Acute appendicitis

A 24-year-old arrives at 23:00 with eighteen hours of central abdominal pain that has migrated to the right iliac fossa, anorexia and one vomit. Every decision you will make for him — score, scan, consent for antibiotics versus theatre, and what you do when the appendix looks normal — is mapped by guideline and trial. This page gives you those decisions with their numbers attached.^[2]

Definition and the classification that matters

Acute appendicitis is acute inflammation of the vermiform appendix. The definition that changes management is not the word but the dichotomy: uncomplicated versus complicated disease. Complicated appendicitis means transmural necrosis (gangrene) or perforation, including the perforated appendix walled off as a phlegmon or presenting as a periappendiceal abscess.^[7] The WSES notes that the precise definition varies between studies — perforation is the common component, and some series also count non-perforated gangrenous appendicitis, a fecalith, or pus and purulent peritonitis.^[2]

The American Association for the Surgery of Trauma (AAST) emergency general surgery grade formalises severity: an overall grade from 1 to 5 is assigned as the highest grade across four subscales — clinical, radiographic, operative and pathologic — with grades 1–2 counting as simple and grades 3–5 as complicated. Validated prospectively across 27 centres in 2,909 appendectomies, the grade predicted infectious complications, overall complications, length of stay and the need for secondary intervention.^[11] WSES recommends adopting an intra-operative grading system such as the AAST EGS or WSES 2015 score so that postoperative management follows the grade rather than the surgeon's impression.^[2]

Two named variants deserve a line each. Recurrent appendicitis is a repeat episode after resolution — the phenomenon that makes antibiotics-first a legitimate discussion. Stump appendicitis is inflammation of the residual appendiceal stump after appendectomy; it follows the same obstructive mechanism as primary disease, a stump longer than 3–5 mm has been suggested to raise the risk, and completion appendectomy is the definitive treatment in most cases.^[23]

Epidemiology

Acute appendicitis is the most common abdominal surgical emergency worldwide and a leading cause of emergency admissions and operations.^[1] The classic life-table data remain the ones examiners quote: a lifetime risk of appendicitis of 8.6% for males and 6.7% for females, against a lifetime risk of appendectomy of 12.0% for males and 23.1% for females — the gap between those numbers is the historical negative and incidental appendectomy burden.^[3]

Incidence peaks between 10 and 30 years, with the highest age-specific rate in the 10–19 band (23.3 per 10,000 population per year in the US discharge data), and males outnumber females at every age (rate ratio 1.4:1).^[2][3] Perforation is a disease of the extremes of age — 40–57% in the youngest and 55–70% in patients over 50 — which is why the elderly section of this page is not optional reading.^[2] Mortality climbs steeply with severity: under 0.1% for non-gangrenous appendicitis, 0.6% once gangrenous, and around 5% once perforated.^[2]

Pathophysiology — one obstruction, two diseases

The traditional model is a cascade: luminal obstruction — usually a faecolith or lymphoid hyperplasia — drives a gradual rise in intraluminal pressure and localised inflammation, progressing to vascular compromise and bacterial invasion, then gangrene and perforation.^[22][23] The organisms that matter clinically are the enteric gram-negatives and anaerobes, including E. coli and Bacteroides species, which is what every antibiotic regimen on this page is designed to cover.^[2]

The fellowship-level refinement is the two-diseases hypothesis. Current evidence suggests perforation is not the inevitable end-point of obstruction: not all appendicitis progresses to perforation, and resolution may be a common event.^[2] Aetiology-based frameworks now describe acute appendicitis as a heterogeneous group of biologically distinct processes — obstruction-dominant disease tending to uncomplicated or slowly progressive courses, while virulent polymicrobial infection or ischaemic processes can precipitate complicated disease directly.^[22] This is the intellectual scaffold under antibiotics-first management: if uncomplicated appendicitis is a different disease from perforated appendicitis, treating the former without an operation stops being heresy and becomes a trial question.^[2][12]

The appendicolith deserves its own warning. It is an independent predictive factor for both perforation and failure of non-operative management, and it recurs throughout this page — in the CODA subgroup numbers, in the WSES exclusion from antibiotics-first recommendations, and in the paediatric failure rates.^[2][12]

