General Surgery

Acute Appendicitis

Acute inflammation of the appendix usually causes migrating abdominal pain and right iliac fossa peritonism, but atypical presentations and complications require early senior assessment, targeted imaging and timely source control.

Definition

Acute appendicitis is acute inflammation of the vermiform appendix. It commonly follows obstruction of the appendiceal lumen but can present variably and may progress to perforation, a contained mass or abscess, generalised peritonitis and sepsis.

Epidemiology

Appendicitis is commonest in children and young adults but occurs at any age. Older age, pregnancy, unusual appendix position and immunosuppression can make diagnosis less typical and complications more consequential.

Pathophysiology

Luminal obstruction can cause distension, bacterial inflammation, venous congestion and progressive wall injury. Visceral pain may be poorly localised initially; parietal peritoneal irritation produces more localised pain. Progression is variable: inflammation may remain uncomplicated, resolve with treatment, or cause perforation with a contained abscess or free peritonitis.

First principles

The inflammatory process explains the classic pain migration

Early appendiceal distension produces poorly localised visceral pain, often around the umbilicus. As inflammation reaches the parietal peritoneum, pain becomes sharper and more localised, classically in the right iliac fossa. This pattern is helpful but not obligatory: appendix position, pregnancy, age and perforation can all alter the presentation.^1,2

Atypical anatomy and patient factors matter

A retrocaecal, pelvic or unusually positioned appendix can produce flank, pelvic or suprapubic symptoms rather than textbook right iliac fossa pain. Children, older adults, pregnant patients and people with cognitive impairment or immunosuppression may present with less specific symptoms or less obvious peritonism, so a reassuring single sign should not end the assessment.^1,2,3

Diagnosis is clinical, supported by tests and imaging

No single symptom, examination sign, blood test or score safely confirms or excludes appendicitis. Use the history, serial examination, physiology and differential diagnosis together. Local pathways may use a validated score to structure communication or select imaging, but a score should not replace senior review when the patient is unwell or the diagnosis remains uncertain.^1,4,3

Perforation changes the problem from local inflammation to source control

A perforated appendix can cause a contained mass or abscess, or free peritonitis with sepsis. A brief improvement in pain followed by worsening, diffuse pain or systemic deterioration is not reassurance. The immediate priorities become resuscitation, appropriate antimicrobial treatment, senior surgical decision-making and source control where required.^2,5,3,6,7

The treatment branch depends on the clinical and anatomical picture

For uncomplicated appendicitis, laparoscopic appendicectomy remains the usual definitive treatment where feasible. Selected patients may follow an antibiotics-first pathway after specialist assessment, while an appendix mass or abscess often needs initial antibiotics with or without radiological drainage. Generalised peritonitis or deterioration requires urgent source-control planning rather than a routine outpatient approach.^2,4,3

Presentation

Pain often starts centrally and migrates to the right iliac fossa, with anorexia, nausea or vomiting and localised tenderness, but children, pregnancy and older age can produce atypical symptoms.^1,2,3,8

Cardinal features

Abdominal pain that may begin centrally and move to the right iliac fossa
Anorexia, nausea or vomiting, usually after the pain begins
Fever, tachycardia or other systemic inflammatory features
Right iliac fossa tenderness, guarding or pain with movement
Change in bowel or urinary symptoms with a pelvic or retrocaecal appendix
Atypical pain location or muted peritonism in pregnancy, children, older adults or immunosuppression

Red flags

Generalised peritonism, rigidity, shock, altered mental state or rapidly worsening physiology
Sudden temporary improvement followed by diffuse abdominal pain, suggesting perforation
Persistent vomiting, dehydration or inability to tolerate oral intake
A palpable right iliac fossa mass or imaging evidence of an appendix abscess
Pain in a person who could be pregnant, especially with vaginal bleeding, syncope or haemodynamic compromise
Severe pain out of proportion to examination or a high-risk older, frail or immunocompromised patient

Investigations

Clinical assessment, serial examination and physiological risk

Record the time course and migration of pain, anorexia, vomiting, bowel and urinary symptoms, menstrual or pregnancy history, previous surgery and comorbidity. Examine for focal or generalised peritonism and assess observations, perfusion and urine output. Repeat assessment when the diagnosis is uncertain or the patient changes.

Expected finding: Migratory pain and right iliac fossa tenderness support appendicitis, but normal observations or absent classic signs do not exclude early, atypical or complicated disease.

^1,2,3

FBC, CRP, U&E and targeted blood tests

FBC and CRP support assessment of inflammation and severity; U&E assesses dehydration and renal function before treatment or imaging. Add venous blood gas with lactate, glucose and ketones, blood cultures, amylase or lipase, liver tests and group-and-save when the presentation or physiology warrants them.

Expected finding: Neutrophilia or raised CRP may support the diagnosis, but early or normal results do not exclude appendicitis. Rising lactate, acidosis or organ dysfunction increases concern for sepsis or another surgical emergency.

