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DOI: 10.1148/rg.242025714
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RadioGraphics 2004;24:481-496
© RSNA, 2004

EDUCATION EXHIBIT

Nontraumatic Emergent Abdominal Vascular Conditions: Advantages of Multi–Detector Row CT and Three-Dimensional Imaging1

Thomas Frauenfelder, MD, Simon Wildermuth, MD, Borut Marincek, MD and Thomas Boehm, MD

1 From the Institute of Diagnostic Radiology, University Hospital of Zurich, Raemistrasse 100, 8091 Zurich, Switzerland. Presented as an education exhibit at the 2002 RSNA scientific assembly. Received August 22, 2002; revision requested November 25, 2002, and received May 21, 2003; accepted July 2. Supported by the NCCR CO-ME of the Swiss National Science Foundation. Address correspondence to S.W. (e-mail: simon.wildermuth@usz.ch).


   Abstract
Top
 Abstract
Introduction
 CT Scanning Technique
 Emergent Vascular Conditions
 Conclusions
 References
 
In the past decade, great strides have been made in the development of helical computed tomography (CT) that have led to shorter scanning time and higher spatial resolution. A wide range of traumatic and nontraumatic emergent conditions may be quickly and accurately diagnosed with multi–detector row CT. Multi–detector row CT angiography is the preferred method for imaging in emergent abdominal vascular conditions because it enables the acquisition of high-spatial-resolution volumetric image data during a single breath hold. Unlike catheter angiography, multi–detector row CT angiography not only depicts the vessels but also allows assessment of perfusion in adjacent organs. To make the most effective diagnostic use of multi–detector row CT angiography and three-dimensional image postprocessing, radiologists must be familiar with the optimal CT angiographic protocols and with the typical CT findings in various emergent vascular conditions. This article describes the protocols used in 11 patients with conditions including ruptured abdominal aortic aneurysm, secondary aortoduodenal fistula, splanchnic segmental arterial mediolysis, and Wegener-type vasculitis with visceral involvement. All of the diagnoses in these 11 cases were made in the emergency department, and the delay between imaging and diagnosis was decreased considerably by avoiding the transfer of patients for catheter angiography.

© RSNA, 2004

Index Terms: Aorta, dissection, 94.74, 89.74 • Arteries, mesenteric, 95.73, 95.76, 95.77 • Computed tomography (CT), angiography, 95.12916, 98.12916 • Mesentery, ischemia, 95.76, 96.76, 98.76 • Veins, mesenteric, 98.73, 98.76, 98.77 • Wegener granulomatosis, 89.622


   Introduction
Top
 Abstract
 Introduction
CT Scanning Technique
 Emergent Vascular Conditions
 Conclusions
 References
 
Computed tomography (CT) is an important imaging modality for noninvasive assessment of the vascular system (1). Multi–detector row CT offers a number of advantages over single-section CT in the work-up of patients with emergent conditions (2). The shorter scanning time with multi–detector row CT scanners permits better visualization of blood vessels and improved contrast material enhancement of the adjacent organ parenchyma. Furthermore, faster data acquisition makes it possible to perform multiple consecutive CT examinations in the same patient in a short time (2).

The development of multi–detector row CT, in combination with advances in computer hardware, software, and display technology, has facilitated three-dimensional (3D) image reconstruction (3). Shaded surface display, maximum intensity projection (MIP), and volume rendering (VR) are the three most commonly used 3D reconstruction techniques. In vascular imaging, MIP and VR of image data from multi–detector row CT angiography can enable visualization that is equal or superior to that obtained with catheter angiography. Postprocessing can be performed quickly and easily to obtain a two-dimensional MIP image, and a 3D effect can be achieved with stepwise rotation of the object. VR has a high diagnostic accuracy and is the method most often used for reconstruction of CT angiographic image data because it enables 3D visualization not only of the vascular system but also of adjacent organs.

These techniques therefore are increasingly the initial or the only imaging methods used for surgical planning in emergent vascular conditions. Their use often obviates that of catheter angiography or digital subtraction angiography and thus leads to a reduction in costs (4). Multi–detector row CT angiography and 3D reconstruction are the preferred methods for planning of angiographic interventional treatments at our institution. For example, they are used for vessel segmentation to enable determination of the optimal stent-graft dimensions prior to treatment of aortic aneurysm. Follow-up of patients after aortic stent-graft placement also is performed with multi– detector row CT angiography for detection and localization of displaced stent-grafts and various endoleaks. Three-dimensional reconstructions have increased the options available for visualization of emergent vascular conditions and are gaining acceptance among clinicians.

Assessment of emergent abdominal vascular conditions is possible today with the exclusive use of multi–detector row CT angiography. To achieve correct diagnosis and avoid unnecessary intervention, however, it is essential to be familiar with the anatomy and physiology of abdominal vascular lesions, as well as with the techniques of image acquisition, postprocessing, and interpretation. In this article, we describe the protocols used at our institution and present axial source images and three-dimensional reconstructions from multi–detector row CT angiography in 11 patients. These images illustrate the typical findings in various nontraumatic emergent abdominal vascular conditions, such as ruptured abdominal aortic aneurysm, secondary aortoduodenal fistula, splanchnic segmental arterial mediolysis, and Wegener-type vasculitis with visceral involvement.


   CT Scanning Technique
Top
 Abstract
 Introduction
 CT Scanning Technique
Emergent Vascular Conditions
 Conclusions
 References
 
Optimal scanning protocols are mandatory for complete and accurate assessment of emergent vascular conditions with CT, and the intravenous contrast material injection protocol must be specific to the vascular region that is being assessed. At our institution, different protocols for each anatomic area and for traumatic and nontraumatic emergent conditions are preprogrammed on the CT scanner and the automated injection system.

For optimal assessment, the scanning and protocol must be tailored to the area of interest in a certain anatomic region. If a pathologic condition such as aortoduodenal fistula is suspected to be present, no oral contrast material should be given; contrast material extravasation into the gastrointestinal tract would not be visible with the presence of orally administered contrast material in the bowel, which would obscure the location of the fistula.

CT assessment of patients who have emergent abdominal vascular conditions is performed at our institution with a multi–detector row scanner (Somatom Volume Zoom; Siemens Medical Solutions, Forchheim, Germany). The scanning protocol includes arterial phase imaging with a collimation of 4 x 1 mm (pitch of 0.85) and venous phase imaging with a collimation of 4 x 2.5 mm (pitch of 1.2). Reconstruction of the source image data is performed with section thicknesses of 1.25 and 3 mm, respectively. Prior to CT angiography, 150 mL of a nonionic contrast material containing 370 mg of iopromide per milliliter (Ultravist; Schering, Berlin, Germany) is injected intravenously at a rate of 3–4 mL per second. The CARE bolus technique (Siemens Medical Solutions, Forchheim, Germany) is used to trigger image acquisition at a predefined level of attenuation for optimal arterial depiction in the region of interest. The region of interest for the measurements of attenuation is placed in the abdominal aorta. Arterial phase and venous phase images of the entire abdomen are acquired to characterize blood supply and drainage. If necessary, 3D postprocessing techniques such as multiplanar reformation (MPR), shaded surface display, MIP, or VR are used for better visualization of pathologic changes and for preoperative or preinterventional planning. Commercially available software (ProVision 2.2; Algotec Systems, Raanana, Israel) was used in the reconstruction of most of the 3D images that appear in this article.


