1. Colonic Polyps

1.1 Epidemiology

• General population prevalence
  • Common: By age 60, at least 30% of individuals in developed countries harbour at least one adenomatous polyp (i.e. a neoplastic polyp).
  • Cancer risk: Roughly 3% have a lifetime risk of developing colorectal carcinoma, although all colorectal cancers arise from an adenoma at some point in the so-called adenoma–carcinoma sequence.
• Proportion of polyp types
  • Neoplastic polyps:
    • Adenomas (tubular, villous, tubulovillous).
    • Sessile serrated polyp/adenoma (SSP/A).
  • Non‐neoplastic polyps:
    • Hamartomas (e.g. Peutz–Jeghers, juvenile polyps, Cowden’s disease, Cronkhite–Canada syndrome).
    • Metaplastic (hyperplastic).
    • Inflammatory (‘pseudo‐polyps’, e.g. in IBD).
• Inherited cancer syndromes involving colonic polyps
  • Familial adenomatous polyposis (FAP): accounts for ~1% of all colorectal cancers.
  • Hereditary non‐polyposis colorectal cancer (HNPCC, or Lynch syndrome): accounts for ~10% of colorectal cancers.

1.2 Aetiology

• Genetic mutations
  • Adenomas: Somatic (acquired) mutations in key regulatory genes (e.g. APC, KRAS, TP53) drive transformation of normal mucosa → adenoma → carcinoma.
  • APC gene on chromosome 5 (FAP) → hundreds to thousands of polyps. In these patients, risk of CRC is near‐100% by the third decade if untreated.
  • Mismatch repair gene mutations (HNPCC / Lynch syndrome) → right-sided colon cancers at younger ages (mean 45 years) but without numerous colonic polyps as in FAP.
• Familial Adenomatous Polyposis (FAP)
  • Autosomal dominant inheritance (25% new mutations).
  • >100 adenomatous colonic polyps forming in teenage years.
  • Extracolonic manifestations: duodenal adenomas, gastric adenomas, ampullary carcinoma, desmoid tumours, and in Gardner’s variant, osteomas.
  • Progression to CRC if colon is not resected typically by 40 years.
• Hereditary Non‐Polyposis Colorectal Cancer (HNPCC / Lynch syndrome)
  • Autosomal dominant (mismatch repair genes).
  • Microsatellite instability is a hallmark.
  • Predominantly right‐sided colonic adenocarcinomas with early onset (~45 years).
  • Also associated with other cancers: endometrial, ovarian, gastric, small bowel.
  • Amsterdam criteria help screen families:
    1. ≥ 3 family members with HNPCC‐related cancers (one a first‐degree relative of the others),
    2. ≥ 2 successive generations affected,
    3. ≥ 1 diagnosis at <50 years.
• Hamartomatous syndromes
  • Peutz–Jeghers syndrome:
    • Autosomal dominant.
    • Multiple hamartomatous small bowel/colonic polyps + mucocutaneous pigmentation (often lips, oral mucosa).
    • Increased risk of GI cancers.
  • Juvenile polyposis:
    • Large pedunculated vascular polyps in stomach, small bowel or colon.
    • ~40% lifetime risk of colorectal cancer, ~20% risk of gastric cancer.
  • Cowden’s disease:
    • Autosomal dominant.
    • Hamartomas in stomach, bowel, plus mucocutaneous lesions, multiple congenital abnormalities.
  • Cronkhite–Canada syndrome:
    • Non‐inherited, with diffuse GI hamartomas, alopecia, nail changes, malabsorption.
• Non‐familial / sporadic causes
  • Age-related: sporadic adenomas often arise in older adults.
  • Diet: high animal fat, low fibre possibly predispose to adenoma formation.
  • Others: smoking, obesity, etc.

