Appendicitis

01OverviewDefinition, clinical context and the essential points that orientate the chapter.

Luminal obstruction, bacterial proliferation, venous congestion and ischaemia can progress from uncomplicated inflammation to gangrene, perforation, abscess or diffuse peritonitis. Time course is variable, so a modest early inflammatory response does not establish safety.

The central decision is whether the patient needs prompt operative source control, further imaging, or observation with serial review. Diagnostic certainty must be balanced against radiation exposure, fertility and pregnancy considerations, and the harm of delayed treatment.

Important mimics include ectopic pregnancy, ovarian torsion, pelvic inflammatory disease, ureteric colic, Crohn terminal ileitis, gastroenteritis, mesenteric adenitis, diverticulitis and caecal malignancy. A diagnosis of appendicitis should explain the complete presentation rather than merely a raised white count.

Key points

Classic appendicitis begins with poorly localised central abdominal pain that migrates to the right iliac fossa as parietal peritoneum becomes inflamed.
Anorexia, nausea, low-grade fever and focal guarding support the diagnosis, but their absence does not exclude appendicitis in older adults, pregnancy or immunosuppression.
Retrocaecal inflammation may cause flank or back pain with little anterior guarding; a pelvic appendix may produce suprapubic pain, diarrhoea or urinary symptoms.
Check pregnancy status in anyone with reproductive potential because ectopic pregnancy changes both urgency and the safest imaging pathway.
Ultrasound is preferred first in many children and pregnant patients; CT is usually the most accurate test for non-pregnant adults with diagnostic uncertainty.
Risk scores organise probability but cannot replace repeated examination, imaging and senior review when the clinical course is discordant.
Appendicectomy remains usual definitive treatment; antibiotics alone may be discussed for carefully selected imaging-confirmed uncomplicated disease with explicit recurrence and failure counselling.
An appendiceal mass or abscess may need antibiotics, image-guided drainage and delayed evaluation rather than hazardous immediate dissection; the colorectal cause must be considered in older patients.

02AetiologyUnderlying causes, associations and risk factors, with why each one matters.

Luminal obstruction

Faecolith, lymphoid swelling or luminal narrowing can obstruct drainage, although a definite obstructing lesion is not found in every case.

Infective and inflammatory factors

Mucosal inflammation and bacterial overgrowth contribute after stasis; enteric infection may precede lymphoid enlargement, particularly in younger patients.

Occult neoplastic obstruction

Appendiceal or caecal neoplasia is an uncommon but important cause in older adults or atypical, recurrent and mass-forming presentations.

03PathophysiologyThe causal sequence from the underlying abnormality to symptoms and harm.

1
Distension and visceral pain
Obstruction causes continuing secretion, luminal pressure and poorly localised midgut visceral pain, commonly felt centrally before localisation.
2
Inflammation and localisation
Venous congestion and bacterial invasion extend to the serosa, irritating adjacent parietal peritoneum and localising tenderness to the right lower quadrant.
3
Gangrene and perforation
Persistent pressure compromises arterial supply, causing necrosis, rupture, local abscess or diffuse faecal contamination and sepsis.

04Clinical features and red flagsSymptoms, examination findings, patterns of presentation and time-critical warnings.

Typical localised appendicitisRed flag

Pain migrates from periumbilical or epigastric discomfort to the right iliac fossa, with anorexia, nausea and focal tenderness near McBurney's point; movement, coughing or percussion may worsen pain.

Complicated appendicitisRed flag

High fever, tachycardia, marked guarding, rebound, a palpable mass, prolonged symptoms or systemic toxicity suggest gangrene, perforation, phlegmon or abscess and require urgent surgical planning.

Pelvic or retrocaecal appendix

Pelvic irritation may cause urinary frequency, loose stool, rectal tenderness or pain on hip rotation; retrocaecal disease can cause flank pain and a psoas sign with sparse anterior findings.

Pregnancy presentationRed flag

Anatomical displacement and physiological leucocytosis can blur classic signs. Maintain early obstetric and surgical involvement and use pregnancy-adapted ultrasound or MRI pathways rather than delaying assessment.

Older or immunocompromised patientRed flag

Pain, fever and leukocytosis can be muted despite perforation. Lower the threshold for CT and senior review, and consider caecal cancer or another structural lesion.

05InvestigationsWhat to request, why it matters and how to interpret it.

Investigation order

Read from the initial assessment onwards. Tests may run in parallel in urgent care; first-line, preferred, confirmatory, definitive and gold-standard labels appear only when the chapter explicitly states them.

