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INTESTINAL OBSTRUCTION, SMALL & LARGE BOWEL PATHOLOGY

Distinction-Level Notes for Final MBBS Examination (25 Marks)

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PART 1: INTESTINAL OBSTRUCTION

Definition

Classification

INTESTINAL OBSTRUCTION
        |
   _____|______
  |            |
DYNAMIC     ADYNAMIC
(Mechanical) (Functional)
  |               |
Acute/         Paralytic ileus
Chronic        Pseudo-obstruction

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Pathophysiology (Bailey Ch. 78)

1. Bowel proximal to obstruction dilates; bowel distal collapses and empties
2. Initially peristalsis increases to overcome obstruction
3. If unrelieved: flaccidity, paralysis, then distension
4. Distension caused by two factors:
   • Gas (90% nitrogen + hydrogen sulphide) from bacterial overgrowth
   • Fluid accumulation - saliva 500 mL + bile 500 mL + gastric juice 500 mL/day = massive third space loss

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Cardinal Clinical Features - The Classic Quartet

┌──────────────────────────────────────────────────────────────┐
│          THE QUARTET OF INTESTINAL OBSTRUCTION               │
│                                                              │
│   1. PAIN          - colicky, central (SBO) / lower (LBO)   │
│   2. VOMITING      - early in high SBO, late in LBO         │
│   3. DISTENSION    - central (SBO), peripheral (LBO)        │
│   4. ABSOLUTE      - neither faeces nor flatus passed       │
│      CONSTIPATION                                            │
└──────────────────────────────────────────────────────────────┘

Comparison: Small vs. Large Bowel Obstruction

Signs of Strangulation (Emergency - NEVER DELAY SURGERY)

• Continuous severe pain unrelieved by opiates
• Tenderness + rigidity (peritonism)
• Shock (tachycardia, hypotension)
• Pyrexia
• In hernia: tense, tender, irreducible lump; no cough impulse; erythema/purplish discolouration of overlying skin

---

Investigations

• SBO: central (valvulae conniventes cross full width)
• LBO: peripheral (haustral folds do NOT cross full width)

---

Treatment (Bailey's "Three Main Measures")

DRIP AND SUCK + SURGERY
         |
    _____|______________________________
   |            |                      |
Nasogastric  IV fluids +         Relief of
suction    electrolytes          obstruction
(Ryle's or  (Hartmann's solution  (surgical or
Salem tube)  is appropriate)       non-operative)

1. Manage the segment at the site of obstruction
2. Manage the distended proximal bowel (decompression)
3. Manage the underlying cause

Surgery should be delayed until resuscitation is complete UNLESS strangulation or closed-loop obstruction is suspected.

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PART 2: VOLVULUS

Definition

• 180° torsion = luminal obstruction

• 360° torsion = vascular occlusion (ischaemia)

DIAGRAM TO DRAW IN EXAM:

SIGMOID VOLVULUS (most common in adults)

        Long pelvic mesocolon
               |
    Overloaded pelvic colon
               |
    Band of adhesions at base
               ↓
      ┌────────────────────┐
      │  SIGMOID COLON     │
      │  TWISTS AROUND     │
      │  ITS MESENTERY     │
      │  (anticlockwise)   │
      └────────────────────┘
              ↓
   "OMEGA LOOP" or "COFFEE BEAN SIGN"
   on plain X-ray

X-RAY: Dilated loop running diagonally from
       RIGHT to LEFT across abdomen
       Two fluid levels (one in each limb)
       "Bird's beak" deformity on barium enema

Types of Volvulus

Primary vs Secondary Volvulus

• Primary: congenital malrotation, abnormal mesenteric attachments, congenital bands
• Secondary (more common): rotation around acquired adhesion or stoma

Compound Volvulus (Ileosigmoid Knotting)

• Rare; ileum twists around sigmoid colon
• Gangrene of both segments
• Presents as acute intestinal obstruction with comparatively mild distension
• Treatment: decompression + resection + anastomosis

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PART 3: SMALL INTESTINAL PATHOLOGY

Key Conditions

A. Small Bowel Obstruction

B. Small Bowel Strictures

• TB, Crohn's disease (most common)
• Malignant: lymphoma (uncommon); carcinoma + sarcoma (rare)
• Presentation: subacute/chronic
• Treatment: resection + anastomosis; strictureplasty for short multiple Crohn's strictures

C. Paralytic Ileus vs Pseudo-obstruction

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PART 4: MECKEL'S DIVERTICULUM

The Rule of 2s (Bailey p.1333)

┌─────────────────────────────────────────────────────┐
│              MECKEL'S RULE OF 2s                     │
│                                                      │
│  • 2% of population                                  │
│  • 2 feet (60 cm) from ileocaecal valve              │
│  • 2 inches (5 cm) long                              │
│  • 2 types of heterotopic mucosa (gastric, colonic)  │
│  • 2x more symptomatic in males                      │
│  • 2 years - most symptomatic in childhood           │
└─────────────────────────────────────────────────────┘

Anatomy

• True diverticulum (all three coats of bowel wall - mucosa, muscularis, serosa)
• Located on the antimesenteric border of the ileum
• Has its own blood supply (persistent vitelline artery)
• Remnant of the vitello-intestinal (omphalomesenteric) duct
• 20% contain heterotopic mucosa (gastric most important - causes peptic ulceration)

DIAGRAM:

MECKEL'S DIVERTICULUM - ANATOMY

        ILEUM
   _______|_______
  |               |
  |   ←60 cm→    |
  |_______________|
         |
         | (antimesenteric border)
         ↓
    ┌─────────┐
    │ MECKEL'S│ ← 5 cm long
    │DIVERTI- │
    │ CULUM   │ ← may have fibrous band
    └────↑────┘    to umbilicus
         |
    (± persistent vitello-
    intestinal band to umbilicus)

Complications (Mnemonic: "HIIBO-P")

Diagnosis

• Tc-99m pertechnetate scan (detects gastric mucosa; investigation of choice for bleeding Meckel's)
• CT scan / capsule endoscopy
• Laparoscopy

Treatment

• Meckel's diverticulectomy: excision with wedge of ileal wall at base
• When symptomatic Meckel's found incidentally at surgery for appendicitis: resect
• Incidental asymptomatic Meckel's in adult: generally leave alone (risk of complications < risk of surgery)
• In children: resect (lifetime risk of complications is higher)

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PART 5: MALROTATION

Embryology Basis

• Normal gut rotates 270° anticlockwise around the superior mesenteric artery during fetal development
• This gives the small bowel mesentery a broad, stable base from DJ flexure (left upper quadrant) to caecum (right lower quadrant)
• Incomplete rotation = narrow, unstable mesenteric base - risk of volvulus

Ladd's Bands

• Fibrous peritoneal bands run from a central upper abdominal caecum to the right lateral abdominal wall
• These bands cross and compress the duodenum, causing obstruction

Clinical Presentation

A baby vomiting bile must be considered to have midgut volvulus until proven otherwise - this is a SURGICAL EMERGENCY.

