Give details on the main topic "Acute abdomen and peritonitis". Focus on the following topic learning outcomes: 1. Define the term acute abdomen and describe its clinical importance 2. Describe the basic anatomy and pathophysiology relevant to peritonitis and acute abdominal pain 3. Identify key symptoms and signs suggestive of peritonitis in a clinical scenario 4. Correlate history and examination findings to localise the likely source of the acute abdomen 5. List common surgical causes of acute abdomen such as appendicitis, perforated peptic ulcer, intestinal obstruction, and peritonitis 6. Formulate appropriate differential diagnoses based on the presenting features 7. Select suitable laboratory and imaging investigations to evaluate a patient with acute abdomen 8. Interpret common investigation findings in related to specific conditions 9. Outline the initial assessment and stabilisation steps in a patient with suspected peritonitis 10. Explain the importance of early surgical consultation, teamwork, and timely intervention in improving outcomes for acute abdomen. Use Bailey and Love Short Practice of Surgery 28th Edition, Sabiston Textbook of Surgery 21st Edition, and Shwartz's Principles of Surgery 11th Edition.

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acute abdomen peritonitis abdominal pain sites diagram

Abdominal Computed Tomography (CT) scan presented in axial (a) and coronal (b) planes, demonstrating features of a chronic inflammatory process and mechanical bowel obstruction. The images reveal significant distension of multiple small bowel loops, consistent with a paralytic ileus or encapsulating peritoneal sclerosis. A key diagnostic feature is the peripheral 'cocooning' or 'shelling' of the intestinal loops by a thickened peritoneum. The coronal view highlights a disorganized clustering of the dilated jejunal loops within the central abdomen. While there is evidence of intra-abdominal effusion (ascites), the volume appears reduced compared to typical acute peritonitis, suggesting a maturing fibro-inflammatory process. There are visible signs of peritoneal thickening and mesenteric fat infiltration. This clinical presentation, in the context of progressive abdominal pain, is highly suggestive of Abdominal Cocoon Syndrome (sclerosing encapsulating peritonitis), which in this immunocompetent patient was secondary to peritoneal histoplasmosis.

This diagnostic image is an axial computed tomography (CT) scan of the lower abdomen and pelvis. The image demonstrates a complex inflammatory process in the right lower quadrant. A solid red arrow points to a calcified hyperdense structure, consistent with an appendicolith, which is acting as the source of obstruction. Adjacent to this, a thin double-headed red arrow delineates a thick, irregular fluid collection and soft tissue stranding indicative of an abscess formation and localized peritonitis. There is associated fat stranding and thickening of the surrounding bowel loops, suggestive of secondary small intestinal obstruction or ileus. These radiological findings are highly characteristic of complicated, perforated appendicitis. The scan provides critical evidence for surgical consultation in the context of acute abdominal pain and suspected intra-abdominal pathology.

**Imaging Modality:** Axial Computed Tomography (CT) of the abdomen and pelvis with intravenous contrast. **Anatomical Region:** Lower abdomen and right iliac fossa. **Observed Pathology:** Findings are consistent with acute appendicitis. The image demonstrates a significantly distended, thick-walled appendix located in the right lower quadrant. **Characteristic Visual Features:** - **Appendiceal Distension:** The appendix appears dilated, exceeding the normal caliber threshold. - **Wall Enhancement:** Prominent peripheral enhancement of the appendiceal wall indicates hyperemic inflammation. - **Periappendiceal Fat Stranding:** Increased attenuation and haziness of the surrounding mesenteric fat suggest an acute inflammatory process and localized peritonitis. - **Secondary Findings:** Mild reactive thickening of the adjacent cecal pole may be present. No definitive evidence of a calcified appendicolith or localized abscess formation is visible in this specific axial slice. **Key Diagnostic Features:** The combination of a dilated appendix (>6 mm), mural thickening, and secondary periappendiceal fat stranding are the hallmark CT signs for diagnosing acute appendicitis. **Clinical Context:** These radiologic findings correlate with clinical presentations of acute lower abdominal pain and signs of systemic inflammation.

