Authors
Craig A. Goolsby, MD
Director, eMedicine Case of the Week
Staff Physician, Department of Emergency Medicine
Wilford Hall Medical Center, Lackland Air Force Base
San Antonio, Texas
Disclosure: Craig A. Goolsby, MD, has disclosed no relevant financial relationships.
Lars Grimm, MD, MHS
House Staff
Department of Internal Medicine
Duke University Medical Center
Durham, North Carolina
Disclosure: Lars Grimm, MD, MHS, has disclosed no relevant financial relationships.
Reviewer
Jose Varghese, MD
Associate Professor of Radiology
Boston University School of Medicine
Boston, Massachusetts
Disclosure: Jose Varghese, MD, has disclosed no relevant financial relationships.
A 76-year-old woman presents to the emergency department with acute intense abdominal pain described as a diffuse, severe, constant ache throughout her abdomen. She feels nauseous and has had 2 liquid bowel movements that were dark brown in color. She denies having any fever, trauma, urinary symptoms, vaginal discharge, or bleeding. Her past medical history is notable for atrial fibrillation, prior myocardial infarction, hypertension, and chronic obstructive pulmonary disease (COPD). She has a 75-pack/year smoking history and reports minimal alcohol use. Her medications include warfarin, atenolol, an ipratropium/salbutamol inhaler, lisinopril, and hydrochlorothiazide; she also takes a multivitamin. She admits to frequently missing doses of her medications. A recent chest x-ray on file reveals flattened diaphragms and hyperinflated lungs, findings consistent with COPD.
On physical examination, she appears to be in intense pain. Her initial vital signs reveal an irregularly irregular heart rate of 118 beats/min, a pulse oximetry reading of 93% on room air, and blood pressure of 101/68 mm Hg. A representative ECG taken in triage is shown. Her abdominal examination reveals diffuse tenderness to palpation, without peritoneal signs, palpable masses, or abnormal pulsations. A rectal examination is negative for occult blood. The rest of her physical examination is grossly unremarkable.
What is the next most important step in this patient's workup and management?
A. Fluid resuscitation
B. Pain control
C. Baseline labs, including international normalized ratio (INR)
D. Chest x-ray
Answer: A, fluid resuscitation. The patient is hypotensive, and although multiple tests may be ordered at once, this is the most critical next step.
Two large-bore peripheral IVs are placed and fluid resuscitation with normal saline is started. The patient is given two 8-mg doses of morphine and 4 mg of ondansetron which improves her symptoms. A stat upright chest x-ray is obtained and demonstrates hyperinflated lungs but no free air under the diaphragm. An ECG demonstrates rapid atrial fibrillation but no acute injury pattern.
An abdominal CT angiogram is ordered and a representative image is shown revealing what critical finding?
A. Aortic aneurysm
B. Free abdominal gas
C. Left lower lobe pneumonia
D. Portal venous air
Answer: D, portal venous air (red arrow).
Additional CT slices through the abdomen reveal thickened loops of bowel (yellow circle), pneumatosis intestinalis, and perienteric fat stranding. The patient's laboratory results return and are notable for a hemoglobin level of 12.1 g/dL and an INR of 1.4. The patient admits that she ran out of her warfarin a week ago.
What is the most likely diagnosis?
A. Budd-Chiari syndrome
B. Clostridium difficile colitis
C. Acute mesenteric ischemia
D. Crohn disease
Answer: C, acute mesenteric ischemia.
Acute mesenteric ischemia (AMI) is a relatively uncommon condition affecting an estimated 0.1% of all patients admitted to hospital. AMI comprises 4 clinical entities: mesenteric venous thrombosis, acute mesenteric arterial thrombosis, acute mesenteric arterial embolus, and nonocclusive mesenteric ischemia. The final common pathway of these entities is bowel ischemia eventually leading to bowel wall necrosis (black arrow), edema, and hemorrhage (red arrow). Because it can be a difficult disease to diagnose and treat, it has a poor prognosis, with mortality rates ranging from 60% to 100%.
What is the most common etiology of AMI?
A. Venous thrombosis
B. Arterial thrombosis
C. Arterial embolism
D. Nonocclusive ischemia
Answer: C, arterial embolism.