   Emergent Vascular Conditions
Top
 Abstract
 Introduction
 CT Scanning Technique
 Emergent Vascular Conditions
Conclusions
 References
 
Rupture of Abdominal Aortic Aneurysm
Aneurysmal dilatation of the infrarenal aorta is defined as a diameter of more than 29 mm. Based on this criterion, 9% of all people older than 65 have an abdominal aortic aneurysm (5). Rupture of an abdominal aortic aneurysm is one of the most urgent vascular conditions and requires rapid intervention. In autopsy studies reported by Lederle et al (6), the 1-year incidence of abdominal aortic aneurysm rupture according to initial diameter was 9.4% for diameters of 5.5–5.9 cm, 10.2% for diameters of 6.0–6.9 cm (19.1% for the subgroup of 6.5–6.9 cm), and 32.5% for diameters of 7.0 cm or more. Other investigators (7,8) have reported similar rupture rates.

A diagnosis of ruptured abdominal aortic aneurysm may be made on the basis of a nonenhanced CT scan that shows an aortic aneurysm with adjacent periaortic hemorrhage that extends into the perirenal and pararenal spaces of the retroperitoneum (2). Multi–detector row CT angiography may depict active bleeding (Fig 1); extension of the aneurysm into the common, external, and internal iliac arteries; the presence and extent of mural thrombosis; the anatomy of arteries that supply blood to the kidneys, including the accessory renal arteries; and stenosis or occlusion of the vessels. This additional information is important for the choice of treatment. Open surgical repair is increasingly being replaced by endovascular repair, which is more efficient and has lower associated morbidity and mortality (9,10). Lee et al (11) found that patient eligibility for endovascular repair depends on the anatomy of the proximal aneurysm neck. Great effort has been put into the development of specialized software for planning endoluminal treatment of abdominal aortic aneurysm. Most of the measurements required for determination of the optimal dimensions and type of aortic stent-graft now are obtained with multi–detector row CT and 3D reconstruction.



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  		Figure 1a. Ruptured infrarenal aortic aneurysm in a 72-year-old man. (a, b) Axial source image (a) and coronal oblique MPR image (b) show a ruptured aneurysm (diameter, 7 cm) with active bleeding (arrowhead) caudad to the aneurysm neck; a resultant large hematoma has displaced the kidney ventrally. (c, d) Coronal MIP (c) and VR (d) images show the anatomic location and configuration of the aneurysm and the bleeding (arrowhead)—important information for treatment planning.

 


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  		Figure 1b. Ruptured infrarenal aortic aneurysm in a 72-year-old man. (a, b) Axial source image (a) and coronal oblique MPR image (b) show a ruptured aneurysm (diameter, 7 cm) with active bleeding (arrowhead) caudad to the aneurysm neck; a resultant large hematoma has displaced the kidney ventrally. (c, d) Coronal MIP (c) and VR (d) images show the anatomic location and configuration of the aneurysm and the bleeding (arrowhead)—important information for treatment planning.

 


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  		Figure 1c. Ruptured infrarenal aortic aneurysm in a 72-year-old man. (a, b) Axial source image (a) and coronal oblique MPR image (b) show a ruptured aneurysm (diameter, 7 cm) with active bleeding (arrowhead) caudad to the aneurysm neck; a resultant large hematoma has displaced the kidney ventrally. (c, d) Coronal MIP (c) and VR (d) images show the anatomic location and configuration of the aneurysm and the bleeding (arrowhead)—important information for treatment planning.

 


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  		Figure 1d. Ruptured infrarenal aortic aneurysm in a 72-year-old man. (a, b) Axial source image (a) and coronal oblique MPR image (b) show a ruptured aneurysm (diameter, 7 cm) with active bleeding (arrowhead) caudad to the aneurysm neck; a resultant large hematoma has displaced the kidney ventrally. (c, d) Coronal MIP (c) and VR (d) images show the anatomic location and configuration of the aneurysm and the bleeding (arrowhead)—important information for treatment planning.

 
Rupture of Iliac Artery Aneurysm
Iliac artery aneurysms are rare: Lawrence et al (12) reported a prevalence of 6.58 per 100,000 hospitalized men and 0.26 per 100,000 hospitalized women in the United States. Iliac artery aneurysms usually involve the common iliac artery (Fig 2), are small, and do not require repair. Those that are smaller than 3.0 cm in diameter tend to be asymptomatic, rarely rupture, and expand slowly; those that are larger than 3.0 cm but smaller than 3.5 cm should be monitored with ultrasonography at 6-month intervals. Iliac artery aneurysms larger than 3.5 cm have a greater tendency to rupture and should be treated expeditiously (13).



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  		Figure 2a. Ruptured aneurysm in a 77-year-old man who presented with acute abdominal pain. Coronal VR image (a) and axial source image (b) show an infrarenal aortic aneurysm with a diameter of 4.5 cm and a right common iliac artery aneurysm with a diameter of 8.5 cm (arrowheads in b), as well as a retroperitoneal hematoma (arrows in b). These findings were diagnostic. Note that the mural thrombus and the remaining lumen are evident, but no active bleeding can be seen.

 


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  		Figure 2b. Ruptured aneurysm in a 77-year-old man who presented with acute abdominal pain. Coronal VR image (a) and axial source image (b) show an infrarenal aortic aneurysm with a diameter of 4.5 cm and a right common iliac artery aneurysm with a diameter of 8.5 cm (arrowheads in b), as well as a retroperitoneal hematoma (arrows in b). These findings were diagnostic. Note that the mural thrombus and the remaining lumen are evident, but no active bleeding can be seen.

 
Type B Aortic Dissection
Acute or type B aortic dissection is a life-threatening condition and must be diagnosed and treated promptly. Aortography, the traditional imaging method for confirming diagnosis, has increasingly been supplanted by transesophageal echocardiography and magnetic resonance (MR) imaging, which have high sensitivities and specificities (95%–100%) for the depiction of acute aortic dissection. Evaluation with these latter modalities is not immediately available, however, and is more time consuming than evaluation with multi–detector row CT angiography. CT has a sensitivity and specificity comparable with those of MR imaging and transesophageal echocardiography for depiction of acute aortic dissection (14).

Findings of a contrast-enhanced double lumen and an intimal flap in the aorta are diagnostic. The frequency of occlusion caused by dissection of the abdominal aortic branch vessels has been estimated as 27% (15). Infradiaphragmatic ischemic complications related to the main abdominal arterial branches are best detected with arterial phase imaging. Sebastià et al (16) described two types of branch-vessel occlusion—static and dynamic. In static occlusion, the intimal flap extends into the wall of the branch vessel. In dynamic occlusion, the intimal flap prolapses across the branch-vessel origin and covers the lumen like a curtain. In the presence of ischemia resulting from compression of the true lumen by the false lumen, endovascular fenestration is one option for minimally invasive treatment. Reliable identification of true lumen and false lumen are important for treatment planning (Fig 3). Le Page et al (17) described the beak sign—a triangular area of high attenuation—and a large cross-sectional area on contrast-enhanced CT images as the most useful indicators of the false lumen in acute and chronic aortic dissection. Less common and less reliable identifiers of the true and false lumina are patterns of eccentric calcification (ie, calcification in the dissection membrane facing only one lumen), intraluminal thrombus, and the cobweb sign (ie, thin linear intraluminal filling defects).



