Acute Appendicitis — Management

• Luminal obstruction and bacterial overgrowth: The appendiceal lumen becomes obstructed by various mechanisms including lymphoid hyperplasia (viral infection-related), fecoliths, or less commonly strictures and malignancy. This obstruction traps intraluminal secretions produced by mucus-secreting goblet cells within the appendical epithelium. The resultant increased intraluminal pressure combines with stasis to create an environment favoring pathogenic bacterial overgrowth. Commensal flora (predominantly Escherichia coli, Bacteroides fragilis, and other gram-negative anaerobes) undergo rapid proliferation as oxygen becomes depleted. The local environment becomes increasingly hypoxic, further selecting for anaerobic species while simultaneously impairing mucosal blood flow through pressure-related microvascular compromise.

• Transmural inflammation and bacterial invasion: Bacterial overgrowth and increased intraluminal pressure trigger secretion of pro-inflammatory cytokines (tumor necrosis factor-alpha, interleukins 1 and 6) by resident macrophages and dendritic cells within the appendiceal lymphoid tissue. These mediators upregulate adhesion molecules on endothelial cells, promoting neutrophil diapedesis through the mucosa. The inflamed mucosa becomes progressively more permeable, allowing bacterial translocation across the epithelial barrier. Once bacteria breach the mucosa, they invade the submucosa and muscularis propria, amplifying the inflammatory cascade. Complement activation via the classical and alternative pathways generates C5a, further recruiting neutrophils. This transmural inflammation causes tissue edema, which paradoxically increases intraluminal pressure further, creating a positive feedback loop.

• Progressive tissue necrosis and perforation: Sustained inflammation and increased intraluminal pressure progressively compromise vascular perfusion, particularly at the antimesenteric border where blood supply is most tenuous. Ischemia-induced cellular injury generates damage-associated molecular patterns (DAMPs) including high-mobility group box 1 (HMGB1) protein, which activate pattern recognition receptors and amplify inflammatory signaling. The muscularis propria becomes thinned and necrotic. If untreated, the appendiceal wall undergoes full-thickness necrosis, leading to perforation. Perforation typically occurs 48–72 hours after symptom onset, though this timeline is highly variable. Perforation releases bacteria and inflammatory mediators into the peritoneal cavity. A localized abscess may form if the perforation is walled off by adjacent viscera and omentum; if containment fails, diffuse peritonitis ensues with profound systemic inflammatory response syndrome (SIRS) physiology.

• Appendiceal wall histology and inflammatory evolution: Histologically, early acute appendicitis demonstrates neutrophilic infiltration of the mucosa and submucosa. As inflammation progresses, suppuration occurs with microabscess formation. The muscularis propria becomes infiltrated with inflammatory cells. In advanced cases, transmural suppuration is evident with fibrinous exudation and tissue necrosis. Gram stain and culture typically reveal mixed aerobic and anaerobic flora reflecting the colonic microbiome.

• Lymphoid hyperplasia (most common precipitant): Accounts for 60% of appendicitis cases, particularly in younger patients. Viral infections (adenovirus, measles, Epstein-Barr virus, cytomegalovirus) and other infectious triggers cause reactive lymphoid hyperplasia within the appendiceal lymphoid tissue (Peyer's patches). This enlargement narrows the appendiceal lumen and obstructs normal drainage of mucus, creating the substrate for bacterial overgrowth. The hyperplasia is typically self-limited, explaining the tendency for appendicitis to follow viral prodromal illnesses by several days to weeks.

• Fecoliths: Present in approximately 40% of appendicitis cases and account for a higher proportion in older patients. Fecoliths are hardened fecal material composed of inspissated stool, mucus, and minerals. They may occlude the appendiceal lumen directly or cause mucosal abrasion leading to bacterial invasion. Patients with a history of constipation carry increased risk. Fecoliths are readily visualized on CT imaging as calcified densities within the appendix.

• Other structural obstructions: Strictures from previous inflammation or Crohn's disease (which has predilection for the terminal ileum and ileocecal region), carcinoid tumors of the appendix, adenocarcinoma, and rarely parasitic infections (Ascaris, Schistosoma) can obstruct the appendiceal lumen. Appendiceal tumors occur in approximately 1% of appendectomy specimens.

• Anatomical variations: Retrocecal positioning of the appendix (most common anatomical variant, occurring in ~65% of individuals) may delay diagnosis because visceral peritoneal irritation is minimal until perforation occurs. Conversely, pelvic positioning increases risk of gynecologic misdiagnosis in females. Long appendices increase perforation risk.