Two-panel laparoscopic images showing an intraoperative exploration for acute abdominal pain. Panel A demonstrates a localized inflammatory mass in the left iliac fossa. The mass is enclosed by the greater omentum and exhibits significant purulent exudate (pus moss) on its surface, indicating a suppurative process. Panel B illustrates the underlying congenital anatomical variation: intestinal malrotation. The ileum is located in the right iliac fossa, displacing the cecum and ascending colon toward the left side of the abdomen. The bowel surfaces appear hyperemic with visible vascularity, consistent with peritonitis. Collectively, these images document a rare clinical presentation of left-sided appendicitis occurring in the context of intestinal malrotation. The visuals focus on the surgical findings of aberrant intestinal positioning and the localized infectious mass causing left-sided symptoms.

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intestinal obstruction small bowel dilated loops X-ray

A supine plain film abdominal X-ray (diagnostic image) demonstrating multiple dilated loops of small bowel, concentrated primarily in the central and lower abdominal regions. The intestinal loops exhibit characteristic valvulae conniventes (plicae circulares) that span the entire diameter of the lumen, distinguishing them as small bowel. The distribution is disorganized and spans from the mid-abdomen toward the pelvic cavity. Notable features include the absence of visible pneumoperitoneum (no free air under the diaphragm) and a lack of significant gas in the distal colon or rectum, findings highly suggestive of a mechanical small bowel obstruction (SBO). Anatomical landmarks such as the lumbar vertebrae and pelvic bones are visible, providing orientation. This imaging is clinically significant for evaluating acute abdominal pain and suspected bowel obstruction, providing early diagnostic evidence for further cross-sectional imaging or surgical intervention.

This diagnostic image is a supine abdominal X-ray (KUB) demonstrating multiple dilated small bowel loops, characteristic of a small bowel obstruction. The dilated loops are primarily distributed throughout the central abdominal cavity and exhibit visible valvulae conniventes (plicae circulares) extending across the full width of the lumen, distinguishing them from large bowel haustra. The image shows horizontal interfaces consistent with air-fluid levels within the distended loops. These radiographic findings indicate a significant intestinal blockage, which in this clinical context was associated with a perforated Meckel's diverticulum and an internal hernia. The anatomical focus includes the mid-to-lower abdomen, providing a clear example of obstructive ileus suitable for medical students and clinicians studying emergency radiology and gastrointestinal pathology.

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pneumoperitoneum free air under diaphragm perforated ulcer erect chest X-ray

An erect posterior-anterior (PA) chest X-ray demonstrating clear signs of pneumoperitoneum and hydropneumoperitoneum. Large, crescent-shaped radiolucent (dark) areas representing free intraperitoneal air are visible beneath both the right and left domes of the diaphragm, distinctly separating the diaphragm from the liver and gastric shadow. Below the air pockets, sharp horizontal radiopaque interfaces are present, indicating air-fluid levels (hydro-pneumoperitoneum) within the abdominal cavity. The lungs appear relatively clear, though the elevated diaphragm secondary to massive free air is evident. This finding is a surgical emergency, typically associated with a perforated hollow viscus, such as a peptic ulcer. The image serves as a classic diagnostic example for medical students and clinicians to recognize the 'cupola sign' or subdiaphragmatic free air in the context of an acute abdomen.

This diagnostic image is an erect posteroanterior (PA) chest X-ray demonstrating pneumoperitoneum. The most significant finding is the presence of subdiaphragmatic free air, visualized as crescent-shaped radiolucent (dark) areas immediately beneath both the right and left hemidiaphragms. White arrows specifically highlight the air-fluid interface on the right side, where gas has accumulated between the superior surface of the liver and the diaphragm. The upright positioning of the patient is confirmed by the upward migration of free intraperitoneal gas to the highest point of the abdominal cavity. This radiographic sign is a critical indicator of hollow viscus perforation, such as a perforated peptic ulcer or bowel rupture, which leads to peritonitis. The lung fields appear relatively clear, and the cardiac silhouette is visible, though the primary diagnostic focus is the abnormal gas collection in the upper abdomen. This image serves as a classic educational example of acute abdominal pathology visualized on a chest radiograph.

