Findings Radiographics 2008 EKhalili Pouya Causal Factors traumatic severe blunt head and neck trauma spontaneous coughing vomiting sports cervical manipulationtrigger in ID: 917604
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Slide1
Craniocervical Arterial Dissection: Spectrum of Imaging Findings
Radiographics
2008
E.Khalili
Pouya
Slide2Causal Factors:traumatic
(severe
blunt head and neck
trauma)
spontaneous (coughing, vomiting, sports, cervical
manipulation),trigger in
pts
with underlying
arteriopathy
(FMD, Ehlers
Danlos
IV
,
Marfan
syndrome, autosomal dominant polycystic kidney disease, and
osteogenesis
imperfecta
type
I
Slide3Anatomic Distribution:The extracranial
segments of the carotid and vertebral arteries are much more likely to undergo dissection than their intracranial
segments
Extracranial
ICA dissection affects the cervical part of the artery distal to the carotid bulb and tends not to extend beyond its entry into the petrous portion
Slide4Slide5Slide6segments of the vertebral artery. V1 = between its origin and its entry into the transverse foramen of the C6 vertebra, V2 =
midcervical
course between the processes of C6 to C2, V3 = atlas loop region, V4 = intracranial segment. Note the asymmetric venous plexus enhancement around the V3 segment (arrow in a).
Slide7Color Duplex US:linear transducers (4–8 MHz).
Mural hematoma and thrombus may be detected as a thickened
hypoechoic
vessel
wall
Usually, wall hematoma and intraluminal thrombus cannot be differentiated with B-mode
imaginginner intimal echo helps in distinguishing wall hematoma from intraluminal thrombus or plaque in patients with thickening of the ICA wall
Slide8Slide9Slide10Slide11CT Angiography:Unenhanced
brain CT is helpful to document associated ischemic and hemorrhagic
events
scanning range from the aortic arch to the circle of
Willis
section thickness of 0.625
mm pitch of
0.9
80
mL of nonionic contrast medium (iodine, 350 mg/mL) followed by a saline bolus at a rate of 3.5 mL/sec.
Slide12ICA dissection is characterized by a narrow eccentric lumen with increase of the external diameter of the
artery
At unenhanced brain CT, a spontaneous crescent-shaped
hyperattenuating
area corresponding to a wall hematoma may be noticed in acute dissection at the upper portion of the cervical ICA. However, when correct window settings are applied for CT angiography, intramural hematoma appears
isoattenuating
to the surrounding muscles and cannot be differentiated from atherosclerotic thickening or thrombus Thus, familiarity with common dissection sites is essential to diagnose ICA dissection with CT angiography.
Slide13The typical target picture (narrow eccentric lumen surrounded by crescent-shaped mural thickening and thin annular enhancement) is a very specific yet less sensitive sign of arterial dissection
Peripheral enhancement is probably due to the contrast enhancement of the vasa
vasorum
in the adventitial layer
Other fairly reliable signs of arterial dissection are an intimal flap, a dissecting
aneurysm
Slide14Slide15Axial image from CT angiography obtained with the same window settings does not show any parietal abnormality.
Slide16On an axial image from CT angiography obtained with wide window settings (width = 500 HU, level = 100 HU), the intramural wall hematoma (arrow) is
isoattenuating
relative to the surrounding muscles and cannot be differentiated from atherosclerotic thickening.
Slide17Axial unenhanced brain CT image shows a crescent-shaped
hyperattenuating
area (arrow), which corresponds to an intramural hematoma in the right ICA.
Slide18Axial image from CT angiography shows the residual lumen (arrowhead)
Slide19Slide20Slide21Volume-rendered image from CT angiography shows a long tapered stenosis that begins distal to the carotid bulb (the string sign)
Slide22Slide23Slide24Vertebral Artery Dissection:Increased external diameter and crescent-shaped mural
thickening
both signs can be found in
nondissected
vertebral
arteries
typical target sign was also demonstrated intimal flap is less frequent than an intramural hematoma
Slide25Slide26Slide27Axial image shows intracranial extension of the dissection with crescent-shaped parietal thickening of the left V4 vertebral artery (arrow).
Slide28Slide29Potential Pitfalls: source images and reformatted 2D and 3D images from CT angiography can be affected by bone artifacts at the skull base and by dental artifacts
Slide30Slide31MR Imaging and MR Angiography:Time-of-flight (TOF) MR angiography can also demonstrate
subacute
intramural
hematoma
phase-contrast MR angiography and contrast-enhanced MR angiography demonstrate only the vessel
lumen
TOF MR angiography and contrast-enhanced MR angiography are commonly used to evaluate the intracranial and extracranial vessels, whereas experience with phase-contrast MR angiography is limited in carotid and vertebral artery dissection.