Clinical presentation

The classic sequence is visceral then somatic pain: poorly localised periumbilical discomfort that migrates to the right iliac fossa as parietal peritoneum becomes involved, accompanied by anorexia, nausea or vomiting, and low-grade fever. Individually, no single clinical variable carries enough diagnostic weight to rule the disease in or out, which is precisely why structured scores exist.^[2]

When Alvarado analysed 305 patients in 1986, eight predictive factors emerged, ranked by diagnostic weight: localised right-lower-quadrant tenderness, leukocytosis, migration of pain, shift to the left, temperature elevation, nausea-vomiting, anorexia-acetone, and direct rebound pain.^[5] Note the order — tenderness outranks the white count, and migration outranks fever. That ranking is the answer to the viva question "which feature matters most?"

Scoring systems — Alvarado, AIR, PAS

Alvarado (1986)

Eight items, maximum 10: right-lower-quadrant tenderness 2, leukocytosis over 10,000 2, and one point each for elevated temperature (over 37.3 °C), rebound tenderness, migration of pain, loss of appetite, nausea or vomiting, and a left shift (over 75% neutrophils).^[21] Its modern role is exclusion, not confirmation: a cutoff of 5 is sufficiently sensitive to exclude appendicitis (sensitivity 99%), but WSES recommends against using the Alvarado score to positively confirm the diagnosis in adults — it is not specific enough, is unreliable at separating complicated from uncomplicated disease in the elderly, and is less sensitive in patients with HIV.^[2]

AIR (2008) — the contemporary frontrunner

The Appendicitis Inflammatory Response score was built from eight variables with independent diagnostic value: right-lower-quadrant pain, rebound tenderness, muscular defence, white cell count, neutrophil proportion, CRP, temperature and vomiting.^[6] The validated scoring (maximum 12): vomiting 1; pain in the right inferior fossa 1; rebound tenderness or muscular defence graded light 1, medium 2, strong 3; body temperature 38.5 °C or above 1; white cell count 10.0–14.9 × 10⁹/L 1, 15.0 × 10⁹/L or above 2; polymorphonuclear proportion 70–84% 1, 85% or above 2; CRP 10–49 mg/L 1, 50 mg/L or above 2.^[7]

The score stratifies three probability bands. In the STRAPPSCORE algorithm, low probability (under 5 points) went to outpatient management with planned 24-hour follow-up, medium probability (5–8) to imaging or observation with rescoring, and high probability (over 8) to immediate evaluation for exploration.^[7] The 2021 validation proposed tightening the low band to 0–3, with 4–8 medium and 9–12 high.^[7] The numbers to quote: complicated appendicitis is unlikely below 4 points (negative predictive value 99%), and appendicitis is likely above 8 points — in that validation, 3,878 patients including 821 with uncomplicated and 724 with complicated disease.^[7]

The performance data justify the preference. In the original study the ROC area was 0.97 for advanced appendicitis versus 0.92 for Alvarado, and 63% of patients were classified into the low- or high-probability group with 97.2% accuracy.^[6] The 2025 meta-analysis (26 reports, 15,699 patients) found an area under the ROC curve of 0.86 for all appendicitis and 0.93 for advanced appendicitis, greater than the Alvarado's 0.79 and 0.88; above 4 points sensitivity was 0.91 for all and 0.95 for advanced disease, and above 8 points specificity was 0.98. Its conclusion: the AIR score has a better diagnostic capacity than the Alvarado score.^[9]

And it changes what a hospital does, not just what a registrar thinks: implementing an AIR-score-based algorithm in the randomised STRAPPSCORE study cut imaging (19.2% vs 34.5%), admissions (29.5% vs 42.8%), negative explorations (1.6% vs 3.2%) and operations for non-perforated appendicitis (6.8% vs 9.7%) in low-risk patients, while intermediate-risk patients randomised to routine imaging versus observation had identical negative appendicectomy rates (6.4% vs 6.7%).^[8]

Pediatric Appendicitis Score (Samuel 2002)

