AJR 2000; 174:1269-1278
© American Roentgen Ray Society
Noninvasive Imaging of Cervical Vascular Injuries
Suzanne D. LeBlang1 and
Diego B. Nunez, Jr.
1
Both authors: Department of Radiology (R-109), University of Miami School of
Medicine, 1611 N.W. 12th Ave., Miami, FL 33136-1094
Received October 8, 1998;
accepted after revision October 7, 1999.
Address correspondence to D. B. Nunez.
Introduction
The evaluation of patients with suspected vascular injuries to the neck is
controversial. Clinical examination has a low (61%) sensitivity
[1]. The use of routine
screening angiography has been challenged because of the high number of
negative examinations [2,
3], and routine surgical
exploration has been largely abandoned because of the high morbidity rate
[4]. Recently, more noninvasive
and rapid screening techniques have been introduced. Duplex sonography can
accurately screen for arterial injuries in patients with penetrating neck
injuries
[5,6,7]
and is thought to be underused in the evaluation of blunt arterial neck trauma
[8]. Helical CT angiography has
emerged as an effective diagnostic examination for the evaluation of cervical
vascular injury [9]. Axial
imaging clearly shows the trajectory of the penetrating injury and provides
objective evidence of proximity and actual injury to neck vessels. Axial
imaging also reveals spinal fractures and canal compromise, and can reveal
indirect signs of pharyngoesophageal injury
[9,10,11].
The use of MR imaging and MR angiography has not been specifically evaluated
in patients with penetrating or blunt trauma, but several reports describe the
ability of both techniques to reveal various types of vascular lesions
[12,13].
The routine screening of patients with penetrating injuries is warranted
because of the high (36%) incidence of vascular injuries in these patients
[7,8,9].
Conversely, the very low incidence of vascular injuries (0.67%) caused by
blunt trauma supports a more selective screening of patients using noninvasive
imaging techniques [8,
14,15,16,17,18].
This article reviews the current status of noninvasive imaging examinations
for detecting traumatic arterial neck lesions including duplex sonography,
helical CT angiography, and MR imaging. The techniques of these diagnostic
examinations (including the advantages and limitations) and appearance of
specific lesions will be discussed. Although specific vascular lesions present
with similar imaging features regardless of location, particular diagnostic
and therapeutic considerations will be made for the carotid and vertebral
circulations.
Imaging Techniques
Duplex Sonography
Duplex sonography is routinely used to screen for atherosclerotic disease
and can depict various associated lesions such as intimal flaps, dissections,
occlusions, and pseudoaneurysms. Therefore, it is not surprising that several
authors report 92-100% sensitivity for detecting these arterial lesions in
penetrating neck trauma
[5,6,7,
19,
20]. Studies include
longitudinal and transverse gray-scale images, longitudinal color-flow images,
and spectral waveform analysis. Montalvo et al.
[5] found that color-flow
sonograms alone revealed all normal and injured vessels and may be adequate as
a rapid screening examination in the acute setting. Demetriades et al.
[19,
20] reported that clinical
examination combined with duplex sonography detected all significant vascular
injuries. Important limitations of duplex sonography include the inability to
directly evaluate the distal internal carotid artery above the angle of the
mandible (zone III) and the more proximal segment under the clavicle (zone I).
Doppler waveform analysis can reveal turbulent or high-resistance flow
suggestive of a remote lesion in the nonvisualized distal internal carotid
artery. Abundant subcutaneous air may prohibit evaluation of the vessels by
blocking wave transmission. Although no studies have reported the accuracy of
sonography in screening blunt trauma patients, duplex sonography is probably
underused as a screening examination in this setting
[8].
Helical CT Angiography
Similar to sonography, helical CT angiography has proven sensitive in
evaluating carotid atherosclerosis and traumatic arterial injuries. In
penetrating neck trauma, helical CT angiography is 100% sensitive in detecting
arterial lesions using both indirect and direct signs of vascular injury
[9]. The indirect findings
include bone and bullet fragments less than 5 mm from a major vessel, path of
the injury through a vessel, and a hematoma in the carotid sheath. Direct
findings of vascular injury include wall irregularity, contrast extravasation,
lack of vascular enhancement, and caliber changes. Although most lesions are
directly visualized on helical CT angiography, small lesions (<2 mm) may
only be suggested by indirect findings. Our most recent protocol consists of a
3-mm slice collimation with a 1.5:1 pitch, 19-cm field of view, and a scan
delay of 20-30 sec after 100 ml of nonionic bolus is injected at 2-3 ml/sec.
