Aorto-Iliac Catheterization/Instrumentation/Surgery (see Peripheral Vascular Disease, [[Peripheral Vascular Disease]])
Open Surgical Cases: almost always affects the distal left colon (occurs due to loss of collateral flow associated with ligation of the inferior mesenteric artery, ligation of the iliac artery, emboli, vascular compression with surgical instruments, or hypotension)
Cardiopulmonary Bypass (see Cardiopulmonary Bypass, [[Cardiopulmonary Bypass]]): likely related to low-flow state during bypass and exposure of patient’s blood to foreign surfaces (resulting in complement activation, microemboli, hypercoagulability, and release of vasoactive mediators)
Epidemiology: occurs in <0.2% of cases, but has an 85% mortality rate
Risk Factors
Emergent Coronary Bypass Surgery
End-Stage Renal Disease
Older Age
Severely Low Post-Operative Cardiac Output
Valve Surgery
Predictors of Increased Severeity of Cardiopulmonary Bypass-Associated Colonic Ischemia
Myocardial Infarction (MI) (see Coronary Artery Disease, [[Coronary Artery Disease]]): may occur with 2 weeks after MI
Ischemic colitis occurring after MI is associated with more complications and a worse in-hospital survival, as compared to other causes of ischemic colitis
Pseudoephedrine (Sudafed) (see Pseudoephedrine, [[Pseudoephedrine]])
Sumatriptan (Imitrex) (see Sumatriptan, [[Sumatriptan]])
Other
Airplane Flight
Extreme Exercise: likely due to shunting of blood flow away from splanchnic circulation with associated dehydration, hyperthermia, and electrolyte abnormalities (hyponatremia, hypokalemia)
Long-Distance Running
Triathlon Competition
Hemodialysis (see Hemodialysis, [[Hemodialysis]]): due to underlying atherosclerosis, diabetes, and hemodialysis-induced hypotension
Usually non-occlusive
Physiology
Normal Colonic and Rectal Blood Supply
Arterial Blood Supply: anatomic variation is rare
Superior Mesenteric Artery (SMA)
Inferior Mesenteric Artery (IMA)
Internal Iliac Arteries
Collateral Arterial Circulation: usually protects the colon from ischemia
Watershed Areas: areas with limited collateral blood supply that may be at risk for hypoperfusion
Splenic Flexure
Rectosigmoid Junction
Venous Drainage of Colon: mesenteric veins parallel the arterial supply and empty into the portal veins
Decreased Colonic Blood Flow Results in Colonic Ischemia
Colon is Vulnerable to Hypoperfusion
Colon receives less blood supply, as compared to the rest of the GI tract
Colonic microvasculature plexus is less developed and is embedded in a relatively thick wall, as compared to the small intestine
Time Course of Colonic Ischemia: colonic ischemic is usually abrupt and transient
However, prolonged severe colonic ischemia can result in transmural infarction within 8-16 hrs
Mechanism of Colonic Injury with Hypoperfusion
Initial Hypoxia: results in superficial mucosal injury within 1 hr
Reperfusion Injury: results in generation of oxygen free radicals, toxic byproducts of ischemic injury, and neutrophil activation
Mechanisms of Colonic Ischemia
Non-Occlusive Hypoperfusion of Mesenteric Vasculature: most common mechanism (accounts for 95% of cases)
Usually affects the watershed areas of colon: splenic flexure and rectosigmoid junction
Left colon is involved in 75% of cases (with splenic flexure being involved in 25% of cases)
May also affect areas that are farther from aorta: distal ileum and right colon
Rectum is involved in only 5% of cases (due to its collateral blood flow from inferior mesenteric artery and systemic circulation through the hemorrhoidal vessels)
Acute Arterial Occlusion
Embolic Arterial Occlusion: from proximal source (heart, etc)
Thrombotic Arterial Occlusion
Inferior Mesenteric Artery Ligation: may occur during aortic repair (in these cases, colonic ischemia is more common in patients with prior colon surgery and altered normal arterial anatomy)
Mesenteric Venous Thrombosis: rarely involves the colon (when present, it almost always involves the distal small intestine/proximal colon)