Built prospectively on 1,170 children: eight variables — cough/percussion/hopping tenderness in the right lower quadrant, anorexia, pyrexia, nausea/emesis, right iliac fossa tenderness, leukocytosis, polymorphonuclear neutrophilia and migration of pain — each scoring 1, except the two physical signs (cough/percussion/hopping tenderness and RIF tenderness), which score 2, for a total of 10. In the derivation cohort it reached sensitivity 1.0, specificity 0.92, positive predictive value 0.96 and negative predictive value 0.99.^[10]

WSES position on all paediatric scores: the Alvarado and PAS are useful tools for excluding appendicitis in children, but do not make the diagnosis on a score alone.^[2]

Investigations and the imaging pathway

The structuring idea is that imaging is prescribed by pre-test probability, not ordered reflexively. WSES recommends a tailored, individualised diagnostic approach stratified by age, sex and clinical picture; clinical scores to exclude disease and to identify the intermediate-risk patients who need imaging; and timely systematic imaging for that intermediate group.^[2]

The adult pathway. Point-of-care ultrasound by an experienced operator is the recommended first-line tool when imaging is indicated, in adults and children — pooled sensitivity and specificity for POCUS are 91% and 97%.^[2] When CT is needed, contrast-enhanced low-dose CT is preferred over standard-dose: summary sensitivity 0.94, statistically indistinguishable from standard-dose (0.95), and overall CT accuracy in adults is a pooled sensitivity 0.95 and specificity 0.94 across 64 studies.^[2] The exception that examiners love: in high-risk patients younger than 40 (AIR 9–12, Alvarado 9–10, AAS 16 or above), WSES suggests cross-sectional imaging may be avoided before diagnostic ± therapeutic laparoscopy — a weak, debated recommendation, quoted here with its grade (2B).^[2] Conversely, patients with normal investigations but non-resolving right iliac fossa pain should have cross-sectional imaging before surgery.^[2]

How good is imaging at the uncomplicated/complicated call? Not as good as you would like, and every candidate quoting antibiotics-first should know it. CT discriminates complicated from uncomplicated appendicitis with a mean sensitivity of 78% and specificity of 91%; at a median prevalence of 25%, the negative predictive value is 93% but the positive predictive value only 74%. Ultrasound and MRI data are too sparse for pooled estimates. A CT that says "uncomplicated" is usually right; a CT that says "complicated" is wrong a quarter of the time.^[19]

MRI. The Cochrane review of 58 studies (7,462 participants) puts MRI at summary sensitivity 0.95 and specificity 0.96, holding up in pregnant women (0.96 and 0.97 across 21 studies) and children (0.96 and 0.96).^[18] WSES adds the crucial caveat: a negative or inconclusive MRI does not exclude appendicitis, and surgery should still be considered when clinical suspicion is high.^[2]

What CT did to the negative appendectomy rate. In an 18-year institutional series, as preoperative CT use in appendectomy patients rose from 1% to 97.5%, the negative appendectomy rate fell from 23.0% to 1.7%. That is the strongest single argument for an image-guided pathway — and the historical benchmark against which "clinical diagnosis alone" is judged.^[4]

Laboratory tests. In children, WSES recommends routine white cell count with differential, CRP and urinalysis; a CRP of 10 mg/L or above and leukocytosis of 16,000/mL or above on admission are strong predictive factors for appendicitis in paediatric patients.^[2]

Differential diagnosis

Right iliac fossa pain is a demographic sieve. In women of reproductive age, the gynaecological mimics head the list and pregnancy status must be established before imaging or incision decisions — WSES recommends against diagnosing appendicitis in pregnant patients on symptoms and signs alone.^[2] In older patients, keep colonic and appendiceal cancer on the board: elderly patients with appendicitis carry a higher risk of colonic and appendiceal cancer, and unexpected malignancy is found at appendectomy in around 3% of elderly cohorts.^[20][2] Where investigations are normal but pain persists, the pathway is cross-sectional imaging, then laparoscopy if pain progresses — laparoscopy both establishes the diagnosis and treats it.^[2]