1.3 Pathophysiology

1. Adenoma–Carcinoma Sequence
   • Main route for CRC development: Normal mucosa → small adenoma → advanced adenoma (dysplasia) → invasive carcinoma.
   • Takes ~10+ years, driven by accumulation of genetic mutations (APC → KRAS → p53).
   • Only a minority of adenomas eventually progress, but given how common adenomas are, this route explains most CRCs.
2. Malignant potential influenced by:
   • Size: >2 cm strongly correlates with increased risk.
   • Multiplicity of polyps: the more polyps, the higher the risk.
   • Histology: villous > tubulovillous > tubular > serrated.
   • Degree of dysplasia (low- vs high-grade).
3. Hyperplastic (metaplastic) polyps
   • Usually small (<5 mm), predominantly in distal colon, with minimal malignant potential except for large sessile serrated variants.
4. Inflammatory (pseudo‐polyps)
   • Regenerative mucosal overgrowth in IBD, not intrinsically neoplastic.
5. Inherited syndrome–specific
   • In FAP, the APC tumour suppressor gene is defective → hundreds to thousands of adenomas from adolescence onwards.
   • In HNPCC, mismatch repair gene mutations → microsatellite instability with earlier progression to malignancy but fewer polyps overall.

1.4 Signs and Symptoms (Clinical Features)

1. Asymptomatic in majority
   • Typically detected on screening or incidental endoscopy.
2. Anaemia or rectal bleeding
   • Chronic occult blood loss or occasionally overt bleeding.
   • Iron‐deficiency anaemia may be the first clue.
3. Altered bowel habit / partial obstruction (uncommon)
   • More likely if polyp is large or numerous.
4. Mucus discharge
   • Large villous adenomas may secrete mucus → watery diarrhoea, electrolyte disturbance in rare cases.
5. Inherited syndromes may have extra‐colonic features
   • FAP: desmoid tumours, osteomas (Gardner’s variant), upper GI polyps, etc.
   • HNPCC: family history of early onset colon cancer ± endometrial, gastric, ovarian, small bowel.
   • Peutz–Jeghers: mucocutaneous pigmentation.

1.5 Complications

1. Malignant transformation
   • Ultimate risk is determined by size, histology, dysplasia.
   • In inherited syndromes (FAP, HNPCC), the cancer risk is extremely high if not managed.
2. Bleeding
   • Commonest acute complication of polypectomy (~2% immediate, ~2% delayed).
   • Chronic polyp bleeding → iron‐deficiency anaemia.
3. Intussusception or obstruction
   • Rarer, but can occur with large pedunculated polyps or multiple juvenile polyps.
4. Perforation
   • ~0.5% risk with polypectomy.
5. Desmoid tumours (in FAP)
   • Intra‐abdominal desmoid tumour can cause mass effect, pain, or bowel compromise.

1.6 Immediate Management

1. Colonoscopic polypectomy
   • Gold standard for diagnosis and removal.
   • Pedunculated polyps typically snared; sessile polyps may require more complex endoscopic resection (e.g. EMR or ESD).
2. Histopathological examination
   • Determines polyp type (adenoma vs non‐neoplastic) + dysplasia grade + completeness of excision.
   • Guides further management or repeat resection.
3. Handling complications
   • Haemorrhage post‐polypectomy: endoscopic haemostasis (e.g. clips, cautery).
   • Perforation: surgical or endoscopic closure, depending on extent.
4. Symptomatic or suspected inherited polyp syndrome patients
   • High suspicion if young age, strong family history.
   • Genetic testing / full colonoscopy.
   • Specialist referral (e.g. to clinical genetics, advanced endoscopic or surgical teams).