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  		Figure 3a. Type B aortic dissection in a 54-year-old woman with acute onset of thoracic and abdominal pain. (a, b) Anterior (a) and posterior (b) shaded surface display images show the true lumen (arrows) and the false lumen (arrowheads), as well as adjacent vessels. (c, d) VR image obtained with a cutting plane (c) and MIP image (d) also depict the two lumina (arrows) but do not permit clear differentiation between them because the entire length of the dissection flap (*) is not visible. (e-i) Contrast-enhanced arterial phase axial source images obtained at successively lower levels show the characteristic signs enabling differentiation between the false (F) and true (T) lumina. In e, the outer, false lumen is wrapped around the inner, true lumen, and the cobweb sign (arrow) is visible. In f and g, the false lumen is clearly larger in diameter than the true lumen and contains a thrombus (arrowheads in g), which is also evident in h (arrows). In h, note the eccentric calcification (arrowhead) alongside the flap facing the true lumen, and, in i, the beak sign (arrowheads) created by the curvature of the flap toward the false lumen.

 


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  		Figure 3b. Type B aortic dissection in a 54-year-old woman with acute onset of thoracic and abdominal pain. (a, b) Anterior (a) and posterior (b) shaded surface display images show the true lumen (arrows) and the false lumen (arrowheads), as well as adjacent vessels. (c, d) VR image obtained with a cutting plane (c) and MIP image (d) also depict the two lumina (arrows) but do not permit clear differentiation between them because the entire length of the dissection flap (*) is not visible. (e-i) Contrast-enhanced arterial phase axial source images obtained at successively lower levels show the characteristic signs enabling differentiation between the false (F) and true (T) lumina. In e, the outer, false lumen is wrapped around the inner, true lumen, and the cobweb sign (arrow) is visible. In f and g, the false lumen is clearly larger in diameter than the true lumen and contains a thrombus (arrowheads in g), which is also evident in h (arrows). In h, note the eccentric calcification (arrowhead) alongside the flap facing the true lumen, and, in i, the beak sign (arrowheads) created by the curvature of the flap toward the false lumen.

 


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  		Figure 3c. Type B aortic dissection in a 54-year-old woman with acute onset of thoracic and abdominal pain. (a, b) Anterior (a) and posterior (b) shaded surface display images show the true lumen (arrows) and the false lumen (arrowheads), as well as adjacent vessels. (c, d) VR image obtained with a cutting plane (c) and MIP image (d) also depict the two lumina (arrows) but do not permit clear differentiation between them because the entire length of the dissection flap (*) is not visible. (e-i) Contrast-enhanced arterial phase axial source images obtained at successively lower levels show the characteristic signs enabling differentiation between the false (F) and true (T) lumina. In e, the outer, false lumen is wrapped around the inner, true lumen, and the cobweb sign (arrow) is visible. In f and g, the false lumen is clearly larger in diameter than the true lumen and contains a thrombus (arrowheads in g), which is also evident in h (arrows). In h, note the eccentric calcification (arrowhead) alongside the flap facing the true lumen, and, in i, the beak sign (arrowheads) created by the curvature of the flap toward the false lumen.

 


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  		Figure 3d. Type B aortic dissection in a 54-year-old woman with acute onset of thoracic and abdominal pain. (a, b) Anterior (a) and posterior (b) shaded surface display images show the true lumen (arrows) and the false lumen (arrowheads), as well as adjacent vessels. (c, d) VR image obtained with a cutting plane (c) and MIP image (d) also depict the two lumina (arrows) but do not permit clear differentiation between them because the entire length of the dissection flap (*) is not visible. (e-i) Contrast-enhanced arterial phase axial source images obtained at successively lower levels show the characteristic signs enabling differentiation between the false (F) and true (T) lumina. In e, the outer, false lumen is wrapped around the inner, true lumen, and the cobweb sign (arrow) is visible. In f and g, the false lumen is clearly larger in diameter than the true lumen and contains a thrombus (arrowheads in g), which is also evident in h (arrows). In h, note the eccentric calcification (arrowhead) alongside the flap facing the true lumen, and, in i, the beak sign (arrowheads) created by the curvature of the flap toward the false lumen.

 


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  		Figure 3e. Type B aortic dissection in a 54-year-old woman with acute onset of thoracic and abdominal pain. (a, b) Anterior (a) and posterior (b) shaded surface display images show the true lumen (arrows) and the false lumen (arrowheads), as well as adjacent vessels. (c, d) VR image obtained with a cutting plane (c) and MIP image (d) also depict the two lumina (arrows) but do not permit clear differentiation between them because the entire length of the dissection flap (*) is not visible. (e-i) Contrast-enhanced arterial phase axial source images obtained at successively lower levels show the characteristic signs enabling differentiation between the false (F) and true (T) lumina. In e, the outer, false lumen is wrapped around the inner, true lumen, and the cobweb sign (arrow) is visible. In f and g, the false lumen is clearly larger in diameter than the true lumen and contains a thrombus (arrowheads in g), which is also evident in h (arrows). In h, note the eccentric calcification (arrowhead) alongside the flap facing the true lumen, and, in i, the beak sign (arrowheads) created by the curvature of the flap toward the false lumen.

 


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  		Figure 3f. Type B aortic dissection in a 54-year-old woman with acute onset of thoracic and abdominal pain. (a, b) Anterior (a) and posterior (b) shaded surface display images show the true lumen (arrows) and the false lumen (arrowheads), as well as adjacent vessels. (c, d) VR image obtained with a cutting plane (c) and MIP image (d) also depict the two lumina (arrows) but do not permit clear differentiation between them because the entire length of the dissection flap (*) is not visible. (e-i) Contrast-enhanced arterial phase axial source images obtained at successively lower levels show the characteristic signs enabling differentiation between the false (F) and true (T) lumina. In e, the outer, false lumen is wrapped around the inner, true lumen, and the cobweb sign (arrow) is visible. In f and g, the false lumen is clearly larger in diameter than the true lumen and contains a thrombus (arrowheads in g), which is also evident in h (arrows). In h, note the eccentric calcification (arrowhead) alongside the flap facing the true lumen, and, in i, the beak sign (arrowheads) created by the curvature of the flap toward the false lumen.

 


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  		Figure 3g. Type B aortic dissection in a 54-year-old woman with acute onset of thoracic and abdominal pain. (a, b) Anterior (a) and posterior (b) shaded surface display images show the true lumen (arrows) and the false lumen (arrowheads), as well as adjacent vessels. (c, d) VR image obtained with a cutting plane (c) and MIP image (d) also depict the two lumina (arrows) but do not permit clear differentiation between them because the entire length of the dissection flap (*) is not visible. (e-i) Contrast-enhanced arterial phase axial source images obtained at successively lower levels show the characteristic signs enabling differentiation between the false (F) and true (T) lumina. In e, the outer, false lumen is wrapped around the inner, true lumen, and the cobweb sign (arrow) is visible. In f and g, the false lumen is clearly larger in diameter than the true lumen and contains a thrombus (arrowheads in g), which is also evident in h (arrows). In h, note the eccentric calcification (arrowhead) alongside the flap facing the true lumen, and, in i, the beak sign (arrowheads) created by the curvature of the flap toward the false lumen.

 


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  		Figure 3h. Type B aortic dissection in a 54-year-old woman with acute onset of thoracic and abdominal pain. (a, b) Anterior (a) and posterior (b) shaded surface display images show the true lumen (arrows) and the false lumen (arrowheads), as well as adjacent vessels. (c, d) VR image obtained with a cutting plane (c) and MIP image (d) also depict the two lumina (arrows) but do not permit clear differentiation between them because the entire length of the dissection flap (*) is not visible. (e-i) Contrast-enhanced arterial phase axial source images obtained at successively lower levels show the characteristic signs enabling differentiation between the false (F) and true (T) lumina. In e, the outer, false lumen is wrapped around the inner, true lumen, and the cobweb sign (arrow) is visible. In f and g, the false lumen is clearly larger in diameter than the true lumen and contains a thrombus (arrowheads in g), which is also evident in h (arrows). In h, note the eccentric calcification (arrowhead) alongside the flap facing the true lumen, and, in i, the beak sign (arrowheads) created by the curvature of the flap toward the false lumen.