Diagnosis

• Upper GI contrast study: DJ flexure should be to LEFT of vertebral column at level of pylorus (stable mesentery)
• If DJ flexure is central or right-sided = malrotation confirmed
• USS: "whirlpool sign" of superior mesenteric vessels

DIAGRAM:

NORMAL vs MALROTATION

NORMAL:                    MALROTATION:
                           
DJ flexure (LUQ)           DJ flexure (central/right)
     \                           \
      \  Broad mesenteric         \ Narrow mesenteric
       \  base                     \ base
        \                           \
   Caecum (RIF)              Caecum (central/upper)
                                + Ladd's bands
                                compressing duodenum

Result: STABLE             Result: Risk of MIDGUT VOLVULUS

Treatment - Ladd's Procedure

LADD'S PROCEDURE (steps):
1. Reduce volvulus (untwist anticlockwise)
2. Divide Ladd's bands (relieve duodenal obstruction)
3. Broaden mesenteric base
4. Place small bowel on RIGHT, large bowel on LEFT
5. Appendicectomy (to avoid diagnostic confusion later)
6. If bowel infarcted: resect non-viable bowel
   ± "second-look" laparotomy at 24-48h

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PART 6: INTUSSUSCEPTION

Definition

DIAGRAM (Draw this - it's a distinction marker):

INTUSSUSCEPTION - COMPONENTS

     ←─ Direction of advance

  ┌─────────────────────────────────┐
  │  OUTER (intussuscipiens)        │
  │  ┌───────────────────────┐      │
  │  │  MIDDLE (return tube) │      │
  │  │  ┌─────────────────┐  │      │
  │  │  │ INNER           │  │      │
  │  │  │ (intussusceptum)│  │      │
  │  │  │   LEAD POINT ▶  │  │      │
  │  │  └─────────────────┘  │      │
  │  └───────────────────────┘      │
  └─────────────────────────────────┘
        NECK          APEX

3 layers: Entering (inner) + Returning (middle) + Sheath (outer)

Types (Bailey Table 78.2 - RE Gross classification, n=702)

Epidemiology & Lead Points

Clinical Features

CLASSIC PRESENTATION (infant):
   Previously healthy male infant
         ↓
   Sudden colicky pain → screaming, draws up legs
         ↓
   Pale; well between episodes initially
         ↓
   Bilious vomiting (later)
         ↓
   "REDCURRANT JELLY" stool
   (blood + mucus = late sign, indicates gangrene)
         ↓
   RUQ sausage-shaped mass (60% cases) + 
   "SIGN OF DANCE" (empty RIF)

Investigations

• Abdominal USS: "Target sign" / "Doughnut sign" - pathognomonic
• CT scan: Target sign (Figure 78.6, Bailey)
• Plain AXR: mass, SBO pattern, paucity of gas in RIF

Treatment

TREATMENT ALGORITHM FOR INTUSSUSCEPTION

   Resuscitation
   (IV fluids + broad-spectrum antibiotics + NGT)
         ↓
   Is there: peritonitis? perforation? shock?
         |                    |
        NO                   YES
         ↓                    ↓
   Non-operative         SURGERY directly
   reduction:
   AIR ENEMA
   (or barium enema)
         ↓
   Success (>70%): air/barium refluxes into SB,
   symptoms resolve
         ↓
   FAILURE or pathological lead point:
   SURGERY - open/laparoscopic
   - Compress intussusception towards its origin (DO NOT PULL)
   - If non-reducible / gangrenous / pathological lead → RESECTION

Recurrence after non-operative reduction: 5-10%

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PART 7: CARCINOMA OF THE CAECUM AND COLON

Epidemiology

• 3rd most common cancer worldwide
• Peak incidence 60-70 years
• M = F (slight male preponderance)
• Right colon (caecum/ascending): ~25%; Left colon (descending/sigmoid): ~35%; Rectum: ~40%

Risk Factors

RISK FACTORS FOR COLORECTAL CANCER

Dietary: ↑ red/processed meat, ↓ fibre, ↑ alcohol
Genetic:  FAP (APC gene mutation) - 100% risk
          HNPCC (Lynch syndrome - MLH1, MSH2)
          Family history
Pre-malignant: Adenomatous polyps (especially villous)
               Long-standing UC (>10 years, pancolitis)
               Crohn's colitis
Lifestyle: Obesity, smoking, sedentary lifestyle

Pathology & Dukes' Staging

DUKES' CLASSIFICATION (Modified Astler-Coller)

   Bowel wall cross-section:

   Mucosa ────────────────
   Submucosa ──────────── A: Confined to mucosa/submucosa
   Muscularis ─────────── A: Penetrates muscularis propria
   Serosa/Pericolic fat── B: Through muscularis, no nodes
   ↓
   B: Beyond muscularis, no nodes
   C1: Any depth + regional nodes (not apex)
   C2: Apical node positive
   D: Distant metastases (liver, lung, peritoneum)

   5-year survival:
   A = 90-95%, B = 65-75%, C = 30-40%, D = <5%

TNM Staging

• T1: submucosa; T2: muscularis; T3: through muscularis; T4: adjacent organs
• N0: no nodes; N1: 1-3 nodes; N2: ≥4 nodes
• M0: no metastasis; M1: distant metastasis

Clinical Features (Site-Dependent)

RIGHT COLON (Caecum/Ascending colon):
- ANAEMIA (occult blood loss - iron deficiency)
- Right iliac fossa mass (palpable in ~25%)
- Dull aching pain RIF
- Weight loss, fatigue
- LATE obstruction (liquid contents, wide lumen)
- May present with perforation or appendix-like picture

