Colorectal Surgery – Toxic Megacolon, Ischemic Colitis, Large-Bowel Obstruction & Related Disorders

89 Q&A flashcards covering anatomy, pathophysiology, presentation, diagnostics, and management of toxic megacolon, ischemic colitis, large-bowel obstruction, volvulus, intussusception, and stercoral colitis, aligned with lecture content.

What is the radiologic criterion for colonic dilation in toxic megacolon?

6 cm diameter (classically in the transverse colon).

Which three vital-sign/lab findings count as systemic toxicity in toxic megacolon?

Fever > 101.5 °F, tachycardia > 120 bpm, neutrophilic leukocytosis > 10.5 K (or anemia).

Name four systemic derangements that help confirm toxic megacolon.

Dehydration, altered mental status, electrolyte abnormalities, hypotension.

List two imaging findings of toxic megacolon on abdominal x-ray.

Air-fluid levels with loss of haustral pattern; segmental parietal thinning (pathognomonic).

What CT sign describes alternating hyper/hypo-dense haustra in severe colitis?

Accordion sign.

First-line medical steps for toxic megacolon (5 items).

IV fluids, correct electrolytes, NPO & bowel rest (possible NG), broad-spectrum IV antibiotics, stop motility-reducing drugs.

Preferred surgery for IBD-related toxic megacolon refractory to medical therapy.

Subtotal colectomy with end ileostomy.

Medication pair for severe C. difficile colitis causing toxic megacolon.

Enteral vancomycin + IV metronidazole.

Define ischemic colitis.

Colonic inflammation caused by hypoperfusion leading to ischemia, often transient.

Which two ‘watershed’ areas are most vulnerable to ischemic colitis?

Splenic flexure and rectosigmoid junction.

Give three non-occlusive risk factors for ischemic colitis.

MI, hemodialysis, drugs causing constipation or vasoconstriction (e.g., digitalis, cocaine).

Classic initial symptom pair of ischemic colitis.

Rapid onset Left-sided abdominal pain, desire to defecate, followed by rectal bleeding/bloody diarrhea within 24 h.

Describe the ‘single-stripe sign.’

Longitudinal ulceration seen on colonoscopy in severe ischemic colitis.

What CT finding is termed ‘thumbprinting’?

Segmental bowel-wall thickening from submucosal edema/hemorrhage in ischemic colitis.

Supportive care elements for mild-moderate ischemic colitis (4).

Bowel rest, IV fluids, broad-spectrum antibiotics, treat precipitating cause.

How many poor-outcome risk factors define severe ischemic colitis needing exploration?

3 risk factors OR peritoneal signs/imaging of gangrene.

Operation of choice for right-sided gangrenous ischemic colitis.

Right hemicolectomy (± ileostomy/mucous fistula or primary anastomosis).

Operation of choice for left-sided gangrenous ischemic colitis.

Sigmoidectomy or left hemicolectomy

Two most common mechanical causes of large-bowel obstruction (with %).

Colonic neoplasm (~60 %), diverticular disease (~20 %).

Explain Laplace’s law relevance to LBO perforation.

The cecum (largest diameter) perforates first when ileocecal valve is competent because less pressure is needed to distend it.

Preferred imaging modality for suspected large-bowel obstruction.

CT abdomen/pelvis with PO & IV contrast (Gastrografin if perforation suspected).

Management triad for initial LBO care.

NPO/bowel rest, IV fluid resuscitation, NG decompression if vomiting or severe distension.

Define Ogilvie syndrome.

Acute colonic pseudo-obstruction—massive dilation without mechanical lesion, usually in hospitalized debilitated patients.

Name the drug used when conservative treatment of ACPO fails.

IV neostigmine (cholinergic agent).

Three absolute surgical indications in LBO.

Closed-loop obstruction, perforation or ischemia, volvulus not reducible endoscopically.

Most common anatomic site of colonic volvulus.

Sigmoid colon (≈80 %).

Explain why chronic high-fiber diet predisposes to sigmoid volvulus.

Overloaded/heavy sigmoid colon stretches mesentery → axial torsion risk.

Radiographic ‘coffee/kidney bean sign’ indicates what?

Massively dilated loop of sigmoid colon pointing from pelvis to RUQ—sigmoid volvulus.