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Acute Abdomen and Peritonitis

Sources: Bailey and Love's Short Practice of Surgery, 28th Edition (B&L); Schwartz's Principles of Surgery, 11th Edition (Schwartz); Sabiston Textbook of Surgery, 21st Edition (Sabiston)

Learning Outcome 1: Definition and Clinical Importance of Acute Abdomen

Definition

The term "acute abdomen" refers to a clinical syndrome of sudden or rapidly developing, severe abdominal pain requiring urgent medical or surgical evaluation. It is not a diagnosis in itself but a clinical presentation that demands prompt assessment to identify a potentially life-threatening underlying cause. As Bailey & Love describes it: "Abdominal pain is one of the most challenging presenting complaints in the emergency department." (B&L, Chapter 63/87)

Clinical Importance

The acute abdomen accounts for a significant proportion of all emergency surgical admissions worldwide
Delayed diagnosis leads to increased morbidity and mortality through complications such as perforation, septic shock, and multi-organ failure
Many causes require emergency surgical intervention within hours (e.g. perforated peptic ulcer, ruptured aortic aneurysm)
Incorrect or delayed management can convert a treatable condition into a life-threatening one - for example, simple appendicitis can progress to perforation and diffuse peritonitis
Pain may arise from inflammatory, infective, obstructive, neurogenic, neoplastic, or ischaemic pathology - sometimes with no identifiable organic cause ("functional or non-specific abdominal pain") (B&L, p. 1074)

Learning Outcome 2: Basic Anatomy and Pathophysiology

Peritoneal Anatomy

The peritoneum is a double-layered serous membrane:

Visceral peritoneum - covers the abdominal organs; supplied by the autonomic (sympathetic) nervous system
Parietal peritoneum - lines the abdominal wall; supplied by somatic nerves (lower 6 intercostal nerves, iliohypogastric and ilioinguinal nerves) (B&L, Summary Box 63.4)

This anatomical distinction is the basis for the two types of abdominal pain:

Feature	Visceral Pain	Somatic/Parietal Pain
Origin	Visceral peritoneum / organ wall	Parietal peritoneum
Character	Dull, deep, poorly localised, crampy	Sharp, well-localised
Location	Referred to midline, T1-L2 dermatomes	Localised to affected quadrant
Movement	Not worsened by movement	Worsened by movement/coughing
Example	Early appendicitis - periumbilical	Late appendicitis - RIF

Pathophysiology of Pain Types

Visceral pain arises from ischaemia, muscle spasm, or stretching of the visceral peritoneum. Afferent pain fibres travel with sympathetic nerves and are referred to the equivalent somatic distribution (T1-L2). When an inflamed organ touches the parietal peritoneum, pain becomes localised to the segmental dermatome. (B&L, Summary Box 63.5)

Pain localisation by embryological origin:

Foregut (stomach, duodenum, liver, biliary, pancreas) - epigastric pain
Midgut (small bowel, appendix, right colon to mid-transverse) - periumbilical pain
Hindgut (distal transverse colon to rectum) - hypogastric/suprapubic pain

The Nine Sites of Abdominal Pain (Bailey & Love, Fig. 63.2)

Nine sites of abdominal pain showing referred conditions by quadrant - Bailey & Love

Figure 63.2 from Bailey & Love: Nine sites of abdominal pain. 1-Right subcostal (hepatitis, cholecystitis); 2-Epigastrium (peptic ulcer, pancreatitis); 3-Left subcostal (splenic injury); 4 & 6-Flanks (renal/ureteric pain); 5-Periumbilical (bowel obstruction, aortic aneurysm); 7-RIF (appendicitis); 8-Suprapubic (pelvic pain); 9-LIF (diverticulitis).

Pathophysiology of Peritonitis

Peritoneal inflammation develops through several mechanisms:

Perforation of a hollow viscus releases bacteria and/or chemical irritants into the peritoneal cavity
Transmural translocation without perforation - e.g. pancreatitis, ischaemic bowel, primary bacterial peritonitis
Exogenous contamination - drains, open surgery, trauma, peritoneal dialysis
Female genital tract infection - pelvic inflammatory disease (PID)
Haematogenous spread (rare) - septicaemia (B&L, Summary Box 65.3)

Once contamination occurs, the peritoneum responds with an acute inflammatory response: hyperaemia, exudation of fluid rich in fibrin and leukocytes, and omental migration to "wall off" the inflammation. If this fails, diffuse peritonitis ensues, leading to systemic inflammatory response syndrome (SIRS) and, ultimately, multi-organ dysfunction syndrome (MODS).

