General Surgery – Colorectal Lecture 2 Comprehensive Notes

Course Objectives

Anatomy & Physiology
- Detail the arterial, venous & lymphatic anatomy of the colon (SMA, IMA, marginal artery of Drummond, portal/mesenteric venous drainage, lymphatic chains).
Disease Recognition & Management
- Distinguish diverticulosis vs diverticulitis; list complications (abscess, fistula, obstruction, perforation, bleeding) and surgical indications.
- Produce differentials, initial management and diagnostic algorithm for LLQ pain.
- Recall etiology, typical presentation, staging & treatment of colorectal carcinoma; order appropriate labs, colonoscopy and radiologic studies.
- Diagnose & treat large-bowel obstruction, volvulus, intussusception, fecal impaction, obstructing cancer.
Anorectal Disorders
- Identify anorectal cancer S/Sx; grade hemorrhoids (I–IV) and describe hemorrhoidal pathogenesis & risk factors.
- Classify perianal infections; manage fissures, fistula-in-ano, abscesses, pilonidal disease.

PANCE Blueprint Emphasis (GI = 8 %)

High-yield colorectal topics (diverticular disease, obstruction, IBD, toxic megacolon, abscess/fistula, hemorrhoids, constipation, impaction, polyps, IBD flares, ischemic bowel, rectal prolapse, ileus, etc.).
Remember exam also asks on biliary, esophageal, gastric, hepatic, pancreatic, nutrition, metabolic & neoplastic disorders.

Toxic Megacolon (TM)

Definition: life-threatening non-obstructive colonic dilatation > $6\,\text{cm}$ (usually transverse colon) plus systemic toxicity.
Micropathology: inflammation extends into $muscularis\,propria$ → paralysis of smooth muscle → massive dilation → cytokine surge.
Precipitants / Etiologies
- IBD flare: ulcerative colitis (MC), Crohn colitis
- Infectious colitis: $Salmonella,\,Shigella,\,Campylobacter,\,Yersinia,\,C!.difficile,\,E.histolytica,\,CMV,\,rotavirus,\,Cryptosporidium,\,aspergillus$
- Radiation, ischemic colitis, chemotherapy, methotrexate, Kaposi sarcoma, Behçet disease
- Drugs that slow motility (opioids, anticholinergics, loperamide, atropine).
Clinical Presentation
- Acute colitis for ≈1 wk → sudden worsened distension
- Symptoms : profuse diarrhea, rectal bleeding, tenesmus, vomiting, fever, malaise
- Exam : distended, tender abdomen, hypoactive sounds; systemic SIRS (fever > $101.5^{\circ}\text{F}$ , HR > $120$ , hypotension, tachypnea).
- Peritonitis (rebound, rigidity) implies perforation.
Diagnostic Criteria
- 1) Radiograph showing colonic diameter > $6\,\text{cm}$
- 2) Any ≥3 of: fever > $101.5^{\circ}\text{F}$ , HR > $120$ , WBC > $10.5\times10^{3}$ or anemia
- 3) Any ≥1 of: dehydration, electrolyte imbalance, AMS, hypotension.
Work-up
- Labs: CBC, CMP/Electrolytes, stool PCR (C. diff), cultures O&P.
- AXR : colonic air–fluid levels, loss of haustra, deep ulcers, segmental thinning (pathognomonic).
- CT : better for severe colitis & complications; look for “accordion” $\&$ “target” signs, fat-stranding, free air.
- Endoscopy: limited (stop at sigmoid, minimal air) only if etiology uncertain.
- US: experimental – shows loss of haustra, wall thick/thin patterns, transverse colon > $6\,\text{cm}$ .
Medical Management
- ICU resuscitation → NPO, NG tube (for decompression of stomach), aggressive IV crystalloids, correct electrolytes.
- Stop motility-slowing drugs.
- Broad-spectrum IV abx (GN + anaerobes).
- Treat underlying cause:
  • Severe UC → IV steroids → if no response 3–5 d → infliximab or cyclosporine.
  • C. diff → oral/NG vancomycin + IV metronidazole (±fidaxomicin).
- TPN if prolonged NPO.
Surgical Indications & Options
- Failure/rebound after max medical therapy (24–72 h).
- Perforation, peritonitis, full-thickness ischemia, sepsis, end-organ failure, abdominal compartment syndrome.
- IBD TM → subtotal colectomy + end ileostomy.
- C. diff TM → total abdominal colectomy ± loop ileostomy.
- Surgical mortality ↑ with perforation or septic shock.