Only the axial images are used for interpretation, although two-dimensional
and three-dimensional reconstructions that simulate conventional angiographic
views can be obtained. Other researchers have substantiated the efficacy of
helical CT angiography as a screening examination for penetrating vascular
injury (Melev JD et al., presented at the American Roentgen Ray Society
meeting, April-May 1998, and Munera F, unpublished data).
Helical CT angiography may be limited in revealing low zone I injuries
because of shoulder streak artifacts and the nonperpendicular course of the
subclavian vessels with respect to the axial CT slices. However, the anatomic
data from the CT scan can be used to indicate proximity to arteries low in
zone I of the neck (below the cricoid cartilage) by showing the path of
injury. Then, if necessary, other more definitive examinations, such as
angiography, can be performed. The trajectory depicted in axial slices adds
critical information. Hollerman et al.
[21] found that "all
seriously damaged structures have been contacted by the intact bullet or
secondary missiles such as bone and bullet fragments." In addition,
retained metallic densities may create streak artifacts that obscure portions
of the vessels. When the vessels are obscured, the trajectory and associated
indirect findings of vascular injury determine the need for any further
workup. To date, the detection of arterial lesions caused by blunt trauma has
not been studied with helical CT angiography. However, vascular lesions have
similar imaging characteristics regardless of the mechanism of injury and thus
future studies may prove its efficacy in this setting.
MR Imaging and MR Angiography
To our knowledge, no reports have been made in the literature regarding the
use of MR imaging for vascular neck trauma. Although a discussion of MR
angiography is beyond the scope of this paper, review articles discuss the
various techniques available such as two-dimensional or three-dimensional
time-of-flight and phase contrast
[22]. Levy et al.
[12] detected carotid
dissections on MR angiography with 95% sensitivity compared with 84%
sensitivity on conventional T1-weighted and T2-weighted sequences, both having
99% specificity. Conversely, the sensitivity for vertebral artery dissections
was only 20% with MR angiography three-dimensional gradient-echo sequences
[12,
13] and 60% for conventional
T1-weighted and T2-weighted sequences, both having 98-100% specificity. The
lower sensitivity of MR angiography was probably related to the difficulty in
detecting caliber changes with the inherent asymmetry of the vertebral
arteries. MR angiography can give a false-negative result because the
high-signal-intensity intramural hematoma is indistinguishable from the
flow-related enhancement in the vessel lumen.
MR imaging of the neck vasculature is continuously evolving. Recently, much
attention has focused on gadolinium-enhanced MR angiography. Important
advantages of this newer application include the ability to rapidly image the
carotid, vertebral, and proximal subclavian arteries from the aortic arch
through the Circle of Willis
[23]. Such a comprehensive
examination may be particularly applicable in evaluating blunt traumatic
arterial injuries where the level of injury is unknown. Additional
conventional MR images of the brain may also show intracranial complications
before CT scans. However, patient monitoring and transport can be cumbersome
for the acutely ill patient. The use of MR imaging is limited in certain cases
of penetrating trauma because of residual metallic debris.
Carotid Artery
More than 80% of cervical vascular injuries involve the carotid arteries
[24]. Most of these injuries
are caused by penetrating trauma. The mortality from penetrating trauma is
higher (22%) than from blunt injuries (7%), although the incidence of stroke
is much higher from blunt trauma (56% versus 15%, respectively)
[18,
25,
26]. Damage to the internal
carotid artery results in a higher stroke rate and mortality rate (41% and
21%, respectively) compared with those of the common carotid artery (11% and
11%, respectively) [25]. Given
these statistics, the available literature has yet to distinguish the
diagnostic evaluation and therapeutic options for lesions involving the
internal carotid artery versus the common carotid artery; however,
differentiation can be made on the basis of the type of arterial abnormality,
regardless of the mechanism of injury.
