Ischemic Colitis

A common disorder arising when arterial blood supply to the colon is insufficient to meet cellular metabolic demand — the most common form of GI ischemia. Reported rates 7.1–22.9/100,000 person-years; true incidence is likely higher given how often it presents with mild, nonspecific symptoms. Content below is from a textbook reference chapter (Sabiston Ch52 - Infectious & Ischemic Colitis), not primary literature.

Distinguishing from acute mesenteric ischemia

Important differential to keep separate: acute mesenteric ischemia involves obstruction of a major bowel vessel, presents with severe pain out of proportion to physical findings, and requires immediate vascular intervention. Ischemic colitis, by contrast, is a disease of the small vessels, typically presents less dramatically, and seldom requires vascular intervention — most cases, recognized and managed promptly, do not need surgery at all. For isolated right-sided ischemic colitis, or when pain is out of proportion to exam/labs, multiphasic CT angiography should still be used to exclude a concurrent acute proximal mesenteric ischemia.

Watershed anatomy

Two well-described watershed areas are especially vulnerable to ischemia because of inconsistent, collateral-dependent blood supply:

• Splenic flexure (Griffiths point) — where the SMA and IMA territories meet; up to 50% of specimens in some studies lack a marginal artery in this region. Surgeons generally avoid siting anastomoses here for fear of insufficient blood supply.
• Rectosigmoid junction (Sudeck’s point) — supplied by the superior hemorrhoidal artery and distal sigmoid branches, both terminal branches of the IMA; prone to atherosclerotic changes.

The right colon, although not classically considered a watershed area, is vulnerable to ischemia from embolic occlusion via the ileocolic artery (a terminal branch of the SMA), and is particularly prone to low-flow states such as heart failure, hemorrhage, and sepsis. The rectum is rarely a victim of ischemic injury given its dual blood supply (IMA and iliac circulation) and strong collateral network.

Risk factors

Category	Examples
Low-flow state	Septic shock, CHF, hemorrhagic shock, hypotension
Atherosclerosis	Ischemic heart disease, cerebrovascular disease, peripheral vascular disease
GI	Constipation, diarrhea, IBS
Surgery/invasive interventions	Abdominal surgery, aortic surgery (esp. AAA repair), cardiovascular surgery, endovascular abdominal manipulation (e.g. chemoembolization), post-colonoscopy
Cardiovascular/pulmonary	COPD, atrial fibrillation, hypertension
Metabolic/rheumatoid	Diabetes, dyslipidemia, SLE, rheumatoid arthritis
Miscellaneous	Hypercoagulable states, sickle cell disease, long-distance running
Drugs	Constipation-inducing drugs (opioid and non-opioid), cocaine/methamphetamines, immunomodulatory drugs (anti-TNF-α, interferons), chemotherapy (taxanes), female hormones/oral contraceptives, decongestants (pseudoephedrine), serotonergic drugs (alosetron, sumatriptan)

Presentation and diagnosis

Most patients present with partial-thickness ischemia of a localized colonic segment and relatively nonspecific signs — a high index of suspicion is needed for early diagnosis. Typical symptoms: sudden abdominal pain/cramping, tenesmus, bloody diarrhea/hematochezia (this combination present in close to 50% of patients, with pain usually preceding bleeding). Bleeding is usually minor and seldom requires transfusion. May have nausea, vomiting, low-grade fever; exam may show distension and tenderness over the involved region.

The left colon (including the splenic flexure) is the most commonly affected region, followed by the sigmoid colon — consistent with the watershed anatomy above. Pancolitis carries a worse prognosis. About a quarter of patients present with isolated right-sided ischemic colitis — these patients are more likely to have atrial fibrillation, coronary artery disease, and/or chronic renal disease, and have a higher chance of requiring surgery with a worse prognosis. A minority present with full-thickness ischemia and are sicker at presentation — high fever, leukocytosis, acidosis, peritonitis.

Labs are nonspecific but assist in predicting severity: increased WBC, BUN, and LDH, and decreased hemoglobin/albumin are associated with more severe disease; acidosis, decreased bicarbonate, and increased lactate are associated with severe ischemic colitis. Stool should also be tested for C. difficile toxin, ova/parasites, and culture/sensitivity to exclude an infectious cause (see Infectious Colitis).

Imaging: plain films may show bowel distension or “thumbprinting” (rounded densities along the colon from submucosal edema) — nonspecific, seen in other inflammatory conditions too. Free intraperitoneal air suggests perforation and should prompt immediate operative management. Water-soluble contrast enemas are largely obsolete for acute diagnosis but may still be used to evaluate chronic ischemic strictures. CT of the abdomen (IV and oral contrast) is now the primary noninvasive diagnostic modality — determines location/severity, identifies complications, and excludes other diagnoses. Suggestive findings: segmental bowel wall thickening, pericolonic fat stranding, thumbprinting. Pneumatosis intestinalis, portal venous gas, and absence of large-bowel enhancement on contrast CT usually indicate severe transmural disease favoring immediate surgical intervention. Vascular imaging is not usually indicated (ischemic colitis is a small-vessel disease), except for sudden-onset pain out of proportion to findings or isolated right-sided disease, where multiphasic CT angiography should be used to exclude acute proximal mesenteric ischemia.