01
Serial abdominal examination and observationsFirst step
Why
Track localisation, peritonism and physiological deterioration over time.
Interpretation and limitations
Increasing focal guarding or spreading tenderness despite analgesia raises concern. A transiently comfortable examination after opioids does not exclude disease; appropriate analgesia improves humane and reliable assessment.
02
Full blood count and C-reactive protein
Why
Support inflammatory assessment and provide a trend.
Interpretation and limitations
Neutrophilia and rising CRP increase probability but are nonspecific. Normal early results do not rule out appendicitis, while very high markers or thrombocytopenia may accompany complicated sepsis.
03
Urinalysis and renal biochemistry
Why
Assess hydration and identify urinary mimics before contrast imaging.
Interpretation and limitations
Mild pyuria or microscopic haematuria can arise from an inflamed pelvic appendix and must not automatically establish urinary infection; marked colic and hydronephrosis point elsewhere.
04
Pregnancy test
Why
Identify pregnancy and trigger the correct differential and imaging route.
Interpretation and limitations
A positive result requires urgent assessment for pregnancy location when pain is present. Do not assume pain is appendicitis until ectopic pregnancy has been addressed.
05
Graded-compression abdominal ultrasound
Why
Look for a non-compressible enlarged appendix, inflammation or gynaecological pathology without radiation.
Interpretation and limitations
A clearly visualised inflamed appendix supports diagnosis; non-visualisation is common and is not a negative test. Escalate imaging or observation according to probability.
06
Contrast-enhanced CT abdomen and pelvis
Why
Confirm appendicitis, identify complications and expose alternative diagnoses.
Interpretation and limitations
Appendiceal enlargement, wall enhancement, fat stranding, appendicolith, collection or extraluminal gas inform treatment. Use protocol and contrast decisions based on renal function and local radiology advice.
07
MRI abdomen in pregnancy
Why
Evaluate suspected appendicitis without ionising radiation when ultrasound is inconclusive.
Interpretation and limitations
Availability and expertise vary; urgent surgical and obstetric assessment continues while imaging is arranged, and instability or peritonitis should not wait for MRI.

06Differential diagnosisRealistic alternatives and the features that help distinguish them.

Gastroenteritis or ileitis

Prominent diarrhoea, diffuse cramps, sick contacts or imaging showing terminal ileitis without an inflamed appendix favours infectious or inflammatory enteritis.

Gynaecological emergency

Pregnancy possibility, vaginal bleeding, discharge or adnexal findings require assessment for ectopic pregnancy, torsion or pelvic inflammatory disease.

Urinary or renal disease

Flank-to-groin colic, haematuria or urinary symptoms favour ureteric stone or infection, although reactive urinary abnormalities may occur beside an inflamed appendix.

Additional chapter-specific clues

Alternative time-critical diagnosisRed flag

Haemodynamic compromise, vaginal bleeding, sudden unilateral pelvic pain, pain out of proportion, pulsatile mass or testicular pain should redirect immediately toward ectopic pregnancy, torsion, ischaemia, aneurysm or torsion.

07ManagementImmediate care, first-line treatment, alternatives and escalation.

01Initial careSuspected uncomplicated appendicitisFirst stepLocalised right iliac fossa pain without shock or generalised peritonitis.

1Assess ABCDE, provide analgesia and antiemetic treatment, establish venous access, check hydration and keep the patient nil by mouth pending a surgical decision.
2Obtain blood tests, urinalysis and a pregnancy test where relevant; involve the acute surgical team and document serial examinations rather than relying on one score.
3Select ultrasound, CT or MRI using age, pregnancy status, probability and local expertise; if imaging remains equivocal, agree observation and reassessment intervals explicitly.
4When confirmed, discuss laparoscopic appendicectomy and perioperative antibiotics; antibiotics-first care is restricted to selected uncomplicated cases with informed consent and reliable follow-up.

02SepsisPerforation and diffuse peritonitisGeneralised guarding, haemodynamic compromise, organ dysfunction or imaging evidence of free perforation.

1Begin sepsis-focused resuscitation, obtain cultures when this does not delay treatment, correct fluids and electrolytes and administer local broad-spectrum intra-abdominal antibiotics promptly.
2Alert senior surgery, anaesthesia and critical care; obtain CT if it will change operative planning and the patient is stable enough, but do not defer source control for unnecessary imaging.
3Proceed to operative source control selected for the findings, with washout and management of any collection; convert or extend the operation when anatomy or safety demands it.
4After intervention, monitor for abscess, ileus, wound infection and ongoing sepsis; narrow antimicrobial therapy using cultures and clinical response under stewardship guidance.

03Contained diseaseAppendiceal mass or abscessA localised collection or inflammatory phlegmon without generalised peritonitis.