 


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  		Figure 3i. Type B aortic dissection in a 54-year-old woman with acute onset of thoracic and abdominal pain. (a, b) Anterior (a) and posterior (b) shaded surface display images show the true lumen (arrows) and the false lumen (arrowheads), as well as adjacent vessels. (c, d) VR image obtained with a cutting plane (c) and MIP image (d) also depict the two lumina (arrows) but do not permit clear differentiation between them because the entire length of the dissection flap (*) is not visible. (e-i) Contrast-enhanced arterial phase axial source images obtained at successively lower levels show the characteristic signs enabling differentiation between the false (F) and true (T) lumina. In e, the outer, false lumen is wrapped around the inner, true lumen, and the cobweb sign (arrow) is visible. In f and g, the false lumen is clearly larger in diameter than the true lumen and contains a thrombus (arrowheads in g), which is also evident in h (arrows). In h, note the eccentric calcification (arrowhead) alongside the flap facing the true lumen, and, in i, the beak sign (arrowheads) created by the curvature of the flap toward the false lumen.

 
Shaded surface display is an image postprocessing method that allows the clear depiction of both lumina and differentiation between the true lumen and the false lumen (Fig 3a and 3b). VR with cutting planes can depict the dissection membrane (Fig 3c), but it may be difficult and time consuming to define the model parameters for depiction of the lumina. With the use of MIP, the dissection membrane is depicted accurately only if its course is exactly perpendicular to the projection plane (Fig 3d). For this reason, MIP is not commonly used for 3D postprocessing of image data in cases of suspected aortic dissection.

Active Renal Bleeding Caused by Anticoagulant Drugs
Hemorrhage is common in patients who have received anticoagulant drug therapy. It may occur spontaneously or result from minor trauma and may affect any organ system (18). Renal hemorrhage may occur in suburothelial, intraparenchymal, subcapsular, or perinephric locations, or in a combination of these (19). Acute hemorrhage is best depicted with nonenhanced CT (Fig 4a). However, an additional examination with contrast-enhanced CT should always be performed to exclude other pathologic renal conditions that may cause hemorrhage and may require specific therapy. The presence of perinephric hemorrhage is confirmed by bridging septa of the perinephric fat, which determine the location of bleeding.



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  		Figure 4a. Spontaneous subcapsular renal hemorrhage in a 70-year-old man who presented, subsequent to oral anticoagulation therapy, with pain in the right side and acute anemia of unknown origin. Nonenhanced axial source image (a), contrast-enhanced coronal MPR (b), and coronal (c) and sagittal (d) VR images depict a subcapsular hematoma (arrowheads) in the right kidney.

 


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  		Figure 4b. Spontaneous subcapsular renal hemorrhage in a 70-year-old man who presented, subsequent to oral anticoagulation therapy, with pain in the right side and acute anemia of unknown origin. Nonenhanced axial source image (a), contrast-enhanced coronal MPR (b), and coronal (c) and sagittal (d) VR images depict a subcapsular hematoma (arrowheads) in the right kidney.

 


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  		Figure 4c. Spontaneous subcapsular renal hemorrhage in a 70-year-old man who presented, subsequent to oral anticoagulation therapy, with pain in the right side and acute anemia of unknown origin. Nonenhanced axial source image (a), contrast-enhanced coronal MPR (b), and coronal (c) and sagittal (d) VR images depict a subcapsular hematoma (arrowheads) in the right kidney.

 


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  		Figure 4d. Spontaneous subcapsular renal hemorrhage in a 70-year-old man who presented, subsequent to oral anticoagulation therapy, with pain in the right side and acute anemia of unknown origin. Nonenhanced axial source image (a), contrast-enhanced coronal MPR (b), and coronal (c) and sagittal (d) VR images depict a subcapsular hematoma (arrowheads) in the right kidney.

 
Acute Bleeding in Renal Angiomyolipoma
Renal angiomyolipomas are a commonly occurring type of renal hamartoma (20). They are usually asymptomatic and are detected incidentally, often in patients with systemic diseases such as tuberous sclerosis. Renal angiomyolipomas are composed of aberrant or anomalous blood vessels, smooth muscle, and fat in various quantities (21). Radiologic diagnosis of these lesions is based on the presence of fat (ie, attenuation values of less than 0 HU), which enables differentiation of renal angiomyolipoma from renal carcinoma (22). Fat-containing solid renal masses are rarely found not to be angiomyolipomas (23). Fat is uncommon in renal carcinoma but may appear in small quantities, generally in association with calcifications. Only one case of fat in renal cell carcinoma without calcifications has been reported (23). Hemorrhage occurs frequently in angiomyolipomas. The vessel walls in these lesions are thicker than those of normal renal vessels, but they lack elasticity and therefore tend to bleed after slight trauma or even without any trauma (24). In 17%–20% of patients with spontaneous perinephric hemorrhage, angiomyolipoma is the cause of bleeding (25). The spontaneous rupture of a large angiomyolipoma with retroperitoneal bleeding is a serious medical condition: Patients present with sudden pain, hypotension, and shock (21). CT findings are retroperitoneal hematoma in combination with a fat-containing renal tumor (Fig 5). The therapy of choice in symptomatic renal angiomyolipomas is selective arterial embolization (Fig 5f). Surgery is reserved for patients in whom embolization is unsuccessful or fails to restore homeostasis (26). The goal of 3D image data reconstruction is to enable simultaneous localization of the source of blood flow and visualization of adjacent anatomic structures on the same image. VR is the preferred postprocessing technique (Fig 5e). MIP images clearly depict extravasation of contrast material and thereby confirm active bleeding, but the lesion and neighboring organs often are not visible because of low attenuation (Fig 5d).



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  		Figure 5a. Angiomyolipoma in a 68-year-old man with hemostatic shock, acute anemia, and right-sided abdominal pain. (a-e) Contrast-enhanced axial source image (a), coronal (b) and sagittal (c) MPR images, posteroanterior MIP image (d), and posterior VR image (e) show contrast material extravasation (arrowheads) from the upper right renal pole into a large retroperitoneal hematoma. The lesion (arrow) in the upper renal pole has attenuation characteristic of angiomyolipoma. Note that the MIP image shows only the vessels and extravasation, whereas the VR image depicts adjacent organs as well as the lesion. (f) Angiogram from catheter angiography performed after therapeutic embolization helps confirm the cessation of bleeding at the lesion site (arrow).

 


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  		Figure 5b. Angiomyolipoma in a 68-year-old man with hemostatic shock, acute anemia, and right-sided abdominal pain. (a-e) Contrast-enhanced axial source image (a), coronal (b) and sagittal (c) MPR images, posteroanterior MIP image (d), and posterior VR image (e) show contrast material extravasation (arrowheads) from the upper right renal pole into a large retroperitoneal hematoma. The lesion (arrow) in the upper renal pole has attenuation characteristic of angiomyolipoma. Note that the MIP image shows only the vessels and extravasation, whereas the VR image depicts adjacent organs as well as the lesion. (f) Angiogram from catheter angiography performed after therapeutic embolization helps confirm the cessation of bleeding at the lesion site (arrow).