Management — antibiotics-first versus appendicectomy

The trial trilogy — quote these precisely

APPAC (JAMA 2015). 530 Finnish adults, 18–60, with CT-confirmed uncomplicated appendicitis, randomised to appendectomy or to intravenous ertapenem 1 g/day for 3 days followed by 7 days of oral levofloxacin 500 mg once daily plus metronidazole 500 mg three times daily. 27.3% of the antibiotic group underwent appendectomy within 1 year; 72.7% did not require surgery. Against a prespecified 24% noninferiority margin, noninferiority was not demonstrated — but those who later needed appendectomy did not suffer significant complications.^[13] The 5-year follow-up, quoted in WSES 2020: late recurrence likelihood 39.1%, but overall complications significantly lower with antibiotics than surgery (6.5% vs 24.4%).^[2]

APPAC II (JAMA 2021). Could the whole course be oral? Oral moxifloxacin 400 mg/day for 7 days versus intravenous ertapenem 1 g/day for 2 days then oral levofloxacin 500 mg/day plus metronidazole 500 mg three times daily for 5 days, in 599 CT-confirmed uncomplicated patients. Treatment success at 1 year: 70.2% oral versus 73.8% intravenous-then-oral — both above the 65% success threshold, but noninferiority of the all-oral regimen was not demonstrated.^[14]

CODA (NEJM 2020). The pragmatic giant: 1,552 adults at 25 US centres, a 10-day antibiotic course versus appendectomy, primary outcome 30-day EQ-5D health status. Antibiotics were noninferior (mean difference 0.01 points, within the 0.05 margin). But by 90 days, 29% of the antibiotics group had undergone appendectomy — 41% of those with an appendicolith versus 25% without — and complications were commoner with antibiotics (8.1 vs 3.5 per 100 participants; rate ratio 2.28), driven by the appendicolith subgroup.^[12] The CODA recurrence analysis adds texture: among those who avoided appendectomy in the first 30 days, the estimated appendectomy rate between 30 days and 1 year was 28.6%, with baseline nausea, vomiting or anorexia — not the appendicolith — the factor most associated with later appendectomy.^[15]

The guideline position

WSES 2020 recommends discussing non-operative management with antibiotics as a safe alternative to surgery in selected patients with uncomplicated appendicitis and absence of appendicolith, advising of the possibility of failure and of misdiagnosed complicated disease (1A) — with the patient told that recurrence risk is up to 39% at 5 years.^[2] WSES 2025 confirms nonoperative management with antibiotics is safe and effective in selected patients with uncomplicated appendicitis, with recommendations tailored to specific populations.^[1] The regimen should start intravenous and switch to oral by clinical response; the empiric regimens WSES lists for non-critically ill community-acquired intra-abdominal infection are amoxicillin/clavulanate 1.2–2.2 g 6-hourly, or ceftriaxone 2 g 24-hourly plus metronidazole 500 mg 6-hourly, or cefotaxime 2 g 8-hourly plus metronidazole 500 mg 6-hourly; for beta-lactam allergy, ciprofloxacin 400 mg 8-hourly plus metronidazole 500 mg 6-hourly or moxifloxacin 400 mg 24-hourly; where ESBL-producing Enterobacterales are a risk, ertapenem 1 g 24-hourly.^[2]

Operative management

Approach. Laparoscopic appendectomy is the preferred approach over open for both uncomplicated and complicated disease where equipment and expertise exist (1A): less pain, lower surgical-site infection rates, shorter stay, earlier return to work.^[2] WSES 2025 states laparoscopic appendectomy remains the standard surgical approach.^[1] The historical caveat — a higher intra-abdominal abscess rate after laparoscopy — has eroded: in the cumulative meta-analysis quoted by WSES, the signal favouring open surgery disappeared for trials published after 2001 (overall cumulative OR 1.32, 95% CI 0.84–2.10).^[2] Three-port conventional laparoscopy beats single-incision laparoscopy (shorter operating time, less pain, fewer wound infections — 1A), and the laparoscopic approach is specifically suggested for obese patients, older patients and those with high perioperative risk (2B).^[2]

