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Multislice CT for vascular
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| Subject: |
Diagnostic imaging CT imaging |
| Author: | Munera, Felipe |
| Pub Date: | 09/01/2006 |
| Publication: | Name: Applied Radiology Publisher: Anderson Publishing Ltd. Audience: Academic Format: Magazine/Journal Subject: Health Copyright: COPYRIGHT 2006 Anderson Publishing Ltd. ISSN: 0160-9963 |
| Issue: | Date: Sept, 2006 Source Volume: 35 Source Issue: 9 |
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| Accession Number: | 209239204 |
| Full Text: |
In the evaluation of vascular injuries, catheter angiography has
been the gold standard imaging modality. As computed tomography (CT)
technology has evolved, helical multislice CT (MSCT) angiography has
become an integral part of the initial assessment of many injured
patients. The ability to obtain high-resolution images with MSCT during
optimal contrast enhancement helps detect the presence and define the
extent of vascular injuries. CT angiography (CTA) has increasingly been
used to diagnose arterial injuries resulting from blunt and penetrating
trauma of the neck and extremities. (1-7) At our institution, CTA has
replaced angiography for diagnosis of most vascular injuries resulting
from penetrating and blunt trauma to these regions. This article
describes the author's current imaging protocol with MSCT, the
spectrum of diagnostic findings seen in vascular trauma, and the role of
CTA in the planning of vascular injury management. CTA technique Scan parameters of our MSCT examinations are as follows: 120 to 140 Kvp; 250 mAs. Other technical parameters vary according to the specific anatomic area and depend upon the specific CT scanner used; at our institution, we currently use 4-channel detector scanners (Table 1). The injection protocol utilizes 100 to 120 mL of intravenous nonionic contrast material at a rate of 4.5-mL/sec by means of a power injector via an 18-gauge catheter placed in an antecubital vein and an automated triggering device (bolus tracking). A fixed scan delay may be used at institutions where the automatic delay is not used or where it is not available (Table 1). An alternative method of establishing the scan delay is to use a test bolus. With the test bolus technique, a small contrast bolus is administered while scanning at a fixed level in the region of interest--for example, the aortic arch. From this test, a time-density curve is obtained. Axial images are reviewed at a workstation or picture archiving and communication system (PACS) station, and multiplanar reformations (MPR) or 3-dimensional (3D) renderings are obtained using volume rendering (VR) algorithms. Scrolling through the images on the PACS workstation using the cine mode allows for easy detection of subtle changes in vessel caliber and small extraluminal collections of contrast. Multiplanar reformations and 3D reconstructions are often useful in the interpretation of challenging cases as well as in planning subsequent interventions because most surgeons prefer these reconstructions that closely resemble the more familiar digital subtraction angiogram images. The 3D images are also useful in the evaluation of arterial segments that course in the plane of the axial CT, such as the subclavian and axillary arteries (Figure 1). CT findings of arterial trauma Direct signs of injury on CT angiography include irregular arterial margins and filling defects, contrast extravasation, lack of vascular enhancement, and vascular caliber changes. Indirect signs of vascular injury include indistinctness of the perivascular fat planes, perivascular hematoma, and bone and bullet fragments <5 mm from a major vessel. The presence of an indirect sign should be considered a potential indication for a conventional angiogram. The decision to perform a catheter angiogram on patients with indirect findings depends on the experience of the interpreter, the quality of the scan, and the clinical condition of the patient. In patients with an indirect finding around the carotid circulation, angiography is usually warranted because of the potential catastrophic consequence of missing an arterial injury on this location. The arterial lesions include intimal tears, dissections (which are visualized as intraluminal linear or round filling defects surrounded by contrast material on both sides) (Figure 2), and pseudoaneurysms (which are seen as extravascular collections of contrast medium) (Figure 3). The CT signs of a pseudoaneurysm also include irregularity of the vessel wall and an abrupt change in caliber (Figure 4). Partial or total occlusions are visualized as a lack of opacification following the administration of contrast material. Arteriovenous fistulas (AVFs) are visualized by early filling of venous structure (Figure 5). These AVFs represent simultaneous