Ischemic Colitis (IC)

Definition: Colonic mucosal injury/inflammation due to hypoperfusion.
Epidemiology: MC ischemic injury in GI tract; incidence ≈ $16/100{,}000$ ; elderly, female > male.
Anatomic Pearl
- Watershed areas (poor collaterals): splenic flexure & rectosigmoid junction.
- Marginal artery of Drummond = SMA–IMA arcade; weak at junction.
Etiologies
- Non-occlusive “low-flow” (≈95 %): hypotension, CHF/MI, dialysis, sepsis, extreme exercise, post-colonoscopy, cocaine, vasoconstrictors, digitalis.
- Arterial occlusion: embolus (AFib), thrombosis, post-EVAR.
- Venous thrombosis (rare) – involves proximal colon ± small bowel.
Clinical Course
- Initial sudden mild crampy LLQ pain + urge to defecate.
- Within 24 h → hematochezia ± diarrhea.
- Progression:
  • Hyperactive phase → bloody diarrhea
  • Paralytic phase → diminished pain, distension, ileus (silent abdomen).
  • Shock phase → gangrene → massive fluid/protein loss → shock, metabolic acidosis.
Diagnostics
- Colonoscopy w/ biopsy = gold standard (minimal insufflation!).
  • Findings: edematous friable mucosa, erythema interspersed with pale “halo,” bluish nodules, single-stripe sign, cyanosis/ulcers if severe.
- CT A/P w IV contrast first-line imaging; shows segmental wall thickening, “thumb-printing,” target sign, pneumatosis or free air if necrosis/perf.
- CT angiography only if suspect mesenteric ischemia.
Management
- Supportive: NPO, IV fluids, bowel rest, NG if ileus, broad IV abx, treat precipitant, stop vasoconstrictors.
- Anticoagulate if mesenteric thrombosis.
- Risk-stratify (poor-outcome markers: male, SBP< $90$ , HR> $100$ , no bleeding, BUN> $20$ , Hgb< $12$ , LDH> $350$ , Na< $136$ , WBC> $15$ ).
- Severe disease (>3 risk factors, peritonitis, pneumatosis/portal gas) → urgent surgery.
- Surgical options:
  • Left IC → sigmoidectomy / left hemicolectomy ± stoma.
  • Right IC → right hemicolectomy ± ileostomy.
  • Fulminant → subtotal colectomy + end ileostomy.

Large Bowel Obstruction (LBO)

