The Deadly Mesenteric Ischemia - TIME IS BOWEL !!

Mesenteric ischemia (MI) is a frightful pathology due to its variable presentations, time‐ sensitive nature, and high morbidity and mortality. It is quite a rare disease; and as Emergency Physicians we are likely to encounter only a few cases of it in our entire careers. As a consequence of that, it gives a hard time to even the most senior physicians to diagnose mesenteric ischemia. Ischemic bowel can progress to infarction within a matter of hours which gives us a very short window to make the diagnosis. Moreover, Emergency Physicians may be the only early healthcare providers who see these patients within such a narrow time‐frame, which makes it pivotal for us to know about this entity. 

Lets look at some key questions regarding Mesenteric Ischemia.

What is Mesenteric Ischemia?

Mesenteric ischemia not a single disease, it is actually group of related disorders, including Acute Occlusions of mesenteric vessels from embolus, thrombosis or dissection, and volvulus; Chronic schema arising from mesenteric atherosclerosis (like Coronary Artery Disease and Peripheral Vascular disease) ; Ischemic colitis from low‐flow hemodynamic states (hypotension due to sepsis, dialysis, aortic surgery, congestive heart failure); and Portal Vein thrombosis (pregnancy and other prothrombotic states).

Relevant Anatomy

The major mesenteric branches of the abdominal aorta are:

1. Celiac artery
2. Superior mesenteric artery (SMA)
3. Inferior mesenteric artery (IMA)

The main vessel draining the bowel is the portal vein (PV). When blood flow through these vessels is compromised, ischemic complications can occur. SMA is of particular concern because it supplies almost the complete small bowel and about two-thirds of large bowel. IMA occlusion can infarct the distal colon, leading to perforation/ sepsis. PV restricts venous drainage of the bowel, in extreme cases leading to ischemia by preventing arterial inflow.

What can cause Mesenteric Ischemia?

1.   External compression - Mass lesions

2.   From internal obstruction - Embolus, Thrombus, or Arterial dissection, PV thrombosis

3.   Volvulus of the mesentery and blood supply - Volvulus with occlusion blood vessels

4.   Compression of obstructed bowel segments by adhesions, and by global hypoperfusion states - Non-Occlusive Mesenteric Ischemia

           Consequences of a vascular occlusion also depend on the rate and the exact point of occlusion. 

• Acute Occlusions (like unstable cardiac angina) are more likely to result in end‐organ ischemia, due to lack of time for the development of collaterals. 
• Chronically Ischemia  (like stable cardiac angina, AKA intestinal angina) may develop collateral blood supplies that limit end‐organ schema. You may get a history of post-prandial pain and an aversion to eating leading to loss of weight.
• Distal Occlusions of smaller vessels injure shorter segments of bowel as compared with proximal occlusions, and collateral networks may be enough to prevent frank infarction. 

What is the “CLASSIC” presentation of Mesenteric Ischemia?

Acute Abdominal pain, Pain which out of proportion to examination in an elderly patient, H/O Atrial fibrillation ++ 

Diagnosis - Acute embolic occlusion of SMA. Labs show an elevated lactate and leukocytosis.

Classic presentations are not always seen: Patients may not always have Atrial Fibrillation (in situ thrombosis can occur) and may not have pain that is out of proportion to examination. 

Elevation of lactate is common and sensitive but nonspecific i.e. Lactate can be elevated in a number of other conditions as well. Additionally, a normal lactate may be encountered early in the course of ischemia before the beginning of infarction. The bottom-line is that an elevated lactate level should raise suspicion of mesenteric schema. High lactate suggests BOWEL NECROSIS. 

Leukocytosis often raises concerns about appendicitis, cholecystitis, or diverticulitis rather than mesenteric ischemia. A high WBC count is again nonspecific i.e. it can be elevated in a number of other conditions. But it is commonly seen with mesenteric 
ischemia and should not be attributed solely to "stress response". In contrast, a falling white 
blood cell count is a worrying prognostic sign. 


Utility of Vital Signs in Mesenteric Ischemia?

Many of these patients may have normal vital signs leading to lower acuity triage which may cause physicians to be falsely reassured about the patient’s stability. Like Acute Coronary Syndromes, Strokes and many other ischemic diseases, MI often presents with a normal set of vitals.

Age:  Does this only affect elderly?

No, MI may also be seen in young patients without known comorbidities, although this is rare but not impossible. Persistent Pain out of proportion to exam, leucocytosis, high lactate should make you think about MI. Once you suspect this diagnosis, chase it promptly because the dictum here is “TIME IS BOWEL”.

What imaging do we need to get for suspected Mesenteric Ischemia?

AXR – Abdominal films rarely show some key findings such as intramural pneumatosis intestinalis or portal venous gas, making x‐rays unhelpful in diagnosing MI. More often, the AXR gives a false sense of reassurance. So if you are suspecting MI, avoid AXR as it can introduce diagnostic delay and if you happen to do an AXR, consider MI a possible diagnosis regardless of x‐ray findings. 