• Age-related risk: Appendicitis demonstrates a bimodal age distribution with peaks in the second decade (15–19 years) and a secondary peak in the 6–9 year age group. Incidence declines after age 40. Very young children (<5 years) and the elderly present diagnostic challenges and have higher perforation and mortality rates due to delayed diagnosis.

• Genetic predisposition: Limited evidence suggests familial clustering and possible genetic susceptibility to appendicitis, though environmental factors predominate.

• Visceral pain with referred somatic component: Pain typically begins periumbilically or in the epigastrium as visceral innervation of the appendix is conveyed via sympathetic fibers accompanying the superior mesenteric artery, synapsing in T10 spinal segments. This referred pain is typically poorly localized, dull, crampy, and relatively mild. Over 4–24 hours, somatic pain develops as inflammation extends to the parietal peritoneum; this pain localizes to the right lower quadrant (RLQ) as the parietal peritoneum overlying the inflamed appendix becomes irritated. The McBurney's point (located approximately one-third the distance from the anterior superior iliac spine to the umbilicus) represents the common site of maximal tenderness. Patients frequently report pain migration from periumbilical to RLQ as a highly suggestive historical feature.

• Anorexia, nausea, and vomiting: Anorexia is often the earliest systemic symptom, occurring before abdominal pain in some patients and reflecting visceral inflammatory signaling. Nausea and vomiting occur in approximately 70% of cases and result from splanchnic innervation of visceral organs and increased intraluminal pressure generating vagal afferent signaling to the chemoreceptor trigger zone. Vomiting typically occurs after pain onset and is often bilious if significant ileal distension occurs.

• Fever: Body temperature elevation occurs in the majority of cases, typically in the range of 38–38.5°C, resulting from bacterial translocation and subsequent endotoxin release stimulating prostaglandin E2 production and resetting the hypothalamic temperature set point. Higher fever (>39°C) suggests perforation and peritonitis. Hypothermia is an ominous sign indicating sepsis or shock.

• Right lower quadrant tenderness and rebound/guarding: Physical examination reveals focal RLQ tenderness most pronounced at McBurney's point. Rebound tenderness (pain on release of manual pressure) and involuntary guarding (reflex abdominal wall muscle contraction) indicate parietal peritoneal irritation and are cardinal findings in acute appendicitis. The Rovsing's sign (RLQ pain elicited by palpation of the left lower quadrant, presumably through colonic gas transmission) is classically taught but less sensitive than direct RLQ tenderness. Psoas sign (pain with hip extension/extension of the right psoas) is more specific and occurs when an inflamed retrocecal appendix irritates the psoas muscle. Obturator sign (pain with internal rotation of the flexed right hip) suggests a pelvic appendix irritating the obturator internus muscle.

• Appendiceal position-dependent variations: When the appendix lies in a retrocecal position, physical findings may be subtle or absent until perforation occurs, as inflammation is initially remote from the parietal peritoneum. A pelvic appendix may produce suprapubic or left-sided pain. A long appendix extending across the midline may cause left lower quadrant tenderness, confounding diagnosis.

• Atypical presentations: In young children and the elderly, presentations are frequently atypical or delayed, contributing to higher perforation rates. Pregnant women present diagnostic challenges; appendicitis occurs in 1 in 1500 pregnancies, and appendiceal position shifts cephalad as pregnancy progresses, displacing pain cranially. Immunocompromised patients may manifest attenuated symptoms despite severe disease.

• Perforated appendicitis: Perforation may cause transient pain relief as intraluminal pressure is released, followed by renewed and more severe pain as peritonitis develops. Systemic toxicity is pronounced with tachycardia, hypotension, and altered mental status. Abdominal rigidity and diffuse peritoneal findings indicate generalized peritonitis.

• Clinical history and physical examination: The most important diagnostic tool remains the patient history with emphasis on pain characteristics (visceral versus somatic), migration from periumbilical to RLQ, temporal relationship to vomiting, and associated symptoms. McBurney's point tenderness with positive rebound and guarding is highly suggestive. Diagnostic scoring systems, particularly the Alvarado score and RIPASA score, quantify clinical findings and laboratory abnormalities to estimate appendicitis probability. The Alvarado score assigns points for migration of pain to RLQ (1), anorexia (1), nausea/vomiting (1), right lower quadrant tenderness (2), rebound tenderness (1), elevated temperature (1), leukocytosis (2), and left shift of white blood cell differential (1), with scores ≥7 suggesting appendicitis. However, these scoring systems have suboptimal sensitivity and specificity and should not replace imaging.