injury of an adjacent artery and a vein. The main CTA finding of vessel transection is the presence of prompt contrast extravasation into surrounding structures (Figure 6). The presence of active extravasation of contrast must be recognized because it indicates a need for urgent surgery to prevent exsanguination. Most patients with vessel transection are hemodynamically unstable and require immediate surgical intervention; therefore, these lesions are rarely encountered on CTA examinations. [FIGURE 1 OMITTED] [FIGURE 2 OMITTED] Neck Injuries to the neck are more frequently the consequence of penetrating trauma. The management of hemodynamically unstable patients who have suffered a penetrating neck injury is emergency surgical exploration. (8-12) On the contrary, the diagnostic evaluation of hemodynamically stable patients who present with wounds that penetrate the platysma muscle is still controversial. Most surgeons currently practice selective conservative management based on the use of multiple diagnostic studies including angiography. Recently, the use of invasive routine angiography in stable patients has been discouraged because of the high number of negative examinations (13-15) and the availability of alternative noninvasive diagnostic methods, such as helical or multislice CTA. (1,2,4,5-7) In some recent series, the sensitivity and specificity of CT angiography for diagnosis of cervical vascular injuries have been reported to be in the range of 90% to 100%. (1,4,5,7) CT angiography can also provide additional information about nonarterial injuries, such as those of the cervical spine and the aerodigestive tract. (2,4,7) In gunshot wounds to the neck, CT can delineate the bullet trajectory and help identify potential injuries, thus reducing the need for additional studies such as endoscopy and/or contrast esophageal studies in patients whose trajectories are clearly away from the aerodigestive tract. Further studies are needed to more precisely define the possible role of CT for the evaluation of the aerodigestive tract injuries. [FIGURE 4 OMITTED] [FIGURE 5 OMITTED] [FIGURE 6 OMITTED] Blunt traumatic injuries of the extracranial carotid and vertebral arteries have been regarded as uncommon injuries with potentially devastating consequences. Recent literature suggests that the true incidence of blunt cerebrovascular injury is higher than was initially described. (16) Centers performing an aggressive screening of selected patients using angiography have reported a higher incidence of 0.33 to 2.7%. (16-21) Although noninvasive techniques, such as multislice CTA and magnetic resonance angiography (MRA), have potential as screening tools in patients with blunt cerebrovascular injury, angiography is still considered the study of choice. (19-22) Recently, CT of the carotid and vertebral arteries in all trauma patients who are scheduled to undergo CT of the cervical spine has been recommended by Mutze et al. (21) The use of CTA as a screening method for these blunt cerebrovascular injuries will require further investigation. Extremities Vascular injury that involves the lower extremities is a serious complication following both penetrating and blunt trauma. In order to reduce morbidity and mortality, prompt diagnosis and subsequent treatment of these injuries are critical. Clinical signs of arterial injury include "hard signs" (such as pulsatile bleeding, expanding hematoma, pulse deficits, distal ischemia, and thrill/bruit due to AVFs) and "soft signs" (such as proximity of the injury to a major artery, stable hematoma, hypotension, and neurological deficit). (6) A penetrating wound in proximity to vascular structures is considered an indication for angiography only in cases in which a bullet follows the course of a major artery over a long segment. (6) Traditionally, patients who remain hemodynamically stable following lower extremity injury undergo evaluation with direct contrast angiography. However, this technique has limitations, including its invasive nature as well as transporting and monitoring issues. Additionally, this invasive procedure may result in unnecessary risks to these patients, as nonsurgical diagnoses (such as nonocclusive intimal flaps, partial narrowing, and branch vessel occlusions) may be revealed. Multislice CTA provides a rapid, minimally invasive study to evaluate lower extremity arterial injury. In addition, CTA aids in diagnosing the location, extent, and type of vascular injury to the lower extremity. Conclusion In many major trauma centers throughout the world, helical and multislice CTA is now being used for the evaluation of arterial injuries. The advantages of CTA include, among many others, the speed at which the examination can be completed and its minimally invasive nature. We believe that CTA might be warranted as an initial method of diagnosis in patients who are hemodynamically stable and who do not have an indication for immediate surgical exploration. CT angiography demonstrates the potential to discriminate between patients who require further invasive imaging/exploration and those who can be safely discharged home. Patients with direct signs of vascular injury on CT do not need further evaluation, and, at many centers, including our own, patients are taken to surgery without angiography. A minority of patients may still require digital subtraction angiography when CTA examinations are nondiagnostic or have equivocal or indirect findings. REFERENCES (1.) LeBlang SD, Nunez DB, Rivas LA, et al. Helical computed tomographic angiography in penetrating neck trauma. Emerg Radiol. 