resonance imaging (MRI) may also have a role in diagnosis, particularly in patients in whom radiation exposure is problematic (such as pregnant women), but its use is limited by accessibility and timeliness.

4. Diagnostic laparoscopy: In the setting of clinical uncertainty diagnostic laparoscopy may be undertaken to evaluate for evidence of appendicitis versus alternative pathology.

5. Clinical scores: The Modified Alvarado Scoring System may help in quantifying the probability of confirmed acute appendicitis.Evidence 1Low Quality of Evidence (low confidence that we know true effects of the intervention). Quality of Evidence lowered due to imprecision and results of the score influencing the decision to perform surgery (lack of test independence). Kalan M, Talbot D, Cunliffe WJ, Rich AJ. Evaluation of the modified Alvarado score in the diagnosis of acute appendicitis: a prospective study. Ann R Coll Surg Engl. 1994 Nov;76(6):418-9. PubMed PMID: 7702329; PubMed Central PMCID: PMC2502264. It gives 2 points for the presence of right lower quadrant tenderness and elevated WBC counts and 1 point each for anorexia, nausea and vomiting, migratory pain in the right inguinal fossa, rebound tenderness in the same area, elevated temperature, and a left shift on WBC evaluation.


1. The standard treatment method is surgical appendectomy via either laparoscopy or laparotomy. Several trials and subsequent meta-analyses have now been conducted comparing surgical therapy to nonsurgical therapy with antibiotics alone in acute uncomplicated appendicitis where no fecalith is evident. Although initial success has been reported with antibiotics alone in the majority of patients, a meaningful number of patients either fail initial medical management (~10%), or have recurrent symptoms that later require surgery (~30% within 1 year). Therefore, appendectomy remains the standard of care, with conservative treatment being a less commonly chosen option.Evidence 2Weak recommendation (benefits likely outweigh downsides, but the balance is close or uncertain; an alternative course of action may be better for some patients). Low Quality of Evidence (low confidence that we know true effects of the intervention). Quality of Evidence lowered due to imprecision, lack of blinding, and risk of bias. Sippola S, Haijanen J, Viinikainen L, et al. Quality of Life and Patient Satisfaction at 7-Year Follow-up of Antibiotic Therapy vs Appendectomy for Uncomplicated Acute Appendicitis: A Secondary Analysis of a Randomized Clinical Trial. JAMA Surg. 2020 Apr 1;155(4):283-289. doi: 10.1001/jamasurg.2019.6028. PMID: 32074268; PMCID: PMC7042917. Ehlers AP, Talan DA, Moran GJ, Flum DR, Davidson GH. Evidence for an Antibiotics-First Strategy for Uncomplicated Appendicitis in Adults: A Systematic Review and Gap Analysis. J Am Coll Surg. 2016 Mar;222(3):309-14. doi: 10.1016/j.jamcollsurg.2015.11.009. Review. PubMed PMID: 26712246; PubMed Central PMCID: PMC4769928. Sallinen V, Akl EA, You JJ, et al. Meta-analysis of antibiotics versus appendicectomy for non-perforated acute appendicitis. Br J Surg. 2016 Mar 17. doi: 10.1002/bjs.10147. [Epub ahead of print] Review. PubMed PMID: 26990957; PubMed Central PMCID: PMC5069642. There is no justification to avoid analgesics before surgery for fear of obscuring symptoms or signs. To minimize the risk of surgical site infection, prior to surgery broad-spectrum IV antibiotics are administered, for instance, ceftriaxone 1 to 2 g/24 hours (50-75 mg/kg/d in children) and metronidazole 500 mg/12 hours (in children 15-30 mg/kg/d and a maximum of 2 g/d). If no perforation has occurred, antibiotics are not necessary after surgery. In case of perforation antibiotics are typically continued for 4 to 7 days after source control is achieved.

2. Periappendiceal abscesses should be drained. In Canada this is most commonly done by interventional radiologists.

3. Periappendiceal phlegmons are treated with IV antibiotics in a hospital setting until general symptoms have resolved and significant reduction in the abdominal guarding in the right iliac region is observed. Oral antibiotic therapy is continued at home. Selective interval appendectomy may be performed after 8 weeks. There is accumulating data suggesting a meaningful rate of underlying malignancy in adults with perforated appendicitis and some advocate routine interval appendectomy for this reason.

We would love to hear from you

Comments, mistakes, suggestions?

We use cookies to ensure you get the best browsing experience on our website. Refer to our Cookies Information and Privacy Policy for more details.