LEFT COLON (Descending/Sigmoid):
- CHANGE IN BOWEL HABIT (alternating constipation/diarrhoea)
- Rectal bleeding (bright red)
- Colicky left-sided pain
- EARLY obstruction (solid faeces, narrow lumen)
- "Apple core" / "napkin ring" appearance on barium enema

RECTUM:
- Tenesmus, bleeding per rectum
- Mucus discharge
- Feeling of incomplete evacuation

Spread of Colorectal Cancer

ROUTES OF SPREAD:

1. LOCAL SPREAD - circumferential then longitudinal (1-2 cm beyond gross tumour)

2. LYMPHATIC - along superior/inferior mesenteric vessels to aortic nodes

3. HAEMATOGENOUS - via portal vein → LIVER (most common first site)
                 → then lung, bone, brain

4. TRANSPERITONEAL - peritoneal seedlings, Krukenberg tumour (ovaries)

5. IMPLANTATION - at anastomotic site, laparoscopic port sites

Investigations

Surgical Treatment

SURGERY BY SITE:

Caecum/Ascending colon → RIGHT HEMICOLECTOMY
                          (ligate ileocolic + right colic arteries)

Transverse colon ──────→ EXTENDED RIGHT HEMICOLECTOMY
                          or TRANSVERSE COLECTOMY

Splenic flexure/        → LEFT HEMICOLECTOMY
Descending colon         (ligate left colic artery)

Sigmoid colon ─────────→ SIGMOID COLECTOMY / ANTERIOR RESECTION

Upper rectum ──────────→ ANTERIOR RESECTION (with anastomosis)

Lower rectum ──────────→ LOW ANTERIOR RESECTION or
                          ABDOMINOPERINEAL RESECTION (APR)
                          (permanent colostomy)

Emergency Presentation - Obstructed Cancer

OBSTRUCTING LEFT COLON CANCER:

Option 1: Hartmann's procedure
  → Resect tumour + end colostomy (reverse later)

Option 2: On-table lavage + primary anastomosis

Option 3: Stenting (self-expanding metallic stent)
  → Bridge to surgery OR palliative

Perforated → Peritonitis → Emergency Hartmann's

Adjuvant Therapy

• Colon cancer: adjuvant FOLFOX chemotherapy for stage III (node-positive)
• Rectal cancer: pre-operative chemoradiotherapy (CRT) for T3/T4 or node-positive
• Biological agents: Bevacizumab (anti-VEGF), Cetuximab (anti-EGFR, for KRAS wild-type)

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SUMMARY TABLE: All Topics at a Glance

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REPRODUCIBLE EXAM DIAGRAMS

Diagram 1: Causes of Intestinal Obstruction (Pie Chart style - draw as labelled segments)

     ADHESIONS ~60%      ← draw the largest segment
  /─────────────────\
 | HERNIAS ~20%      |   ← second largest
 | MALIGNANCY ~10%   |
 | CROHN'S/OTHER ~5% |
 | VOLVULUS ~5%      |
  \─────────────────/

Diagram 2: Sigmoid Volvulus X-ray Appearance

      ┌──────────────────────────────┐
      │    ABDOMINAL X-RAY           │
      │                              │
      │              ╱╲             │
      │             /  \            │
      │            / ↑  \           │
      │           / LOOP \          │
      │          /        \         │
      │   RIGHT  \  OMEGA  /  LEFT  │
      │           \       /         │
      │            \─────/          │
      │         PELVIS               │
      │  "Coffee bean" / "Omega loop"│
      │  Two fluid levels (erect)    │
      └──────────────────────────────┘

Diagram 3: Dukes' Staging (draw this transverse section)

   ┌──────────────────────────────┐
   │ LUMEN                        │
   ├──────── Mucosa ──────────────│ ← Dukes A
   ├──────── Submucosa ───────────│ ← Dukes A
   ├──────── Muscularis ──────────│ ← Dukes B (if breached)
   ├──────── Serosa ──────────────│
   │                              │
   │  Pericolic fat                │ ← Dukes B (into fat, no nodes)
   │                              │
   │  ○ Lymph node                │ ← Dukes C (node +ve)
   │                              │
   │  Liver / Lung (distant) ─────│ ← Dukes D
   └──────────────────────────────┘

Diagram 4: Meckel's Diverticulum

       UMBILICUS
           │
    fibrous band (remnant)
           │
     ┌─────┴─────┐
     │  MECKEL'S │
     │DIVERTICULUM│
     └─────┬─────┘
           │ 5 cm
      ──────┴──────────────────── ILEUM
      ←────60 cm────→ ICV
      (antimesenteric border)

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HIGH-YIELD DISTINCTION POINTS

1. Strangulation - the only indication to NOT wait for resuscitation in obstruction
2. Sign of Dance in intussusception = empty RIF
3. Redcurrant jelly stool = late sign (gangrene has set in)
4. Bilious vomiting in neonate = midgut volvulus until proven otherwise
5. Tc-99m scan = investigation of choice for bleeding Meckel's
6. Ladd's procedure = treatment of malrotation (broadens mesenteric base)
7. ICV competence matters in LBO: if competent → caecal distension + risk of perforation; if incompetent → decompresses into SB
8. HNPCC = Lynch syndrome (MLH1/MSH2 mutations); FAP = APC gene mutation
9. Apple core lesion on barium = carcinoma of colon (left side)
10. CEA is NOT for screening; used for post-op monitoring
11. Air enema is contraindicated in intussusception with peritonitis/perforation/shock

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How to Score Full Marks (25/25)

1. Definition + Classification (2-3 marks) - always start here
2. Pathophysiology (3-4 marks) - the "why" behind the signs
3. Clinical features (4-5 marks) - use the comparison table
4. Investigations (3-4 marks) - name the gold standard first
5. Management (5-6 marks) - operative + non-operative
6. Diagram (2-3 marks) - even a rough but labelled diagram gets marks

• Dukes' staging - transverse bowel section with layers
• Intussusception components - the three-layer telescoping diagram
• Meckel's diverticulum - antimesenteric position with Rule of 2s
• Sigmoid volvulus X-ray - omega loop / coffee bean

• Sign of Dance, redcurrant jelly stool, Ladd's procedure, ileosigmoid knotting (compound volvulus), ICV competence in LBO, Tc-99m scan for Meckel's bleeding - these details show you read the textbook, not just memorized lists.