Phlebosclerotic Colitis: rare form of ischemic colitis that results from venous obstruction caused by fibrotic sclerosis and calcification of the walls of the mesenteric veins
Usually involves the right colon
Linear calcifications in the region of the right colon can be seen on plain abdominal films, while CT scan may reveal colonic wall thickening associated with mesenteric venous calcifications
“Thumbprinting”: may be seen in some cases, due to the presence of submucosal edema
Abdominal/Pelvic CT
General Comments
Preferred First Diagnostic Test
Scan may initially be normal
Thickening of Colonic Wall in Segmental Pattern: non-specific (also may be seen in infectious colitisor Crohn’s disease)
“Target” Sign: due to hyperdensity of the mucosa and muscularis with submucosal edema
“Double-Halo” Sign: due to hyperdensity of the mucosa and muscularis with submucosal edema
Irregular Bowel Contours
Mesenteric inflammation with stranding of the fat
Free Peritoneal Fluid
Pneumatosis Coli
Gas in Mesenteric/Portal Vein (see Portal Vein Gas, [[Portal Vein Gas]]): presence of hepatic portal veins gas predicts a >50% mortality
Pneumoperitoneum: in cases with perforation
Colonoscopy
Sensitive for detecting mucosal abnormalities, allows biopsy of suspicious areas, and does not interfere with subsequent angiogram
Note: sigmoidoscopy is limited in its ability to diagnose ischemic colitis
Pale mucosa with petechial bleeding: early changes
Bluish hemorrhagic nodules: due to submucosal bleeding (equivalent to thumbprints seen on KUB)
Cyanotic mucosa: seen later in course
Hemorrhagic ulcerations: seen later in course
Pseudomembranous colitis with yellowish round plaques or confluent membranes: seen in some cases
Findings of colonic ischemia may be misdiagnosed as inflammatory bowel disease or infectious colitis
The diagnosis of ischemic colitis is suggested by segmental distribution, abrupt transition between injured and noninjured mucosa, rectal sparing, and rapid resolution on serial endoscopy or CT scan
A single linear ulcer running along the longitudinal axis of the colon (the “single-stripe sign”) favors the diagnosis of ischemic colitis
Colonoscopic Biopsy: nonspecific changes (hemorrhage, crypt destruction, capillary thrombosis, granulation tissue with crypt abscesses, and pseudopolyps) -> these may mimic those seen in Crohn’s disease
Chronic Ischemic Colitis: mucosal atrophy and areas of granulation tissue may be found
Post-Ischemic Stricture: extensive transmural fibrosis and mucosal atrophy
Mesenteric Angiogram
Utility: rarely useful in the diagnosis of colonic ischemia
Resucitation usually needs to be performed prior to angiography (to treat dehydration, acidosis) -> angiogram is likely to be negative by the time it is obtained
In the absence of instrumentation/aortoiliac surgery, the major mesenteric arteries are usually patent: the ischemic changes are usually limited to the arterioles (and changes here are rarely detected)
Angiogram may be required is the clinical examination cannot exclude small bowel ischemia, and colonoscopy is negative
Risks: patients with non-occlusive colonic ischemia are often dehydrated, acidotic, and have cardiac/kidney disease -> increases the risks of contrast administration
Exploratory Laparotomy/Laparoscopy
May be required to confirm the diagnosis
Clinical Manifestations
General Comments
Degree and Nature of Symptoms: depend on the onset of colonic ishemia, duration of colonic ishemia, extent of colonic ischemia, and clinical setting
Patients usually do not appear severly ill (in contrast to small intestinal ischemia, where patients appear severely ill)
Acute Colonic Ischemia
Clinical Stages
Hyperactive Phase: soon after the onset of hyperperfusion, severe abdominal pain and frequent passage of bloody diarrhea develop
GI bleeding is usually mild without the need for packed red blood cell transfusion
Paralytic Phase: abdominal pain usually diminishes, becomes more continuous, and diffuses
Abdomen becomes more tender and distended with absent bowel sounds
Shock Phase (affects only 10-20% of patients): massive fluid, protein, and electrolytes leak through the damaged, gangrenous mucosa