Learning Outcome 3: Key Signs and Symptoms of Peritonitis

Clinical Features (Bailey & Love, Summary Box 65.4)

Symptoms:

Abdominal pain, worse on movement, coughing, and deep respiration
Constitutional upset: anorexia, malaise, lassitude
Gastrointestinal: nausea ± vomiting
Pyrexia (may be absent in immunosuppressed patients)

Signs:

Tenderness - localised or generalised
Involuntary guarding - reflex abdominal wall contraction to reduce further peritoneal irritation
Board-like rigidity - seen in diffuse peritonitis; the entirety of the abdominal musculature undergoes reflex contraction
Rebound tenderness - worsening of pain on lifting the examining hand off the abdominal wall
Raised pulse rate (tachycardia)
Absent or reduced bowel sounds - from generalised ileus
Pain/tenderness on rectal or vaginal examination - indicates pelvic peritonitis

Collectively, tenderness with guarding and rebound tenderness constitute "peritonism" - the patient is described as "peritonitic." (B&L, p. 1109)

Advanced/Late Signs:

Hypotension (septic shock)
Hippocratic facies - the patient is gravely ill, sunken eyes, cold extremities
Confusion, drowsiness, disorientation
SIRS and MODS in later stages (B&L, Summary Box 65.4)

Special Circumstances:

Diaphragmatic involvement - shoulder tip pain (referred pain via C5 dermatome - "phrenic pain")
Pelvic peritonitis - abdominal signs may be limited; deep-seated tenderness detected on rectal or vaginal examination
Obese or immunosuppressed patients - signs may be masked or limited (B&L, p. 1109)

Learning Outcome 4: Correlating History and Examination to Localise the Source

A systematic approach to history and examination allows localisation:

Key Historical Features to Elicit (B&L, p. 1074)

Feature	Clinical Value
Site of pain	Initial site reflects visceral origin (foregut/midgut/hindgut)
Radiation	Biliary - right scapular; pancreatic/AAA - back; ureteric - loin to groin
Nature	Colicky = hollow viscus obstruction; Constant = inflammation/ischaemia
Onset	Sudden/explosive = perforation, rupture; Gradual = inflammation
Migration	Periumbilical → RIF = classic appendicitis migration
Associated vomiting	Early in proximal obstruction; late in distal obstruction
Absolute constipation	Colonic obstruction
Haematuria	Ureteric/renal pathology

Classic Pain Patterns by Condition

Biliary colic: colicky RUQ pain radiating to the angle of the scapula, associated with food intake (CCK-driven)
Acute appendicitis: periumbilical pain migrating and localising to RIF (likelihood ratio+ 2.06)
Acute pancreatitis: abrupt onset severe epigastric pain radiating to the back
Peptic ulcer perforation: sudden epigastric pain (similar to pancreatitis but more abrupt, with peritonism)
Intestinal colic/obstruction: periumbilical pain in waves (small bowel), distension increasing with more distal pathology
Ureteric colic: intense flank pain radiating toward lower midline/scrotum, with haematuria (B&L, p. 1074)

Examination Findings by Region

Region	Finding	Likely Cause
RUQ	Tenderness, Murphy's sign	Cholecystitis
Epigastrium	Tenderness, rigidity	Peptic ulcer, pancreatitis
RIF	Tenderness, guarding, Rovsing's sign, psoas sign	Appendicitis
LIF	Tenderness, guarding	Diverticulitis
Generalised	Board-like rigidity	Diffuse peritonitis (perforation)
Groin	Irreducible mass, tenderness	Strangulated hernia
Flank	Loin tenderness	Renal/ureteric colic

Learning Outcome 5: Common Surgical Causes of Acute Abdomen

1. Acute Appendicitis

The most common urgent general surgical operation in the United States, responsible for approximately 300,000 hospitalisations annually (Sabiston, p. 2038). Lifetime incidence: 6-7% of the general population, peaking in the second decade.

