What is appendicitis

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Appendicitis

Definition

Appendicitis is acute inflammation of the vermiform appendix - a blind-ended, finger-shaped tubular pouch that arises from the cecum at the junction of the small and large intestine in the right iliac fossa. It is the most common nontraumatic surgical emergency in both adults and children, affecting approximately 1 in every 15 people over a lifetime. - Rosen's Emergency Medicine, p.3240

Anatomy

The appendix is technically a true diverticulum of the cecum, containing all three intestinal wall layers. It is not simply a vestigial organ - it contains immunologically active gut-associated and mucosal-associated lymphoid tissue (MALT). Its position is variable: most commonly retrocecal (~65%) or pelvic, which can alter the clinical presentation significantly. - Fischer's Mastery of Surgery, p.7831

Epidemiology

Peak incidence: 9 to 30 years of age
Slightly more common in males
Uncommon in children under 5, and incidence declines after age 30 (possibly because the appendiceal lumen becomes progressively obliterated)
Perforation rate is inversely related to age: >50% of children under 5 are already perforated at surgery due to delayed presentation and less protective omentum

Pathophysiology

The core mechanism is obstruction of the appendiceal lumen, which sets off a cascade: - Fischer's Mastery of Surgery, p.7831

Obstruction - caused by:
- Fecaliths / appendicoliths (most common in adults)
- Lymphoid hyperplasia (most common cause in children and adolescents)
- Less often: tumors, parasites, foreign bodies
Rising intraluminal pressure - continued mucus secretion inside the obstructed lumen increases pressure
Vascular compromise - per the Law of Laplace, increased wall tension causes venous and lymphatic outflow obstruction, leading to tissue ischemia
Bacterial translocation - gut flora penetrate the mucosal barrier, potentiating inflammation
Necrosis and perforation - transmural necrosis leads to perforation, causing either a localized phlegmon/abscess (if the omentum walls it off) or diffuse peritonitis and sepsis

Clinical Features

Symptoms (classic progression)

Stage	Symptoms
Early (hours 1-6)	Vague periumbilical or central crampy pain; general malaise; anorexia
Mid (hours 6-24)	Pain migrates to right lower quadrant (RLQ); nausea; vomiting (typically after pain onset, not before); low-grade fever
Late / perforated	Sudden brief improvement in pain (at moment of perforation), then worsening diffuse pain; high fever; rigidity

Key point: Nausea and vomiting follow the onset of pain in appendicitis. If vomiting comes first, think gastroenteritis instead.

Classic Signs on Exam

McBurney's point tenderness - maximal tenderness at a point one-third of the distance from the right anterior superior iliac spine (ASIS) to the umbilicus
Rebound tenderness / guarding - peritoneal irritation
Rovsing's sign - RLQ pain reproduced by palpating the left lower quadrant
Psoas sign - RLQ pain with passive extension of the right hip (suggests retrocecal appendix)
Obturator sign - RLQ pain with passive internal rotation of the flexed right hip (suggests pelvic appendix)
Dunphy's sign - RLQ pain worsened by coughing

Note: None of these signs individually has adequate sensitivity or specificity to confirm or exclude the diagnosis. - Tintinalli's Emergency Medicine

Atypical Presentations

Retrocecal appendix: right flank or back pain instead of RLQ pain
Pelvic appendix: pelvic or groin pain; may mimic ovarian pathology
Pregnancy: appendix is displaced superiorly - pain may be in the right upper quadrant in the third trimester
Children <5 years: nonspecific symptoms; >50% present with perforation
Elderly: blunted signs; higher perforation rate due to delayed diagnosis

Diagnosis

Laboratory Tests

No single lab test confirms or excludes appendicitis. - Fischer's Mastery of Surgery, p.7833

WBC count: elevated >10,000 in ~87-92% of cases, but 8-13% have a normal WBC
CRP: elevated (>0.6 mg/dL) is supportive but not diagnostic
Urinalysis: mild sterile pyuria (<5-10 WBC/hpf) can occur due to appendix proximity to the ureter - does not rule out appendicitis
Pregnancy test (beta-hCG): mandatory in women of childbearing age to exclude ectopic pregnancy

Scoring Systems

The Alvarado (MANTRELS) score combines signs, symptoms, and labs:

Score 0-3: appendicitis unlikely
Score ≥4: further evaluation warranted
Score ≥7: high probability

It is not specific enough alone to rule in or rule out the diagnosis.