1.7 Long‐Term Management

1. Surveillance
   • Adenomatous polyps: guidelines typically recommend colonoscopy at intervals dependent on:
     • Number of polyps.
     • Size (>1 cm vs >2 cm).
     • Advanced histology (villous, high‐grade dysplasia).
   • After polypectomy of 1–2 small tubular adenomas, surveillance may be in 5 years.
   • Multiple or large adenomas → colonoscopy in 1–3 years.
2. Family screening
   • FAP: prophylactic colectomy in teenage years (pan‐proctocolectomy + ileoanal pouch or ileostomy).
     • Colonoscopy from teenage years if not operated.
     • Upper endoscopy for duodenal/ampullary lesions.
   • HNPCC: colonoscopic screening from age 20–25 (or 2–5 years earlier than the youngest case in the family), repeated every 1–2 years.
     • Additional screening (upper GI endoscopy, pelvic ultrasound) for associated malignancies.
3. Surgical
   • Local surgical resection for large or difficult polyps if endoscopic resection incomplete or not feasible.
   • In FAP, prophylactic total proctocolectomy typically in the second or third decade.
   • In HNPCC (Lynch syndrome), prophylactic or early segmental colectomy if carcinoma is detected, plus continued endoscopic follow‐up.
4. Diet and chemoprevention
   • High‐fibre, low‐fat diet is sometimes recommended, though evidence is inconsistent.
   • Aspirin/NSAIDs can decrease adenoma recurrence by COX inhibition but not standard for all.
5. Manage extra‐colonic manifestations
   • For syndromic polyp disorders (Peutz–Jeghers, juvenile polyposis, etc.), watch for upper GI or other malignancies (breast, pancreatic).

2. Colorectal Carcinoma

2.1 Epidemiology

• Incidence and mortality
  • Second most common cancer in the UK, with about 30,000 new cases per year.
  • Accounts for roughly 10%–15% of all new cancer diagnoses in developed nations.
  • Two-thirds of patients die from the disease, making it the second most common cause of cancer-related death in the UK.
• Age and distribution
  • Median age at diagnosis is 60–70 years; over 80% of cases occur above 60 years of age.
  • Location of tumours:
    • 65% in the rectosigmoid region.
    • ~10% in the left/transverse colon.
    • ~25% in the right colon.
  • About 5% of cases can be synchronous (i.e. more than one primary tumour detected at the same time).
• Aetiological subgroups
  • 75% sporadic.
  • 10–12% associated with inherited polyposis syndromes, e.g., Familial Adenomatous Polyposis (FAP) and Lynch syndrome (HNPCC).
  • 10% have a non-syndromic family history.
  • 2% are IBD-related (long-standing ulcerative colitis or Crohn’s disease).

2.2 Aetiology

• Adenoma–carcinoma sequence
  • Most colorectal cancers arise through the stepwise transformation of normal epithelium → adenomatous polyp → carcinoma.
  • This progression typically takes around 10 years.
• Inherited predispositions
  • Familial Adenomatous Polyposis (FAP)
    • Autosomal dominant mutation in the APC gene on chromosome 5.
    • Characterised by >100 adenomatous polyps in the colon and rectum.
    • 25% of cases arise from new (de novo) mutations.
    • If untreated, nearly 100% progression to colorectal cancer by age 40.
    • Variants:
      • Gardner’s syndrome: FAP + osteomas, skin cysts, desmoid tumours.
      • Turcot syndrome: FAP + CNS tumours (e.g., medulloblastoma).
  • Hereditary Non–Polyposis Colorectal Cancer (HNPCC or Lynch syndrome)
    • Autosomal dominant.
    • Caused by germline mutations in DNA mismatch repair genes (MLH1, MSH2, MSH6, PMS2).
    • Accounts for ~10% of all colorectal cancers.
    • Typically right-sided, younger onset (mean age ~45).
    • Associated with other malignancies: endometrial, ovarian, upper GI, small bowel, and urinary tract cancers.
    • Diagnosis typically guided by the Amsterdam criteria and microsatellite instability testing.
• Dietary and lifestyle factors
  • Diets high in red meat, processed fats, and low in fibre increase risk.
  • Protective elements:
    • Adequate dietary fibre (cereals, fruit and vegetables).
    • Possibly calcium and folic acid.
  • Chronic alcohol overuse and smoking increase risk.
• Inflammatory bowel disease
  • Chronic inflammation in ulcerative colitis or Crohn’s disease predisposes to malignant change, especially after 8–10 years of disease.
• Other medical conditions
  • Primary sclerosing cholangitis (often with IBD).
  • Obesity and metabolic syndrome.
  • Acromegaly.
  • Prior ureterosigmoidostomy (rare, but possible risk).