Pathophysiology (Sabiston/Schwartz): Luminal obstruction (by fecalith, lymphoid hyperplasia, foreign body, or neoplasm) → elevated intraluminal pressure → bacterial overgrowth → impaired venous drainage → mucosal ischaemia → bacterial translocation → gangrene → perforation. Common organisms: E. coli and Bacteroides fragilis (aerobic and anaerobic). (Sabiston, p. 2038-2039; Schwartz, p. 1359)

Key signs in appendicitis (Schwartz, Table 30-1, likelihood ratios):

Pain migration (periumbilical → RIF): LR+ 2.06
Rebound tenderness: LR+ 1.99
Percussion tenderness: LR+ 2.86
Guarding: LR+ 2.48
Psoas sign: LR+ 2.31
Anorexia: LR+ 1.27
Fever: LR+ 1.64

Alvarado Score is commonly used to stratify risk (score 0-10, ≥7 highly suspicious).

Complications: Perforation → pericaecal abscess or diffuse peritonitis; the most common sequela of perforation is periappendiceal abscess (Sabiston, p. 2039).

2. Perforated Peptic Ulcer

"Perforation is the second most common complication of peptic ulcer, but nowadays it is a much more common indication for operation than bleeding." - Schwartz, p. 1162

Key features:

Strong association with NSAID/aspirin use, especially in the elderly
Sudden onset of severe epigastric pain - the classic "first episode of acute abdominal pain"
Rapid development of generalised peritonitis (chemical peritonitis initially from gastric acid, then bacterial)
Pneumoperitoneum (free air under the diaphragm) on erect CXR - seen in ~70-80% of cases
Surgery is almost always indicated; simple patch (Graham) closure is the procedure of choice in haemodynamically unstable patients or those with exudative peritonitis (>24h perforation)

3. Intestinal Obstruction

Mechanical small bowel obstruction classically presents with:

Colicky central/periumbilical abdominal pain (distension of midgut)
Vomiting - early and prominent in proximal obstruction
Abdominal distension - more marked in distal obstruction
Absolute constipation - late sign or colonic obstruction
Tinkling/high-pitched bowel sounds, later absent

"Central colicky abdominal pain is a classic presentation of small bowel obstruction. The central distribution is because of the segmental nerve supply of the midgut." (B&L, p. 1074)

A closed-loop obstruction (e.g. sigmoid volvulus, obstructed hernia) is a surgical emergency due to risk of vascular compromise and perforation.

Causes: Adhesions (most common in adults, post-operative), hernias (most common worldwide), volvulus, malignancy, intussusception, inflammatory strictures.

4. Peritonitis

Peritonitis is inflammation of the peritoneum, most usefully classified clinically as localised or diffuse. (B&L, p. 1109)

Causes of peritoneal inflammation (B&L, Summary Box 65.2):

Bacterial (gastrointestinal and non-gastrointestinal)
Chemical (bile, barium, gastric acid)
Allergic (e.g. starch peritonitis)
Traumatic (operative handling)
Ischaemia (strangulated bowel, vascular occlusion)
Miscellaneous (familial Mediterranean fever)

Diffuse peritonitis arises from pressure-related perforation of a viscus (obstructed colon), large volume haemoperitoneum (ruptured AAA), or continuous contamination (perforated duodenal ulcer, anastomotic leak). (B&L, p. 1110)

Other Surgical Causes

Condition	Key Feature
Acute cholecystitis	RUQ pain, Murphy's sign, fever
Acute pancreatitis	Epigastric pain radiating to back, raised amylase/lipase
Ruptured AAA	Sudden back/flank pain, pulsatile mass, haemodynamic instability
Strangulated hernia	Irreducible, tense, tender hernia with systemic illness
Diverticulitis	LIF pain, localised peritonism, fever
Mesenteric ischaemia	Severe pain disproportionate to examination findings
Ectopic pregnancy	RIF/LIF pain, missed period, positive β-hCG
Adnexal torsion	Sudden onset pelvic pain, palpable adnexal mass, peritonism (B&L, p. 2351)

Learning Outcome 6: Differential Diagnosis Formulation

A structured approach using age, sex, pain characteristics, and associated features narrows differentials:

By Anatomical Region

Epigastric/RUQ:

Perforated peptic ulcer, acute pancreatitis, acute cholecystitis, biliary colic, hepatitis, Boerhaave syndrome, right basal pneumonia (mimicker)

RIF:

Acute appendicitis (most common), mesenteric adenitis, Meckel's diverticulitis, Crohn's disease, ileal TB, ectopic pregnancy (female), ovarian torsion/cyst rupture (female), right ureteric colic, right inguinal hernia, Yersinia ileitis