Mechanical Causes
- Colorectal cancer (≈60 %)
- Diverticular strictures (20 %)
- Volvulus (sigmoid, cecal)
- Hernia, inflammatory stricture, fecal impaction, intussusception, foreign body.
Pseudo-obstruction (ACPO/Ogilvie): massive dilation without lesion; thought autonomic imbalance; seen in elderly, post-op, trauma, infection, cardiac pts.
Pathophysiology: Closed-loop distension ↑ intraluminal pressure → venous congestion → arterial compromise → ischemia → mucosal permeability ↑ → bacterial translocation → sepsis ± perforation (cecum at highest risk per Laplace: $T = P\times r$ – wall tension proportional to radius).
Presentation
- Distension + crampy pain, nausea/vomiting, obstipation (complete) or flatus passage (partial).
- Cancer: insidious, pencil stools, weight loss.
- Diverticulitis: recurrent LLQ pain.
- Volvulus: sudden distension.
- Intussusception (adult): intermittent colic + weight loss.
- Exam: abdominal tympany, initially normal BS → silent; peritonitis = perforation.
Work-up
- CT A/P w PO + IV contrast (Gastrografin if perf): differentiates partial vs complete, mechanical vs ACPO, localizes transition point.
- AXR: less sensitive; sigmoid/cecal volvulus shows “kidney/coffee bean”; contrast enema → “bird’s beak.”
Initial Management
- NPO, NG decompression (if vomiting or severe distension), IV fluids/electrolytes.
- Treat ACPO conservatively 24 h; if fails → neostigmine or colonoscopic decompression (success 80 %).
- Emergent surgery for closed-loop, ischemia, perforation, volvulus with peritonitis.
Etiology-Specific
- Volvulus – see dedicated section.
- Intussusception – adult usually surgery; peds contrast reduction.
- Cancer – oncologic resection; if poor candidate → stent/dilation.
- Diverticulitis stricture – elective resection if persistent obstruction.

Colonic Volvulus

Definition: axial twist of colon around mesentery → closed-loop LBO.
Location Frequency: sigmoid 80 % > cecal 15 % > transverse 3 %.
Sigmoid Volvulus Pathogenesis
- Chronic constipation/high-fiber → heavy redundant sigmoid; torsion along mesenteric axis; preg uterus/pelvic mass predispose; recurrent torsion → adhesions → “paddle” loop.
Cecal Volvulus Pathogenesis
- Congenitally mobile cecum due to incomplete peritoneal fixation; needs a fulcrum (adhesion, band) to twist.
- Type 1: clockwise RLQ twist; Type 2: counter-clockwise LUQ; Type 3: cecal bascule (folding).
Risk Groups: nursing-home, neuropsychiatric, laxative abuse, Chagas, pregnancy; mortality 30–40 % if delayed.
Clinical: massive distension, crampy/constant pain; obstipation; tympanitic abdomen; peritonitis = ischemia/perf.
Diagnostics
- AXR: sigmoid “kidney/coffee/inner-tube” sign; gastrografin enema “bird’s beak.”
- Cecal: less obvious on AXR; CT defines twist & ischemia.
Management Algorithm
- Sigmoid, no peritonitis → colonoscopic detorsion + rectal tube (>90 % success) → elective sigmoid colectomy w primary anastomosis after bowel prep (recurrence 40–50 % if no surgery).
- Sigmoid w peritonitis / ischemia → emergent laparotomy, Hartmann procedure (resection + end colostomy) → reversal 3–6 mo.
- Cecal volvulus → colonoscopy reduction unreliable (15–20 %) → emergent right hemicolectomy + ileocolic anastomosis (± ileostomy).
  • Non-surgical candidates → percutaneous endoscopic cecostomy (high infection & recurrence).
  • Cecopexy not favored (20–30 % recurrence).

