Comprehensive Seminar Notes on Colorectal and Anal Disorders

Anatomy of the Large Bowel and Rectum

• Vascular Supply of the Colon:

  • Superior Mesenteric Artery (SMA): Supplies the right side (ascending colon and right half of the transverse colon).

    • Middle Colic Artery: Supplies the transverse colon.

    • Right Colic Artery: Supplies the ascending colon.

    • Ileocolic Artery: Supplies the cecum and appendix.

  • Inferior Mesenteric Artery (IMA): Supplies the left side (left half of the transverse colon, descending colon, and sigmoid colon).

    • Left Colic Artery: Has ascending and descending branches.

    • Sigmoid Arteries: Supply the sigmoid colon.

    • Superior Rectal Artery: The terminal branch of the IMA.

  • Marginal Artery (of Drummond): Provides collateral circulation between the SMA and IMA systems.

• Arteries of the Rectum and Anal Canal:

  • Superior Rectal Artery: Branch from the Inferior Mesenteric Artery.

  • Middle Rectal Artery: Branch from the Internal Iliac Artery.

  • Inferior Rectal Artery: Branch from the Internal Pudendal Artery (which exits the Pudendal Canal/Alcock's canal near the ischial tuberosity).

  • Median Sacral Artery: A small branch arising from the abdominal aorta just above the bifurcation.

• Muscular Anatomy:

  • Internal Anal Sphincter Muscle: An extension of the circular smooth muscle layer of the rectum (involuntary).

  • External Anal Sphincter Muscle: Comprising deep, superficial, and subcutaneous parts (voluntary).

  • Levator Ani Muscle: Supports the pelvic floor; consists of the puborectalis, pubococcygeus, and iliococcygeus muscles.

Lower Gastrointestinal (GI) Bleeding

• Epidemiology:

  • Lower GI bleeding has an annual incidence of $20$ to $27$ cases per $100,000$ population.

• Etiologies and Clinical Presentations:

  • Ischemic Colitis: Characterized by sudden onset of left-sided abdominal pain followed by bloody diarrhea. It is often secondary to conditions like hemodialysis, myocardial infarction, postcardiopulmonary bypass, or postaortoiliac surgery. It predominantly affects the mucosa.

  • Hemorrhoids: Bright red blood on toilet paper or the bowl; rarely hemodynamically significant.

  • Inflammatory Bowel Disease (IBD): Small amounts of blood mixed with mucus and feces.

  • Tumors: Color becomes brighter as the tumor location moves from proximal to distal colon.

  • Diverticular Disease and Angiodysplasia: Typically sudden, brisk, but self-limiting bleeding. Diverticular bleeding occurs when a vessel breaks down as it passes through the weakened diverticulum wall. Angiodysplasia involves age-related degeneration of submucosal veins.

  • Brisk Upper GI Bleed: Can present as bright red blood per rectum if transit is very rapid.

• Diagnostic Procedures:

  • Nasogastric (NG) Tube Placement: Used to rule out an upper GI source. If clear bilious fluid is aspirated, the source is likely distal to the Ligament of Treitz.

  • Colonoscopy: The definitive diagnostic tool for ischemic colitis and visualizing polyps/tumors.

  • Computed Tomography (CT): May reveal colonic wall thickening, pneumatosis, or portal venous gas in severe ischemic cases.

  • Technetium-$99m$ Sulphur Colloid Isotope Red Cell Scan: Most sensitive; detects extravasation with bleeding as low as $0.05$ to $0.1\,ml/min$.

• Management Strategies:

  • Minor Bleeding: History, physical exam, anorectal exam, anoscopy, proctosigmoidoscopy, and colonoscopy.

  • Major Bleeding:

    • Resuscitation first.

    • Surgery indicated if hemodynamic instability persists or if patients require more than $6$ units of red blood cells in $24$ hours.

    • Segmental Resection: Ideal if the segment is localized.

    • Total Abdominal Colectomy with Ileorectal Anastomosis: For uncontrolled, nonlocalized bleeding.

  • Diverticular Bleeding Management: $90\%$ stop bleeding spontaneously; supportive care (fluids/transfusion) is usually sufficient. Recurrent bleeding requires resection.

Diverticular Disease

• Pathophysiology:

  • Mucosal outpouchings through the submucosa and muscular layer.

  • Usually occur between the antimesenteric taenia and mesenteric taenia at the site where blood vessels enter the wall.

  • Sigmoid colon is involved in nearly all cases; $10\%$ involve the entire colon.

• Epidemiology: An acquired condition associated with consumption of refined foods and low dietary fiber (rare in rural Africa and Asia).