LIF:

Sigmoid diverticulitis, sigmoid volvulus, left inguinal hernia, left ureteric colic, sigmoid/descending colon carcinoma with obstruction, PID

Periumbilical/generalised:

Small bowel obstruction, mesenteric ischaemia, diffuse peritonitis (any perforation), early appendicitis, aortic pathology

Pelvis:

Ectopic pregnancy, PID, ovarian torsion, endometriosis, fibroid torsion, testicular torsion (radiates to groin/lower abdomen)

By Demographics (Sabiston, p. 2039)

Children: mesenteric adenitis (post-viral), acute gastroenteritis, intussusception, Meckel's diverticulitis, IBD, testicular torsion
Young adults (2nd-3rd decade): appendicitis most likely; gynaecological causes in females
Elderly: diverticulitis, colorectal carcinoma, ischaemic colitis, AAA, perforated ulcer (often NSAID-related)
Pregnant: appendicitis (appendix displaced superiorly), ectopic pregnancy, abruption, uterine rupture (B&L, p. 2334)
Immunocompromised: atypical presentations; CMV colitis, spontaneous bacterial peritonitis

Learning Outcome 7: Laboratory and Imaging Investigations

Laboratory Investigations

Investigation	Clinical Use
FBC	Leucocytosis suggests infection/inflammation; anaemia
CRP	Elevated in inflammation; CRP + bilirubin + IL-6 + procalcitonin helpful in predicting perforated appendicitis (Schwartz, p. 1380)
Serum amylase/lipase	Pancreatitis (lipase more specific); amylase also elevated in perforation
LFTs	Biliary pathology, hepatitis
U&E/Creatinine	Renal function, guide fluid resuscitation
Serum lactate	Tissue hypoperfusion/ischaemia; elevated in mesenteric ischaemia, septic shock
Coagulation (PT/INR/APTT)	Pre-operative assessment, DIC in sepsis
Group & Save/Cross-match	Pre-operative preparation
Urine dipstick/MC&S	UTI, haematuria (ureteric colic), exclude renal cause
Urine β-hCG	Must be done in all women of reproductive age - exclude ectopic pregnancy
Blood cultures	If sepsis/fever present
ABG	Metabolic acidosis in ischaemia, shock; lactate

Imaging Investigations

1. Erect Chest Radiograph (CXR)

First-line for suspected perforation
Pneumoperitoneum: free gas (crescent-shaped) under the diaphragm = perforated hollow viscus
Visible in ~70-80% of perforations
If patient too unwell to sit, a lateral decubitus abdominal X-ray can demonstrate free air (B&L, p. 1110)

Erect PA CXR showing pneumoperitoneum - free air under both hemidiaphragms, indicating perforated hollow viscus

Erect CXR demonstrating crescent-shaped pneumoperitoneum beneath the diaphragm - the hallmark of perforated peptic ulcer or other hollow viscus perforation.

2. Supine Abdominal X-Ray (AXR)

Intestinal obstruction: multiple dilated loops with air-fluid levels; valvulae conniventes identify small bowel; haustra identify large bowel
Volvulus: "coffee bean" sign (sigmoid) or "bent inner tube" (caecal)
Calcified gallstones, renal calculi (minority are radio-opaque)
Absent psoas shadow suggests retroperitoneal haematoma

Supine AXR showing multiple dilated small bowel loops with visible valvulae conniventes - classic appearance of small bowel obstruction

Supine abdominal X-ray: multiple centrally-located dilated small bowel loops with characteristic valvulae conniventes spanning the full lumen width - consistent with mechanical small bowel obstruction.

3. Ultrasound (USS)

First-line for RUQ: cholecystitis (gallstones, thickened gallbladder wall, pericholecystic fluid, sonographic Murphy's sign), biliary dilation
Gynaecological pathology: ectopic pregnancy, ovarian torsion (Doppler), cysts
Appendicitis: non-compressible, >6mm aperistaltic tubular structure; limited by body habitus/bowel gas
Free fluid (ascites/haemoperitoneum): useful in trauma (FAST scan)
Adnexal torsion: ovarian enlargement, "whirlpool sign" on Doppler, peripheral follicle displacement (B&L, p. 2394-2398)