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COMPLETE DISTINCTION-LEVEL NOTES

Intestinal Obstruction, Volvulus, Small & Large Bowel Pathology, Meckel's Diverticulum, Malrotation, Intussusception, Ca Caecum & Ca Colon

Final MBBS Examination - 25 Marks

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SECTION 1: INTESTINAL OBSTRUCTION

Definition

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Classification

┌─────────────────────────────────────────────────────┐
│            INTESTINAL OBSTRUCTION                    │
│                                                      │
│        DYNAMIC                 ADYNAMIC              │
│      (Mechanical)            (Functional)            │
│           |                       |                  │
│      ┌────┴────┐            ┌─────┴──────┐           │
│    Acute    Chronic    Paralytic    Pseudo-           │
│                           ileus   obstruction        │
└─────────────────────────────────────────────────────┘

• Paralytic ileus (postoperative, sepsis, metabolic)
• Pseudo-obstruction (Ogilvie's syndrome)

---

Pathophysiology

1. Proximal bowel dilates; distal bowel collapses and empties
2. Initially peristalsis increases (trying to overcome the block) → produces colicky pain and high-pitched bowel sounds
3. If unrelieved → flaccidity → paralysis → silent abdomen
4. Two sources of distension:
   • Gas (90% nitrogen + H₂S) from aerobic and anaerobic bacterial overgrowth
   • Fluid accumulation: saliva (500 mL) + bile (500 mL) + gastric juice (500 mL) + pancreatic + intestinal secretions = massive third-space fluid loss → dehydration + electrolyte imbalance
5. Strangulation = vascular compromise → ischaemia → gangrene → perforation → peritonitis → death
   • Closed-loop obstruction (both ends of loop blocked) → most rapid strangulation
   • ICV competence is critical: competent valve → closed loop in LBO → caecal distension → perforation risk when caecum ≥12 cm

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Cardinal Clinical Features

╔═══════════════════════════════════════════════════════╗
║         THE QUARTET (Bailey Summary Box 78.7)         ║
║                                                       ║
║  1. PAIN            Colicky; umbilical (SBO),         ║
║                     lower abdomen (LBO)               ║
║                                                       ║
║  2. VOMITING        Early & bilious (high SBO),       ║
║                     faeculent (low SBO),              ║
║                     late/absent (LBO)                 ║
║                                                       ║
║  3. DISTENSION      Central (SBO);                    ║
║                     peripheral/flanks (LBO)           ║
║                                                       ║
║  4. ABSOLUTE        Neither flatus nor faeces passed  ║
║     CONSTIPATION                                      ║
╚═══════════════════════════════════════════════════════╝

Detailed Comparison: SBO vs LBO

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Signs of Strangulation (SURGICAL EMERGENCY - Do not delay)

BEWARE STRANGULATION - signs to watch:
• Continuous severe pain (not relieved by IV opiates)
• Tenderness localised → peritonism → rigidity
• Pyrexia, tachycardia
• SHOCK (hypotension)
• In hernia: tense, tender, irreducible lump;
  NO cough impulse; skin erythema / purplish discolouration

---

Investigations

Radiological Features (Bailey Summary Box 78.9)

X-RAY IDENTIFICATION:
┌────────────────────────────────────────────────────┐
│ JEJUNUM: Valvulae conniventes                      │
│          ← completely cross full width →           │
│          Regular spacing; "concertina/ladder"      │
│          Central in abdomen                        │
├────────────────────────────────────────────────────┤
│ ILEUM:   Featureless (distal)                      │
├────────────────────────────────────────────────────┤
│ COLON:   Haustral folds                            │
│          Do NOT cross full width                   │
│          Irregularly spaced                        │
│          No opposite indentations                  │
│          Peripheral in abdomen                     │
└────────────────────────────────────────────────────┘

---

Treatment

The Three Main Measures (Bailey Summary Box 78.11)

╔══════════════════════════════════════════════════╗
║    TREATMENT OF ACUTE INTESTINAL OBSTRUCTION     ║
║                                                  ║
║  1. NGT → Gastrointestinal drainage              ║
║     (Ryle's tube or Salem sump;                  ║
║      free drainage + 4-hourly aspiration)        ║
║                                                  ║
║  2. IV fluids + electrolytes                     ║
║     (Hartmann's solution; correct Na+ and K+     ║
║      losses; monitor urine output)               ║
║                                                  ║
║  3. RELIEF OF OBSTRUCTION                        ║
║     (surgical or non-operative)                  ║
║                                                  ║
║  Surgery delayed until resuscitation complete    ║
║  UNLESS: strangulation or closed-loop suspected  ║
╚══════════════════════════════════════════════════╝

Principles of Surgical Intervention (Bailey Summary Box 78.12)

1. Manage the segment at the site of obstruction
2. Manage the distended proximal bowel (decompression)
3. Manage the underlying cause

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Adynamic Obstruction

Paralytic Ileus (Bailey Ch. 78)

• No bowel sounds on auscultation
• No passage of flatus

1. NGT suction + nil by mouth until bowel sounds/flatus return
2. Correct electrolytes (especially K⁺)
3. Treat underlying cause
4. ERAS (Enhanced Recovery After Surgery) protocols - early oral fluids

Pseudo-obstruction (Ogilvie's Syndrome)

• Predominantly large bowel dilation without mechanical obstruction
• Causes: opiates, anticholinergics, spinal injury, retroperitoneal pathology
• AXR: massive colonic dilation (especially caecum)
• Danger: Caecal perforation when diameter >12 cm
• Treatment: colonoscopic decompression first; neostigmine (IV, 2 mg); if fails → caecostomy

---

---

SECTION 2: VOLVULUS

Definition

• 180° torsion = luminal obstruction

• 360° torsion = vascular occlusion (ischaemia/gangrene)

• Bacterial fermentation adds to distension; rising intraluminal pressure impairs capillary perfusion; mesenteric veins thrombose → ischaemia

Types

Primary vs Secondary

• Primary: congenital malrotation, abnormal mesenteric attachments, congenital bands (e.g. volvulus neonatorum, caecal volvulus)
• Secondary (more common): rotation around acquired adhesion or stoma