 


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  		Figure 5c. Angiomyolipoma in a 68-year-old man with hemostatic shock, acute anemia, and right-sided abdominal pain. (a-e) Contrast-enhanced axial source image (a), coronal (b) and sagittal (c) MPR images, posteroanterior MIP image (d), and posterior VR image (e) show contrast material extravasation (arrowheads) from the upper right renal pole into a large retroperitoneal hematoma. The lesion (arrow) in the upper renal pole has attenuation characteristic of angiomyolipoma. Note that the MIP image shows only the vessels and extravasation, whereas the VR image depicts adjacent organs as well as the lesion. (f) Angiogram from catheter angiography performed after therapeutic embolization helps confirm the cessation of bleeding at the lesion site (arrow).

 


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  		Figure 5d. Angiomyolipoma in a 68-year-old man with hemostatic shock, acute anemia, and right-sided abdominal pain. (a-e) Contrast-enhanced axial source image (a), coronal (b) and sagittal (c) MPR images, posteroanterior MIP image (d), and posterior VR image (e) show contrast material extravasation (arrowheads) from the upper right renal pole into a large retroperitoneal hematoma. The lesion (arrow) in the upper renal pole has attenuation characteristic of angiomyolipoma. Note that the MIP image shows only the vessels and extravasation, whereas the VR image depicts adjacent organs as well as the lesion. (f) Angiogram from catheter angiography performed after therapeutic embolization helps confirm the cessation of bleeding at the lesion site (arrow).

 


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  		Figure 5e. Angiomyolipoma in a 68-year-old man with hemostatic shock, acute anemia, and right-sided abdominal pain. (a-e) Contrast-enhanced axial source image (a), coronal (b) and sagittal (c) MPR images, posteroanterior MIP image (d), and posterior VR image (e) show contrast material extravasation (arrowheads) from the upper right renal pole into a large retroperitoneal hematoma. The lesion (arrow) in the upper renal pole has attenuation characteristic of angiomyolipoma. Note that the MIP image shows only the vessels and extravasation, whereas the VR image depicts adjacent organs as well as the lesion. (f) Angiogram from catheter angiography performed after therapeutic embolization helps confirm the cessation of bleeding at the lesion site (arrow).

 


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  		Figure 5f. Angiomyolipoma in a 68-year-old man with hemostatic shock, acute anemia, and right-sided abdominal pain. (a-e) Contrast-enhanced axial source image (a), coronal (b) and sagittal (c) MPR images, posteroanterior MIP image (d), and posterior VR image (e) show contrast material extravasation (arrowheads) from the upper right renal pole into a large retroperitoneal hematoma. The lesion (arrow) in the upper renal pole has attenuation characteristic of angiomyolipoma. Note that the MIP image shows only the vessels and extravasation, whereas the VR image depicts adjacent organs as well as the lesion. (f) Angiogram from catheter angiography performed after therapeutic embolization helps confirm the cessation of bleeding at the lesion site (arrow).

 
Secondary Aortoduodenal Fistula
Secondary aortoduodenal fistula is a rare complication of aortic graft implantation (Fig 6) and is associated with a high mortality rate (27). Symptoms of abdominal pain, gastrointestinal bleeding, and sepsis occur in 30% of patients with this condition.



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  		Figure 6a. Aortoduodenal fistula in a 70-year-old man who presented with anemia caused by intestinal bleeding of unknown origin, 10 years after aortoiliac graft implantation. (a, b) Contrast-enhanced axial source image (a) and coronal MPR image (b) show extravasation of contrast material (arrowheads) into the horizontal or inferior duodenum. (c, d) Coronal MIP image (c) and coronal VR image (d) from venous phase imaging show the advantage of two-phase CT: On an arterial phase image, only a small amount of contrast material is evident in the duodenum, whereas the venous phase images show active bleeding (arrow) into the duodenum. (Blood is depicted in yellow.) (e, f) Axial VR image (e) and sagittal MPR image (f) show the exact location of the fistula (arrow).

 


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  		Figure 6b. Aortoduodenal fistula in a 70-year-old man who presented with anemia caused by intestinal bleeding of unknown origin, 10 years after aortoiliac graft implantation. (a, b) Contrast-enhanced axial source image (a) and coronal MPR image (b) show extravasation of contrast material (arrowheads) into the horizontal or inferior duodenum. (c, d) Coronal MIP image (c) and coronal VR image (d) from venous phase imaging show the advantage of two-phase CT: On an arterial phase image, only a small amount of contrast material is evident in the duodenum, whereas the venous phase images show active bleeding (arrow) into the duodenum. (Blood is depicted in yellow.) (e, f) Axial VR image (e) and sagittal MPR image (f) show the exact location of the fistula (arrow).

 


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  		Figure 6c. Aortoduodenal fistula in a 70-year-old man who presented with anemia caused by intestinal bleeding of unknown origin, 10 years after aortoiliac graft implantation. (a, b) Contrast-enhanced axial source image (a) and coronal MPR image (b) show extravasation of contrast material (arrowheads) into the horizontal or inferior duodenum. (c, d) Coronal MIP image (c) and coronal VR image (d) from venous phase imaging show the advantage of two-phase CT: On an arterial phase image, only a small amount of contrast material is evident in the duodenum, whereas the venous phase images show active bleeding (arrow) into the duodenum. (Blood is depicted in yellow.) (e, f) Axial VR image (e) and sagittal MPR image (f) show the exact location of the fistula (arrow).

 


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  		Figure 6d. Aortoduodenal fistula in a 70-year-old man who presented with anemia caused by intestinal bleeding of unknown origin, 10 years after aortoiliac graft implantation. (a, b) Contrast-enhanced axial source image (a) and coronal MPR image (b) show extravasation of contrast material (arrowheads) into the horizontal or inferior duodenum. (c, d) Coronal MIP image (c) and coronal VR image (d) from venous phase imaging show the advantage of two-phase CT: On an arterial phase image, only a small amount of contrast material is evident in the duodenum, whereas the venous phase images show active bleeding (arrow) into the duodenum. (Blood is depicted in yellow.) (e, f) Axial VR image (e) and sagittal MPR image (f) show the exact location of the fistula (arrow).

 


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  		Figure 6e. Aortoduodenal fistula in a 70-year-old man who presented with anemia caused by intestinal bleeding of unknown origin, 10 years after aortoiliac graft implantation. (a, b) Contrast-enhanced axial source image (a) and coronal MPR image (b) show extravasation of contrast material (arrowheads) into the horizontal or inferior duodenum. (c, d) Coronal MIP image (c) and coronal VR image (d) from venous phase imaging show the advantage of two-phase CT: On an arterial phase image, only a small amount of contrast material is evident in the duodenum, whereas the venous phase images show active bleeding (arrow) into the duodenum. (Blood is depicted in yellow.) (e, f) Axial VR image (e) and sagittal MPR image (f) show the exact location of the fistula (arrow).

 


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  		Figure 6f. Aortoduodenal fistula in a 70-year-old man who presented with anemia caused by intestinal bleeding of unknown origin, 10 years after aortoiliac graft implantation. (a, b) Contrast-enhanced axial source image (a) and coronal MPR image (b) show extravasation of contrast material (arrowheads) into the horizontal or inferior duodenum. (c, d) Coronal MIP image (c) and coronal VR image (d) from venous phase imaging show the advantage of two-phase CT: On an arterial phase image, only a small amount of contrast material is evident in the duodenum, whereas the venous phase images show active bleeding (arrow) into the duodenum. (Blood is depicted in yellow.) (e, f) Axial VR image (e) and sagittal MPR image (f) show the exact location of the fistula (arrow).