Occlusion
Vessel occlusion is the most common type of carotid artery injury in
penetrating and blunt trauma. Vessel occlusion occurs in 36% of penetrating
injuries to the internal carotid artery
[26] and 33% of all blunt
carotid artery injuries [16].
Interestingly, traumatic occlusion results in the highest mortality rate (40%)
among all blunt carotid artery injuries
[16]. On sonography,
occlusions are best indicated by a lack of color flow
(Fig. 1A). Gray-scale images
may show clots of variable echogenicity or an intimal flap
(Fig. 1B). Other findings
include a high impedance waveform with absent or reversed diastolic flow
(preocclusive thump pattern) (Fig.
1C). However, this spectral waveform pattern is not specific for
occlusions and can be seen with high-grade stenoses and, thus, another
confirmatory examination such as angiography is recommended
(Fig. 1D).
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Fig. 1A. —25-year-old woman ejected from car presented at 8 on Glasgow Coma
Scale and developed clinical and radiographic signs of left middle cerebral
artery infarct. Longitudinal color sonogram reveals bidirectional flow in
proximal left internal carotid artery (black arrows) and nonfilling
of more distal artery (white arrow), consistent with occlusion.
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Fig. 1B. —25-year-old woman ejected from car presented at 8 on Glasgow Coma
Scale and developed clinical and radiographic signs of left middle cerebral
artery infarct. Longitudinal gray-scale sonogram shows linear echogenicity
(arrows), representing underlying intimal flap.
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Fig. 1C. —25-year-old woman ejected from car presented at 8 on Glasgow Coma
Scale and developed clinical and radiographic signs of left middle cerebral
artery infarct. Spectral waveform analysis of internal carotid artery bulb
shows absent diastolic flow (preocclusive thump pattern).
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Fig. 1D. —25-year-old woman ejected from car presented at 8 on Glasgow Coma
Scale and developed clinical and radiographic signs of left middle cerebral
artery infarct. Oblique arteriogram of common carotid artery reveals severe
narrowing of internal carotid artery, indicative of dissection
(arrow) leading to total occlusion.
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Helical CT angiography reveals occlusions as a lack of vascular
enhancement, with or without proximal dissection (Fig.
2A,2B).
The direct visualization of a contrast-enhanced string sign allows
differentiation of an occlusion from a high-grade stenosis.
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Fig. 2A. —22-year-old man with gunshot wound to zone III right neck in whom
neurologic examination findings were normal. Axial helical CT angiogram
reveals normal enhancement in right internal carotid artery (solid
arrow) and no enhancement in region of left internal carotid artery
(open arrow), indicating occlusion.
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Fig. 2B. —22-year-old man with gunshot wound to zone III right neck in whom
neurologic examination findings were normal. Lateral view from common carotid
arteriogram confirms total occlusion (arrow) of internal carotid
artery.
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Several reports describe the MR appearance of occlusions caused by
spontaneous dissection or atherosclerotic disease
[12,
13,
42,
46]. Conventional T1-weighted
and T2-weighted spin-echo MR sequences lack the normal signal void and have
increased signal intensity. On MR angiography, occlusions manifest as a lack
of flow-related enhancement. The majority of cases were correctly diagnosed as
occlusions, although a few false-negative and false-positive cases caused by
technical factors have been reported. The axial source images need to be
carefully analyzed to detect any residual flow-related enhancement. In
questionable cases, two-dimensional phase-contrast images are more sensitive
to slow-flow states that may otherwise manifest as an occlusion
[22]. Evaluation for the
string sign may be limited because visualization depends on flow-related
enhancement. Gadolinium-enhanced MR angiography will probably improve the
detection and differentiation of high-grade stenoses from occlusions by
detecting the signal from the IV contrast material flowing within the lumen
versus the physical motion of blood.
Treatment options for arterial occlusion include definitive endovascular
embolization, anticoagulation, or revascularization procedures, such as
surgical bypass or primary vessel repair
[26,27,28,29].
Similar to the current revascularization procedures performed during acute
strokes, surgical revascularization is probably beneficial during a small
window of time. Advanced imaging techniques, such as perfusion and diffusion
MR imaging, may prove useful in selecting those patients in whom
revascularization procedures would be most beneficial.