4. CT Abdomen/Pelvis (Gold Standard)

Most accurate investigation for the acute abdomen
Identifies perforation (free air), obstruction (transition point), appendicitis, diverticulitis, pancreatitis (Balthazar grading), renal/ureteric calculi, AAA, mesenteric ischaemia, and tumours
CT appendicitis: dilated appendix >6mm, mural thickening, periappendiceal fat stranding, appendicolith
Should be performed with IV contrast unless contraindicated (allergy, renal failure) (B&L, p. 1110; Schwartz, Sabiston)

CT scan of lower abdomen showing dilated thick-walled appendix with periappendiceal fat stranding - CT diagnosis of acute appendicitis

CT abdomen/pelvis: dilated appendix (>6 mm), wall enhancement, and periappendiceal fat stranding - hallmark CT signs of acute appendicitis.

5. MRI

Preferred in pregnant patients (avoids radiation) for suspected appendicitis
Also useful for pelvic pathology

6. Diagnostic Laparoscopy

When imaging inconclusive; allows direct visualisation and therapeutic intervention (especially in young women with RIF pain where gynaecological causes common)

Learning Outcome 8: Interpreting Common Investigation Findings

Finding	Interpretation	Associated Condition
Pneumoperitoneum on CXR	Free gas under diaphragm	Perforated peptic ulcer, perforated bowel
Dilated SB loops + air-fluid levels	Mechanical SBO	Adhesions, hernia, volvulus
Dilated large bowel + "cut-off"	Large bowel obstruction	Carcinoma, sigmoid volvulus, volvulus
Leucocytosis + raised CRP	Systemic inflammation	Appendicitis, peritonitis, cholecystitis
Raised amylase/lipase (>3x normal)	Pancreatitis	Gallstone or alcohol-related pancreatitis
Elevated lactate + metabolic acidosis	Tissue hypoperfusion	Mesenteric ischaemia, septic shock
Positive β-hCG + adnexal mass on USS	Ectopic pregnancy	Fallopian tube ectopic
Gallstones + thickened GB wall + Murphy's sign	Acute cholecystitis	Calculous cholecystitis
Appendicolith + fat stranding on CT	Perforated/complicated appendicitis	Appendicitis with abscess
Neutrophilic leucocytosis + high CRP + raised bilirubin	Predictive of perforated appendicitis	Complex appendicitis (Schwartz)
Pericolic fat stranding + diverticula on CT	Diverticulitis	Sigmoid/descending colon
Grossly elevated serum amylase + ascites	Acute pancreatitis or perforation	Pancreatitis; exclude duodenal/gastric perforation
Collapsed IVC + hypotension on CT	Haemodynamic shock	AAA rupture, haemoperitoneum

Learning Outcome 9: Initial Assessment and Stabilisation

Systematic ABCDE Approach (Primary Survey)

A - Airway: Ensure patent; high-flow oxygen; RSI if GCS impaired

B - Breathing: SpO₂ monitoring; supplemental O₂; look for respiratory splinting (shallow breathing due to peritonitis)

C - Circulation:

Establish two large-bore IV cannulae
Draw bloods simultaneously (FBC, U&E, LFTs, amylase, CRP, coagulation, Group & Save, cultures)
IV fluid resuscitation: 0.9% NaCl or Hartmann's solution; guided by HR, BP, urine output, lactate
Attach cardiac monitor, pulse oximeter
Consider urinary catheter to monitor urine output (target >0.5 mL/kg/hr)

D - Disability: GCS, glucose; confusion may indicate septic encephalopathy

E - Exposure: Full exposure; examine abdomen systematically; measure temperature

Specific Management Steps (Bailey & Love, Summary Box 65.5)

General care - nursing the patient appropriately, NBM status
Correction of fluid and electrolyte imbalance - aggressive IV fluid resuscitation
Nasogastric tube - decompress the stomach (especially obstruction, peritonitis)
Urinary catheter - monitor urine output; guide fluid resuscitation
Broad-spectrum antibiotics - cover gram-negative organisms and anaerobes (e.g. piperacillin-tazobactam, or cefuroxime + metronidazole); initiate within 1 hour if septic
Analgesia - IV opioid analgesia is safe and does NOT obscure signs; withholding analgesia is not evidence-based
Vital system support - vasopressors/inotropes if septic shock despite fluid resuscitation (ICU/HDU)
Surgical treatment of the underlying cause - "source control" by removal or exclusion of the cause
Peritoneal lavage ± drainage - if diffuse contamination