Slide32The hematoma shows a typical evolution of signal intensity related to the paramagnetic effects of the products of hemoglobin breakdown
.In
the early and chronic stage, the hematoma is usually
isointense
to surrounding structures, whereas between 7 days and 2 months it is almost invariably bright on T1-weighted images
.Acute
dissection can hardly be detected on T1-weighted images with fat saturation because isointense hematoma may be obscured when surrounded by isointense tissues.
Slide33The hematoma usually becomes isointense within 6 months or disappears
Subacute
hematoma is more clearly visualized on T1-weighted images with fat saturation and appears characteristically as a crescent-shaped
hyperintense
area around an eccentric flow void corresponding to the vessel lumen
Slide34Axial T1-weighted MR image shows
isointense
wall thickening of the right ICA (arrowheads), a finding consistent with an acute intramural hematoma (
oxyhemoglobin
or
deoxyhemoglobin
phase
Slide35fat-saturated T1-weighted MR image obtained in another patient shows slightly
hyperintense
wall thickening of the left ICA (arrowheads), a finding consistent with an early
subacute
intramural hematoma (
methemoglobin
phase).
Slide36Axial T1-weighted MR images obtained with fat saturation (a obtained at a higher level than b) show a narrowed eccentric flow void (arrowhead) surrounded by a crescent-shaped circumferential
subacute
intramural hematoma that expands the vessel diameter. The hematoma spirals around the
vessel lumen
.
Slide37The criteria used for dissection are:increase
in the external diameter of the artery and narrowing of the lumen.
flow
void narrowing is a less useful indicator of dissection because it can be encountered in other conditions.
“
train track” sign, a sign of
poststenotic laminar flow in the petrosal
horizontal portion of the ICA, can be mistaken for
intrapetrous
extension of ICA dissection
.
Increase
in the external diameter of the artery may be present in cases of dissecting aneurysm
Slide38MR imaging is not as helpful in diagnosis of vertebral artery dissection Dissection at V2 may be difficult to identify because inflow enhancement in the venous plexus of the foramen
transversarium
may mimic
subacute
hematoma
Another problem with diagnosis of vertebral artery dissection is the common exclusion of V1 from the imaged volume MR imaging demonstrated excellent sensitivity in diagnosis of internal carotid dissection
Slide39Axial
T1-weighted MR image obtained with fat saturation shows
hyperintense
crescent-shaped mural thickening, a finding consistent with a
subacute
intramural hematoma. Note the intermediate signal intensity of the venous plexus around the left vertebral artery and in the anterior epidural space.
Slide40Three-dimensional TOF MR image shows
pseudoenlargement
of the lumen due to a
subacute
intramural hematoma (arrowhead).
Slide41Axial
diffusion-weighted MR image demonstrates the
hyperintense
subacute
intramural hematoma (arrowhead) owing to the T2 “shine-through” effect.
Slide42contrast-enhanced MR angiography of the cervical vasculature occasionally results in segmental blurring or signal intensity loss within the vertebral arteries, especially in young patients with rapid circulation
times
This “feathering” artifact results from rapidly changing signal intensity in small vascular structures around the vertebral arteries
This
pseudostenosis
artifact may mimic vertebral artery dissection
Slide43Our protocol for craniocervical arterial dissections
:
cross-sectional
T1-weighted
+
fat saturation of the neck
contrast-enhanced MR angiography.Additional axial T1- and T2-weighted images may be required in cases of acute dissections.
nonenhanced
MR angiography when gadolinium-containing contrast agents are contraindicated.
Slide44Digital Subtraction Angiography: string sign, the angiographic hallmark of ICA dissection, is a long, tapered, usually eccentric and irregular stenosis that begins distal to the carotid bulb
Focal narrowing with a distal site of dilatation is referred to as the “string and pearl”
sign
Pathognomonic signs, such as a double lumen or intimal flap, are rarely observed
“flame” sign, a tapered occlusion that spares the carotid bulb, is highly suggestive of dissection
Slide45Angiogram shows the string sign (thin arrow) and the “string and pearl” sign (thick arrow), findings consistent with bilateral ICA dissections. Note the “string of beads” sign (arrowhead), which is consistent with
fibromuscular
dysplasia of the left vertebral artery.