          CT - Oral Contrast in not required. The use of oral contrast is associated with unnecessary delay. Tell the Radiologist what you want them to look for specifically.

      CT findings: Occlusion of mesenteric blood vessels, as well as for secondary findings of mesenteric ischemia including bowel wall thickening, pneumatosis, abdominal free fluid, mesenteric fat stranding, and pneumoperitoneum.

Pneumatosis intestinal i.e. refers to gas within the wall of the bowel.on

Acute SMA occlusion

                                              

The sensitivity of CT may also vary depending on the degree of ischemia and the time lapsed from symptom onset to performance of CT. In patients with significant concern for ischemia, a negative CT should be viewed suspiciously.

Non‐contrast CT cannot demonstrate vascular filling defects. However, it may show secondary CT findings such as bowel wall thickening, free fluid, free air, and fat stranding. Therefore,  a normal non‐contrast CT scan does not rule out mesenteric ischemia. 


      Bottom-line with CT: Oral contrast administration is unnecessary for the diagnosis of mesenteric schema, use CT with IV contrast. If IV contrast cannot be safely administered due to renal dysfunction, then request for a CT 
without oral or IV contrast which may reveal a range of important findings including pneumoperitoneum, small bowel obstruction, free fluid, fat stranding, other inflammatory processes (appendicitis, diverticulitis) or abdominal aortic aneurysm.

How do we treat mesenteric Ischemia?

•           Pain Relief
•           IV Fluids
•           NG Tube for gut decompression, Foleys Catheterisation  
•           Broad Spectrum Antibiotics
•           Correct Electrolyte Abnormalities
•           Vasopressors (Can exacerbate Ischemia)
•           Anticoagulants (inhibits further thrombogenesis)
•           Surgical embolectomy with resection of infarcted bowel OR Intra‐arterial thrombolytic therapy. 

Time until surgery is an important prognostic factor. Surgery permits visual inspection of bowel for ischemia or infarction, and may pick up findings which were missed by CT. 

Key Points:

• Whenever you suspect Mesenteric Ischemia, do not dilly-dally – Do a quick assessment and come up with a plan. Get senior help early enough. Involve your Surgical colleagues and Radiologists ASAP.
• Start suspecting MI despite normal vital signs and laboratory values. Do not overly on White cell count and lactate. Remember, Nothing is 100% in Medicine!
• X-rays and CT with oral contrast rarely provide any useful information. Use CT with IV contrast in those patients with normal renal function to pick vascular filling defects. 

References:

• Lange H, Jackel R. Usefulness of plasma lactate concentration in the diagnosis of acute abdominal disease. Eur J Surg 1994;160:381‐4.
• Smerud MJ, Johnson CD, Stephens DH. Diagnosis of bowel infarction: a comparison of plain films and CT scans in 23 cases. AJR Am J Roentgenol 1990;154:99‐103. 
• Kirkpatrick ID, Kroeker MA, Greenberg HM. Biphasic CT with mesenteric CT angiography in the evaluation of acute mesenteric ischemia: initial experience. Radiology 2003;229:91‐8.
• Zandrino F, Musante F, Gallesio I, Benzi L. Assessment of patients with acute mesenteric ischemia: multislice computed tomography signs and clinical performance in a group of patients with surgical correlation. Minerva Gastroenterol Dietol 2006;52:317‐25.
• Urban BA, Fishman EK. Tailored helical CT evaluation of acute abdomen. Radiographics 2000;20:725‐49.
• Balthazar EJ, Hulnick D, Megibow AJ, Opulencia JF. Computed tomography of intramural intestinal hemorrhage and bowel ischemia. J Comput Assist Tomogr 1987;11:67‐72. 
• De Filippo M, Sagone C, Zompatori M. Unenhanced MDCT findings of acute bowel ischemia. AJR Am J Roentgenol 2008;190:W271.
• De Filippo M, Sverzellati N, Zompatori M. Unenhanced CT in patients with chronic renal failure with clinical suspicion of small‐bowel infarct. AJR Am J Roentgenol 2009;192:W266.
• Kim AY. Reply to "Unenhanced MDCT findings of acute bowel ischemia". AJR Am J Roentgenol 2008;190:W383.
• Pear BL. Pneumatosis intestinalis: a review. Radiology 1998;207:13‐9. 

• Image1 - http://emedicine.medscape.com/article/1892253-overview
• Image2 - Case courtesy of Dr N Sravani, <a href="http://radiopaedia.org/">Radiopaedia.org</a>. From the case <a href="http://radiopaedia.org/cases/46946">rID: 46946</a>
• Image3 - Case courtesy of Dr Abdallah Khateeb , < a href="http://radiopaedia.org/">Radiopaedia.org</a>. From the case <a href="http://radiopaedia.org/cases/43593">rID: 43593</a>

Author:

              

     Lakshay Chanana
     
     Speciality Doctor
     Northwick Park Hospital
     Department of Emergency Medicine
     England

     @EMDidactic