 
CT has a high sensitivity for the detection of most aortic graft complications, such as endoleak, thrombosis, or stent-graft migration. Because secondary aortoduodenal fistulas occur less commonly than other complications, the sensitivity of CT specifically for the detection of these fistulas has not yet been determined. For the initial diagnostic assessment of patients with gastrointestinal bleeding, endoscopy is the modality of choice. If the rate of blood loss exceeds 0.5 mL per minute and the source of gastrointestinal bleeding cannot be identified with upper gastrointestinal endoscopy or colonoscopy, selective angiography is performed for this purpose (28). Contrast-enhanced helical CT also is recommended because it can be performed easily and rapidly (29) and because it provides more complete information, especially with regard to coexistent pathologic conditions, that may be useful in treatment planning.

A CT scanning protocol that includes two successive (arterial phrase and portal phase) acquisitions is important for the depiction of small fistulas with a minimal flow volume (Fig 6b and 6c) (29). The appearance of contrast enhancement in the duodenum is diagnostic of aortoduodenal fistula. The delay between the start of arterial phase imaging and the start of venous phase imaging should be about 60 seconds. It is important that oral contrast material not be used when a fistula is suspected, because its use would obscure the source of bleeding. The finding of periaortic air also is specific for the diagnosis of secondary aortoduodenal fistula (30).

Acute Mesenteric Ischemia
Three categories of acute mesenteric ischemia are recognized: arterial occlusion, nonocclusive ischemia, and venous thrombosis (31). Nonspecific findings at radiography may include the sentinel loop sign or paralytic ileus, as well as pneumatosis coli and portal venous air (Fig 7). Secondary to submucosal hemorrhage or edema, bowel wall thickening with a "thumbprinting" appearance may be seen (32).



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  		Figure 7a. Nonocclusive mesenteric ischemia in a 51-year-old woman with a history of left-sided heart failure. (a) Abdominal radiograph shows signs of pneumatosis coli (arrowheads). (b-d) Coronal VR image (b), sagittal MPR image (c), and curved MPR image (d) show air in the wall of the small bowel and ascending colon (arrowheads). (e, f) Axial source images show air collections in the intrahepatic vessels (arrows in e) and in the portal confluence (arrow in f) and an intraaortic balloon pump device in the aortic lumen (arrowhead in f). The device is shown in a to be in the correct position, and no occlusion is visible in the mesenteric arteries (arrow in d). The absence of occlusion was confirmed at pathologic analysis. The ischemia from low cardiac output probably was exacerbated by a reduction in peak systolic pressure caused by the intraaortic balloon pump.

 


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  		Figure 7b. Nonocclusive mesenteric ischemia in a 51-year-old woman with a history of left-sided heart failure. (a) Abdominal radiograph shows signs of pneumatosis coli (arrowheads). (b-d) Coronal VR image (b), sagittal MPR image (c), and curved MPR image (d) show air in the wall of the small bowel and ascending colon (arrowheads). (e, f) Axial source images show air collections in the intrahepatic vessels (arrows in e) and in the portal confluence (arrow in f) and an intraaortic balloon pump device in the aortic lumen (arrowhead in f). The device is shown in a to be in the correct position, and no occlusion is visible in the mesenteric arteries (arrow in d). The absence of occlusion was confirmed at pathologic analysis. The ischemia from low cardiac output probably was exacerbated by a reduction in peak systolic pressure caused by the intraaortic balloon pump.

 


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  		Figure 7c. Nonocclusive mesenteric ischemia in a 51-year-old woman with a history of left-sided heart failure. (a) Abdominal radiograph shows signs of pneumatosis coli (arrowheads). (b-d) Coronal VR image (b), sagittal MPR image (c), and curved MPR image (d) show air in the wall of the small bowel and ascending colon (arrowheads). (e, f) Axial source images show air collections in the intrahepatic vessels (arrows in e) and in the portal confluence (arrow in f) and an intraaortic balloon pump device in the aortic lumen (arrowhead in f). The device is shown in a to be in the correct position, and no occlusion is visible in the mesenteric arteries (arrow in d). The absence of occlusion was confirmed at pathologic analysis. The ischemia from low cardiac output probably was exacerbated by a reduction in peak systolic pressure caused by the intraaortic balloon pump.

 


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  		Figure 7d. Nonocclusive mesenteric ischemia in a 51-year-old woman with a history of left-sided heart failure. (a) Abdominal radiograph shows signs of pneumatosis coli (arrowheads). (b-d) Coronal VR image (b), sagittal MPR image (c), and curved MPR image (d) show air in the wall of the small bowel and ascending colon (arrowheads). (e, f) Axial source images show air collections in the intrahepatic vessels (arrows in e) and in the portal confluence (arrow in f) and an intraaortic balloon pump device in the aortic lumen (arrowhead in f). The device is shown in a to be in the correct position, and no occlusion is visible in the mesenteric arteries (arrow in d). The absence of occlusion was confirmed at pathologic analysis. The ischemia from low cardiac output probably was exacerbated by a reduction in peak systolic pressure caused by the intraaortic balloon pump.

 


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  		Figure 7e. Nonocclusive mesenteric ischemia in a 51-year-old woman with a history of left-sided heart failure. (a) Abdominal radiograph shows signs of pneumatosis coli (arrowheads). (b-d) Coronal VR image (b), sagittal MPR image (c), and curved MPR image (d) show air in the wall of the small bowel and ascending colon (arrowheads). (e, f) Axial source images show air collections in the intrahepatic vessels (arrows in e) and in the portal confluence (arrow in f) and an intraaortic balloon pump device in the aortic lumen (arrowhead in f). The device is shown in a to be in the correct position, and no occlusion is visible in the mesenteric arteries (arrow in d). The absence of occlusion was confirmed at pathologic analysis. The ischemia from low cardiac output probably was exacerbated by a reduction in peak systolic pressure caused by the intraaortic balloon pump.

 


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  		Figure 7f. Nonocclusive mesenteric ischemia in a 51-year-old woman with a history of left-sided heart failure. (a) Abdominal radiograph shows signs of pneumatosis coli (arrowheads). (b-d) Coronal VR image (b), sagittal MPR image (c), and curved MPR image (d) show air in the wall of the small bowel and ascending colon (arrowheads). (e, f) Axial source images show air collections in the intrahepatic vessels (arrows in e) and in the portal confluence (arrow in f) and an intraaortic balloon pump device in the aortic lumen (arrowhead in f). The device is shown in a to be in the correct position, and no occlusion is visible in the mesenteric arteries (arrow in d). The absence of occlusion was confirmed at pathologic analysis. The ischemia from low cardiac output probably was exacerbated by a reduction in peak systolic pressure caused by the intraaortic balloon pump.

 
Specific contrast-enhanced CT findings in patients with mesenteric ischemia typically include focal or segmental thickening in the bowel wall, caused by submucosal hemorrhage or edema, pneumatosis coli, or portal venous air. Emboli in the mesenteric arteries may appear as filling defects with soft-tissue attenuation. In mesenteric venous thrombosis, typical findings are thrombus and lack of enhancement in the mesenteric veins after intravenous administration of contrast material (32).

Systemic embolism is often caused by bacterial endocarditis, paradoxical embolism, or atrial fibrillation. One of the most common and severe clinical manifestations of systemic embolism is neurologic deficit caused by cerebral embolism and infarction. Splenic infarction also is common, and embolism due to cardiac thrombus caused by wall motion abnormalities is well known (33). We describe the case of a patient with cardiac aneurysm and thrombus who had multiple symptomatic arterial emboli and infarction. Infarction usually occurs in the kidneys or spleen (Fig 8a and 8b) and is more rarely seen in the liver. Infarcts are typically wedge shaped, nonenhancing, and peripheral (ie, close to the capsule) and are easily differentiated from normal parenchyma (34). The typical CT findings in intestinal ischemia are similar and may include bowel wall thickening with associated submucosal edema or hemorrhage, pneumatosis coli, mesenteric infiltration, and paralytic ileus. In the previously described patient, thromboembolism of the left iliac artery also was seen (Fig 8e).