---

Sigmoid Volvulus

Predisposing factors

SIGMOID VOLVULUS - PREDISPOSING ANATOMY (Bailey Fig. 78.7):

    ┌────────────────────────────────────┐
    │  1. LONG pelvic mesocolon          │
    │  2. OVERLOADED pelvic colon        │
    │     (high-residue diet/constipation│
    │  3. BAND of adhesions at base      │
    │     tethering the two limbs        │
    └────────────────────────────────────┘
                    ↓
          Sigmoid twists anticlockwise
                    ↓
          ┌──────────────────────┐
          │   OMEGA LOOP forms   │
          └──────────────────────┘

Clinical Presentation

• Fulminant: sudden onset, severe pain, early vomiting, rapid deterioration
• Indolent: insidious onset, slow progression, less pain (more common in elderly)
• Early, progressive abdominal distension (may be visible through abdominal wall)
• Absolute constipation; hiccough/retching

Radiology

AXR APPEARANCES OF SIGMOID VOLVULUS:

SUPINE AXR:                      BARIUM ENEMA:
                                 
    ╱╲  Massively dilated         "BIRD'S BEAK"
   ╱  ╲  sigmoid loop             or "ACE OF SPADES"
  ╱    ╲  running diagonally      deformity at
 ╱  OMEGA╲  from RIGHT → LEFT     the twist
╱   LOOP   ╲                     
━━━━━━━━━━━━━━
PELVIS
                                 
"Coffee bean sign"               Bird's beak
Two fluid levels                 deformity
(one in each limb)               (if erect)

Treatment

SIGMOID VOLVULUS TREATMENT:

Step 1: Resuscitate (IV fluids, NGT)
Step 2: SIGMOIDOSCOPE / FLATUS TUBE per anum
        → decompresses >80% of cases
        → pass tube through twist; a gush of gas = success
Step 3: Elective surgery (after 48-72h, when patient optimised)
        → Hartmann's procedure (resect + end colostomy)
        OR
        → Sigmoid colectomy + primary anastomosis
           (if bowel viable + patient fit)

IF gangrenous / peritonitis at presentation:
        → IMMEDIATE surgery (Hartmann's procedure)

---

Caecal Volvulus

• Usually a clockwise twist; more common in females in 4th-5th decades
• Caecum twists → displaced to left upper quadrant
• May be partial initially (passage of flatus/faeces possible early)
• 25% → palpable tympanic swelling in midline or left abdomen
• Ischaemia common; diagnosis rarely made preoperatively

---

Compound Volvulus (Ileosigmoid Knotting)

• Rare; ileum twists around sigmoid colon
• Long pelvic mesocolon allows ileum to knot around sigmoid
• Gangrene of either or both bowel segments
• AXR: distended ileal loops within distended sigmoid colon
• Treatment: decompression + resection + anastomosis (both segments often need resection)

---

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SECTION 3: SMALL INTESTINAL PATHOLOGY

A. Small Bowel Obstruction

B. Small Bowel Strictures

• TB and Crohn's disease - most common causes
• Malignant (lymphoma - uncommon; carcinoma/sarcoma - rare)
• Presentation: subacute or chronic
• Treatment:
  • Resection + anastomosis (preferred)
  • Strictureplasty for multiple short strictures in Crohn's (preserves bowel length)

C. Adhesions

• Most common cause of SBO (60%)
• From previous surgery, infection, or peritoneal inflammation
• First episode: non-operative management with "drip and suck" (success ~70%)
• Failure or strangulation: laparoscopic or open adhesiolysis
• Recurrent obstruction from adhesions: repeat adhesiolysis ± Noble's plication

D. Paralytic Ileus and Pseudo-obstruction

---

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SECTION 4: MECKEL'S DIVERTICULUM

The Rule of 2s

╔═════════════════════════════════════════════════════╗
║              MECKEL'S RULE OF 2s                    ║
║                                                     ║
║  • 2% of the population                             ║
║  • 2 feet (60 cm) from the ileocaecal valve         ║
║  • 2 inches (5 cm) long                             ║
║  • 2x more common/symptomatic in MALES              ║
║  • 20% contain heterotopic mucosa                   ║
║    (gastric, colonic or pancreatic)                 ║
╚═════════════════════════════════════════════════════╝

Anatomy (Diagram - Draw this in the exam)

       UMBILICUS
           │
    fibrous band (remnant of
    vitello-intestinal duct)
           │
     ┌─────┴──────┐
     │  MECKEL'S  │ ← 5 cm (2 inches) long
     │DIVERTICULUM│ ← TRUE diverticulum (all 3 coats)
     │            │ ← own blood supply (vitelline artery)
     └──────┬─────┘
            │
────────────┴─────────────────────── ILEUM
            ←────60 cm (2 feet)────→ ICV

(Arises from ANTIMESENTERIC border of ileum)

Nature

• True diverticulum (all three layers: mucosa, muscularis propria, serosa)
• Arises from antimesenteric border of ileum
• Persistent remnant of the vitello-intestinal (omphalomesenteric) duct
• Has its own blood supply (persistent vitelline artery)
• 20% contain heterotopic mucosa (gastric > colonic > pancreatic)
• Heterotopic mucosa (especially gastric) predisposes to complications

Complications (Mnemonic: HOBIP)

Diagnosis

• Tc-99m pertechnetate scan - investigation of choice for bleeding Meckel's (detects gastric mucosa)
• CT scan + CT enterography
• Capsule endoscopy / enteroscopy
• Laparoscopy (gold standard for definitive diagnosis)

Treatment

TREATMENT OF MECKEL'S DIVERTICULUM:

SYMPTOMATIC (bleeding/obstruction/inflammation):
→ MECKEL'S DIVERTICULECTOMY
  (excision with wedge of ileal wall at the base
   OR segmental ileal resection if base is wide/indurated)

INCIDENTAL FINDING AT SURGERY:
→ CHILD: RESECT (lifetime risk of complications > risk of surgery)
→ ADULT: Generally LEAVE (risk-benefit ratio usually favours
          non-intervention unless inflammation, narrow neck,
          palpable heterotopic tissue or abnormal appearance)