Pseudoaneurysms
Carotid pseudoaneurysms, commonly referred to as false aneurysms, are
caused by partial or complete disruption of the vessel wall resulting in a
periluminal hemorrhage contained by the surrounding soft tissues.
Pseudoaneurysms are common in penetrating injuries to the neck and account for
33% (20/61) of lesions to the internal carotid artery as reported by Kuehne et
al. [26]. Patients with
pseudoaneurysms may present with neurologic symptoms in 40% of cases, and up
to 56% can present with a palpable mass. Epistaxis, otorrhagia, and hemorrhage
may also occur. Still, many patients remain asymptomatic
[30]. In blunt trauma,
pseudoaneurysms are rare and have only a 9% mortality rate
[16].
Sonography shows widening of the vessel contour (Fig.
3A,3B)
and variable color flow, depending on whether the pseudoaneurysm is thrombosed
[9]. Spectral waveform analysis
shows a characteristic turbulent to-and-fro flow.
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Fig. 3A. —59-year-old man who attempted suicide by gunshot to zone II left
neck. Longitudinal color sonogram of left common carotid artery shows
pseudoaneurysm (PSA) with partial thrombus (T) and intimal flap (F).
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Fig. 3B. —59-year-old man who attempted suicide by gunshot to zone II left
neck. Lateral view from common carotid arteriogram confirms the pseudoaneurysm
(thick arrow) and intimal flap (thin arrow).
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On helical CT angiography, pseudoaneurysms are seen as an irregular
widening of the vessel contour with an outpouching of contrast from the vessel
lumen [9]. Even small
pseudoaneurysms are easy to detect because the carotid arteries should be
symmetric with a round contour (Fig.
4A,4B).
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Fig. 4A. —21-year-old man who presented with stab wound to right neck
traversing zones I and II. Axial slice from helical CT angiogram reveals
irregular contour of proximal right common carotid artery with contrast
material extending outside confines of vessel lumen (large straight
arrow) corresponding to site of pseudoaneurysm formation. Note hematoma
surrounding artery (small arrows) and fracture through right lobe of
thyroid gland (curved arrow).
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Fig. 4B. —21-year-old man who presented with stab wound to right neck
traversing zones I and II. Anteroposterior view from arteriogram shows
pseudoaneurysm (arrow) of proximal right common carotid artery.
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MR imaging can detect some pseudoaneurysms, which are similar in appearance
to true aneurysms. However, pseudoaneurysms may not be seen
[31] because of flow-related
artifacts and thus MR imaging is not a reliable examination for detecting such
lesions.
The treatment of pseudoaneurysms is variable. McCann
[30] reported a combined
stroke and mortality rate of 45% after surgical ligation of the parent vessel,
23% with observation only, and 10% if the native vessel was reconstructed and
repaired. In lesions involving the more distal inaccessible internal carotid
artery, occlusion of the parent vessel (by surgical ligation or embolization)
or bypass surgery (cervical to petrous carotid or external carotid-internal
carotid bypass) can be performed
[27]. Conservative observation
may lead to enlargement, spontaneous resolution, thrombosis, or no change
[26]. Currently, no findings
have been found to prognosticate whether lesions will improve. Prospective
studies need to be performed to study whether anticoagulation should be used
with clinical observation.
Intimal Flaps and Dissection
In blunt trauma, as many as 33% of arterial injuries in the neck are a
result of an underlying dissection and the mortality rate is 8%
[16]. This dissection is rare
in penetrating trauma, occurring in fewer than 2% of patients
[25]. Most blunt traumatic
dissections result from hyperextension and rotation, hyperflexion, or lesser
trauma such as chiropractic manipulation. If no definable event preceded the
injury, it is labeled spontaneous or a result of an underlying predisposing
condition (hypertension, fibromuscular dysplasia, or connective tissue
diseases). Although most injuries affect the proximal internal carotid artery,
Resnick et al. [32] reported
that fractures of the skull base caused by significant blunt trauma involving
the carotid canal resulted in a 20% incidence of injury to the petrous portion
of the internal carotid artery.
