PICTORIAL IMAGING SPECTRUM OF ACUTE INTESTINAL ISCHEMIA

B Toosi, BSc; D Tso, BSc; K Lee, MD; C Davison, MBChB; A Reimann, MD; F Berger, MD; J Inacio, MD; A Albuali, MD; Amit Ahuja, MD; S Nicolaou, MD

PURPOSE/AIM

Review imaging modalities to investigate acute intestinal ischemia

Review role of MDCT in diagnosing acute intestinal ischemia & introduce an ultra high pitch low dose protocol

Differentiate between mesenteric arterial vs. venous ischemia on imaging

Discuss an imaging algorithm for the evaluation of acute intestinal ischemia

Acute Mesenteric Ischemia

• Responsible for:

1 in 100 of patients presenting with acute abdominal pain.

1 in 1000 of all hospital admissions.

• Associated with 60 -100% mortality rate.

• Results from decreased blood flow to the intestines.

• Patient present with severe abdominal pain in absence of

significant findings on physical examination resulting in delay of

diagnosis, morbidity and mortality.

Gore RM, et al. Clin Gastroenterol Hepatol. 2008 Aug;6(8):849-58

Acute Mesenenteric Ischemia

Arterial (superior mesenteric) Occlusion

Venous Thrombosis Non-Occlusive

Arterial Embolism

Arterial Thrombosis

60-70% of PMI 5-10% of PMI 20% of PMI

40-50% of PMI 20-30% of PMI

Note: PMI: Primary Mesenteric Ischemia (Arterial or Venous occlusive or nonocclusive bowel ischemia) Furukawa A, et al. AJR Am J Roentgenol. 2009 Feb;192(2):408-16.

Arterial embolism Arterial thrombosis

Most frequent cause of AMI.

(60-70%)

Most emboli lodge in the

superior mesenteric artery, 3-10

cm distal to the origin.

50% lodge distally to the origin

of the middle colic artery.

Collateral circulation is poorly

developed, therefore the

presentation is abrupt.

Responsible for 25% to 30% of all

AMI.

Most occur in patients with severe

atherosclerotic disease at the origin of

the superior mesenteric artery.

The extent of ischemia is more distally

distributed than arterial embolism

and can reach the transverse colon.

Atherosclerosis progresses slowly

overtime allowing for development of

a collateral arterial system.

Oldenburg WA, et al. Arch Intern Med. 2004 May 24;164(10):1054-62.

Sites of mesenteric thrombosis vs. embolism

Emboli lodge distal to the origin. Therefore proximal SMA perfusion is maintained and Jejunum remains viable. A clear demarcation seen on laparotomy.

Thrombi

Emboli

Gray Th, Sullivan TM. Curr Treat Options Cardiovasc Med. 2001 Jun;3(3):195-206.

Nonocclusive Mesenteric Ischemia. Mesenteric venous thrombosis

Accounts for 20% of all cases.

Usually no pain, abdominal distension.

Usually due to shock

Involves a low cardiac output setting

with diffuse mesenteric

vasoconstriction

Vasoconstriction in response to

hypovolemia, decreased cardiac

output, hypotension, vasopressors.

Vasoactive drugs and DIC may play a

role.

Accounts for 5-10% of all cases.

Sub acute presentation

Mostly due to hypercoagulable state.

Can also be caused by cirrhosis,

neoplasm, surgical injury.

Wide clinical spectrum, from

asymptomatic to acute, severe, life

threatening.

Oldenburg WA, et al. Arch Intern Med. 2004 May 24;164(10):1054-62.

Clinical characteristics of acute mesenteric ischemia.Cause Incidence Age Presentation Risk factors Arterial embolism

40-50% Elderly Acute Arrhythmia, Myocardial infarction, Valve disease

Arterial Thrombosis

20-30% Elderly Acute Atherosclerosis,prolonged hypotension

Venous Thrombosis

5-10% Younger(30-60 years)

Subacute Portal hypertension, right-sided heart failure,Hypercoagulopathy.

Nonocclusive 20% Elderly Acute or Subacute

Hypovolemia, hypotension, digoxin, cardiogenic shock

Furukawa A, et al. AJR Am J Roentgenol. 2009 Feb;192(2):408-16.