KEY: When normal appendix found at surgery for
     "appendicitis" → ALWAYS look for Meckel's diverticulum
     (examine 60 cm of terminal ileum)

---

---

SECTION 5: MALROTATION

Embryology

• Normal gut undergoes 270° anticlockwise rotation around the superior mesenteric artery (SMA) during fetal development (weeks 6-12)
• This creates a broad, stable mesenteric base running from the DJ flexure (left upper quadrant) → caecum (right lower quadrant)
• Malrotation = incomplete rotation → narrow, unstable mesenteric base → risk of midgut volvulus

Ladd's Bands

• Fibrous peritoneal bands from a central/upper abdominal caecum to the right lateral abdominal wall
• These bands cross and compress the duodenum, causing duodenal obstruction

DIAGRAM (Draw in exam)

NORMAL vs MALROTATION:

NORMAL ROTATION:              MALROTATION:

DJ flexure (LUQ)              DJ flexure (midline/right)
     \                               |
      \  Broad, stable               | Narrow, unstable
       \  mesenteric base            | mesenteric base
        \                           /
    Caecum (RIF)              Caecum (central/upper)
                               + Ladd's bands crossing
                                 duodenum
                               + Risk of MIDGUT VOLVULUS

Result: STABLE                 Result: LIFE-THREATENING

Clinical Presentations

GOLD RULE: Any neonate vomiting bile = midgut volvulus until proved otherwise - this is a surgical emergency.

Investigations

• Upper GI contrast study: The DJ flexure should lie to the LEFT of the vertebral column at the level of the pylorus (stable). If central or right-sided → malrotation confirmed.
• USS: "Whirlpool sign" of SMA/SMV (vessels wrap around each other)
• AXR: Gasless abdomen (ischaemic midgut); dilated duodenal loop; scaphoid abdomen
• Acidotic baby vomiting bile with gasless AXR = IMMEDIATE LAPAROTOMY without further imaging

Treatment: Ladd's Procedure

LADD'S PROCEDURE (Steps):

1. REDUCE VOLVULUS (untwist anticlockwise)
          ↓
2. ASSESS BOWEL VIABILITY
   (warm saline packs; reassess at 2nd look if uncertain)
          ↓
3. DIVIDE LADD'S BANDS (relieve duodenal compression)
          ↓
4. BROADEN MESENTERIC BASE
   (separate duodenum from ascending colon)
          ↓
5. REPOSITION: Small bowel on RIGHT side
              Large bowel on LEFT side
              (non-rotated position - most stable)
          ↓
6. APPENDICECTOMY
   (caecum now in LUQ - avoids diagnostic confusion)
          ↓
7. If infarcted bowel: RESECT non-viable segments
   ± "SECOND-LOOK" LAPAROTOMY at 24-48 hours
    (if viability of remaining bowel in doubt)

---

---

SECTION 6: INTUSSUSCEPTION

Definition

DIAGRAM - Draw this (distinction marks guaranteed)

INTUSSUSCEPTION - COMPONENTS:

←──── Direction of advance ────

┌─────────────────────────────────────────────────┐
│  OUTER TUBE = INTUSSUSCIPIENS (sheath)           │
│  ┌───────────────────────────────────┐           │
│  │  MIDDLE TUBE (returning layer)    │           │
│  │  ┌─────────────────────────────┐  │           │
│  │  │  INNER TUBE = INTUSSUSCEPTUM│  │           │
│  │  │  ──────────── LEAD POINT ►  │  │           │
│  │  └─────────────────────────────┘  │           │
│  └───────────────────────────────────┘           │
└─────────────────────────────────────────────────┘
        NECK                  APEX

3 layers: 
• Entering/inner tube = INTUSSUSCEPTUM (the invaginated part)
• Returning/middle tube
• Sheath/outer tube = INTUSSUSCIPIENS (the receiving part)

Ischaemia occurs at the NECK (where it's tightest)
Most constriction is at the ILEOCAECAL VALVE

Types (Bailey Table 78.2, after RE Gross, n=702 children)

Age and Lead Points

Clinical Features

CLASSIC PRESENTATION OF INTUSSUSCEPTION IN INFANT:

Previously healthy MALE infant (2-12 months)
                ↓
SUDDEN COLICKY PAIN → screaming, draws up legs,
                       becomes PALE
                ↓
Between episodes: initially appears well / listless
                ↓
BILIOUS VOMITING (develops later)
                ↓
"REDCURRANT JELLY" STOOL
(blood + mucus = LATE sign → indicates gangrene!)
                ↓
ON EXAMINATION (between episodes):
• Abdomen not initially distended
• Sausage-shaped mass in RUQ (60% of cases)
• SIGN OF DANCE = EMPTINESS in RIF
  (caecum has migrated into the intussusception)
• PR exam → blood-stained mucus on finger
• Apex may protrude from anus (extensive colocolic)

Investigations

• Abdominal USS - "Target sign" / "Doughnut sign" - pathognomonic (concentric rings of bowel)
• CT scan - "Target sign" (Figure 78.6, Bailey) - also good for adults
• Plain AXR - SBO pattern; mass in RUQ; paucity of gas in RIF

Treatment Algorithm

MANAGEMENT OF INTUSSUSCEPTION:

STEP 1: RESUSCITATION
        IV fluids + broad-spectrum antibiotics + NGT
                    ↓
STEP 2: ASSESS CONTRAINDICATIONS to non-operative reduction:
        • Peritonitis?    →  YES → SURGERY
        • Perforation?    →  YES → SURGERY  
        • Profound shock? →  YES → SURGERY
        • Known pathological lead point? → YES → SURGERY
                    ↓ (if NO to all)
STEP 3: NON-OPERATIVE REDUCTION
        AIR ENEMA (preferred) or barium enema
        → Success = air/barium freely refluxes into small bowel
          AND symptoms/signs resolve
        → SUCCESS RATE: >70%
        → Colonic perforation during pneumatic reduction: rare
                    ↓
STEP 4: IF NON-OPERATIVE FAILS OR CONTRAINDICATED:
        SURGERY (open or laparoscopic)
        → Transverse right-sided abdominal incision
        → Reduce by COMPRESSING distal end towards origin
          (DO NOT PULL the intussusceptum out)
        → Last part of reduction is hardest (tightest at ICV)
                    ↓
STEP 5: IF IRREDUCIBLE / GANGRENOUS / PATHOLOGICAL LEAD POINT:
        RESECTION (e.g. right hemicolectomy for ileocolic)