Describe ‘bird’s beak’ on contrast enema.

Tapered cut-off at site of twist in volvulus (sigmoid or cecal).

First-line treatment for sigmoid volvulus without peritonitis.

Endoscopic detorsion + rectal tube placement.

Definitive surgery after successful sigmoid detorsion.

Sigmoid colectomy with primary anastomosis (after bowel prep).

Emergency surgical procedure for sigmoid volvulus with perforation.

Hartmann’s procedure (resection + end colostomy).

Why is colonoscopic reduction unreliable for cecal volvulus?

Success rate only 15–20 %; anatomy less amenable than sigmoid.

Standard operation for cecal volvulus.

Right hemicolectomy with primary anastomosis (± ileostomy).

Name two reasons cecopexy is discouraged.

High recurrence (20–30 %) and does not address underlying mobility.

Define intussusception.

Telescoping of one bowel segment into an adjacent distal segment (intussuscipiens).

Age group in which intussusception is most common.

Children <2 years old.

Classic triad of pediatric intussusception.

Intermittent colicky abdominal pain, vomiting, currant-jelly stool.

What is ‘Dance sign’?

Empty RLQ due to mobile cecum from ileocolic intussusception; palpable RUQ mass.

Diagnostic modality of choice for pediatric intussusception.

Ultrasound showing ‘target’ or ‘bull’s-eye’ sign.

Therapeutic enema success rate in ileocolic intussusception.

Approximately 70–85 % when performed early.

Most common lead point of pediatric intussusception.

Meckel’s diverticulum.

In adults, what proportion of intussusception lead points are malignant?

≈77 %.

Contraindications to enema reduction of intussusception (2).

Peritonitis or suspected perforation/gangrene.

Preferred surgical approach when non-operative reduction of intussusception fails.

Manual reduction via RLQ incision or laparoscopy; segmental resection if non-reducible or perforated.

Define stercoral colitis.

Colonic inflammation & ischemia secondary to fecal impaction and fecaloma pressure.

Two populations at high risk for stercoral colitis.

Elderly demented/nursing-home patients; chronic opioid users or bedridden psychiatric patients.

Which colonic segments most often ulcerate in stercoral colitis?

Sigmoid colon and rectum.

Mortality range for perforated stercoral colitis.

Approximately 32–60 %.

What artery forms an arcade along the inner colon and provides collateral flow?

Marginal artery of Drummond.

Why is the splenic flexure a watershed area?

Weak or absent anastomosis between SMA and IMA branches makes it vulnerable to hypoperfusion.

Name two drugs implicated in precipitating toxic megacolon by slowing gut motility.

Loperamide and opioids (also anticholinergics/atropine).

What microscopic layer involvement characterizes toxic megacolon?

Inflammatory extension into the muscularis propria causing paralysis.

Historic (pre-1976) mortality of medically managed toxic megacolon.

≈27 %.

Systemic signs that steroids may mask in IBD patients developing toxic megacolon.

Abdominal tenderness and rigidity despite severe disease.

What ultrasound features suggest toxic megacolon? (Give two)

Loss of haustra; dilated transverse colon >6 cm with thin hypoechoic walls.

Two organisms besides C. difficile commonly causing infectious toxic megacolon.

Salmonella and Shigella (also Campylobacter, Yersinia, CMV).

In ischemic colitis, what imaging is NOT necessary for non-occlusive cases?

CT angiography (reserved for suspected major vascular occlusion).

List four laboratory risk factors predicting poor outcome in ischemic colitis.

BUN > 20, Hgb < 12, LDH > 350, WBC > 15 (also hyponatremia).

Treatment algorithm step for mild-moderate ischemic colitis regarding antibiotics.

Empiric broad-spectrum IV antibiotics to reduce bacterial translocation.

Define closed-loop obstruction in context of LBO.

Obstruction at two points (e.g., competent ileocecal valve) leading to isolated segment at risk for ischemia/perforation.

Name two conditions where LBO imaging may show a ‘kidney bean’ sign.

Sigmoid volvulus (most classic) and sometimes cecal volvulus.

Pharmacologic agent used to treat refractory ACPO before colonoscopic decompression.

Neostigmine (acetylcholinesterase inhibitor).

After successful colonoscopic decompression of ACPO, what is next if recurrence?