^1,3,5

Urinalysis and pregnancy test

Urinalysis helps assess urinary mimics; mild urinary abnormalities can occur when a pelvic appendix irritates the urinary tract. Perform a pregnancy test in anyone who could be pregnant, because ectopic pregnancy can mimic appendicitis and pregnancy changes imaging and specialist pathways.

Expected finding: A positive pregnancy test with pain or tenderness requires urgent early-pregnancy or gynaecology assessment; a negative urine test does not exclude appendicitis.

^1,2,8,3

Risk score as an adjunct, not a rule-out test

Alvarado or another local pathway score can make the clinical reasoning explicit and support observation or imaging decisions. Do not use a score alone to discharge a patient with concerning examination, physiology or an alternative diagnosis; current UK surgical guidance notes limited evidence for routine reliance on scoring systems.

Expected finding: An intermediate or discordant score should lead to serial examination, imaging or senior review rather than false reassurance.

^1,4

Ultrasound in children, pregnancy and selected presentations

Use ultrasound according to the local pathway, particularly in children and pregnancy or when a pelvic or gynaecological cause is possible. It may identify an inflamed appendix or an alternative diagnosis, but a non-diagnostic scan does not exclude appendicitis and should be followed by reassessment and specialist-directed imaging.

Expected finding: A non-compressible inflamed appendix, periappendiceal fluid or an alternative pelvic pathology may be seen; sensitivity is operator- and patient-dependent.

^2,4,8

CT abdomen and pelvis for an equivocal or complicated adult presentation

In a stable adult with diagnostic uncertainty or concern for perforation, abscess, obstruction or another intra-abdominal diagnosis, CT can define the appendix and complications and reduce unnecessary negative surgery. Select the protocol with senior and radiology input; do not delay resuscitation, senior surgical review or source control in an unstable patient.

Expected finding: A dilated inflamed appendix, appendicolith, periappendiceal inflammation, abscess, free gas, free fluid or an alternative diagnosis may be demonstrated.

^1,2,4,3

Management

Step	Detail	Source
Stabilise, relieve symptoms and involve senior surgery early	Use ABCDE, monitoring, IV access, appropriate fluids, analgesia and antiemetics. Keep a patient likely to need a procedure nil by mouth, but do not withhold analgesia because of a fear that it will obscure the diagnosis. Reassess observations and the abdominal examination after treatment; urgent senior surgical review is required for peritonism, deterioration or suspected complication.^3,5	RCEM emergency-laparotomy advisory statement; NICE suspected-sepsis guidance
Exclude dangerous mimics in parallel	Ask about pregnancy possibility and perform a pregnancy test where relevant. Use urinalysis and targeted assessment for urinary disease, pelvic emergencies, gastroenteritis, inflammatory bowel disease, bowel obstruction, pancreatitis and other causes. Consider DKA, ACS, sickle-cell disease or lower-lobe respiratory disease when the presentation is atypical.^8,2,3	NICE NG126; NHS appendicitis; RCEM emergency-laparotomy advisory statement
Investigate according to the patient group and diagnostic uncertainty	Send FBC, CRP and U&E, adding lactate, glucose and ketones, cultures, amylase or lipase, liver tests and group-and-save when clinically indicated. Use a local validated score only as an adjunct. In children and pregnancy, follow the local ultrasound-first pathway; in a stable adult with unresolved uncertainty or suspected complication, discuss CT with senior surgery and radiology.^1,2,4	NICE CKS appendicitis; NHS appendicitis; RCS/ASGBI emergency general surgery guide
Treat suspected intra-abdominal sepsis without unsafe delay	If perforation, abscess, generalised peritonitis or systemic infection is suspected, follow the current NICE sepsis pathway and local antimicrobial policy. For adults at high risk of severe illness or death, NICE recommends broad-spectrum IV antibiotics within 1 hour of the first NEWS2 score and IV fluid treatment without delay unless contraindicated. Use BNF and local policy for the chosen regimen, allergies, renal function and duration; do not invent a dose in a general textbook pathway.^5,6,7	NICE NG253; BNF co-amoxiclav and metronidazole monographs
Offer laparoscopic appendicectomy for usual uncomplicated disease	For a fit patient with suspected or imaging-confirmed uncomplicated appendicitis, discuss laparoscopic appendicectomy with the surgical team; it remains the usual definitive treatment and is preferred over open surgery where feasible. Timing should follow the local emergency-surgery pathway and the patient's physiology. Do not convert a stable case into unsafe haste, but do not treat a time-critical deterioration as a routine elective case.^2,4	NHS appendicitis; RCS/ASGBI emergency general surgery guide
Use an antibiotics-first pathway only in selected patients	Antibiotics without immediate appendicectomy may be considered for selected patients, particularly when operative risk is high or surgery is declined, after specialist assessment and an explicit local pathway. Discuss failure or recurrence, ensure reliable review and give clear return precautions. Antibiotics-only treatment is not a universal substitute for source control in perforation, generalised peritonitis or clinical deterioration.^2,4,5	NHS appendicitis; RCS/ASGBI emergency general surgery guide
Escalate perforation, peritonitis or deterioration for source control	Generalised peritonitis, shock, worsening sepsis, uncontrolled pain or suspected perforation require urgent senior surgical, anaesthetic and critical-care planning. Continue resuscitation and appropriate antimicrobial treatment while arranging operative or procedural source control. Do not delay referral while waiting for a definitive scan or a perfect diagnostic label.^3,5	RCEM emergency-laparotomy advisory statement; NICE suspected-sepsis guidance
Manage an appendix mass or abscess as a complicated presentation	Use imaging and senior surgical review to distinguish a contained mass or abscess from free peritonitis. Initial treatment may include antibiotics and, where feasible, image-guided drainage; surgery is individualised according to anatomy, response, recurrence, underlying pathology and local specialist practice. A later appendicectomy is not an automatic rule for every patient.^2,3,5	NHS appendicitis; RCEM emergency-laparotomy advisory statement
Monitor after surgery or non-operative treatment	Review pain, fever, tachycardia, abdominal findings, wound, bowel function, oral intake and inflammatory or organ-function trends. Persistent or recurrent fever, worsening pain, ileus, sepsis or failure to improve should prompt senior review and consideration of CT for a postoperative or residual collection. Check the operative and histology findings and arrange follow-up according to the surgical plan.^2,1	NHS appendicitis; NICE CKS appendicitis
Make discharge and longer-term follow-up safe	Do not discharge with uncontrolled pain or vomiting, residual high-risk diagnostic uncertainty, concerning physiology or inadequate follow-up. Give return precautions for worsening or diffuse pain, fever, persistent vomiting, collapse, wound problems or inability to eat and drink. In an older patient, or anyone with persistent bowel symptoms, anaemia or concerning imaging or histology, discuss colorectal assessment; NICE recommends FIT-based suspected-colorectal-cancer pathways in relevant symptomatic adults and says strong clinical concern should not be delayed by a negative or missing FIT.^2,9	NHS appendicitis; NICE HTG690