1Discuss promptly with experienced general or colorectal surgery and radiology teams, because immediate operation can be technically difficult and is not mandatory for every stable patient.
2Treat selected stable cases with antimicrobial therapy and close observation; request image-guided drainage when a drainable abscess, sepsis or poor response makes this appropriate.
3EscalationEscalate to surgery for deterioration, uncontrolled sepsis, diagnostic doubt or failed non-operative management rather than persisting with an ineffective plan.
4Arrange follow-up to consider interval appendicectomy and colonic evaluation based on age, imaging, recurrence and suspicion of appendiceal or caecal neoplasia.

Key medicines and prescribing safety3 treatments · regimens, roles and cautions

Reduces wound and intra-abdominal infection associated with operative appendicitis treatment.

Perioperative antibiotic prophylaxis

Give the local appendicectomy prophylaxis regimen within the approved pre-incision window.

Check allergy, renal function, pregnancy and local resistance patterns. Prophylaxis duration differs from therapeutic courses used for perforation and should not be extended automatically.

Treat complicated appendicitis, abscess, perforation or sepsis and selected non-operative uncomplicated disease.

Therapeutic broad-spectrum antibiotics

Use the local intra-abdominal infection protocol and review after source control.

Antibiotics do not replace drainage of uncontrolled infection. Obtain cultures when useful, adjust for organ impairment, document review dates and follow antimicrobial stewardship advice.

Provides humane pain control while diagnostic and operative decisions continue.

Opioid-sparing analgesia

Titrate paracetamol and, when suitable, anti-inflammatory or opioid rescue to effect.

Do not withhold analgesia to preserve signs. Check renal, hepatic, gastrointestinal and pregnancy cautions; titrate opioids with respiratory and sedation monitoring.

08ComplicationsImportant consequences, why they occur and why they matter clinically.

Perforation and abscess

Necrosis may produce a contained right iliac fossa collection or free perforation with generalised peritonitis requiring urgent source control.

Sepsis and organ dysfunction

Delayed treatment can lead to bacteraemia, hypotension, kidney injury and respiratory or circulatory failure, especially in frail patients.

Postoperative infection or ileus

Contamination increases wound and intra-abdominal abscess risk, while inflammation and surgery can temporarily impair bowel motility and prolong recovery.

09Monitoring and follow-upTreatment response, safety checks and longer-term review.

Repeat pulse, blood pressure, respiratory rate, temperature, oxygen saturation, mental state and urine output; calculate the local early-warning score and act on deterioration.
Re-examine the abdomen after analgesia and at agreed intervals, recording localisation, guarding, distension and whether symptoms are resolving or spreading.
Trend white count, CRP, renal function, electrolytes and lactate when severe disease is suspected; biochemical improvement cannot overrule worsening peritonism.
After appendicectomy, monitor oral intake, bowel function, pain, fever, wound condition and signs of intra-abdominal collection, with clear discharge safety-netting.
During non-operative treatment, define failure criteria, review timing and rapid re-access; counsel that recurrence remains possible after apparent initial success.

10Special situationsVariants, exceptions and circumstances that change the usual approach.

Migration is informative but imperfect

Visceral midgut pain may precede local parietal irritation, producing classic migration. Some patients start with right-sided pain, and retrocaecal anatomy can conceal it.

Urinary abnormalities can mislead

An adjacent inflamed appendix may cause leukocytes or blood on urinalysis. Diagnose urinary infection only when the history, culture and imaging support it.

Pregnancy changes the route

Physiology, anatomy and fetal radiation considerations alter thresholds and imaging choice, but pregnancy does not protect against perforation; surgical and obstetric teams should coordinate early.

Antibiotics require shared decisions

Selected uncomplicated appendicitis can resolve without immediate operation, but failure, recurrence and missed alternative pathology must be discussed and follow-up must be dependable.

An abscess is not always an immediate operation

Contained inflammation may be safer to cool with antibiotics and radiological drainage. The plan must include rescue criteria and later exclusion of neoplasia where indicated.

Histology closes the loop

Routine pathological examination can reveal neuroendocrine tumour, mucinous neoplasm, endometriosis or another unexpected diagnosis that changes follow-up.

11Common pitfallsFrequent interpretation and management errors.

01
Using a normal early CRP or white count to discharge a patient with evolving focal pain.
02
Calling pyuria a urinary infection without considering adjacent appendiceal inflammation.
03
Failing to test for pregnancy before imaging or operative planning.
04
Letting an appendicitis score replace senior review and repeated examination.
05
Offering antibiotics-first treatment without confirming uncomplicated disease or discussing recurrence.
06
Forgetting caecal or appendiceal neoplasia after a mass presentation in an older adult.