Timing. Plan laparoscopic appendectomy for the next available operating list within 24 hours for uncomplicated appendicitis, and do not delay beyond 24 hours from admission (both 1B).^[2] WSES 2025 reiterates that appendectomy for uncomplicated appendicitis may be safely delayed within 24 hours without increased adverse outcomes.^[1] The NSQIP data behind the rule: operations on hospital day 1 or 2 fare alike; day-3 appendectomies carry significantly worse outcomes (30-day mortality 0.6% and major complications 8%, versus 0.1% and 3.4% on day 1).^[2]

Intra-operative detail — the viva checklist.^[2]

• Stump closure: endoloops/suture ligation or polymeric clips for uncomplicated and complicated disease; endostaplers reserved for complicated cases at the surgeon's discretion (1B). Simple ligation over stump inversion, open or laparoscopic (1A).
• Peritoneal toilet: suction alone, not irrigation, for intra-abdominal collections in complicated appendicitis (1B) — irrigation adds operating time without reducing abscess or SSI.
• Drains: recommended against after appendectomy for complicated appendicitis in adults (1B); they do not prevent abscess and lengthen stay.
• Wound (open cases): wound ring protectors reduce SSI (1B); primary skin closure with a single absorbable intradermal suture rather than delayed primary closure (2B).
• Grading: adopt an intra-operative grading system (AAST EGS or WSES 2015) to steer postoperative care (2B).
• Histology: routine histopathology after appendectomy is recommended (1B) — 27% of appendices the surgeon calls normal show inflammation histologically, and 9.6% of macroscopically inflamed ones are normal.^[2]

Ambulatory appendectomy. Outpatient laparoscopic appendectomy for uncomplicated disease is feasible and safe where an ambulatory pathway with defined ERAS protocols and proper consent exists (2B).^[2]

Complicated appendicitis — phlegmon and abscess

Phlegmon and abscess account for 2–10% of acute appendicitis.^[17] The conservative pathway works: non-surgical treatment of appendiceal abscess or phlegmon succeeds in over 90% of patients, with an overall recurrence risk of 7.4% and only 19.7% of abscesses requiring percutaneous drainage.^[2] Where advanced laparoscopic expertise is unavailable, WSES suggests antibiotics plus — if available — percutaneous drainage for a periappendiceal abscess (2B); where that expertise exists, the laparoscopic approach is the suggested treatment of choice, with a low threshold for conversion (2B).^[2] The Cochrane review of early versus delayed appendicectomy for phlegmon or abscess — two RCTs, 80 participants in total — concludes honestly that it is unclear whether early appendicectomy prevents complications; the evidence is very low quality and the data are sparse.^[17]

Interval appendectomy. Recurrence after non-surgical treatment of perforated appendicitis and phlegmon runs 12–24%, yet routine interval appendectomy means operating on eight patients to prevent one recurrence, with its own morbidity. WSES recommends against routine interval appendectomy after non-operative management in young adults (under 40) and children, reserving it for those with recurrent symptoms (1B).^[2]

Antibiotics around surgery — get the durations right

This is the most quotable drug section on the page.^[2]

• Preoperative: a single dose of broad-spectrum antibiotics before appendectomy (from 0–60 minutes before skin incision) reduces wound infection and intra-abdominal abscess (1A).
• Uncomplicated appendicitis: no postoperative antibiotics at all (1A).
• Complicated appendicitis with adequate source control: do not prolong antibiotics beyond 3–5 days postoperatively (1A); WSES 2025 tightens this to short courses of 2–3 days in complicated disease.^[1]
• The trial behind the duration: STOP-IT randomised 518 patients with complicated intra-abdominal infection and adequate source control to a fixed 4±1-day course versus antibiotics until 2 days after resolution of fever, leukocytosis and ileus (median 8 days). The composite of surgical-site infection, recurrent infection or death was identical — 21.8% versus 22.3% — establishing that four days is enough when the source is controlled.^[16]
• Children with complicated appendicitis: switch to oral antibiotics after 48 hours, total course shorter than seven days (1B); the target organisms remain enteric gram-negatives and anaerobes including E. coli and Bacteroides species.^[2]