• Clinical Definitions:

  • Diverticulosis: Presence of noninflamed diverticula (may be asymptomatic or cause colicky pain).

  • Diverticulitis: Inflammation of one or more diverticula.

• Management of Complications:

  • Acute Diverticulitis/Phlegmon: IV fluids, antibiotics, and bowel rest.

  • Abscess: Percutaneous drainage under CT guidance.

  • Fecal Peritonitis: Emergency laparotomy. The standard procedure is the Hartmann Procedure (resection of sigmoid colon, proximal stoma, and oversewn rectal stump).

  • Hinchey Classification:

    • Hinchey I: Pericolic or mesenteric abscess.

    • Hinchey II: Contained pelvic abscess.

    • Hinchey III: Generalised purulent peritonitis.

    • Hinchey IV: Generalised feculent peritonitis (mortality rate approximately $50\%$).

  • Fistulae: Common sites include erosion into adjacent viscera (e.g., bladder).

Ulcerative Colitis (UC)

• Epidemiology: $1$ to $15$ new cases per $100,000$ population annually. Bimodal distribution (teens and early $40s$).

• Pathology:

  • The disease is limited to the mucosa and submucosa.

  • Continuous involvement: The rectum is always involved; spreads proximally.

  • Macroscopic: Ulcerated mucosa with pseudopolyps (regenerating mucosa).

  • Microscopic: Crypt abscesses at the base of the mucosa.

• Clinical Features:

  • Frequent blood-stained stools or diarrhea with mucus.

  • Tenesmus and lower abdominal pain.

  • $20\%$ of patients suffer a severe attack/pancolitis (unremitting bloody diarrhea $10$ to $24$ times per day).

• Medical Management:

  • Aminosalicylic acid (5-ASA): Mainstay; linked with stabilizing compounds to release at high pH in the colon. Used to induce and maintain remission.

  • Steroids: For moderate to severe cases; not for maintenance of remission.

  • Biologic Agents/Immunomodulators: For resistant disease.

• Surgical Management:

  • Indications: Intractability, high-grade dysplasia/cancer risk (surveillance begins $10$ years after diagnosis, every $3$ years), hemorrhage, perforation, or toxic dilatation.

  • Total Proctocolectomy: Gold standard for cure; requires a permanent Brooke ileostomy.

  • Restorative Proctocolectomy (J-Pouch): Creation of an ileal reservoir to replace the rectum. Complications include pouchitis, stricture, and sexual dysfunction.

Comparison: Ulcerative Colitis vs. Crohn Disease

• Ulcerative Colitis:

  • Location: Colon only.

  • Lesions: Continuous from rectum.

  • Inflammation: Mucosa/Submucosa (shallow).

  • Neoplasms: High risk.

  • Fistulae/Fissures/Granulomas: None.

• Crohn Disease:

  • Location: Entire GI tract.

  • Lesions: Skip lesions.

  • Inflammation: Transmural (full thickness).

  • Neoplasms: Lower risk.

  • Fistulae: Frequent.

  • Fissures: Through submucosa.

  • Granulomas: Noncaseating.

Colorectal Polyps

• Epidemiology: Found in $20\%$ to $40\%$ of asymptomatic patients over $50$. $30\%$ to $50\%$ with one adenoma have a synchronous one elsewhere.

• Neoplastic Mucosal Polyps (Adenomas):

  • Precursors to $70\%$ of all colorectal cancers (CRC).

  • Cancer Risk Factors: Size (polyps > 2\,cm have a $30\%-40\%$ malignancy risk; < 1\,cm have $1\%-2\%$), degree of dysplasia, and villous architecture.

  • Types: Tubular ($75\%$), Tubulovillous ($15\%$), Villous ($10\%$).

  • Physical Structure: Sessile (broad-based) or Pedunculated (on a stalk).

• Non-neoplastic Polyps:

  • Hyperplastic: Small, sessile, no malignant potential. Found in $1/3$ of population over $50$.

  • Juvenile (Retention) Polyps: Common in children (<10 years old). No individual malignant potential but can cause bleeding or intussusception.

  • Inflammatory Polyps: Associated with IBD.

• Management: All polyps must be removed via endoscopic polypectomy or segmental resection if too large/suspicious.

Colorectal Cancer (CRC)

• Incidence: 3rd most common tumor in men, 2nd in women; accounts for $10\%$ of all tumor types and $8\%$ of cancer deaths worldwide.

• Risk Factors: Age > 40, family history, inherited syndromes (FAP < 1\%, Lynch/HNPCC $3\%-5\%$), chronic IBD, and pelvic radiation.