Flexible endoscopy is the gold standard for diagnosis. Early colonoscopy (within 48 hours) is recommended, except in acute peritonitis or suspected severe transmural ischemia. Despite a theoretical concern about increased perforation risk with endoscopy in this setting, published literature has not shown a higher perforation rate compared with other patients — but overinsufflation should still be avoided, and the scope should not be advanced beyond the distal extent of disease. Characteristic endoscopic findings: edematous/friable mucosa, erythema, petechial hemorrhage, mucosal ulceration. The “single-stripe sign” — a single linear ulcer along the longitudinal axis of the colon — is rare but considered specific for ischemic colitis. Segmental distribution with an abrupt transition between injured and noninjured mucosa, and rectal sparing, support ischemia over IBD as the diagnosis. Endoscopy usually cannot distinguish partial-thickness from full-thickness ischemia.

Treatment

The majority of patients (~80%) respond to conservative, nonoperative treatment, with significant improvement within a few days. Mainstay: bowel rest, IV fluids, broad-spectrum antibiotics; NG tube if ileus is present. Efforts should also correct low-flow states/hypotension with aggressive fluid resuscitation and optimal treatment of associated conditions (heart failure, sepsis). Colonic ischemia can cause failure of the intestinal epithelial barrier with bacterial translocation leading to overt sepsis — for this reason, empiric broad-spectrum antibiotics covering both anaerobic and aerobic coliform bacteria (the normal colonic flora) are prescribed. Cathartics are not recommended (perforation risk); glucocorticoids should be avoided unless treating a preexisting disorder (e.g. lupus, RA).

Most episodes are mild and self-limiting. Failure to improve, or worsening symptoms within a few days, should raise concern for progression to full-thickness ischemia and prompt repeat imaging or endoscopy to guide further treatment. A small proportion of patients with mild-to-moderate symptoms go on to develop chronic colitis with ongoing/recurrent bouts of abdominal pain, bloody diarrhea, and sepsis — these patients have a higher complication rate and commonly require surgical resection of the involved segment. Some patients who initially recover from partial-thickness ischemic colitis eventually develop a chronic stricture at the involved segment (constipation, narrowed stools, abdominal pain); diagnosis can be confirmed with contrast enema, CT, or endoscopy. Symptomatic patients, or those in whom malignancy cannot be excluded, should undergo elective resection.

Emergent surgery is required for patients with signs of transmural ischemia and perforation — peritonitis, hemodynamic instability, free peritoneal air, portal venous gas, or other ominous CT signs. Surgery for ischemic colitis carries substantial mortality: one large database study found a 25% 30-day postoperative mortality rate, with other studies reporting up to 47% following acute surgical intervention. Risk factors independently associated with perioperative mortality after colectomy for ischemic colitis: elderly age, poor functional status, multiple comorbidities, preoperative septic shock, preoperative acute renal failure, and delay from hospital admission to surgery.

Surgical technique

Visualize and assess the entire small and large intestine for ischemia/gangrene — ischemia commonly affects a recognizable segment, frequently in a watershed area. An anatomic resection should be performed to ensure sufficient blood supply to the remaining colon, with minimal reliance on stressed collateral vessels. Deciding how much to resect, or whether a specific segment will survive, can be difficult — visual examination alone tends to be inaccurate, especially for bowel that is ischemic but still viable. Intraoperative infrared angiography (indocyanine green) is a relatively new, increasingly popular adjunct for assessing bowel viability and anastomotic integrity: ICG is injected IV, distributes through the circulation, and laser excitation of the dye demonstrates real-time tissue perfusion.

Creating an anastomosis is usually not recommended in the acute setting, given the risk of evolving ischemia plus the hemodynamic instability/sepsis commonly present. A temporary abdominal closure with a planned second-look at 24 hours may be prudent to determine the need for further resection; stapling the bowel ends and leaving them in the abdomen avoids the complications of a stoma, which is particularly relevant in very obese patients. Pancolic ischemia is rare but requires total colectomy with ileostomy when it occurs.

In contrast to mesenteric ischemia of the small intestine, there is usually no indication for revascularizing the large bowel in primary colonic ischemia — colonic ischemia is not generally related to large-artery disease the way small-bowel mesenteric ischemia is.

Open items / gaps

• No primary trial data yet on ICG angiography’s impact on anastomotic leak rates or resection margin accuracy — described here as a promising adjunct, not a validated standard.
• No detail yet on how chronic ischemic strictures are definitively distinguished from malignancy preoperatively beyond “contrast enema, CT, or endoscopy” — worth a dedicated source if this comes up clinically.