2.3 Pathophysiology

1. Classic adenoma–carcinoma sequence
   • Initial APC gene mutation → small adenomatous polyp.
   • KRAS mutations → polyp grows.
   • Loss of tumour suppressor genes (e.g. p53) and gain of COX-2 → progression to invasive carcinoma.
2. Microsatellite instability pathway
   • Defective DNA mismatch repair (e.g., MLH1, MSH2) → accumulation of mutations in repetitive (microsatellite) DNA.
   • Commonly seen in HNPCC.
3. Serrated pathway
   • Sessile serrated adenomas/polyps (SSA/P) can progress via BRAF mutations.
   • Different morphological and molecular features compared to classic adenomas.
4. Spread
   • Local extension through the bowel wall into adjacent structures.
   • Lymphatic spread to regional lymph nodes.
   • Haematogenous to liver (portal circulation), lungs and others (systemic).

2.4 Clinical Features

• Symptoms by location
  • Rectosigmoid (~65%)
    • Haematochezia (fresh bleeding per rectum).
    • Altered bowel habit (tenesmus, urgency).
    • Obstruction (more common with left-sided tumours).
  • Right colon (~25%)
    • Occult bleeding → iron deficiency anaemia, fatigue, pallor.
    • Weight loss, vague abdominal pain.
    • Less common to have obstructive symptoms early.
• General symptoms
  • Change in bowel habit (especially if new onset in an older patient).
  • Rectal bleeding not explained by haemorrhoids alone.
  • Anaemia, either microcytic (chronic blood loss) or normocytic in advanced disease.
  • Abdominal pain or mass on examination.
  • Tenesmus with low rectal lesions.
  • Perforation or peritonitis (rare initial presentation).

2.5 Complications

1. Obstruction
   • Especially for distal (left-sided) lesions; can present as acute large-bowel obstruction.
2. Perforation
   • Can lead to faecal peritonitis; emergent, life-threatening scenario.
3. Haemorrhage
   • Chronic low-grade blood loss → iron deficiency anaemia.
   • Acute massive bleeding is rare but possible.
4. Fistula formation
   • Especially with locally advanced or recurrent tumour, e.g. colovesical fistula.
5. Spread
   • Local infiltration, lymphatic spread, and distant metastases (particularly liver).

2.6 Immediate Management

• Stabilisation
  • In cases of acute complications (obstruction, perforation, haemorrhage):
    • Resuscitation with IV fluids, correct electrolytes.
    • Blood transfusion if significant anaemia or haemodynamic instability.
    • Nil by mouth and NG tube for decompression if ileus/obstruction suspected.
    • Broad-spectrum antibiotics if sepsis or perforation.
    • Urgent surgical or endoscopic input.
• Diagnostic confirmation
  • Colonoscopy: gold standard for visualisation and biopsy.
  • Flexible sigmoidoscopy: may visualise up to splenic flexure only; not definitive for right-sided lesions.
  • Imaging:
    • CT abdomen/pelvis with IV contrast → tumour extent and staging.
    • Pelvic MRI for rectal tumours.
    • CT colonography if colonoscopy not possible.
• Staging
  • Lab tests: FBC, U&Es, LFTs (liver metastases or comorbidity), iron studies.
  • Serum CEA: tumour marker for baseline and subsequent surveillance (not for initial screening or diagnosis).
  • TNM or Dukes’ staging (see below).

2.7 Long-Term Management

2.7.1 Surgery

• Aim: curative resection of tumour and involved lymphatic drainage.
• Procedure depends on tumour location:
  1. Right hemicolectomy: for caecal, ascending, or proximal transverse colon tumours.
  2. Left hemicolectomy: for distal transverse or descending colon lesions.
  3. Sigmoid colectomy: for sigmoid tumours.
  4. Anterior resection: for high rectal or upper sigmoid lesions.
  5. Abdominoperineal (AP) resection: for very low rectal tumours → permanent colostomy.
  6. Hartmann’s procedure: in emergencies (obstruction, perforation) or palliation.
  7. Total mesorectal excision (TME): in rectal cancers to reduce local recurrence.
• Liver metastases resection: 10–20% of patients with liver metastases may be candidates for hepatic resection or ablation, potentially offering cure or long-term remission.