1997;4:200-206. (2.) LeBlang SD, Nunez DB Jr. Helical CT of cervical spine and soft tissue injuries of the neck. Radiol Clin North Am. 1999;37:515-532, v-vi. (3.) Soto JA, Munera F, Cardoso N, et al. Diagnostic performance of helical CT angiography in trauma to large arteries of the extremities. J Comput Assist Tomogr. 1999;23:188-196. (4.) Munera F, Soto JA, Palacio D, et al. Diagnosis of arterial injuries caused by penetrating trauma to the neck: Comparison of helical CT angiography and conventional angiography. Radiology. 2000; 216:356-362. (5.) Gracias VH, Reilly PM, Philpott J, et al. Computed tomography in the evaluation of penetrating neck trauma: A preliminary study. Arch Surg. 2001;136: 1231-1235. (6.) Soto JA, Munera F, Morales C, et al. Focal arterial injuries of the proximal extremities: Helical CT arteriography as the initial method of diagnosis. Radiology. 2001;218:188-194. (7.) Munera F, Soto JA, Palacio D, et al. Penetrating neck injuries: Helical CT angiography for initial evaluation. Radiology. 2002;224:366-372. (8.) Gens DR. Imaging priorities in the admitting area. In: Mirvis SE, Young YWR, eds. Imaging in Trauma and Critical Care. Baltimore, MD: Williams & Wilkins; 1992;1-22. (9.) Kendall JL, Anglin D, Demetriades D. Penetrating neck trauma. Emerg Med Clin North Am. 1998;16: 85-105. (10.) Demetriades D, Skalkides J, Sofianos C, et al. Carotid artery injuries: Experience with 124 cases. J Trauma. 1989;29:91-94. (11.) McIntyre WB, Ballard JL. Cervicothoracic vascular injuries. Semin Vasc Surg. 1998;11:232-242. (12.) Asensio JA, Valenziano CP, Falcone RE, Grosh JD. Management of penetrating neck injuries. The controversy surrounding zone II injuries. Surg Clin North Am. 1991;71:267-296. (13.) Demetriades D, Theodorou D, Cornwell E, et al. Evaluation of penetrating injuries of the neck: Prospective study of 223 patients. World J Surg. 1997; 21:41-47; discussion 47-48. (14.) Jarvik JG, Philips GR 3rd, Schwab CW, et al. Penetrating neck trauma: Sensitivity of clinical examination and cost-effectiveness of angiography. AJNR Am J Neuroradiol. 1995;16:647-654. (15.) Rivers SP, Patel Y, Delany HM, Veith FJ. Limited role of arteriography in penetrating neck trauma. J Vasc Surg. 1998;8:112-116. (16.) Smirniotopoulos JG, Mirvis SE, Lefkowitz DM. Imaging of craniocerebral trauma. In: Mirvis SE, Shanmuganathan K, ed. Imaging in Trauma and Critical Care. 2nd ed. Philadelphia, PA: Elsevier Science; 2003;27-132. (17.) Biffl WL, Moore EE, Ryu RK, et al. The unrecognized epidemic of blunt carotid arterial injuries: Early diagnosis improves neurologic outcome. Ann Surg. 1998;228:462-470. (18.) Fabian TC, Patton JH Jr, Croce MA, et al. Blunt carotid injury: Importance of early diagnosis and anticoagulant therapy. Ann Surg. 1996;223:513-522; discussion 522-525. (19.) Kerwin AJ, Bynoe RP, Murray J, et al. Liberalized screening for blunt carotid and vertebral artery injuries is justified. J Trauma. 2001;51:308-314. (20.) Biffl WL, Ray CE Jr, Moore EE, et al. Noninvasive diagnosis of blunt cerebrovascular injuries: A preliminary report. J Trauma. 2002;53:850-856. (21.) Mutze S, Rademacher G, Matthes G, et al. Blunt cerebrovascular injury in patients with blunt multiple trauma: Diagnostic accuracy of duplex Doppler US and early CT angiography. Radiology. 2005;237:884-892. (22.) Biffl WL, Moore EE, Offner PJ, et al. Optimizing screening for blunt cerebrovascular injuries. Am J Surg. 1999;178:517-522. Dr. Munera is an Assistant Professor of Radiology, Department of Radiology, University of Miami, Jackson Memorial Hospital, Ryder Trauma Center, Miami, FL. Table 1. Variable scan parameters used for multislice CT
angiography examinations
Anatomic Field Collimation Scan delay
region (cm) of view (mm) Pitch (sec)
Neck 20 1.33 0.88 20
Thoracic inlet 1.3 0.8 0.6 20-25
subdavian-axillary
Lower extremities 28-30 1.25 1.5 400
Anatomic
region (cm) Positioning Coverage
Neck -- Top of the aortic arch to base
of the skull
Thoracic inlet Arms raised Lower neck through
subdavian-axillary above the head aortic arch
Lower extremities -- Aortic bifurcation through
the ankle |
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