9.3 Acute Abdomen: Appendicitis, Peritonitis & Intestinal Obstruction

9.3 Acute Abdomen: Appendicitis, Peritonitis & Intestinal Obstruction

UPSC CMS High-Yield Core Focus: Diagnostic evaluation of acute appendicitis (Alvarado score, clinical signs), classification and surgical control of peritonitis, radiologic hallmarks of perforated peptic ulcer, and differentiation between mechanical small vs. large bowel obstruction.

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1. Acute Appendicitis

Etiology & Pathophysiology

• Initiating Mechanism: Acute appendicitis is primarily caused by obstruction of the appendiceal lumen.
  • Adults: Most commonly obstructed by an appendicolith / fecalith (stercolith).
  • Children & Young Adults: Most commonly caused by submucosal lymphoid hyperplasia (secondary to viral gastroenteritis or respiratory infections).
  • Uncommon Causes: Foreign bodies, Enterobius vermicularis (pinworm), impact of barium, or carcinoid tumor of the appendiceal tip.
• Pathogenesis Cascade: Luminal obstruction $\rightarrow$ continuous mucosal fluid secretion $\rightarrow$ elevated intraluminal pressure $\rightarrow$ venous congestion and lymphatic ischemia $\rightarrow$ bacterial translocation (Escherichia coli, Bacteroides fragilis) $\rightarrow$ transmural gangrene $\rightarrow$ perforation and localized or generalized peritonitis.

Clinical Presentation & Diagnostic Physical Signs

• Pain Progression: Visceral pain initially begins as a dull, vague, poorly localized periumbilical pain (referred along T10 dermatome via sympathetic visceral afferents). As transmural inflammation involves the parietal peritoneum over 12–24 hours, pain shifts to the Right Iliac Fossa (RIF) as sharp, localized somatic pain.
• Associated Symptoms: Anorexia (classic "hamburger sign"), nausea, low-grade fever ($37.5–38.5^\circC$), and 1–2 episodes of vomiting.

Classical Eponymous Signs on Physical Exam

• McBurney's Point Tenderness: Maximal tenderness located precisely one-third of the distance from the Right Anterior Superior Iliac Spine (ASIS) to the umbilicus.
• Rovsing's Sign: Deep palpation in the Left Iliac Fossa (LIF) elicits pain in the Right Iliac Fossa (retrograde displacement of colonic gas stretches the inflamed cecum and appendix).
• Psoas Sign (Cope's Psoas Test): Pain in the RIF elicited by passive extension of the right hip (indicates an inflamed retrocecal appendix resting on the psoas major muscle).
• Obturator Sign: Pain in the RIF elicited by passive internal rotation of the flexed right hip (indicates an inflamed pelvic appendix abutting the obturator internus muscle).
• Dunphy's Sign: Sharp exacerbation of RIF pain caused by coughing.

Diagnostic Scoring: Alvarado Score (MANTRELS)

• Score $\le 4$: Appendicitis unlikely; evaluate alternative causes.
• Score 5 – 6: Equivocal / Possible appendicitis; perform abdominal USG or CT scan.
• Score $\ge 7$: High probability of acute appendicitis; proceed directly to surgical intervention (Appendectomy).

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2. Peritonitis and Perforated Viscus

Peritonitis is inflammation of the peritoneal serosa, classified into Primary, Secondary, and Tertiary forms.

Etiological Classification

1. Primary Peritonitis (Spontaneous Bacterial Peritonitis - SBP): Infection of ascitic fluid without intra-abdominal organ rupture. Occurs in patients with liver cirrhosis or nephrotic syndrome. Causative organisms: Monomicrobial (E. coli, Klebsiella, Streptococcus pneumoniae). Ascitic fluid analysis reveals Absolute Neutrophil Count (ANC) $\ge 250 cells/mm^3$. Medical treatment with 3rd-generation cephalosporins (Ceftriaxone); surgery contraindicated.
2. Secondary Peritonitis: Direct bacterial or chemical contamination from loss of integrity of a hollow viscus (perforated peptic ulcer, perforated appendicitis, diverticulitis, ischemic intestinal necrosis). Polymicrobial infection (aerobic coliforms + anaerobic Bacteroides fragilis). Requires emergency surgical intervention.
3. Tertiary Peritonitis: Persistent or recurrent peritoneal infection persisting $>48$ hours after adequate surgical management of secondary peritonitis, typically involving opportunistic, multi-drug resistant pathogens (Candida, Pseudomonas, Enterococcus).

Clinical Manifestations of Peritonitis

• Agonizing, continuous, generalized abdominal pain worsened by motion or coughing.
• Involuntary Board-Like Abdominal Rigidity: Reflex tonic spasm of the anterior abdominal wall muscles.
• Rebound Tenderness (Blumberg's Sign): Sudden release of manual abdominal pressure induces sharp pain.
• Silent Abdomen: Complete absence of bowel sounds due to reflex paralytic ileus.

Radiological Signatures

• Erect Chest X-ray: Shows Pneumoperitoneum (free gas under the right hemidiaphragm visible as a thin radiolucent crescent in 75–80% of perforated peptic ulcers).
• Contrast-Enhanced CT Abdomen: Gold standard for identifying occult perforation, contained pelvic/subphrenic collections, and retroperitoneal air.

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3. Intestinal Obstruction: Mechanical vs. Paralytic

Intestinal obstruction is divided into mechanical blockage and functional neuromuscular failure (Paralytic Ileus).

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4. Small Bowel vs. Large Bowel Mechanical Obstruction

Etiology

• Small Bowel Obstruction (SBO):
  • Postoperative Adhesions: Most common cause overall (60–70% of SBO cases).
  • Incarcerated / Strangulated Hernias: Second most common cause overall (most common cause in unoperated abdomens worldwide).
  • Other causes: Crohn's disease strictures, intussusception, gallstone ileus.
• Large Bowel Obstruction (LBO):
  • Colorectal Adenocarcinoma: Most common cause (60% of LBO cases).
  • Sigmoid Volvulus: Second most common cause; produces classic "coffee bean sign" on X-ray.
  • Diverticular strictures, cecal volvulus, fecal impaction.

Clinical and Radiological Differentiating Features

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5. Surgical Management Protocols

Initial Conservative Management ("Drip and Suck")

• NPO (Nothing by Mouth): Rest the gastrointestinal tract.
• Nasogastric Decompression (Ryle's Tube): Low continuous or intermittent suction to decompress proximal stomach and bowel.
• Aggressive Intravenous Fluid Resuscitation: Correction of dehydration and electrolyte imbalances (especially hypokalemia).
• Broad-Spectrum Parenteral Antibiotics: Coverage against Gram-negative coliforms and anaerobes.

Indications for Immediate Emergency Surgery

1. Signs of Bowel Strangulation / Ischemia: Constant non-colicky pain, localized tenderness, guarding, fever, leukocytosis, tachycardia, or metabolic acidosis.
2. Incarcerated or Strangulated Hernia: Immediate repair after fluid resuscitation.
3. Closed-Loop Obstruction: Sigmoid or cecal volvulus with impending gangrene.
4. Cecal Diameter $\ge 9–12 cm$: Imminent risk of cecal perforation (Laplace's Law: Tension = Pressure $×$ Radius).