Colorectal carcinoma is one of the few oncological diseases where the presence of a metastatic deposit can be treated with curative intent. A solitary liver lesion should be surgically resected. In fact, the purpose of following-up patients with CEA is to identify patients with solitary metastatic lesions amenable to surgical resection - transarterial chemoembolisation & radiofrequency ablation are used as palliative procedures when the lesions are too numerous or large to resect.

2.7.2 Chemotherapy

• Adjuvant chemotherapy
  • Usually 5-FU (5-fluorouracil)–based combinations.
  • Oxaliplatin or capecitabine may be added.
  • Indicated in Dukes’ C (any T, N+) or high-risk Dukes’ B (T4, poor differentiation, vascular invasion).
  • Improves 5-year survival by 5–15%.
• Neoadjuvant chemotherapy
  • For locally advanced rectal cancer (T3/T4, or node-positive rectal tumours), often combined with radiotherapy.
• Palliative chemotherapy
  • For metastatic disease.
  • Common regimens: FOLFOX (5-FU, folinic acid, oxaliplatin), FOLFIRI (5-FU, folinic acid, irinotecan).
  • Targeted agents (e.g., bevacizumab [anti-VEGF], cetuximab [anti-EGFR], panitumumab) in selected cases depending on KRAS, BRAF, and other molecular markers.

2.7.3 Radiotherapy

• Rectal cancer
  • Preoperative short-course radiotherapy or long-course chemoradiotherapy can reduce local recurrence and enable resectability.
  • Postoperative radiotherapy is less commonly used.
• Colon cancer
  • Typically not used in routine management except in palliation of local symptoms (e.g., pain or bleeding).

2.7.4 Palliation

• Symptom control: e.g., management of pain, bleeding, obstruction.
• Stenting: self-expanding metal stents for inoperable obstructing lesions of the left colon.
• Chemotherapy or short-course radiotherapy to reduce tumour bulk and symptoms.
• Palliative resection or bypass: occasionally needed to relieve obstruction, bleeding, or pain.

2.7.5 Follow-up and Surveillance

• Colonoscopy at 1 year post-resection, then every 3–5 years if normal.
• CT scan (chest/abdomen/pelvis) can be performed every 6–12 months for the first 3–5 years to detect metastatic disease early.
• CEA measurements every 6–12 months to monitor for recurrence.

2.8 Prognosis

• Staging
  • Dukes’ staging (historical)
    • Dukes’ A: Confined to mucosa ± submucosa.
    • Dukes’ B: Extends beyond muscularis propria into serosa ± local tissues, but no nodal involvement.
    • Dukes’ C: Lymph node involvement.
    • Dukes’ D: Distant metastases.
  • TNM classification
    • T1–T4 for tumour depth, N0–N2 for nodal involvement, M0–M1 for metastasis.
• Survival
  • Five-year survival by stage:
    • Dukes’ A > 90%.
    • Dukes’ B ~ 70–80%.
    • Dukes’ C ~ 40–50%.
    • Dukes’ D ~ 5–10%.
• Risk of local or distant recurrence is highest in the first 2–3 years post-surgery.

2.9 Prevention and Screening

2.9.1 Risk reduction

1. Dietary changes: high-fibre, low red/processed meat intake; adequate calcium and folate.
2. Aspirin/NSAIDs: some evidence for polyp recurrence prevention; routine prophylaxis not recommended due to side effects.
3. Lifestyle modifications: limit alcohol, avoid smoking, maintain healthy BMI.

2.9.2 Screening

• Faecal Occult Blood Test (FOBT) or Faecal Immunochemical Test (FIT)
  • In the UK, performed 2-yearly for people aged 60–74 (NHS Bowel Cancer Screening Programme).
  • Being extended to younger age groups (50–59) in some regions.
  • Reduces mortality by about 16% through earlier detection.
• Flexible sigmoidoscopy (one-off)
  • Historically offered at age 55.
  • Reduces mortality by 35% from left-sided lesions.
  • Currently overshadowed by the 2-yearly FOBT/FIT approach in many areas.
• High-risk groups
  • FAP: annual sigmoidoscopy from early teens; prophylactic colectomy.
  • HNPCC: colonoscopy every 1–2 years from age 25 or earlier (10 years younger than earliest known case in family).