Arterial embolism is responsible for roughly half of all cases of AMI. Emboli can come from many different sources, including cardiac thrombi or atherosclerotic disease. The ECG shown demonstrates a large apical thrombus (arrow). Risk factors for arterial embolism include cardiac disease (eg, atrial fibrillation, congestive heart failure), hypercoagulable state, and hypovolemia.
The vascular anatomy of the abdomen is notable for extensive collaterals which helps protect the intestines from transient periods of inadequate perfusion. The celiac artery supplies the esophagus to the duodenum, the superior mesenteric artery (SMA) supplies the duodenum to the colonic splenic flexure, and the inferior mesenteric artery (IMA) supplies the colonic splenic flexure to the distal sigmoid colon. The primary collaterals are the pancreaticoduodenal arteries between the celiac artery and the SMA, as well as the marginal artery of Drummond between the SMA and IMA.
Which of the following is a clinical finding most worrisome for AMI?
A. Pain out of proportion to physical exam
B. Rapid onset of crampy abdominal pain, vomiting, and diarrhea in a patient with poorly controlled atrial fibrillation
C. Severe diffuse abdominal pain radiating to the back
D. Abdominal pain in conjunction with low-grade fevers and bloody stools
E. Nausea and vomiting without passage of stool or flatus
Answer: A, pain out of proportion on physical exam.
Patients with AMI often have a difficult clinical picture. However, the classic hallmark sign is poorly localized, intense abdominal pain that seems to be out of proportion with the physical exam. Diarrhea occurs in half of patients, often in conjunction with nausea and vomiting. Leukocytosis and elevated lactate levels are nonspecific but are more likely to develop late in the presentation. The patient in this case had many factors in her history and physical examination that raised concern for mesenteric ischemia. She had sudden, poorly localized abdominal pain that seemed subjectively much worse than her abdominal examination suggested. She also had atrial fibrillation, known vascular disease, and admitted poor treatment compliance.
Given the protean presentation of AMI, abdominal x-rays are frequently the first ordered imaging study. What finding is present on this x-ray that is concerning for AMI?
A. Bowel wall edema
B. Free air
C. Pneumatosis intestinalis
D. Obstruction
Answer: C, pneumatosis intestinalis.
Pneumatosis intestinalis (white arrows) is air within the intestinal wall from necrosis, a classic plain x-ray finding in mesenteric ischemia. Plain x-rays are typically normal in AMI but are useful to screen for bowel perforation or obstruction. Another classic finding is "thumb-printing" (red arrow), which is thickening of the bowel wall due to edema from necrosis. In rare cases, portal venous gas may be identifiable.
Traditionally, barium enema studies were performed to better delineate intraluminal pathology. An irregular bowel lumen or thumb-printing (arrowheads) is readily apparent on single-contrast barium studies. However, this modality has fallen out of favor due to the potential delay in diagnosis, patient discomfort, and high diagnostic accuracy of CT.
What is the preferred imaging modality for diagnosing mesenteric ischemia?
A. Ultrasonography
B. Magnetic resonance angiography
C. CT angiography
D. Traditional angiography
Answer: C, CT angiography.
Although multiple imaging modalities can lead to the diagnosis of AMI, CT angiography has the advantage of speed, minimal invasiveness, and high sensitivity and specificity that make it ideal for the emergency diagnosis of AMI. A sagittal reformat of the CT angiogram in our case confirmed the diagnosis of AMI by revealing thrombosis of the SMA (arrow).
CT has been proven to be highly accurate in the diagnosis of mesenteric ischemia. Typically, CT shows mesenteric edema with irregular thickening of the wall of the small or large bowel that is greater than 3 mm (arrows). In addition, CT can depict the underlying etiology, diagnose associated complications (such as perforation), and rule out other potential pathology. With respect to the extent of ischemia, large-vessel disease (either SMA, superior mesenteric vein [SMV], IMA, or inferior mesenteric vein [IMV]) is often diffuse, whereas small-vessel disease is more likely to be focal.
Portal-venous air in the left hepatic lobe (arrows) may be seen on CT in patients with mesenteric ischemia. The gas collects in the least dependent portion of the liver. Extension of the gas to the very periphery of the liver distinguishes portal venous gas from pneumobilia (gas in the biliary tree). Fat stranding and ascites is relatively rare compared with other causes of bowel wall thickening.