Severity: generally mild (in contrast to pain that is more severe in small intestinal ischemia)
Location: usually left-sided (in contrast to peri-umblical pain that is more characteristic of small intestinal ischemia)
Abdominal Tenderness: present
Association of Abdominal Pain with Gastrointestinal Hemorrhage: 15% of cases have abdominal pain without gastrointestinal hemorrhage
Lower Gastrointestinal Hemorrhage (see Gastrointestinal Hemorrhage, [[Gastrointestinal Hemorrhage]]): hematochezia/bloody diarrhea
Severity: usually mild-moderate
Association of Gastrointestinal Hemorrhage with Abdominal Pain: hemorrhage usually occurs within 24 hrs of abdominal pain (but may occur without abdominal pain)
Location: gastrointestinal hemorrhage is more common with left colonic ischemia than right colonic ischemia
Colonic Infarction: occurs in 15% of cases
Colonic Perforation/Pneumoperitoneum (see Pneumoperitoneum, [[Pneumoperitoneum]]): may occur
Peritonitis (see Peritonitis, [[Peritonitis]]): peritoneal signs are present in only 7.4% of cases
Frequency of Exploratory Laparotomy/Laparoscopy: exploratory laparotomy is required in about 20% of cases
Bowel Preparation: bowel preparation should not be used prior to surgery, as it can precipitate perforation or toxic dilatation of the colon
Indications: may be life-saving in these settings
Clinical deterioration (suggesting colonic infarction/necrosis) despite aggressive medical management
Clinical suspicion of ischemia with ongoing abdominal pain that is out of proportion to the clinical examination
Colonoscopic evidence of full-thickness irreversible necrosis of the colonic muscularis
Laparoscopy : there is theoretical concern about laparoscopy related to the effect of pneumoperitoneum on mesenteric blood flow
The intraperitoneal pressure should be lowered (about 10 mmHg) in those suspected with suspected mesenteric ischemia
Procedure
Right-Sided Colonic Ischemia/Necrosis: requires right hemicolectomy and primary anastomosis
Right colectomy with end-ileostomy and distal mucocutaneous fistula may be needed if perforation is associated with gross spillage
Left-Sided Colonic Ischemia/Necrosis: requires sigmoid resection or left hemicolectomy with either proximal stoma and distal mucous fistula, or Hartmann’s procedure depending upon the extent of ischemia
Colonic Ischemia Involving Most of the Colon and Rectum: may require subtotal colectomy with terminal ileostomy
Patients with Aortic or Iliac Vascular Graft: primary colonic anastomosis is also contraindicated in those who require bowel resection, as any subsequent anastomotic leak could contaminate the graft
Second-Look: in most cases following exploration or colonic resection, repeat exploration, should be considered within 12-24 hrs to assess the viability of the remaining bowel and integrity of anastomoses
Vascular Interventions
Local Vasodilator Infusion (Papaverine): can attenuate vasospasm, but systemic side effects often limit its use in patients with nonocclusive colonic ischemia
Embolectomy/Bypas Grafting/Endarterectomy: not indicated in most cases of primary colonic ischemia, which are not related to large artery obstruction
However, in selected patients with early post-operative colonic ischemia after aortic surgery, delayed reimplantation of the inferior mesenteric artery or revascularization of the hypogastric artery may be an option
Chronic Ischemic Colitis
Chronic Ischemic Colitis in Long-Distance Runners
Rehydration
Correction of Electrolyte Abnormalities
Prognosis
Expected Course in Non-Occlusive Colonic Ischemia
Most patients with non-occlusive colonic ischemia will improve within 1-2 days
Most patients with non-occlusive colonic ischemia will have complete clinical and radiological resolution within 1-2 wks
Non-Gangrenous Colonic Ischemia: usually has a low mortality rate
Recurrence: recurrence of colonic ischemia is uncommon
References
Systematic review of the management of ischaemic colitis. Colorectal Dis. 2012 Nov;14(11):e751-63. doi: 10.1111/j.1463-1318.2012.03171.x [MEDLINE]