3. Miscellaneous Colonic Disorders

3.1 Colonic Diverticular Disease

3.1.1 Epidemiology

• Prevalence: Diverticula (outpouchings of colonic mucosa/submucosa) are extremely common in developed countries, increasing with age.
• By age 50, ~50% have diverticulosis; prevalence increases further in older age groups.
• Geographical pattern:
  • Western populations: predominantly left-sided (sigmoid) diverticula.
  • Asian populations and rare younger patients (<40 years): often right-sided.

3.1.2 Aetiology

• Dietary fibre deficiency: A low intake of unrefined fibre → small-volume stool → increased intracolonic pressure → circular muscle hypertrophy → mucosal herniation (diverticula).
• Other factors: Ageing, connective tissue changes, comorbidities (though diet/fibre concept is primary explanation).

3.1.3 Pathophysiology

• Diverticulum formation: Mucosal herniations occur at points of weakness where blood vessels (vasa recta) enter the colonic wall.
• Inflammation: Faecal matter may impact in the neck of a diverticulum, triggering micro-perforations and local inflammation. This can spontaneously resolve or lead to complications such as bleeding, abscess formation, stricturing, or perforation.

3.1.4 Signs and Symptoms / Clinical Features

• Diverticulosis (asymptomatic diverticula)
  • Usually incidental finding on colonoscopy or imaging.
  • Often no symptoms.
• Diverticular disease (symptomatic)
  • Colicky left iliac fossa pain relieved by defaecation.
  • Abdominal bloating, flatulence.
  • Altered bowel habit: intermittent diarrhoea or constipation.
  • Possible passage of pellet-like stools.
• Diverticulitis
  • Pain and tenderness in the left lower quadrant (mimicking left-sided appendicitis).
  • Fever, chills, elevated inflammatory markers (CRP, WCC).
  • Nausea, possible diarrhoea or constipation.

3.1.5 Complications

1. Bleeding:
   • Usually painless haematochezia, more commonly right-sided.
   • Elderly patients and those on NSAIDs/anticoagulants are at higher risk.
   • Major haemorrhage is uncommon but possible; rebleeding risk increases over time.
2. Diverticulitis:
   • Local inflammation can lead to phlegmon or abscess formation.
   • Severe cases → fever, leucocytosis, CT evidence of abscess or complicated disease.
3. Perforation:
   • Can lead to peritonitis; a surgical emergency with high mortality.
4. Stricture:
   • Chronic inflammation → scarring → partial colonic obstruction.
5. Fistula:
   • Commonly colovesical fistula (to bladder) → pneumaturia, faecaluria.
   • Or less commonly colovaginal, colo-uterine, or colo-cutaneous.

3.1.6 Immediate Management

• Uncomplicated Diverticular Disease
  • Typically no acute ‘immediate’ intervention; ensure adequate hydration, analgesia, dietary advice (increase fluid/fibre).
  • Exclude colorectal cancer if any ‘red flag’ features (rectal bleeding, significant weight loss, anaemia) via colonoscopy/CT colonography.
• Diverticular Bleeding
  • Most episodes are self-limiting.
  • Resuscitation if needed (IV fluids, blood transfusion if significant).
  • Endoscopic or interventional radiological therapy for major bleed (e.g., angio-embolisation).
• Acute Diverticulitis
  • Mild cases: oral antibiotics (e.g., metronidazole + ciprofloxacin or co-amoxiclav), analgesia, bowel rest or clear fluids if needed.
  • Severe cases: hospital admission, IV antibiotics, analgesia, fluid resuscitation.
  • CT abdomen/pelvis: rule out abscess or complicated disease.
    • Abscess may need radiologically guided drainage.