Monitoring and Reassessment

Serial abdominal examination is mandatory
Repeated clinical assessment guides the decision for operative vs. non-operative management
If the patient deteriorates despite resuscitation, urgent surgical intervention must not be delayed

Learning Outcome 10: Importance of Early Surgical Consultation, Teamwork, and Timely Intervention

Why Timing Matters

"Investigation and treatment must be undertaken expediently as the time available to salvage may be limited." - Bailey & Love, p. 1110

Appendicitis: perforation risk increases significantly with delayed diagnosis. Schwartz notes that "immediate surgery is necessary in patients that appear septic" - delay is associated with higher complication rates (abscess, fistula formation) due to dense adhesions and inflammation. (Schwartz, p. 1382)
Perforated peptic ulcer: mortality rises sharply with delay >6 hours - "Boey score" risk stratification guides urgency
Mesenteric ischaemia: every hour of delay without reperfusion increases bowel necrosis and irreversible damage
Ruptured AAA: mortality approaches 100% without emergency surgery
Strangulated bowel obstruction: closed-loop obstruction can progress from viable to gangrenous in hours

Multidisciplinary Team (MDT) Approach

Emergency physician - initial resuscitation, triage, investigations
Surgeon (general) - urgent review and decision-making; must be contacted early
Anaesthesiologist - pre-operative optimisation, risk stratification
Interventional radiology - CT-guided drainage of abscesses; endovascular management of vascular emergencies
ICU/HDU - post-operative care, management of septic shock and MODS
Nursing staff - monitoring, fluid balance, medication administration
Microbiology - guidance on antibiotic choice and de-escalation

Principles of Surgical Decision-Making

"Source control" is the fundamental surgical goal: remove or exclude the source of contamination (Sabiston, Schwartz, B&L)
Damage control surgery in haemodynamically unstable patients - staged approach, avoid prolonged initial surgery
Laparoscopic vs. open - laparoscopy is increasingly favoured for appendectomy, perforated peptic ulcer, and diagnostic cases; associated with fewer wound complications and shorter hospital stay
Early involvement of a senior surgeon reduces decision-to-incision time and improves outcomes
The Sabiston textbook specifically emphasises that "Appendicitis must be considered in every patient who has not had an appendectomy and presents with acute abdominal pain" - a disciplined clinical mindset preventing missed diagnoses (Sabiston, p. 2039)

Communication and Documentation

Clear, contemporaneous documentation of clinical findings, decisions, and time of surgical referral
Structured handover (SBAR format) between clinical teams
Informed consent should be obtained as early as possible
Family communication with appropriate urgency and transparency

Summary Reference Table: Key Features by Condition

Condition	Classic Pain	Key Sign	Investigation Finding	Immediate Action
Appendicitis	Periumbilical → RIF	Rebound/guarding RIF, Rovsing's	WCC↑, CT fat stranding	IV fluids, antibiotics, appendectomy
Perforated PU	Sudden epigastric	Board-like rigidity	CXR: pneumoperitoneum	NBM, NG tube, IV PPI, laparotomy
SB Obstruction	Colicky periumbilical	Distension, tinkling BS	AXR: dilated SB loops	NBM, NG tube, IV fluids, surgery if strangulation
Peritonitis	Generalised, worse on movement	Generalised rigidity, rebound	WCC↑, CRP↑, CT findings	IV fluids, antibiotics, laparotomy
Cholecystitis	RUQ, radiates to scapula	Murphy's sign	USS: gallstones, thick GB wall	Antibiotics, IV fluids, cholecystectomy
Pancreatitis	Epigastric → back	Epigastric tenderness	Amylase/lipase ↑↑	Aggressive IV fluids, analgesia, NBM
Ruptured AAA	Sudden back/flank	Pulsatile mass, shock	CT aorta (unstable → theatre directly)	Immediate surgical emergency

Sources cited: Bailey and Love's Short Practice of Surgery, 28th Edition (Chapters 63, 65, 87); Schwartz's Principles of Surgery, 11th Edition (Chapters 26, 30); Sabiston Textbook of Surgery, 21st Edition (Chapters 22, 28, 94)

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