Colonic Ischemia

Due to decrease colonic blood supply associated with a lowered systemic perfusion or an anatomic occlusion.

Cause may include: Age, hypotension/ hypovolemia, cardiac thromboembolism , MI, hypercoagulable states, medications

Rapid onset of mild abdominal pain Tenderness over the affected bowel area

Elder K, Leshner B, Solaiman F. Cleve Clin J Med. 2009 Jul;76(7):401-9

Differentiating from Mesenteric Ischemia

Acute mesenteric ischemia Colonic mesenteric ischemia

Sudden onset of severe abdominal pain out of proportion to the tenderness on physical examination.

Profoundly ill, no bloody stools until late stages.

Report of recurrent severe postprandial abdominal pain

Weight loss Hematochezia beginning

within 24 hours of the onset of pain.

Elder K, Leshner B, Solaiman F. Cleve Clin J Med. 2009 Jul;76(7):401-9

Summary of imaging modalities used to investigate acute intestinal ischemiaModality Utilization/ setting LimitationsRadiograph Limited value NonspecificBarium studies Some value in a chronic setting Barium interferes with future

MDCT studies. Insensitive in evaluation of mural, mesenetric, and valvular signs.

Angiography Immediately before transcatheter intervention

Invasive

Doppler Ultrasound Evaluation of chronic intestinal angina and SMA stenosis

Depends on patient factors- body habitus, presence of air filled bowl loops.

MR Non-acute setting, if patient allergic to iodinated contrast

Longer time, difficult to use with critically ill patients

MDCT Acute/chronicPerformed quicklyLess dependent on patient Superior spatial resolution.

Patient with allergies to iodinated contrast.

Gore RM, et al. Clin Gastroenterol Hepatol. 2008 Aug;6(8):849-58

MDCT Protocol for acute intestinal ischemia with low dose alternative

Protocol mAs(Tube A) kV 120 Kernel B Kernel B Collimation Pitch Rot Time CTDI vol

Arterial Phase(Abdomen)(Scan time 6 sec)

270B43

(Mediastinum)Axial

1mmx0.9mm

B43(Mediastinum)C

oronal 3mmx1mm

128 mmx 0.6mm 0.6 0.5sec 18.22mGy

PV Abdo Pelvis (Scan time 9 sec) 260

B35(Mediastinum)

Axial5mmx2.5mm

B35(Mediastinum)C

oronal5mm x 2.5mm

128 mmx 0.6mm 0.6 0.5 sec 17.54

Note-Arterial Phase is triggered at the descending aorta at level of diaphragm when 100 HU of contrast density is reached followed by a 5 sec delay. PV AbdoPelvis is started at 70sec post injection.

Typical CT findings of mesenteric ischemia. Characteristic Sensitivity/

Specificity Arterial occlusion

Venous Occlusion

Nonocclusion Colonic Ischemia

Bowel wall 85-88%/61-72%

Thinning, no change, or thickening with reperfusion

Thickening No change or thickening with reperfusion.

Mural Thickening

Attenuation of bowel wall on enhanced CT

Not characteristic Low with edema, high with hemorrhage

Not characteristic

Enhancement of bowel wall on contrast-enhanced CT

42%/97-100%

Diminished, absent, target appearance, or increased

Diminished, absent, target appearance, or increased

Diminished,abscent, heterogeneous in distribution

Bowel Dilatation Not apparent Moderate to prominent

Not apparent Apparent

Mesenteric vessels 12-15%/94-100%

Defect(s) in arteries, presence of emboli or thrombi, SMA>SMV in diameter.

Defect(s) in veins, presence of emboli or thrombi,venous engorgement

No defect, Arterial constriction

Other Pneumatosis coli, Pericolic stranding

Furukawa A, et al. AJR Am J Roentgenol. 2009 Feb;192(2):408-16.

Portal venous gas on plain film.

Acute aortic dissection with involvement of SMA origin and left renal vein.Non-perfusion of left kidney. Very poor enhancement of bowel with extensivepneumatosis intestinalis. Gas fills several mesenteric veins and intrahepatic portal veins.

48 years old male patient with acute abdominal distention.

Acute aortic dissectionPneumatosis Intestinalis.Non-perfusion of left kidney.