3.1.7 Long-Term Management

• Diet and Lifestyle:
  • Adequate fluid, increased dietary fibre, exercise.
  • Avoiding seeds or nuts is sometimes advised anecdotally, but evidence is lacking.
• Recurrent Diverticulitis:
  • Elective surgical resection (usually sigmoid colectomy) may be considered for recurrent or complicated diverticulitis, especially in younger patients.
  • Each case is individualised: number of episodes, severity, comorbidities.
• Follow-up and Prognosis:
  • ~80–85% of patients remain asymptomatic with diverticulosis.
  • ~10% may develop diverticulitis.
  • Prognosis depends on severity and complications. Perforation has high mortality.

3.2 Megacolon

Megacolon refers to a markedly dilated large bowel. It can be congenital (Hirschsprung’s disease) or acquired (idiopathic megacolon or megarectum).

3.2.1 Hirschsprung’s Disease

3.2.1.1 Epidemiology

• Incidence ~1 in 5000 live births.
• More common in males (~4:1 ratio).
• 35% have a family history; certain inherited forms involve RET tyrosine kinase gene mutations.
• 10% of children with Hirschsprung’s disease also have Down syndrome.

3.2.1.2 Aetiology

• Congenital absence of ganglion cells (neural crest–derived) in the submucosal (Meissner’s) and myenteric (Auerbach’s) plexuses of the distal colon, typically the rectum ± sigmoid.
• Failed craniocaudal migration of neural crest cells during embryonic development.

3.2.1.3 Pathophysiology

• Lack of ganglion cells → no coordinated peristalsis → functional obstruction.
• Internal anal sphincter fails to relax (absent rectoanal inhibitory reflex).
• Proximal normal ganglionic bowel becomes massively dilated (megacolon).

3.2.1.4 Signs and Symptoms / Clinical Features

• Neonatal: Delayed passage of meconium (>48 hours), abdominal distension, bilious vomiting, feeding intolerance.
• Older children / Adults (rare presentations): Chronic constipation, abdominal distension, failure to thrive.
• Digital rectal exam: often reveals an empty rectum with explosive release of stool/gas on withdrawal.

3.2.1.5 Complications

• Enterocolitis (potentially life-threatening with fever, diarrhoea, toxic megacolon).
• Growth impairment.
• Bowel obstruction and perforation if left untreated.

3.2.1.6 Immediate Management

• Acute severe obstruction or Hirschsprung’s enterocolitis:
  • Nasogastric decompression, IV fluids, correction of electrolyte imbalances.
  • IV antibiotics if sepsis.
  • Rectal decompression (rectal tube).

3.2.1.7 Long-Term Management

• Definitive surgical resection of the aganglionic segment with pull-through anastomosis (e.g., Soave, Swenson, or Duhamel procedure).
• Prognosis: Good if diagnosed and treated early. Some children may have residual constipation or soiling.

3.2.2 Idiopathic Megacolon & Megarectum

3.2.2.1 Epidemiology

• Less common than Hirschsprung’s.
• Affects older children or adults.

3.2.2.2 Aetiology

• True cause unknown (“idiopathic”) but often associated with:
  • Habitual withholding of stools in childhood.
  • Underlying psychological or neurogenic disorders (spinal cord lesions, multiple sclerosis).
  • Chronic opiate use, scleroderma, etc.

3.2.2.3 Pathophysiology

• Megarectum: The rectum is abnormally enlarged; stool accumulates → constipation ± overflow soiling.
• Megacolon: May affect the entire colon; results in chronic, intractable constipation.

3.2.2.4 Clinical Features

• Chronic constipation, infrequent urge to defaecate.
• Possible faecal soiling (commoner in megarectum).
• Abdominal distension; digital rectal exam may reveal large amounts of stool.

3.2.2.5 Complications

• Faecal impaction, overflow incontinence.
• Social/psychological impact.
• Rarely acute colonic pseudo-obstruction.

3.2.2.6 Immediate Management

• Usually no acute ‘crisis’ unless impaction is severe.
• If severely impacted:
  • Suppositories, enemas, or manual evacuation.
  • Intravenous fluids/electrolyte correction if complicated.