The sensitivity and specificity of CT in the detection of AMI are very good. Data from a recent study in the journal Radiology are presented. The authors performed a meta-analysis of the diagnostic accuracy of multidetector CT in diagnosing AMI and found a pooled sensitivity of 0.93 and specificity of 0.96. The author concluded that these high values confirm the utility of CT as the first-line imaging modality. (Menke J. Diagnostic accuracy of multidetector CT in acute mesenteric ischemia: systematic review and meta-analysis. Radiology. 2010;256:93-101.)
In our patient with the recently diagnosed AMI, what is the most appropriate immediate action?
A. Emergency vascular surgery consultation
B. Systemic thrombolysis with tissue-plasminogen activator
C. Initiate systemic beta-blockers to control vascular sheer stress
D. Immediately transfuse 2 units of packed red blood cells
Answer: A, emergency vascular surgery consultation.
Although multiple treatments may need to be initiated in concert, the high mortality rate of AMI mandates the need for early consultation with vascular surgery. It may be appropriate to consult vascular surgery before confirmation of AMI if the clinical suspicion is high. Even if the patient is not taken to the operating room for resection of necrotic bowel (shown), care should be managed by vascular surgery on an inpatient basis, possibly in the intensive care unit.
The goal of therapy in AMI is to restore blood flow to the affected tissue. Cardiac parameters should be optimized, early broad-spectrum antibiotics should be administered, and pain medications should be liberally administered. Multiple percutaneous and surgical options are available depending on the location of occlusion, extend of ischemia, and hemodynamic stability. Guidelines are available from multiple professional organizations, but in general, stable patients may benefit from nonsurgical interventions, whereas unstable patients or those with peritoneal signs should immediately proceed to the operating room.
Angiography provides the best radiographic means to identify intraluminal pathology, including thrombosis, stenosis, vasoconstriction, and spasm. The classic appearance of mesenteric ischemia is an abrupt cut-off of an attenuated vessel (arrow). The presence of collateral vessels can be used to help differentiate between acute and chronic processes. Angiography is minimally invasive and may provide definitive therapy. Even if it proves to be unsuccessful therapeutically, it still provides valuable information for subsequent surgery.
When surgical laparotomy is indicated, the goals are to restore perfusion and resect nonviable bowel. Patients with SMA occlusion may have the majority of their small bowel resected, making it important to retain every centimeter of viable bowel during the operation. The use of intraoperative Doppler ultrasonography or intravenous fluorescein followed by bowel examination under Wood lamp may help identify poorly perfused bowel. Frequently, a repeat operation 24-48 hours after initial surgery may be needed because it is difficult to differentiate at-risk bowel during the initial operation. An intraoperative image demonstrating bowel necrosis is shown.
There is a growing body of evidence regarding the utility of endovascular therapy over surgery for patients with AMI. Data from a recent study published in the Journal of Vascular Surgery demonstrate that when technically successful (87% of cases), endovascular repair improves patient mortality (P < .05) even if patients required subsequent laparotomy to remove necrotic bowel. This study represents the largest series of patients with AMI treated with endovascular therapy. (Arthurs ZM, Titus J, Bannazadeh M, et al. A comparison of endovascular revascularization with traditional therapy for the treatment of acute mesenteric ischemia. J Vasc Surg. 2011 Jan 12 [Epub ahead of print])
Authors
Craig A. Goolsby, MD
Director, eMedicine Case of the Week
Staff Physician, Department of Emergency Medicine
Wilford Hall Medical Center, Lackland Air Force Base
San Antonio, Texas
Disclosure: Craig A. Goolsby, MD, has disclosed no relevant financial relationships.
Lars Grimm, MD, MHS
House Staff
Department of Internal Medicine
Duke University Medical Center
Durham, North Carolina
Disclosure: Lars Grimm, MD, MHS, has disclosed no relevant financial relationships.
Reviewer
Jose Varghese, MD
Associate Professor of Radiology
Boston University School of Medicine
Boston, Massachusetts
Disclosure: Jose Varghese, MD, has disclosed no relevant financial relationships.
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