Imaging

Modality	Notes
CT abdomen/pelvis (with contrast)	Gold standard in adults; sensitivity ~94-98%; shows dilated appendix (>6mm), periappendiceal fat stranding, appendicolith, abscess
Ultrasound	Preferred first-line in children and pregnant women (avoids radiation); operator-dependent; sensitivity ~75-90%; non-visualization does not exclude
MRI	Used in pregnancy when ultrasound is inconclusive; comparable diagnostic accuracy without radiation
Plain X-ray	Low utility; may show appendicolith in ~10%; not routinely recommended

Classic radiographic findings: appendicolith, dilated appendix with adjacent hazy (inflammatory) fat, periappendiceal abscess. - Textbook of Family Medicine, p.1122

Imaging is most useful when clinical probability is equivocal. In high or low probability, clinical management can proceed without imaging.

Differential Diagnosis

Mesenteric adenitis (especially in children)
Ovarian cyst / torsion, ectopic pregnancy (right-sided in women)
Pelvic inflammatory disease (PID)
Ureterolithiasis (right ureteral stone)
Meckel's diverticulitis
Crohn's disease (terminal ileitis)
Cecal carcinoma / carcinoid tumor
Psoas abscess
Gastroenteritis

Treatment

1. Appendectomy (Standard of Care)

Surgical removal of the appendix is the definitive treatment for most patients.

Laparoscopic appendectomy is now the preferred approach: shorter hospital stay, less postoperative pain, lower wound infection rate, and faster return to activity - compared to open surgery. - Mulholland & Greenfield's Surgery, p.458
A Cochrane review of 67 trials confirmed laparoscopic appendectomy has lower surgical site infection (SSI) rates but a slightly higher intra-abdominal abscess rate
Timing: perforation is predominantly a pre-hospital event; in-hospital delay with IV antibiotics does not increase perforation risk in uncomplicated cases

2. Antibiotics Alone (Non-operative Management)

An evolving alternative for uncomplicated appendicitis (no perforation, no appendicolith, no abscess):

The APPAC trial (Finland, n=530): 72.7% of antibiotic-treated patients avoided surgery at 1 year, but 39.1% had required appendectomy by 7-year follow-up. Long-term quality of life was similar, but patients who failed antibiotics and later needed surgery were less satisfied. - Mulholland & Greenfield's Surgery, p.457
The CODA trial (USA, n=1552) also supported antibiotics as a reasonable alternative in selected patients
Antibiotics alone are not suitable for: patients with appendicolith, abscess, perforation, or surgical contraindications removed
Laparoscopic appendectomy remains the standard due to higher treatment efficacy and shorter stay

Recent meta-analysis in pediatrics (JAMA Pediatrics, 2026, PMID 41046476) reexamined non-operative management in uncomplicated pediatric appendicitis - confirming 80-90% short-term success but noting recurrence rates up to 40%, supporting that most pediatric surgeons still prefer operative management.

3. Perforated Appendicitis / Abscess

Phlegmon or abscess: can be managed with IV antibiotics ± percutaneous drainage (interventional radiology), followed by interval appendectomy at 6-8 weeks
Frank perforation with peritonitis: emergency appendectomy
Antibiotic duration after surgery for perforated disease is individualized based on fever, leukocytosis, source control, and ileus

Pre-operative antibiotics

IV antibiotics are given pre-operatively to all patients to reduce wound infection. Common regimens include coverage for gram-negative rods and anaerobes (e.g., cefoxitin, or piperacillin-tazobactam in complicated cases).

Complications

Complication	Notes
Perforation	~20-30% of all cases; higher at extremes of age
Periappendiceal abscess	Loculated infection post-perforation
Diffuse peritonitis	Spillage with free perforation
Sepsis / septic shock	Particularly in elderly and immunocompromised
Pylephlebitis	Septic portal vein thrombosis (rare but serious)
Wound infection / intra-abdominal abscess	Post-surgical complication
Stump appendicitis	Rare recurrence in appendiceal stump

Special Populations

Pregnancy: Most common surgical emergency in pregnancy. Delayed diagnosis increases perforation risk with potential fetal mortality. Ultrasound first, MRI if inconclusive. Appendix may be displaced superiorly - pain location shifts in later pregnancy. - Rosen's Emergency Medicine, p.3360
Children: Ultrasound and MRI preferred to avoid radiation; >50% perforated under age 5; non-operative management gaining evidence but recurrence rates up to 40%
Elderly: Blunted inflammatory response, atypical presentation, higher mortality due to comorbidities

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