Cervical dissections may be clinically silent; 50% of patients present with
a normal or nonfocal examination consisting of headaches and neck pain
[33]. The other 50% can
develop symptoms such as transient ischemic attacks, Horner's syndrome, or a
neck bruit caused by a dissection with slow propagation of thrombus or delayed
embolization [18,
33]. Diagnosis is often
delayed in such patients because symptoms can be attributable to closed head
trauma or other major injuries to the chest and abdomen that need immediate
attention. Clinical indications to proceed with the diagnostic examination for
vascular injuries in blunt trauma include: neurologic symptoms that are not
explained by CT findings in the brain or spine; monoparesis or hemiparesis
with a normal mental status; severe cervical trauma with abnormal physical
examination; or basilar skull fractures with abnormal mental status
[32,
34]. Because many of these
findings are seen in patients meeting trauma criteria and the incidence of
vascular injury is low, the noninvasive screening of patients is
warranted.
Duplex sonography can reveal numerous changes that indicate a dissection
and is inexpensive, noninvasive, and fast. Sonography shows abnormal color
flow with diminished forward flow and, at times, reversal of flow (Fig.
5A,5B,5C).
A linear filling defect that represents the intimal flap may be seen. Dampened
spectral waveforms with persistent yet decreased antegrade flow in diastole
suggest a nonocclusive dissection. Sequential sonographic examinations can
easily monitor dissections and reveal progression to occlusion or
improvement.
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Fig. 5A. —46-year-old man presenting with diploplia and right-sided headaches
after trivial head trauma. Longitudinal view of color sonogram shows
incomplete filling of internal carotid artery (arrow) with some
reversal of flow more distally (arrowheads).
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Fig. 5B. —46-year-old man presenting with diploplia and right-sided headaches
after trivial head trauma. Spectral waveform reveals decreased diastolic flow
suggesting more distal narrowing or occlusion. Common carotid arteriogram (not
shown) confirmed severe stenosis from long segment dissection.
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Fig. 5C. —46-year-old man presenting with diploplia and right-sided headaches
after trivial head trauma. After 6 months of anticoagulation therapy,
follow-up sonogram revealed normal antegrade color flow (red) in
internal carotid artery.
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Helical CT angiographic findings of acute vessel dissection are similar to
those seen on MR images and include a narrowed eccentric lumen with
enlargement of the vessel diameter caused by an intramural hematoma. As
previously mentioned, the normal symmetric appearance of the carotid arteries
aids in the evaluation of dissections. LeClerc et al.
[35,
36] have described numerous
examples of carotid dissections shown on helical CT angiography. Associated
findings include mural thickening, aneurysm formation, and arterial occlusion.
Nonocclusive dissections or intimal flaps can also present as a focal
intraluminal filling defect with contrast opacification distal to the lesion
[9] (Fig.
6A,6B).
At the skull base, helical CT angiography may prove helpful; unlike
sonography, it directly visualizes the internal carotid artery and does not
have as many flow-related artifacts as MR imaging. Helical CT angiography
reveals findings similar to those of catheter angiography and provides
additional information regarding wall thickening and the true extent of
pseudoaneurysm formation, regardless of the amount of thrombosis
[35,36,37].
MR imaging reveals a dissection as an increase in the external diameter of
the artery with narrowing of the residual lumen compressed by the
high-signal-intensity intramural hematoma
[12] (Fig.
7A,7B,7C,7D,7E).
On conventional sequences, T1-weighted axial fat-suppressed images are useful
in detecting the high-signal-intensity intramural hematoma in contrast to the
surrounding tissues. On MR angiography, the high-signal-intensity hematoma
caused by methemoglobin may be similar to the high-signal-intensity
flow-related enhancement in the residual lumen. Therefore, careful evaluation
is necessary to avoid a false-negative finding.
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Fig. 7A. —40-year-old man who presented with acute right-sided Horner's
syndrome. Axial T1-weighted image with fat saturation shows crescentic
high-signal-intensity intramural hematoma (arrow) around right
internal carotid artery compressing residual lumen, which is still with normal
signal void.
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Fig. 7C. —40-year-old man who presented with acute right-sided Horner's
syndrome. Axial MR angiography T2-weighted source image, at same level as
A, reveals posterior crescentic hematoma with slightly less signal
intensity (arrow) than narrowed residual lumen
(arrowhead).