• Symptoms by Site:

  • Right Colon: Iron deficiency anemia, weight loss, dull abdominal pain.

  • Left Colon/Sigmoid: Change in bowel habits (constipation/diarrhea), colicky pain, obstructive symptoms.

  • Rectum: Rectal fullness, urgency, tenesmus, bleeding, pelvic pain.

• Diagnosis and Staging:

  • Screening: FOBT (can have false positives from red meat/peroxidase), FIT, Colonoscopy (every $10$ years for average risk), CT Colonography.

  • Carcinoembryonic Antigen (CEA): Useful for postoperative follow-up; low predictive value for initial diagnosis.

  • TNM Classification:

    • Tis: Carcinoma in situ.

    • T1: Invades submucosa.

    • T2: Invades muscularis propria.

    • T3: Invades through muscularis into pericolorectal tissues.

    • T4a: Penetrates visceral peritoneum.

    • T4b: Invades other organs.

    • N1: Metastasis in $1-3$ regional nodes.

    • N2: Metastasis in $4+$ regional nodes.

    • M1a: Metastasis in one organ.

    • M1b: Metastasis in multiple organs/peritoneum.

  • Staging Note: At least $12$ lymph nodes must be examined for adequate pN staging.

• Management:

  • Surgery: Wide resection (at least $5\,cm$ margins) and lymph node removal.

  • Adjuvant Therapy: Recommended for Stage III and high-risk Stage II. Includes 5-FU/FA or Oxaliplatin combinations (FOLFOX, XELOX).

  • Follow-up: recurrences likely within $18$ months ($50\%$) to $3$ years ($90\%$).

Specialty Tumors and Anal Disorders

• Carcinoid Tumors: Rectal carcinoids are usually submucosal yellow-gray nodules. Small lesions ( < 1\,cm) are treated with local transanal excision. Large lesions ( > 2\,cm) are malignant.

• Anal Cancer:

  • Squamous Cell Carcinoma (SCC): Grows slowly, drains to inguinal lymph nodes. Local excision unless invading sphincter.

  • Basal Cell Carcinoma: Rare; locally excised.

• Hemorrhoids:

  • Downward displacement of anal cushions (left lateral, right anterior, right posterior).

  • Grading:

    • 1st Degree: No prolapse.

    • 2nd Degree: Prolapse with spontaneous reduction.

    • 3rd Degree: Prolapse requiring manual replacement.

    • 4th Degree: Permanently prolapsed, irreducible.

  • Treatment: Rubber band ligation (1st-3rd), Hemorrhoidectomy (4th or complicated), and Stapled Hemorrhoidopexy.

• Anal Fissure: An ulcer in the lower anal canal, usually in the posterior midline. Fissure triad: Chronic fissure, sentinel skin tag, and hypertrophied anal papilla. Treatment: Lateral internal sphincterotomy.

• Anorectal Abscess: Results from infection of anal glands. Classified as Perianal (most common), Ischiorectal, Intersphincteric, or Supralevator. Treatment: Primary incision and drainage.

• Fistula in Ano: Chronic inflammatory tract connecting anal crypt to perianal skin. Management: Fistulotomy (unroofing the tract).

• Pilonidal Sinus: Infection of a hair follicle in the sacrococcygeal area, most common in high-hirsute patients in their $20s-30s$. Treatment: Drainage and local excision.

Questions & Discussion

• Clinical Case 1: A 30-year-old female with colitis in transverse/descending colon. BIopsy shows inflammatory process confined to mucosa and submucosa. Diagnosis: Ulcerative Colitis.

• Clinical Case 2: A 28-year-old with hematochezia, negative endoscopy, blood noted above ileocecal valve. Test of choice: Technetium $99m$ pertechnetate scan (to look for Meckel's diverticulum/ectopic gastric mucosa).

• Clinical Case 3: 4-cm carcinoid mass found in appendix during appendectomy. Correct management: Right hemicolectomy (masses > 2\,cm require radical resection).

• Clinical Case 4: Correct use of CEA: To monitor for postoperative recurrence.

• Surgical Matches:

  1. 37-year-old with UC and high-grade dysplasia rectally: Total proctocolectomy with ileoanal J-pouch.

  2. 60-year-old with recurrent anal SCC after chemoradiation: Abdominoperineal resection.

  3. 68-year-old with fixed adenocarcinoma $3\,cm$ from anal verge and incontinence: Abdominoperineal resection.

  4. 33-year-old with Crohn, tachycardia, fever, and dilated colon: Subtotal colectomy with end ileostomy (Emergency treatment for toxic megacolon/perforation).