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  		Figure 8a. Cardiac pseudoaneurysm and thrombus in a 59-year-old man who presented with diffuse abdominal pain, vomiting, and diarrhea accompanied by hematochezia. (a, b) Axial source image (a) and coronal VR image (b) depict pseudoaneurysm with thrombus (arrow) in the left cardiac apex, as well as extensive infarction in the spleen (arrowhead in a). (c, d) Ax- ial source image (c) and VR image (d) depict atrophy of the left kidney (arrows) with chronic infarction and partial occlusion of the left common iliac artery (arrowheads in d). (e) Axial source image shows ileal wall thickening caused by ischemia (arrowheads) and partial occlusion of the left common iliac artery (arrow).

 


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  		Figure 8b. Cardiac pseudoaneurysm and thrombus in a 59-year-old man who presented with diffuse abdominal pain, vomiting, and diarrhea accompanied by hematochezia. (a, b) Axial source image (a) and coronal VR image (b) depict pseudoaneurysm with thrombus (arrow) in the left cardiac apex, as well as extensive infarction in the spleen (arrowhead in a). (c, d) Ax- ial source image (c) and VR image (d) depict atrophy of the left kidney (arrows) with chronic infarction and partial occlusion of the left common iliac artery (arrowheads in d). (e) Axial source image shows ileal wall thickening caused by ischemia (arrowheads) and partial occlusion of the left common iliac artery (arrow).

 


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  		Figure 8c. Cardiac pseudoaneurysm and thrombus in a 59-year-old man who presented with diffuse abdominal pain, vomiting, and diarrhea accompanied by hematochezia. (a, b) Axial source image (a) and coronal VR image (b) depict pseudoaneurysm with thrombus (arrow) in the left cardiac apex, as well as extensive infarction in the spleen (arrowhead in a). (c, d) Ax- ial source image (c) and VR image (d) depict atrophy of the left kidney (arrows) with chronic infarction and partial occlusion of the left common iliac artery (arrowheads in d). (e) Axial source image shows ileal wall thickening caused by ischemia (arrowheads) and partial occlusion of the left common iliac artery (arrow).

 


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  		Figure 8d. Cardiac pseudoaneurysm and thrombus in a 59-year-old man who presented with diffuse abdominal pain, vomiting, and diarrhea accompanied by hematochezia. (a, b) Axial source image (a) and coronal VR image (b) depict pseudoaneurysm with thrombus (arrow) in the left cardiac apex, as well as extensive infarction in the spleen (arrowhead in a). (c, d) Ax- ial source image (c) and VR image (d) depict atrophy of the left kidney (arrows) with chronic infarction and partial occlusion of the left common iliac artery (arrowheads in d). (e) Axial source image shows ileal wall thickening caused by ischemia (arrowheads) and partial occlusion of the left common iliac artery (arrow).

 


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  		Figure 8e. Cardiac pseudoaneurysm and thrombus in a 59-year-old man who presented with diffuse abdominal pain, vomiting, and diarrhea accompanied by hematochezia. (a, b) Axial source image (a) and coronal VR image (b) depict pseudoaneurysm with thrombus (arrow) in the left cardiac apex, as well as extensive infarction in the spleen (arrowhead in a). (c, d) Ax- ial source image (c) and VR image (d) depict atrophy of the left kidney (arrows) with chronic infarction and partial occlusion of the left common iliac artery (arrowheads in d). (e) Axial source image shows ileal wall thickening caused by ischemia (arrowheads) and partial occlusion of the left common iliac artery (arrow).

 
Nonocclusive mesenteric ischemia involves a decrease in perfusion, without occlusion of the mesenteric arteries (Fig 7). The condition is commonly caused by decreased cardiac output with resultant splanchnic hypoperfusion and generally affects patients older than 50 years who have a history of myocardial infarction, congestive heart failure, aortic insufficiency, or renal or hepatic disease (35). Although selective angiography of the mesenteric arteries remains the standard examination for diagnosis of peripheral splanchnic vessel disease, multi–detector row CT with 3D postprocessing also may be used to examine the small bowel and mesenteric vessels. Multi–detector row CT scanners provide increased spatial resolution (thin sections) and decreased scanning time and thus enable the depiction of even the smallest branches of the mesenteric vasculature without motion artifacts. This capability allows the diagnosis or the exclusion of small thrombi. Curved MPR enables the depiction of vessels along their entire course, from the origin of the superior mesenteric artery to the bowel wall. Other signs on CT images are thickening of the bowel wall, absence of bowel wall enhancement, intramural hemorrhage, intestinal pneumatosis, and portal venous air collections (Fig 7).

Inflammatory Arterial Occlusion
Wegener granulomatosis is a multisystemic disease of unknown cause that is characterized by necrotizing granulomatous vasculitis of the respiratory system, often in association with glomerulonephritis. Active disease can be diagnosed with a sensitivity and specificity of 90% on the basis of findings of cytoplasmic antineutrophil cytoplasmic antibodies (c-ANCA) in the blood serum (36). CT findings of bowel involvement are nonspecific for differentiation of Wegener granulomatosis from other types of small-vessel vasculitis (Fig 9). Common CT findings include bowel dilatation, focal or diffuse bowel wall thickening, abnormal bowel wall enhancement, engorged mesenteric vessels in a comblike configuration (comb sign), ascites, and lymphadenopathy (37).



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  		Figure 9a. Wegener granulomatosis in a 48-year-old woman with recurrent epigastric pain and with c-ANCA in blood serum. (a, b) Axial source images depict multiple hypoattenuating lesions in the spleen (arrow in a), which indicate infarction, and thickening of the jejunal bowel wall (arrow in b). (c, d) Axial source image (c) and coronal MPR image (d) show occlusion (arrowheads) in a branch of the superior mesenteric artery. These CT findings are nonspecific, but, when combined with the finding of c-ANCA in blood serum, are highly suggestive of Wegener granulomatosis.

 


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  		Figure 9b. Wegener granulomatosis in a 48-year-old woman with recurrent epigastric pain and with c-ANCA in blood serum. (a, b) Axial source images depict multiple hypoattenuating lesions in the spleen (arrow in a), which indicate infarction, and thickening of the jejunal bowel wall (arrow in b). (c, d) Axial source image (c) and coronal MPR image (d) show occlusion (arrowheads) in a branch of the superior mesenteric artery. These CT findings are nonspecific, but, when combined with the finding of c-ANCA in blood serum, are highly suggestive of Wegener granulomatosis.

 


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  		Figure 9c. Wegener granulomatosis in a 48-year-old woman with recurrent epigastric pain and with c-ANCA in blood serum. (a, b) Axial source images depict multiple hypoattenuating lesions in the spleen (arrow in a), which indicate infarction, and thickening of the jejunal bowel wall (arrow in b). (c, d) Axial source image (c) and coronal MPR image (d) show occlusion (arrowheads) in a branch of the superior mesenteric artery. These CT findings are nonspecific, but, when combined with the finding of c-ANCA in blood serum, are highly suggestive of Wegener granulomatosis.