• Laboratory investigations: Leukocyte count is elevated (typically 10,500–18,000/μL) in 80% of cases, resulting from inflammatory cytokine-stimulated bone marrow release of immature and mature neutrophils. Very high counts (>18,000/μL) or leukopenia suggests complicated appendicitis with perforation. Leukocyte differential typically shows left shift with increased band forms reflecting acute inflammatory response. C-reactive protein (CRP) is elevated in 80–90% of acute appendicitis cases (>10 mg/L) and provides nonspecific confirmation of inflammation; CRP is more sensitive than ESR but still lacks specificity. Urinalysis should be obtained to exclude urinary pathology; pyuria may occur with a retrocecal appendix irritating the ureter, occasionally causing diagnostic confusion. Pregnancy testing (β-human chorionic gonadotropin) is mandatory in all women of childbearing age before imaging or surgery.

• Imaging—Computed tomography (CT): High-resolution CT scanning with IV contrast is the reference standard for appendicitis diagnosis, with sensitivity and specificity exceeding 95% when appendiceal wall thickness >2 mm, periappendiceal fat stranding, appendicolith, or appendiceal distension (>6 mm diameter) is present. CT findings may be graded by severity: simple appendicitis (appendiceal inflammation without perforation or abscess), perforated appendicitis with abscess (contained perforation), and perforated appendicitis with peritonitis (diffuse peritoneal inflammation). CT is readily available, operator-independent, and simultaneously evaluates the differential diagnosis including mesenteric lymphadenitis, gynecologic pathology, renal stones, and diverticulitis. Disadvantages include radiation exposure (10–30 mSv) and risk of contrast reactions.

• Imaging—Ultrasound: Graded compression ultrasound with a high-frequency linear transducer is an attractive alternative, particularly in pregnant women and young patients, offering 88–94% sensitivity and >90% specificity when performed by experienced operators. Findings include non-compressible appendix (diameter >6 mm), echogenic appendicolith, appendiceal wall hyperechogenicity, and periappendiceal free fluid. Advantages include lack of radiation, real-time assessment, and ability to perform dynamic maneuvers. Disadvantages include operator dependence, limited field of view, and difficulty in obese patients.

• Magnetic resonance imaging (MRI): Increasingly employed in pregnant women and selected pediatric cases, offering sensitivity and specificity comparable to CT (90–97%) without ionizing radiation. T2-weighted sequences demonstrate the inflamed appendix as a hyperintense, fluid-filled structure. MRI is superior for evaluating complications and gynecologic pathology but requires longer acquisition time and greater cost.

• Diagnostic criteria and algorithms: Current evidence-based approaches recommend imaging in all clinically equivocal cases rather than relying on clinical scoring systems alone. In patients with high clinical suspicion (>80% probability based on history and examination), imaging confirmation is still recommended prior to surgery to exclude alternative diagnoses. In intermediate-probability patients, imaging guides management. Low-probability patients may be observed with serial examination and repeat imaging if symptoms persist.

• Differential diagnosis considerations: The broad differential diagnosis includes mesenteric lymphadenitis (viral prodrome, usually self-limited), gynecologic pathology (ovarian torsion, ruptured cyst, pelvic inflammatory disease—more common in females), inflammatory bowel disease (Crohn's disease with terminal ileal inflammation), ureterolithiasis (colicky flank pain, hematuria, non-specific exam findings), diverticulitis (older age, left-sided), gastroenteritis (prodromal exposure, vomiting before pain), and mesenteric ischemia (older patients, atrial fibrillation). Imaging typically clarifies these entities.

• Preoperative preparation and medical optimization: Upon clinical suspicion of appendicitis, patients should be NPO (nothing by mouth) and established on intravenous fluid resuscitation (typically 0.9% normal saline at 1–2 mL/kg/hour titrated to urine output >0.5 mL/kg/hour and normalization of lactate if elevated). Electrolyte abnormalities should be corrected. Broad-spectrum antibiotics should be initiated promptly upon diagnosis and have become standard preoperative therapy. Delay in antibiotic administration beyond 3 hours is associated with increased morbidity. Cefoxitin (2 g IV q6h) or ceftriaxone (1 g IV q12h) plus metronidazole (500 mg IV q6–8h) provides excellent gram-negative and anaerobic coverage; alternatively, piperacillin-tazobactam (4.5 g IV q6h) achieves similar spectrum in a single agent. Fluoroquinolones with anaerobic coverage (moxifloxacin 400 mg IV daily) are reasonable alternatives in penicillin-allergic patients. Pain control should be addressed with opioid analgesia (morphine or hydromorphone IV); studies demonstrate that adequate analgesia does not impair diagnostic accuracy. Nasogastric decompression is reserved for patients with ileus or significant vomiting.