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Fig. 7D. —40-year-old man who presented with acute right-sided Horner's
syndrome. Oblique projection from maximum-intensity-projection MR angiogram
confirms dissection with less intense signal intensity in intramural hematoma
(arrowheads) compared with residual lumen. Also note focal
enlargement in vessel diameter inferior to dissection representing
pseudoaneurysm (arrow).
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The natural progression of dissection is variable. Intimal flaps can either
resolve spontaneously or evolve into a more severe dissection and produce
vessel occlusion. Additionally, it can serve as a nidus for thrombus formation
with distal embolization. Anticoagulation is often used in the nonoperative
treatment of intimal flaps and dissections to prevent thrombus and distal
embolization [16]. More than
90% of patients with spontaneous dissections have a good prognosis with
conservative anticoagulant therapy
[33]. Other therapeutic
options include endarterectomy, bypass, interposition graft, endovascular
occlusion, or surgical ligation
[26].
Arteriovenous Fistula and Transection
Patients with injuries that are more clinically apparent usually undergo
catheter angiography for rapid diagnosis and treatment rather than a
noninvasive screening. Demetriades et al.
[19,
20] suggested that patients
presenting with a bruit should proceed directly to angiography for diagnostic
and therapeutic purposes, given the likelihood of finding an arteriovenous
fistula. Patients with a transected vessel usually present with hypotension or
an expanding hematoma, and have a 100% mortality rate in blunt trauma
[16]. Such patients can be
treated with surgical repair, in the unstable patient, or with endovascular
occlusion, provided that adequate collateral circulation exists.
Vertebral Artery
In blunt trauma, vertebral artery injuries are more common than carotid
injuries. It is paradoxic that the spinal column that is supposed to protect
the vertebral artery also renders it particularly susceptible to injury. The
artery can be directly injured from transverse foramen fractures or indirectly
damaged as it stretches across the surrounding bones. In blunt trauma,
vertebral artery injuries were detected on catheter angiography in 46% of
patients with transverse foramen fractures and 75% with facet dislocations
[38,
39]. Yee et al.
[40] and Golueke et al.
[41] found that nearly 44% of
patients with vertebral artery injuries had spine fractures, almost all caused
by penetrating trauma. Bear et al.
[11] found 42% (21/50) of
patients with gunshot wounds to the neck had spinal fractures and 43% (9/21)
had a vertebral artery injury. They concluded that if there are no cervical
spine fractures and the bullet trajectory does not cross the vertebral artery,
a vascular injury to this vessel is unlikely.
Patients with vertebral artery lesions can be asymptomatic, have
nonspecific findings such as headaches and neck stiffness, or develop
transient ischemic attacks and stroke. Willis et al.
[38] reported that all of
their 12 patients with proven blunt vertebral artery injuries were
asymptomatic with respect to their vascular injuries. These patients more
often suffered neurologic symptoms referable to the spinal cord or nerve root
damage. In penetrating trauma, only 2.6% (1/39) of patients had neurologic
symptoms caused by vertebral artery injury manifesting as transient
vertebrobasilar ischemia [40,
41]. In contrast, patients
with spontaneous vertebral artery dissections present more frequently (56%)
with vertebrobasilar ischemic symptoms
[42]. Dissections of the
intradural segment of the vertebral artery can also present with subarachnoid
hemorrhage. Therefore, one should not assume that posterior fossa extraaxial
blood is necessarily the result of blunt head trauma
[43,
44].
Because vertebral artery injuries are common in patients with complex
cervical spine fractures, the routine screening of such patients for vertebral
artery injuries may be justified. Although Montalvo et al.
[5] found no significant
difference between duplex sonography and catheter angiography in detecting
various vertebral artery injuries, small lesions can potentially be missed in
segments that are nonvisualized as a result of shadowing from the transverse
processes. Because CT is the most sensitive examination for detecting cervical
spine fractures in patients with significant blunt or penetrating trauma
[9,
45], the concomitant use of IV
contrast material could allow screening of both the vertebral and carotid
arteries. Helical CT angiography reveals occlusions as nonopacification of the
vertebral artery (Fig.
8A,8B,8C).
On MR imaging, occlusions are seen as a loss of the normal signal void on all
MR imaging and a lack of flow-related enhancement on angiographic sequences.