Intussusception

Definition: telescoping of proximal segment (intussusceptum) into distal (intussuscipiens).
Epidemiology: MC abdominal emergency age < $2$ y (1/2000 births); rare in adults (1–5 % SBO). M:F ≈ 3:1.
Types
- Idiopathic ileocolic (95 % pediatric) starts at ileocecal valve.
- Entero-enteral (jejuno-jejunal/ileal) often in older kids/lead point.
- Adult variant almost always has lead point (malignancy 77 %).
Pathophysiology
- Post-viral lymphoid hyperplasia (Peyer patches) hypothesized.
- Telescoping → venous/lymphatic obstruction → edema → arterial compromise → ischemia → mucosal slough → "currant jelly" stool.
- Lead points (12–15 % kids): Meckel diverticulum (MC), polyps, duplication cyst, H-S purpura hematoma, CF stool plug, lymphoma, jejunal tube.
- Adult lead points: tumors (adenocarcinoma, lymphoma, lipoma), AIDS lesions (Kaposi, lymphoid hyperplasia), strictures, diverticula.
Clinical Triad:
1. Intermittent severe colicky pain (draws knees)
2. Vomiting – non-bilious → bilious with obstruction
3. Bloody mucus stool (“currant jelly”).
- Exam: RUQ sausage mass + empty RLQ (Dance sign); distension/guarding if perforation.
Diagnostics
- Ultrasound – test of choice in children; target/bull’s-eye/“coiled-spring”; color Doppler ↓ flow if ischemic.
- AXR: obstruction pattern, target or crescent sign, exclude free air.
- Fluoroscopy contrast enema – diagnostic & therapeutic under air/barium.
- CT (adults) : target on axial, ‘sausage’ on coronal; identifies lead point.
Management
- Stabilize: NPO, IV fluids, NG tube.
- Children 5 mo–3 y, no peritonitis → pneumatic or hydrostatic enema under fluoro/US (success 70–85 % if <4 h). Contraindicated with perforation/peritonitis.
- Older children (>3 y) or adults, failed enema, peritonitis → operative exploration (lap or RLQ incision)
  • Attempt gentle manual reduction; recurrence <5 %.
  • If non-reducible or ischemic/perforated → segmental resection + primary anastomosis.

Stercoral Colitis & Fecal Impaction

Definition: Segmental colitis due to fecaloma pressure necrosis.
Mechanism: Hard stool → distension → luminal pressure ↑ → vascular compromise → focal ischemia/ulcer → possible perforation (MC at sigmoid & rectum).
At-risk Patients: Elderly dementia, bedridden, chronic opioid, psychiatric; chronic constipation affects ≈ $1/3$ of adults > $60$ .
Prognosis: Involvement > $40\,\text{cm}$ or perforation predicts high mortality (32–60 %).
Management (not fully detailed in transcript but infer): manual disimpaction, enemas, endoscopic removal; surgical resection for perforation.

Key Equations & Numeric Facts

Toxic megacolon diameter threshold: >6\,\text{cm}.
Systemic toxicity vitals: T>101.5^{\circ}\text{F},\ HR>120\,\text{bpm}.
Laplace law: $Tension\,(T)=Pressure\,(P)\times Radius\,(r)$ – explains cecal perforation risk.
Ischemic colitis poor-outcome if >3 risk markers (see list).
Endoscopic sigmoid detorsion success > $90\%$ but recurrence 40$–$50\%.
Sigmoid volvulus recurrence after detorsion alone up to $50\%$ .
Enema reduction successful in 70$–85\% pediatric ileocolic intussusception.

Ethical / Practical Considerations

Prompt recognition & intervention markedly reduce mortality in TM & volvulus—delay carries ethical weight in providing timely care.
Radiation minimization in children (US preferred over CT, avoid unnecessary fluoroscopy).
Surgical consent: discuss stoma creation (ileostomy/colostomy) and quality-of-life impact.
High recurrence of sigmoid volvulus after non-operative detorsion → inform patients of need for planned resection.

Clinical Linkages

Previous IBD lectures: flare recognition, steroid & biologic dosing tie directly into TM management.
Vascular surgery material: mesenteric ischemia vs ischemic colitis; CTA interpretation parallels.
Pharmacology: opioids & anticholinergics causing constipation, TM, ACPO.
Geriatrics & psychiatry: stool-retention syndromes in dementia & psychotropic medications.

Mnemonics / Memory Aids

"FAT SNAP" for TM systemic derangements: Fever, Anemia, Tachycardia; Sepsis (AMS), Na/K (electrolytes), Arterial hypotension, Pressure >6 cm.
"SAME" causes of LBO: Stricture, Adhesion/hernia (rare), Malignancy (MC), Entanglement (volvulus/intussusception).
"CURRANT" jelly for intussusception: Crampy pain, Upset stomach (vomit), RUQ mass, RLQ void (Dance), Air/contrast enema Rx, Non-bilious→bilious vomit, Target sign.