3.2.2.7 Long-Term Management

• Conservative
  • High-fibre diet, adequate hydration, and toilet training in children.
  • Stool softeners, osmotic laxatives, bulking agents.
  • Encourage regular toileting habits; psychological support if indicated.
• Surgery
  • Rarely required (e.g., resection of severely dilated and dysfunctional segment).

3.3 Acute Colonic Pseudo-Obstruction (Ogilvie’s Syndrome)

3.3.1 Epidemiology

• Primarily older, hospitalised patients with comorbidities or postoperative states.
• Precipitated by electrolyte disturbance, severe infection, trauma, recent major surgery, or prolonged immobilisation.

3.3.2 Aetiology

• Precise cause unclear; likely autonomic dysregulation → acute severe dilatation of the caecum and right colon in the absence of any mechanical obstruction.

3.3.3 Pathophysiology

• Dysfunction of autonomic innervation of the colon leads to reduced peristalsis and significant colonic distension, often confined to the right colon and/or transverse colon.

3.3.4 Clinical Features

• Painless abdominal distension (typically marked).
• Minimal abdominal pain (if any).
• Bowel movements and flatus are reduced or absent.
• On examination:
  • Tympanic, distended abdomen.
  • Bowel sounds can be present, reduced, or high-pitched; variable.
  • Usually no obvious mechanical obstruction on imaging.

3.3.5 Complications

• Risk of perforation especially if caecal diameter exceeds 12 cm.
• Risk of peritonitis if perforation occurs.
• Electrolyte imbalances, dehydration if vomiting or poor intake.

3.3.6 Immediate Management

1. Exclude Mechanical Obstruction
   • CT scan or water-soluble contrast enema to confirm no obstructing lesion.
2. Supportive Care
   • IV fluids, correct electrolytes.
   • Bowel rest, NG tube if vomiting.
3. Colonoscopic decompression
   • Diagnostic and therapeutic; reduces risk of perforation by decompressing colon.
4. Neostigmine (cholinesterase inhibitor)
   • Induces colonic contraction → may rapidly decompress the colon.
   • Requires cardiac monitoring (risk of bradycardia).
5. Surgery
   • Rarely needed unless there is perforation or failed endoscopic decompression with ongoing risk.

3.3.7 Long-Term Management

• Treat underlying cause (correct immobility, infections, electrolyte derangements).
• Prevent recurrence with careful monitoring and addressing any contributory factors (e.g., medication review, physiotherapy/mobility).

3.4 Pneumatosis Cystoides Intestinalis

A rare condition involving multiple air-filled cysts in the submucosa of the bowel (often colon, but can affect small bowel).

3.4.1 Epidemiology

• Rare and typically incidental; true prevalence not well-established.

3.4.2 Aetiology

• Unclear; possibly from alveolar rupture with tracking of air along vascular sheaths to the bowel, or bacterial gas production in the submucosa.
• Associated with chronic obstructive pulmonary disease, immunosuppression, or connective tissue disorders in some cases.

3.4.3 Pathophysiology

• Gas accumulates in the submucosal or subserosal layer, forming characteristic cysts.
• Usually benign if no ischaemia or perforation.

3.4.4 Clinical Features

• Often asymptomatic.
• May present with mild abdominal pain, diarrhoea, rectal bleeding, or occasionally more severe symptoms.

3.4.5 Complications

• Rare: tension pneumatosis (risk of rupture), pneumoperitoneum (if cysts rupture), confusion with perforation on imaging.

3.4.6 Immediate Management

• Generally no urgent intervention if asymptomatic.
• Exclude signs of perforation or ischaemia (CT scan, lactate, peritonitis on exam).

3.4.7 Long-Term Management

• Observation for asymptomatic patients.
• High-flow oxygen therapy for symptomatic or extensive disease, theoretically reducing nitrogen content in cysts → shrinkage.
• Elemental diets have been tried in certain resistant cases.
• Surgery (resection) is extremely rare unless there is suspicion of complications (e.g., ischaemia, perforation).