To our knowledge, the evaluation of vertebral artery dissections with helical
CT angiography has not been reported. As previously discussed, MR imaging and
MR angiography are not as sensitive for detecting vertebral dissections as for
detecting carotid dissections
[12]. When present, vertebral
dissections show a crescentic intramural hematoma with a narrowed eccentric
signal void lumen or a double-lumen sign if both the true and false channel
have antegrade flow [12,
42,
46]
(Fig. 9). Several factors are
responsible for the low sensitivity, including inherent asymmetry of the
vertebral arteries, poor delineation of the intermediate- to
high-signal-intensity intramural hematoma against the surrounding
mixed-signal-intensity soft tissues, and flow-related enhancement in the
vertebral veins that may mimic a dissection
[46]. Because of the low
sensitivity of MR imaging on all sequences, any alteration in the normal
appearance of the vertebral artery in a patient at risk for injury should be
evaluated more definitively. Small pseudoaneurysms may be obscured by the
surrounding bones on helical CT angiography and missed on MR imaging because
of flow-related artifacts [12,
13]. Thus, catheter
angiography remains the gold standard in evaluating the cervical vertebral
arteries but may not be cost-effective as a screening examination.
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Fig. 8A. —14-year-old boy with gunshot wound across zone II who presented as
C4-level quadreplegic. Axial helical CT angiogram filmed in bone windows shows
path of bullet and fractures across C4 vertebral body involving both
transverse foramina. Note contrast-enhanced right vertebral artery (white
arrow) and nonvisualization of left vertebral artery (black
arrow) in left transverse foramen.
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Fig. 8B. —14-year-old boy with gunshot wound across zone II who presented as
C4-level quadreplegic. Axial T1-weighted MR image shows horizontal fracture
extending through vertebral body and both transverse foramina. Note normal
signal void in right vertebral artery (arrow) but lack of flow void
in region of left vertebral artery (arrowhead).
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Fig. 8C. —14-year-old boy with gunshot wound across zone II who presented as
C4-level quadreplegic. Coronal maximum-intensity-projection image from
two-dimensional time-of-flight MR angiogram, acquired with axial slices,
reveals absent flow-related enhancement of left vertebral artery beyond origin
consistent with occlusion (short arrow). Also note external
compression of right vertebral artery at level of fracture (long
arrow).
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Fig. 9. —63-year-old woman who sustained iatrogenic vertebral artery injury
during conventional angiography. Coronal maximum-intensity-projection image
from three-dimensional time-of-flight MR angiogram shows enhancement in two
separate lumens of left vertebral artery consistent with dissection
(arrows). Flow is antegrade within true and false lumina because
presaturation pulse was used to suppress venous signal on source images.
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After detection, the treatment of vertebral artery injuries remains
controversial. Yee et al. [40]
reported that nonocclusive narrowings and occlusions can be safely observed.
Other researchers have suggested using transcatheter embolization to prevent
distal clot embolization (Becerra JL et al., presented at the American Society
of Emergency Radiology meeting, March 1993). Small lesions such as
nonobstructing intimal flaps and small pseudoaneurysms can be closely
monitored, with or without anticoagulation, and may even resolve
[47]. Other vertebral artery
abnormalities resolve in 70-80% of patients, few progressing to occlusion
[42,
46]. Pseudoaneurysms,
arteriovenous fistulas, and lacerations can be treated with interventional
embolization or surgical ligation. For definitive therapeutic procedures,
interventional techniques are favored because surgical access to the vertebral
artery is technically difficult. Endovascular embolization should be performed
proximal and distal to the site of injury to prevent retrograde filling of the
lesion from the contralateral vertebral artery and collaterals. Documenting
the presence of the contralateral vertebral artery and its connection to the
basilar artery is imperative as part of the angiography and before any
therapeutic procedure.
Summary
Various imaging examinations can be used to diagnose cervical vascular
injuries. The challenge in the current medical environment is to choose the
imaging examination that is the most rapid, least invasive, and least costly.
One must recognize the ability of each technique to detect lesions, taking
into consideration the type of abnormality and whether the carotid or
vertebral arteries are at risk for injury.
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Top
Introduction
Imaging Techniques