RECURRENCE: 5-10% after non-operative reduction

---

---

SECTION 7: CARCINOMA OF THE CAECUM AND COLON

Epidemiology (Bailey, p.1380)

• In UK: 2nd most common cause of cancer death
• ~42,000 new cases/year in UK
• Colon (67%): caecum 12%, ascending 5%, transverse 5.5%, sigmoid 21%
• Rectum (33%)
• Males > Females (56% vs 44%)
• Peaks in 8th decade; emergency presentation in 20% (worse prognosis)

The Adenoma-Carcinoma Sequence (Bailey Summary Box 77.4)

ADENOMA → CARCINOMA SEQUENCE (Fearon-Vogelstein model):

Normal epithelium
        ↓  APC gene mutation (2/3 of colonic adenomas)
Early adenoma
        ↓  K-ras mutation (larger adenomas)
Late adenoma (↑ dysplasia)
        ↓  p53 mutation (marker of invasion)
Carcinoma (invasive)

Evidence for this sequence:
• Distribution of adenomas = distribution of cancers (70% left-sided)
• Larger adenomas more likely to be dysplastic
• 1/3 of resected cancer specimens contain adjacent adenoma
• Screening colonoscopy + polypectomy reduces cancer incidence

Aetiology / Risk Factors

RISK FACTORS FOR COLORECTAL CANCER:

DIETARY:     ↑ Red/processed meat (haem + N-nitroso compounds)
             ↓ Fibre → ↑ colonic transit time → ↑ carcinogen exposure
             ↑ Alcohol
             ↓ Aspirin/NSAIDs (protective - COX-2 inhibition)

GENETIC:     FAP (APC gene) - 100% lifetime risk without surgery
             Lynch syndrome (HNPCC) - 80% lifetime risk
               → MLH1, MSH2, MSH6, PMS2 mutations
               → Microsatellite instability (MSI)
               → Proximal colon predominance
             Family history of CRC (1st degree relative <50y)

PRE-MALIGNANT: Adenomatous polyps (villous > tubular)
               Long-standing UC (>10y, pancolitis - 30x risk)
               Crohn's colitis

LIFESTYLE:   Obesity, sedentary, smoking, type 2 diabetes

Lynch Syndrome (HNPCC) - Amsterdam II Criteria (Bailey Summary Box 77.3)

• ≥3 family members with Lynch-related cancer (CRC, endometrial, small bowel, ureter, renal pelvis)
• ≥2 successive generations affected
• ≥1 diagnosed before age 50 years
• FAP excluded; pathological confirmation of tumours
• Lifetime CRC risk: 80%; endometrial risk: 30-50% in females
• Surveillance: 2-yearly colonoscopy from age 25 (MLH1/MSH2) or 35 (MSH6/PMS2)

---

Pathology (Bailey, p.1380)

• Macroscopic forms:
  • Annular (napkin ring) → obstructive symptoms
  • Ulcerating → presents with bleeding
  • Polypoid → less obstructive
• Microscopy: Columnar cell adenocarcinoma
• Distribution: Rectum 38%, sigmoid 21%, caecum 12%, ascending 5%, transverse 5.5%, descending 4%

---

Spread of Colorectal Cancer (Bailey, p.1380)

ROUTES OF SPREAD:

1. LOCAL (DIRECT)
   • Radial: retroperitoneal (ureter, duodenum, posterior muscles)
             intraperitoneal (adjacent organs, anterior wall)
   • Longitudinal: 1-2 cm beyond gross tumour (excision margin)

2. LYMPHATIC
   • Pericolic nodes → intermediate nodes → central/aortic nodes
   • Follows course of blood supply (SMA for right colon,
     IMA for left colon)

3. HAEMATOGENOUS (via portal vein)
   • LIVER - 1/3 have liver mets at diagnosis
            - 50% develop mets eventually
   • Then: LUNG, bone, brain, ovary

4. TRANSPERITONEAL (TRANSCOELOMIC)
   • Peritoneum, omentum, ovary (Krukenberg tumour)
   • Indicates incurability

5. IMPLANTATION
   • Anastomotic recurrence
   • Port-site recurrence (laparoscopy)

---

Staging

Dukes' Classification (Bailey Summary Box 77.5)

DUKES' STAGING (DRAW THIS CROSS-SECTION):

┌─────────────────────────────────────────────────────┐
│ BOWEL LUMEN                                          │
├─────── Mucosa ──────────────────────────────────────┤ ←─┐
├─────── Submucosa ───────────────────────────────────┤   │ Dukes A
├─────── Muscularis propria ──────────────────────────┤ ←─┘ (confined to/not
│        ↑ Dukes A: invasion but NOT breaching this   │      breaching muscularis)
├─────── Serosa / Pericolic fat ──────────────────────┤ ←── Dukes B (beyond
│                                                      │     muscularis; NO nodes)
│   ○ Regional lymph node ────────────────────────────│ ←── Dukes C (nodes +ve)
│                                                      │     C1: apical node -ve
│                                                      │     C2: apical node +ve
│   LIVER / LUNG (distant metastasis) ────────────────│ ←── Dukes D (metastases)
└─────────────────────────────────────────────────────┘
   (Note: Dukes never described stage D himself)

TNM Classification (Bailey Summary Box 77.6 - UICC 8th edition)

---

Clinical Features (Bailey, p.1381)

SITE-DEPENDENT PRESENTATION:

RIGHT COLON (Caecum / Ascending colon):
━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
  • IRON DEFICIENCY ANAEMIA (occult blood loss)
    → fatigue, pallor, breathlessness
  • RIF MASS (palpable in ~25% at diagnosis)
  • Dull, aching pain RIF (may mimic appendicitis)
  • Weight loss
  • LATE obstruction (liquid faeces + wide lumen
    → presents late)
  • Can present with perforation or appendix-like picture

LEFT COLON (Descending / Sigmoid):
━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
  • CHANGE IN BOWEL HABIT
    (alternating constipation + diarrhoea)
  • Rectal bleeding (bright red blood ± mucus)
  • Colicky left iliac fossa pain
  • EARLY obstruction (solid faeces + narrow lumen)
  • "Apple core" / "napkin ring" on barium enema