 


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  		Figure 9d. Wegener granulomatosis in a 48-year-old woman with recurrent epigastric pain and with c-ANCA in blood serum. (a, b) Axial source images depict multiple hypoattenuating lesions in the spleen (arrow in a), which indicate infarction, and thickening of the jejunal bowel wall (arrow in b). (c, d) Axial source image (c) and coronal MPR image (d) show occlusion (arrowheads) in a branch of the superior mesenteric artery. These CT findings are nonspecific, but, when combined with the finding of c-ANCA in blood serum, are highly suggestive of Wegener granulomatosis.

 
Arteriovenous Fistula after Aortic Stent-Graft Placement
The formation of false aneurysms or arteriovenous fistulas is mostly caused by inadvertent laceration of major vessels during surgery (38). Arteriovenous fistulas are likely to be overlooked initially if angiography is performed with a single-section CT scanner. The key finding at multi–detector row CT angiography, as at catheter-based angiography, is the identification of early contrast enhancement in a draining vein with an attenuation-time curve that parallels that of enhancement in the aorta (Fig 10). Only an optimal scanning delay between the arterial and venous phases allows the depiction of early venous filling. Because of its high temporal and spatial resolution, multi–detector row CT with specific scanning delays is the ideal technique for depicting the exact anatomic location of arteriovenous fistula. Although various 3D postprocessing techniques are useful for clearly demonstrating other pathologic conditions and adjacent organs or vessels, MPR—especially curved MPR—is the preferred method for optimal depiction of arteriovenous fistula.



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  		Figure 10a. Arteriovenous fistula in an 84-year-old man after abdominal aortic stent-graft implantation. (a, b) Coronal (a) and sagittal (b) MIP images show early filling in the left iliac and inferior caval veins (arrowheads in a) and the ascending lumbar vein (arrow), which indicates iatrogenic arteriovenous fistula from stent-graft implantation. (c, d) The location of the small fistula (arrowhead in d) between the left common iliac artery and the corresponding vein was not evident on the MIP images or the VR image (c) but only on the curved MPR image (d). Note that no contrast enhancement is seen in the lower abdominal venous system in this early scanning phase.

 


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  		Figure 10b. Arteriovenous fistula in an 84-year-old man after abdominal aortic stent-graft implantation. (a, b) Coronal (a) and sagittal (b) MIP images show early filling in the left iliac and inferior caval veins (arrowheads in a) and the ascending lumbar vein (arrow), which indicates iatrogenic arteriovenous fistula from stent-graft implantation. (c, d) The location of the small fistula (arrowhead in d) between the left common iliac artery and the corresponding vein was not evident on the MIP images or the VR image (c) but only on the curved MPR image (d). Note that no contrast enhancement is seen in the lower abdominal venous system in this early scanning phase.

 


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  		Figure 10c. Arteriovenous fistula in an 84-year-old man after abdominal aortic stent-graft implantation. (a, b) Coronal (a) and sagittal (b) MIP images show early filling in the left iliac and inferior caval veins (arrowheads in a) and the ascending lumbar vein (arrow), which indicates iatrogenic arteriovenous fistula from stent-graft implantation. (c, d) The location of the small fistula (arrowhead in d) between the left common iliac artery and the corresponding vein was not evident on the MIP images or the VR image (c) but only on the curved MPR image (d). Note that no contrast enhancement is seen in the lower abdominal venous system in this early scanning phase.

 


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  		Figure 10d. Arteriovenous fistula in an 84-year-old man after abdominal aortic stent-graft implantation. (a, b) Coronal (a) and sagittal (b) MIP images show early filling in the left iliac and inferior caval veins (arrowheads in a) and the ascending lumbar vein (arrow), which indicates iatrogenic arteriovenous fistula from stent-graft implantation. (c, d) The location of the small fistula (arrowhead in d) between the left common iliac artery and the corresponding vein was not evident on the MIP images or the VR image (c) but only on the curved MPR image (d). Note that no contrast enhancement is seen in the lower abdominal venous system in this early scanning phase.

 
Splanchnic Segmental Arterial Mediolysis
Segmental arterial mediolysis is a rare nonsystemic noninflammatory arteriopathy that is limited to a few topographically related arteries in the abdomen or heart. The pathogenesis of this condition is unclear. Slavin et al (39) have postulated that the condition is the result of an inappropriate vasoconstrictive response to shock or severe hypoxemia in a splanchnic vascular bed. Armas et al (40) reported morphologic and clinical findings that support this hypothesis. Vasospastic arterial changes have histologic similarities to segmental arterial mediolysis.

Typical radiologic findings in this condition include arterial wall thickening and dissection (Fig 11), as well as multiple saccular aneurysms of the small abdominal arteries, which may become elongated and kinked. Arteriovenous fistula occurs rarely. Nonocclusive ischemic bowel diseases or retroperitoneal bleeding caused by rupture of aneurysms in the splanchnic arteries are the most frequent severe complications of segmental arterial mediolysis.



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  		Figure 11a. Segmental arterial mediolysis in a 51-year-old man with pain in the right upper abdominal quadrant. (a, b) Sagittal MPR image (a) and its magnified view (b) depict thickening of the superior mesenteric artery wall (arrowheads). (c, d) Axial source image (c) and VR image (d) show dissection of the dilated celiac trunk (arrow), as well as mesenteric artery wall thickening (arrowheads).

 


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  		Figure 11b. Segmental arterial mediolysis in a 51-year-old man with pain in the right upper abdominal quadrant. (a, b) Sagittal MPR image (a) and its magnified view (b) depict thickening of the superior mesenteric artery wall (arrowheads). (c, d) Axial source image (c) and VR image (d) show dissection of the dilated celiac trunk (arrow), as well as mesenteric artery wall thickening (arrowheads).

 


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  		Figure 11c. Segmental arterial mediolysis in a 51-year-old man with pain in the right upper abdominal quadrant. (a, b) Sagittal MPR image (a) and its magnified view (b) depict thickening of the superior mesenteric artery wall (arrowheads). (c, d) Axial source image (c) and VR image (d) show dissection of the dilated celiac trunk (arrow), as well as mesenteric artery wall thickening (arrowheads).

 


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  		Figure 11d. Segmental arterial mediolysis in a 51-year-old man with pain in the right upper abdominal quadrant. (a, b) Sagittal MPR image (a) and its magnified view (b) depict thickening of the superior mesenteric artery wall (arrowheads). (c, d) Axial source image (c) and VR image (d) show dissection of the dilated celiac trunk (arrow), as well as mesenteric artery wall thickening (arrowheads).

 

   Conclusions
Top
 Abstract
 Introduction
 CT Scanning Technique
 Emergent Vascular Conditions
 Conclusions
References
 
Multi–detector row CT angiography is a fast, safe, and noninvasive imaging technique. In combination with 3D image reconstruction techniques, multi–detector row CT may be used to clarify complex vascular anatomies. It is the modality of choice for assessment of nontraumatic emergent abdominal vascular conditions. An optimal protocol including thin-section collimation, intravenous contrast material injection, appropriate use of oral contrast material, and at least two scanning phases is absolutely necessary. In addition, radiologists must be aware of the shortcomings of this image modality with regard to the depiction of low-flow bleeding and small vessel disease. Future technical developments, such as a further increase in axial spatial resolution, combined with dose modulation protocols, may strengthen the role of CT in the assessment of emergent abdominal vascular conditions.


   Footnotes
 
Abbreviations: c-ANCA = cytoplasmic antineutrophil cytoplasmic antibodies, MIP = maximum intensity projection, MPR = multiplanar reformation, 3D = three-dimensional, VR = volume rendering


   References
Top
 Abstract
 Introduction
 CT Scanning Technique
 Emergent Vascular Conditions
 Conclusions
 References
 

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