Special populations

Pregnancy. Do not diagnose on symptoms and signs alone — WSES says so explicitly, and physiological leukocytosis plus first-trimester nausea degrade the Alvarado score's accuracy.^[2] Image with graded-compression transabdominal ultrasound first (2C), then MRI after inconclusive ultrasound where available (2B) — MRI in pregnancy performs at sensitivity 0.96 and specificity 0.97 in the Cochrane subgroup, but a negative MRI does not exclude the disease when suspicion is high.^[18][2] When surgery is indicated, laparoscopic appendectomy is suggested over open (2B). Non-operative management during pregnancy is recommended against until higher-level evidence exists (2C). A short in-hospital delay with observation and repeat ultrasound for equivocal cases is acceptable and does not appear to increase maternal or fetal adverse outcomes.^[2]

Children. Ultrasound first-line; against routine CT as first-line imaging for right iliac fossa pain in children (2B); scores exclude but never diagnose alone (2C). Non-operative management is feasible, safe and effective as initial treatment for uncomplicated appendicitis without an appendicolith (2B) — but say the appendicolith number out loud: non-operative failure with an appendicolith was 60% at a median follow-up under five months in the Mahida prospective trial. Laparoscopy is preferred in children where expertise exists (1B).^[2]

Elderly. The SIFIPAC/WSES 2019 elderly guideline summarises why this group is different: higher mortality, higher perforation rate, lower diagnostic accuracy, longer delay from symptom onset to admission, higher postoperative complication rate, and a higher risk of colonic and appendiceal cancer.^[20] WSES 2025 covers patients of 65 and over as a named population within its 35 recommendations.^[1] The perforated-rate number from the epidemiology section — 55–70% over 50 — belongs in every elderly answer.^[2]

Immunocompromised. In patients with haematological malignancy or chemotherapy-induced leukopenia, presentation is often atypical with blunted fever and inflammatory markers, and clinical scoring systems demonstrably underestimate the likelihood of appendicitis — abdominal pain with an elevated CRP should trigger multidisciplinary evaluation and timely imaging, and laparoscopic appendectomy appears safe and feasible.^[21] WSES 2025 includes immunocompromised individuals and patients with obesity (BMI 30 or above) in its scope.^[1]

Complications and prognosis

The disease complications are the cascade made clinical: gangrene, perforation, periappendiceal abscess or phlegmon, generalised peritonitis and sepsis, with mortality stepping from under 0.1% through 0.6% to around 5% as severity rises.^[2] The operation's complications — wound infection, intra-abdominal abscess and ileus — occur more often after open than laparoscopic appendectomy (overall complication rates 11.1% versus 8.7%).^[2] The AAST grade is the validated yardstick: length of stay, infectious complications, overall complications and secondary interventions all climb with grade in the EAST multicentre validation.^[11]

And one number to end the prognosis discussion: with modern imaging, a negative appendectomy should now be rare — the CT era took one institution's negative appendectomy rate from 23.0% to 1.7%, and an AIR-based pathway safely reduces imaging, admissions and negative explorations rather than trading them for missed disease.^[4][8]

Revision summary

• The pivotal classification is uncomplicated versus complicated (gangrenous, perforated, phlegmon, abscess); grade it with AAST EGS.^[7][11]
• AIR first, Alvarado to exclude, PAS in children — and no score diagnoses a child or a pregnant woman alone.^[2][9]
• Imaging is prescribed by risk band: POCUS/US first, low-dose CT, MRI in pregnancy; CT's uncomplicated/complicated call has a 93% NPV but only a 74% PPV.^[2][19]
• Antibiotics-first is legitimate for CT-confirmed uncomplicated disease without an appendicolith — counselled with CODA (29% appendectomy by 90 days; 41% with an appendicolith) and APPAC (72.7% surgery-free at 1 year; 39.1% recurrence at 5 years).^[12][13][2]
• Laparoscopic appendectomy on the next list within 24 hours; single preoperative dose, no postoperative antibiotics if uncomplicated, 3–5 days if complicated with source control (STOP-IT logic).^[2][16]
• Phlegmon/abscess: antibiotics ± drainage where laparoscopic expertise is scarce; no routine interval appendectomy under 40; colonoscopy and interval CT over 40.^[2]