• Appendectomy—surgical standard of care: Emergency appendectomy remains the definitive treatment for acute appendicitis. The operation may be performed via open approach (single midline or RLQ incision

Complications of the disease

• Perforation with diffuse peritonitis — surgical emergency: full-thickness necrosis releases enteric flora into the peritoneum. Signaled by rigid abdomen, diffuse rebound, high fever, tachycardia, and free fluid or extraluminal gas on CT. Requires resuscitation, broad-spectrum antibiotics, and prompt source control; WSES (Jerusalem) guidelines favor immediate appendectomy in generalized peritonitis.
• Periappendiceal abscess or phlegmon: perforation walled off by omentum and adjacent bowel. Suggested by a longer symptom duration (typically several days), a palpable RLQ mass, and a rim-enhancing fluid collection on CT. Managed initially with antibiotics plus image-guided percutaneous drainage rather than immediate appendectomy, since dense inflammation raises the risk of enterotomy.
• Sepsis and septic shock — emergency: bacterial translocation drives SIRS physiology; hypotension, lactate elevation, and hypothermia are ominous. Treat per Surviving Sepsis Campaign principles with early antibiotics, fluids, and source control.
• Pylephlebitis (septic thrombophlebitis of the portal vein) — emergency: infection propagates along the appendiceal vein into the superior mesenteric and portal system. Classic clue: persistent spiking fevers with jaundice and transaminase/alkaline phosphatase elevation after appendicitis; portal venous gas or thrombus on CT. May seed pyogenic hepatic abscesses. Requires prolonged antibiotics with anticoagulation frequently added.
• Fetal loss and preterm labor in pregnancy: risk rises sharply with perforation, which is why ACOG supports appendectomy in pregnancy at any trimester rather than delay.

Complications of treatment

• Surgical site infection: more frequent after open than laparoscopic appendectomy; erythema, purulent drainage, and fever days postoperatively.
• Postoperative intra-abdominal abscess: mainly after perforated appendicitis. Suspect with fever, ileus, and leukocytosis around postoperative days 5–7; diagnose by CT and drain.
• Stump appendicitis or stump leak: an over-long residual appendiceal stump reinflames, or the cecal staple/ligature line leaks, producing recurrent RLQ pain or a fecal fistula.
• Adhesive small bowel obstruction: a late complication of any laparotomy, with colicky pain, distension, and air–fluid levels.
• Recurrence after nonoperative management: a meaningful minority fail antibiotics, highest with an appendicolith (CODA trial).
• Missed appendiceal neoplasm: incidental carcinoid/adenocarcinoma on pathology may mandate right hemicolectomy.

• Migratory pain is the single most discriminating historical feature: periumbilical/T10 visceral pain that shifts to the RLQ over hours. A stem that gives anorexia → periumbilical pain → vomiting → RLQ pain is describing appendicitis; vomiting before pain points instead to gastroenteritis.
• The first step in any reproductive-age woman is a urine or serum β-hCG, not imaging and not the operating room. This is the most commonly missed "next best step" on Step 2 CK, and it also changes the imaging pathway (ultrasound first, MRI if inconclusive, per ACR Appropriateness Criteria and ACOG).
• Imaging by population: CT with IV contrast in nonpregnant adults; graded-compression ultrasound first in children and pregnancy to avoid radiation, escalating to MRI when nondiagnostic. The Alvarado score risk-stratifies but does not substitute for imaging.
• Peritonitis or hemodynamic instability = go to the OR, not to the scanner. Resuscitate, give broad-spectrum antibiotics covering gram-negatives and anaerobes, and obtain source control.
• Antibiotics-first is a legitimate option in selected uncomplicated appendicitis (CODA trial), but an appendicolith predicts failure and favors appendectomy — the association examiners most like to test.
• A walled-off abscess or phlegmon is drained, not resected acutely; immediate appendectomy in that setting risks enterotomy and ileocecal resection.
• Do not withhold opioid analgesia for fear of "masking" the exam — evidence shows diagnostic accuracy is preserved. This is a classic distractor.
• Retrocecal appendix explains a deceptively benign abdomen with a positive psoas sign and sterile pyuria from ureteral irritation — do not be diverted to a diagnosis of UTI or nephrolithiasis.
• Appendicitis in an adult over ~40 with an atypical or recurrent course raises suspicion for an obstructing cecal or appendiceal neoplasm; interval colonoscopy is reasonable after nonoperative management.