Illustrations

Mechanism of migratory pain in appendicitisDiagram showing appendiceal inflammation, early visceral peri-umbilical pain and later parietal peritoneal irritation localising pain to the right iliac fossa. Include a note that appendix position and patient factors can make the pattern atypical.PassFinals · original

CT appearance of acute appendicitisAxial contrast CT image showing a dilated, thick-walled appendix with surrounding fat stranding and a possible appendicolith; image is for recognition and does not replace clinical assessment.James Heilman, MD, Wikimedia Commons · CC-BY-SA-3.0

Gross pathology of acute appendicitisResected inflamed appendix with an exudate-covered serosal surface, illustrating the macroscopic correlate of transmural inflammation.Ed Uthman from Houston, TX, USA, Wikimedia Commons · CC-BY-2.0

Differentials

Ectopic pregnancy

Abdominal or pelvic pain with a positive pregnancy test, vaginal bleeding, syncope or haemodynamic compromise; urgent early-pregnancy or gynaecology assessment is required.

Ovarian torsion or ruptured ovarian cyst

Sudden pelvic pain, vomiting or adnexal tenderness; assess urgently with gynaecology and appropriate ultrasound.

Mesenteric adenitis

Often follows a viral illness in a child and can mimic appendicitis; clinical course and imaging help distinguish it.

Ureteric colic or urinary infection

Loin-to-groin colic, haematuria, dysuria or fever; an infected obstructed system is an emergency.

Terminal ileitis, Crohn disease or Meckel diverticulitis

Persistent or recurrent symptoms, diarrhoea, systemic inflammation or imaging findings suggesting small-bowel disease.

Gastroenteritis or bowel obstruction

Diarrhoea and sick contacts favour gastroenteritis; distension, vomiting and obstipation favour obstruction, especially after previous surgery.

Colorectal or appendiceal neoplasia

Older age, recurrent symptoms, iron-deficiency anaemia, altered bowel habit, weight loss or concerning imaging or histology should prompt colorectal assessment.

Complications

Perforation with a contained appendix mass or abscess
Generalised peritonitis, sepsis and septic shock
Pelvic or intra-abdominal collection
Wound infection, postoperative ileus or adhesional bowel obstruction
Failure or recurrence after selected non-operative treatment
Missed alternative or underlying pathology, including colorectal or appendiceal neoplasia

Prognosis

Most uncomplicated cases recover well after timely treatment. Complications, delayed diagnosis, older age, frailty, pregnancy and immunosuppression increase the risk of perforation, sepsis, prolonged admission and postoperative morbidity.

Guidelines

Appendicitis (NICE CKS, 2026)
Appendicitis (NHS, 2024)
Advisory Statement regarding adults presenting to the Emergency Department who may require an emergency laparotomy (Royal College of Emergency Medicine, 2024)
Suspected sepsis in people aged 16 or over: recognition, assessment and early management (NG253) (NICE, 2025)

References

Evidence checked: 2026-08-03

This page is exam revision material, not medical advice, and must not be used for patient care. Always check drug doses against the BNF and current guidance. Full disclaimer.