Severe stenosis at the proximal SMA by non calcified plaque. SMV gas is present.Pneumatosis intestinalis seen within several loops.

86 years old female with history of renal disease presented with abdominal pain.

Pneumatosis intestinalisPortal venous gas Bowel thickening

Dilated and thickened loops of small bowelFilling defect in the superior mesenteric artery Mesenteric stranding

89 years old male patient with two day history of abdominal pain

SMA long segment stenosis with poor collateralization.Dilated loops of small bowel

76 years old patient with severe abdominal pain and hypotension.

Target sign is observed. A long segment of the proximal jejunum demonstratesmural thickening.Mesenteric stranding

71 years old female with sudden onset of severe abdominal pain and elevated lactate levels.

22

Dilated bowel loops with decreased enhancement.Large retroperitoneal hematoma.Oral contrast is from a scan 2 days previously

77 year old patient with increased lactate levels and history of atrial fibrillation.

23

Dilated bowel loops with decreased enhancement.

Multiple loops of dilated, fluid filled small bowel.Occluded SMA.Free fluid.

73 years old patient with history of abdominal surgeries including a SMA bypass.

Thickened loop of small bowel with hypo-attenuationFree fluid.

Pneumatosis intestinalis in cecum. Portal venous gas and focal thrombusis seen within the superior mesenteric vein.

43 years old patient with acute pancreatitis.

70 years old male with left atrial thrombusand acute SMA occlusion.

SMV occlusion from a pancreatic tumor with demonstration of venous collaterals.

Collateral formation from the marginal artery of Drummond.SMA occlusion

74 years old female with history of proximal SMA , celiac occlusion and worsening ischemia.

Mural wall thickening of bowel with minimal mesenteric fat stranding. SMV thrombus is present.

57 years old female with central abdominal pain

Dilated and thickened loops of small bowel.Filling defect in the superior mesenteric artery. Likely early mesenteric ischemia.

Large venous collaterals.Bowel thickening.

Patient with history of chronic pancreatitis and SMV thrombosis.

Pneumatosis intestinalis is present within the right colon. Free gas from perforation

70 year old male hypotensive patient with rising lactate levels.

Near complete occlusion of the proximal SMA just distal to the recently placed stent. Poor enhancement of the left side of the colon.

80 years old woman with history of grafting of the abdominal aorta and red blood per rectum.

Role of MDCT in diagnosis of acute Mesenteric ischemia. According to Oferet al. MDCT Angiography has an

accuracy of 95.6%.

93 consecutive studies on 91 patients with clinically suspected AMI CT Angiography was diagnostic in 92 studies. AMI diagnosed in 18 patients Positive CTA findings were confirmed by surgery in 13 patients and by clinical follow

up in 3 cases. There were two false positives and two false negatives.

According to Menke’s meta-analysis, MDCT has a pooled sensitivity of 93.3% and pooled specificity of 94%.

MDCT is fast and accurate in diagnosis of AMI.Ofer A, et al. Eur Radiol. 2009 Jan;19(1):24-30. Epub 2008 Aug 9.Menke J. Radiology. 2010 Jul;256(1):93-101.

Mesenteric Angiography

Pertinent History

Plain film

Dynamic CT Peritoneal findings

No persistent Peritoneal

findings

Persistent peritoneal

findings

Mesenteric Angiography Laparatomy

YES NO

YESNO

LaparatomyObserve

Normal Findings

Imaging algorithm for the evaluation of acute intestinal ischemia

Tendler DA, LaMount JT. Acute mesenteric ischemia In: UpToDate, Basow, DS (Ed), UpToDate, Waltham, MA, 2010

Future imaging directions

Dual Energy CTMaterial decomposition can improve hyper enhancement detection,

reduce use of contrast material and radiation dose in comparison to conventional CT.

Decrease in need for non-contrast CT studies radiation exposure due to virtual reconstruction.

MRI Advances of MRI techniques reduce artifactsdue to bowel peristalsis

or respiration leading to more clear images.

Yeh BM, et al. AJR Am J Roentgenol. 2009 Jul;193(1):47-54.Lee, HH, et al. J Magn Reson Imaging. 1998 Mar-Apr;8(2):375-83.