Colorectal care, diverticulitis and anorectal symptoms

Australian National Bowel Cancer Screening Program (NBCSP)

• Bowel screening: People aged 45–49 can request their first national-program kit; those aged 50–74 are routinely mailed kits every two years. Subsequent kits follow the program’s two-year cycle. Symptoms require diagnostic assessment rather than waiting for screening.
• Test Mechanism: The iFOBT utilizes specific antibodies directed against human globin. It requires no dietary restrictions (unlike older guaiac-based tests) and detects microscopic, intermittent lower GI bleeding.
• Positive iFOBT: Refer promptly for colonoscopy after assessing the patient. Do not repeat the test to invalidate a positive result. The national program does not supply a universal mandatory 30-day completion rule.

Diagnostic Staging and Surgical Resection Principles

• Diagnostic Confirmation: Complete colonoscopy with multiple tissue biopsies to establish histopathology (most commonly adenocarcinoma). If complete colonoscopy cannot be completed due to an obstructing tumor, CT colonography or postoperative colonoscopy is mandatory to exclude synchronous lesions (present in 3% to 5% of patients).
• Staging Workup: Contrast-enhanced CT of the chest, abdomen, and pelvis to detect distant metastases (liver is the commonest site of haematogenous spread via the portal vein; lungs via systemic venous drainage).
• Serum Carcinoembryonic Antigen (CEA): Baseline CEA is measured prior to surgery. CEA is not a diagnostic screening tool (due to low sensitivity in early disease) but serves as a vital prognostic marker and surveillance baseline; persistent elevation or postoperative rise indicates residual or recurrent disease.
• Rectal cancer staging: Pelvic MRI evaluates local stage and mesorectal anatomy; other imaging addresses distant disease. Endorectal ultrasound is selected for particular early lesions rather than required alongside MRI in every case. Management is multidisciplinary.
• Surgical Resection Principles:
  • Curative Resection: Requires en bloc removal of the primary tumor with at least a $5\text{ cm}$ proximal and distal longitudinal clearance margin ($2\text{ cm}$ for distal rectal cancers) and complete excision of the intact regional mesentery containing lymphovascular channels.
  • Vascular Ligation & Lymph Node Yield: High ligation of the primary feeding arteries at their aortic origins, ensuring harvest of at least 12 regional lymph nodes to provide accurate pathological nodal staging ($N0$ vs $N1/N2$).
  • Procedures: Right hemicolectomy (ileocolic resection) for caecal/ascending tumors; left hemicolectomy for splenic flexure/descending tumors; high anterior resection (HAR) for sigmoid tumors; low anterior resection (LAR) with total mesorectal excision (TME) and temporary diverting loop ileostomy for mid-to-low rectal cancers; abdominoperineal resection (APR) with permanent end colostomy when rectal cancer invades the levator ani or external anal sphincter.

Acute Diverticulitis: Hinchey Classification & Contemporary Care

Colonic diverticula are false (pulsion) diverticula—herniations of mucosa and submucosa through the muscularis propria at weak points where nutrient arterioles (vasa recta) penetrate the colonic wall. In Western nations, 95% involve the sigmoid colon.

Pathogenesis

Acute diverticulitis begins with micro-perforation or macro-perforation of a diverticulum, initiated by inspissated faecal material (faecalith) causing localized pressure necrosis, mucosal abrasion, and bacterial proliferation. It is fundamentally an extraluminal peridiverticular infection, ranging from mild phlegmon to life-threatening feculent peritonitis.

Diagnostic Confirmation

• Clinical Presentation: Constant, dull or sharp left lower quadrant (LLQ) pain, low-grade fever, anorexia, nausea, constipation or loose stools, and localized LLQ tenderness with voluntary guarding.
• Investigation of Choice: Contrast-enhanced CT of the abdomen and pelvis is the diagnostic gold standard (sensitivity $> 95\%$). CT confirms colonic wall thickening ($> 4\text{ mm}$), pericolonic fat stranding, diverticula, intramural air, and evaluates for complications (abscess, fistula, free perforation).
• After diverticulitis: Colonoscopy depends on complicated disease, suspicious imaging, age, symptoms and prior high-quality examination. It is not automatically required after every uncomplicated CT-confirmed episode.

Modified Hinchey Classification and Evidence-Based Management

• Stage 0: Pathological Description: Mild clinical diverticulitis; localized colonic wall thickening and fat stranding without abscess or perforation; Evidence-Based Clinical Management: Uncomplicated Diverticulitis: Outpatient management with oral analgesia (paracetamol) and clear fluids for 48 hours. Per Australian Therapeutic Guidelines, routine antibiotics are NOT recommended in immunocompetent, systemically well patients without high-risk features. Antibiotics are reserved for immunocompromised, septic, pregnant, or severely comorbid patients.
• Stage Ia: Pathological Description: Confined pericolic phlegmon or localized pericolic inflammatory mass; Evidence-Based Clinical Management: Inpatient admission, bowel rest (clear fluids or NBM), intravenous crystalloids, and intravenous antibiotics (e.g., amoxicillin-clavulanic acid or ceftriaxone + metronidazole).
• Stage Ib: Pathological Description: Confined pericolic or mesenteric abscess ($< 4\text{ cm}$); Evidence-Based Clinical Management: Intravenous antibiotics and close clinical observation. Abscesses $< 3-4\text{ cm}$ typically resolve with antibiotic therapy alone.
• Stage II: Pathological Description: Distant retroperitoneal, pelvic, or intra-abdominal abscess ($> 4\text{ cm}$); Evidence-Based Clinical Management: CT-guided percutaneous pigtail catheter drainage combined with intravenous broad-spectrum antibiotics. Avoids emergency laparotomy in over 80% of patients, permitting elective delayed single-stage resection.
• Stage III: Pathological Description: Generalized purulent peritonitis resulting from rupture of a pelvic abscess; Evidence-Based Clinical Management: Emergency resuscitation, aggressive IV fluids, broad-spectrum IV antibiotics, and emergency surgical intervention: Hartmann's procedure (sigmoid resection, rectal stump closure, end colostomy) or primary resection with anastomosis and diverting loop ileostomy.
• Stage IV: Pathological Description: Generalized feculent peritonitis resulting from unsealed perforation of diverticulum; Evidence-Based Clinical Management: Emergency resuscitation, broad-spectrum IV antibiotics, and immediate emergency Hartmann's procedure. High operative mortality ($15-30\%$).

Anorectal pain and bleeding

A fissure often causes sharp pain during/after defecation with a small amount of bright blood; constipation management and suitable local treatment help typical cases. Haemorrhoids can bleed, but finding them does not exclude colorectal cancer or another cause. Persistent bleeding, altered bowel habit, anaemia or systemic symptoms requires appropriate investigation. Constant severe pain, fever or swelling raises perianal abscess and requires drainage assessment; antibiotics alone may not provide source control. Immunocompromised patients can have less visible inflammation. Examine with consent and adequate comfort, avoiding a forced painful examination, and refer when the assessment is incomplete or concerning. Lateral/multiple fissures or atypical lesions can raise inflammatory, infectious or malignant disease.

Primary references (checked 7 October 2026): National bowel screening.