RECTUM:
━━━━━━━
  • Rectal bleeding (fresh blood)
  • Tenesmus (feeling of incomplete evacuation)
  • Mucus discharge PR
  • Altered bowel habit

GENERAL (any site):
━━━━━━━━━━━━━━━━━━━
  • Weight loss, anorexia
  • Anaemia
  • Abdominal mass
  • Perforation → peritonitis (emergency)
  • Obstruction (20% emergency presentation)

---

Investigations (Bailey Ch. 77)

---

Surgical Treatment

OPERATION BY SITE (Bailey Ch. 77):

   Caecum / Ascending colon
         ↓
   RIGHT HEMICOLECTOMY
   (ligate ileocolic artery + right colic artery
    close to SMA origin - "high-tie" / CME)
   Anastomosis: ileum-to-transverse colon

   Hepatic flexure / Transverse colon
         ↓
   EXTENDED RIGHT HEMICOLECTOMY
   (divide right branch of middle colic artery)
   Anastomosis: ileum-to-descending colon

   Splenic flexure
         ↓
   EXTENDED RIGHT HEMICOLECTOMY
   OR LEFT HEMICOLECTOMY

   Descending colon
         ↓
   LEFT HEMICOLECTOMY
   (ligate left colic artery from IMA)

   Sigmoid colon
         ↓
   SIGMOID COLECTOMY / HIGH ANTERIOR RESECTION

   Upper rectum
         ↓
   ANTERIOR RESECTION (with anastomosis)

   Lower rectum
         ↓
   LOW ANTERIOR RESECTION (±covering loop ileostomy)
   OR
   ABDOMINOPERINEAL RESECTION (APR)
   → permanent end colostomy

• High ligation of vessels at origin from SMA/IMA
• Sharp dissection along embryological planes
• Removes entire mesocolic envelope
• Improves survival in node-positive disease (Hohenberger principle)

---

Emergency Presentation: Obstructing Colorectal Cancer

TREATMENT OF ACUTE LARGE BOWEL OBSTRUCTION
(Bailey Ch. 78, Summary Box - Ch. 77):

Resuscitation → midline incision → assess

RIGHT COLON LESION (caecum, ascending, hepatic flexure):
→ Emergency RIGHT HEMICOLECTOMY
→ Primary anastomosis safe if patient condition reasonable

SPLENIC FLEXURE LESION:
→ Extended right hemicolectomy
   + ileo-descending colonic anastomosis

LEFT COLON / RECTOSIGMOID LESION:
→ Option 1: HARTMANN'S PROCEDURE
   (resect tumour + end colostomy + rectal stump)
   Reversal later (if fit)

→ Option 2: On-table lavage + primary anastomosis
   (if viable bowel + experienced surgeon)

→ Option 3: COLONIC STENT
   (self-expanding metallic stent, SEMS)
   - "Bridge to surgery" in fit patients
   - Palliative in unfit/metastatic patients

UNRESECTABLE LESION:
→ Proximal colostomy / ileostomy (if ICV incompetent)
   OR ileotransverse bypass (palliative)

CAECAL PERFORATION IMMINENT (caecum >12 cm):
→ Emergency caecostomy or loop transverse colostomy
   (to "buy time" for resuscitation before definitive surgery)

---

Adjuvant and Palliative Therapy (Bailey, p.1383-1385)

ADJUVANT CHEMOTHERAPY:
Stage II (Dukes B): FOLFOX (5-FU + leucovorin + oxaliplatin)
                    - Benefit uncertain; offered selectively
Stage III (Dukes C): FOLFOX → improves 5y DFS by ~20% (to 67-70%)

METASTATIC DISEASE - FIRST LINE:
FOLFIRI (5-FU + leucovorin + irinotecan)
± BEVACIZUMAB (anti-VEGF monoclonal antibody)

SECOND LINE (KRAS wild-type):
CETUXIMAB or PANITUMUMAB (anti-EGFR)

MSI-HIGH tumours:
PEMBROLIZUMAB (immunotherapy - PD-1 inhibitor)

BRAF V600E mutation (~10%):
ENCORAFENIB (BRAF inhibitor) + BINIMETINIB (MEK inhibitor)

LIVER METASTASES:
- 1/3 present at diagnosis; 50% develop at some point
- Resectable mets → surgical resection (potentially curative)
- Chemotherapy ± downsizing → "convert to resectable"
- Ablation (radiofrequency, microwave) for small/peripheral mets

---

Prognosis (Bailey, p.1384)

---

Colorectal Cancer Follow-up (Bailey, p.1385)

• 3% have synchronous bowel tumours (missed at original diagnosis)
• 3% develop metachronous colonic cancer
• 50% develop liver metastases at some point
• NICE guidelines: CT chest/abdomen/pelvis + CEA measurement during first 3 years after curative treatment

---

GIST and Carcinoid (Bailey, p.1385-1386)

• GIST: Arise from interstitial cells of Cajal; c-kit mutation; 30% malignant; treat with surgical resection ± imatinib (targeted therapy)
• Carcinoid: Well-differentiated neuroendocrine tumours; appendix most common site; may cause carcinoid syndrome if liver mets

---

---

MASTER SUMMARY TABLE

---

EXAM DIAGRAMS - QUICK REFERENCE SHEET

Diagram A: Intussusception (three-layer)

Diagram B: Meckel's Diverticulum

Diagram C: Dukes' Staging Cross-section

Diagram D: Sigmoid Volvulus X-ray

Diagram E: Normal vs Malrotation Mesentery

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---

EXAM STRATEGY FOR 25/25

1. Structure your answer as: Definition → Classification → Pathophysiology → Clinical features → Investigations → Management → Prognosis
2. Draw at least 2 diagrams per question (label everything - examiner loves labelled diagrams)
3. Quote Bailey's summary boxes word-for-word - examiners recognize them
4. Include the "distinction details" that others miss: Auerbach's plexus, Sign of Dance, Tc-99m scan, ICV competence, CME (complete mesocolic excision), MSI, BRAF mutation therapy
5. Never miss strangulation signs in any obstruction question - it's always worth marks
6. In colorectal cancer, always mention Dukes AND TNM staging - use both
7. For Meckel's: write "Rule of 2s" as a bullet list - it's instant marks