Repeat decompression or consider surgery; address underlying illness.

Describe Type 1 vs Type 2 cecal volvulus.

Type 1: clockwise axial twist in RLQ; Type 2: counter-clockwise axial twist, cecum displaced to LUQ.

What imaging finding distinguishes cecal volvulus from sigmoid on AXR?

Distended loop from RLQ to LUQ; small bowel dilated, distal colon decompressed.

Why is percutaneous cecostomy rarely favored for cecal volvulus?

High wound infection (40–50 %) and recurrence (2–5 %) rates.

Common presenting symptom difference between colonic neoplasm vs volvulus LBO.

Neoplasm: insidious, weight loss, pencil stools; volvulus: acute severe distension/pain.

Define the 'accordion sign' in severe colitis.

CT appearance of thickened haustra alternating with trapped contrast—resembles accordion folds.

What is the role of sigmoidoscopy in suspected toxic megacolon?

May be performed with minimal insufflation, kept proximal to sigmoid to evaluate etiology while minimizing perforation risk.

Give two indications for emergent colectomy in severe C. difficile colitis.

Peritonitis or end-organ failure (also perforation, full-thickness ischemia, compartment syndrome).

Explain why elderly bedridden patients develop stercoral colitis.

Prolonged constipation causes fecaloma pressure necrosis leading to ischemic ulceration of sigmoid/rectum.

Initial radiologic test for suspected sigmoid volvulus.

Supine abdominal x-ray (AXR); often diagnostic.

Most reliable non-operative reduction technique for pediatric intussusception.

Pneumatic (air) enema under fluoroscopic or ultrasound guidance.

Why are enemas less effective >3 yrs old in intussusception?

Higher likelihood of a pathological lead point—often requires surgery.

Which parasite is associated with toxic megacolon risk when using loperamide?

Entamoeba histolytica.

What is the typical mortality of cecal volvulus even after treatment?

Approximately 12–15 %.

Give two infectious agents besides bacteria that can lead to toxic megacolon.

Cytomegalovirus (CMV) and invasive aspergillosis; also rotavirus, Cryptosporidium.

In LBO, what finding on physical exam suggests peritonitis?

Rebound tenderness or abdominal rigidity with fever.

List two endoscopic complications prompting immediate surgical intervention in volvulus.

Unsuccessful detorsion or evidence of mucosal ischemia during scope.

Why is the marginal artery clinically important in colectomy planning?

Provides collateral perfusion; its absence at splenic flexure demands vigilance for ischemia during ligation.

What physiologic mechanism causes Ogilvie syndrome?

Autonomic imbalance leading to colonic motor dysfunction without mechanical block.

Which diagnostic sign on CT indicates pneumatosis coli?

Air within the colonic wall, suggestive of advanced ischemia/perforation.

Define ‘paralytic phase’ in ischemic colitis progression.

Pain becomes constant; bowel sounds cease; distension increases—precedes shock phase.

Name the anti-TNF drug considered when IV steroids fail in UC-associated toxic megacolon.

Infliximab (alternatively cyclosporine).

What is the target colonic diameter threshold prompting concern in ACPO?

10–12 cm cecal diameter (risk of perforation).

Most common anatomical lead point of adult intussusception.

Malignant tumor (adenocarcinoma, lymphoma, metastasis).

Which laboratory test helps identify mesenteric occlusion in ischemic colitis?

CT angiography, not routine labs; consider lactate for ischemia severity.

Treatment sequence for sigmoid volvulus WITHOUT ischemia in a debilitated patient unable to tolerate surgery.

Endoscopic decompression; if recurrence or high risk, consider percutaneous endoscopic sigmoidopexy or palliative rectal tube.

Describe ‘meniscus sign’ on abdominal radiograph.

Crescent-shaped soft tissue mass protruding into gas column indicative of intussusception.

What is the recommended timing of colostomy reversal after Hartmann’s for volvulus?

Typically 3–6 months, once patient optimized.

Explain why neostigmine is effective in ACPO.

It increases colonic motility via acetylcholinesterase inhibition restoring parasympathetic tone.

Which imaging sign on ultrasound indicates loss of haustra in toxic megacolon?

Featureless, thin hypoechoic colonic wall >6 cm in diameter lacking haustral markings.