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8 • Imaging for the Evaluation and Treatment of Vascular Trauma 95
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Fig. 8.3 Pelvic crush injury with external iliac artery dissection. (A) A 25-year-old man sustained a crush injury to the pelvis. three-dimen-
sional (3-D) computed tomography angiography (CTA) (left) and digital subtraction angiography (DSA) (right) demonstrate interruption of
the external iliac artery due to dissection and thrombosis. (B) After recanalizing the occluded external iliac artery with self-expanding bare metal
nitinol stents, intimal flap and thrombus are seen at the level of the inguinal ligament, distal to the stents. (C) Extravasation of contrast is seen
after placement of an overlapping stent. This was successfully treated with a covered stent. (D) Embolization of thrombus to the anterior tibial
and peroneal arteries is demonstrated with DSA. Acute arterial occlusion results in a sharp cut off of the contrast and almost no collateral flow.
Aspiration thrombectomy cleared the distal vessels of thrombus. (E) The final arteriogram (left) shows the stented left external iliac artery to be
patent. The distal vessels show smooth tapering, consistent with vasoconstriction. Vasospasm is commonly seen in younger patients, as trauma
patients often are. The posterior and anterior elements of the fractured pelvis were subsequently stabilized with compression screws (right).
(F) Follow-up CTA (left) and duplex scan (right) confirm patency of the injured segment and normal flow patterns after treatment with stenting.
structures, but a small vessel disrupted by fractures can
bleed substantially and transcatheter angiography often
directly identies these sources of bleeding. Endovascular
treatment with embolization is effective for management of
hemodynamically unstable patients with pelvic fractures,
though external xation and pelvic packing may be better
initial therapies.
13,14
As detailed in another chapter of this textbook, selective
catheterization with ow-directed particulate embolization
is one method of controlling bleeding from small arteries at
sites of injury.14 Embolic coils may be deployed to proximally
occlude an injured vessel, but temporary occlusion alone
may be inadequate for pelvic trauma. As such, catheterdirected use of inexpensive and readily available materials,
such as Gelfoam pledgets or slurry into the source vessels
(Upjohn, Kalamazoo, MI) can also be effective.
Angiographic ndings indicative of extremity vascular
injury or disruption include uncontained extravasation
of contrast, pseudoaneurysm or contained extravasation
of contrast, arteriovenous stulae, intimal tear, spasm, or
occlusion. Covered stents and other endovascular strategies can be used for extremity vascular injuries (although
the benet of peripheral artery endovascular therapy is
less obvious than the superiority of endovascular treatment of blunt traumatic aortic injuries).15 Because injuries
in patients who are in shock require immediate attention
and because extremity vascular injuries are often associated with skeletal, soft-tissue, or other trauma, open surgical repair remains the more common approach. Still,
endovascular techniques may be advantageous when the
extremity exposure is difcult or associated with considerable morbidity, as with injuries to the subclavian or axillary arteries.
Operative strategy may vary with the situation. Factors to
consider include the patient’s hemodynamic and physiologic
status, the level of endovascular expertise, the quality of the
available imaging systems, and the inventory. Endovascular
maneuvers may be used to temporize or denitively control
hemorrhage (e.g., balloon catheter occlusion or embolization). Some endovascular treatments may be safely delayed
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and not performed for hours, or even days after the original
injury, for example, TEVAR for mild or moderate blunt traumatic aortic injury (BTAI) (see Fig. 8.2).
9
Surgeon training and experience (or the availability
of an interventional specialist) may determine whether
an open surgical therapy, an endovascular treatment, or
a mixed or hybrid approach is most practical for a given
injury scenario. Simple endovascular maneuvers for arterial access and pressure monitoring, hemorrhage control
and resuscitation (i.e., resuscitative endovascular balloon
occlusion of the aorta [REBOA]), and arteriography should
be in the armamentarium of general and trauma surgeons.
Advanced endovascular techniques, subselective catheterization, use of aortic endografts, and other complex interventions require additional training and credentialing.
When possible, complex vascular interventions should be
performed with optimal imaging equipment.
Angiography and simple endovascular interventions can
be performed with a relatively limited inventory of access
needles, wires, and sheaths as well as catheters, working
wires, balloons, and stents. As more complex interventions
are contemplated, sufcient inventory of endovascular
devices and supplies is needed to ensure success. Supplies
needed for trauma interventions may include aortic endograft systems, large sheaths and compliant aortic balloons,
snares, microcatheters, embolic devices and agents, and
covered stents. It is also important to have an appropriate
range of device sizes to meet a variety of needs. The availability of anticipated implants and supplies must be conrmed before embarking on a plan of endovascular therapy.
Fig. 8.4 Intraoperative arteriography can confirm the presence of and
can localize vascular injuries in injured extremities. This example demonstrates disruption and occlusion of the proximal left popliteal artery
in a patient with a comminuted supracondylar femur fracture.
Operative Technique for Angiography
On-table angiography does not require advanced skills or
specialized equipment. Contrast is injected by hand, and a
single radiograph is obtained. This technique may be of practical use during operative management of extremity injuries
when the presence, location, or extent of an injury is uncertain (Fig. 8.4). It can also be used to evaluate the technical
result of a vascular repair. Vascular access is obtained, either
in a percutaneous manner or after open surgical exposure of
the vessel. The artery in question is accessed using a hollowtip needle, a buttery set, a catheter, or a sheath placed using
the Seldinger over-the-wire exchange technique. The imaging plate can be inserted in a sterile wrap and positioned on
the surgical eld under a limb to be imaged.
Although this simple and useful arteriographic technique is
available for use in any situation, it has limitations. First, the
delay between contrast injection and imaging must be estimated, and errors in timing the transit of contrast to the area
of interest will result in failure to opacify the vascular segment
of interest. Second, this technique provides only one image per
injection. Each individual image must be processed for evaluation of the adequacy of the technique, the projection, and the
eld of view. This approach can be time consuming.
The limitations of single-image, on-table angiography can
be overcome by the use of a portable C-arm uoroscopy system with cine loop recording and digital subtraction capabilities. By using cine loop angiography, timing of imaging
is less critical. Multiple images can be recorded with each
single contrast injection. Digital subtraction angiography
(DSA) provides superior denition of vessels as it removes
the image of overlying or surrounding structures, including
bone, from the vessels of interest. Because of this advantage,
DSA generally requires less contrast than nonsubtracted
angiography, including that of the aorta and visceral vessels.
Intraoperative use of a C-arm uoroscopy system can provide the real-time imaging needed for selective catheterization with shaped wires and catheters as well as guidance for
interventions, such as placement of an occlusion balloon,
therapeutic embolization, or placement of covered stents. In
order to use uoroscopy, the patient must be positioned on a
radiolucent operating table. Use of a surgical table designed
for endovascular procedures is helpful. The surgeon can
move the endovascular table to position the anatomic area
of interest in the eld of view while the uoroscopy unit
remains stable. Many other tables used for trauma surgery
and orthopedic procedures (including the Jackson table) are
radiolucent and sufce for basic uoroscopic imaging and
endovascular intervention. Use of a xed table, however,
often requires a radiology or equipment technician to be
more actively involved in C-arm positioning to center the
eld of view.
Fixed imaging systems are standard in larger hospitals
with busy vascular surgery and interventional radiology
programs. These have wall, ceiling, or oor mounted systems, typically integrated with a contrast management or
injection system. Fixed imaging units have table mounted
controls for use by the operating surgeon. They are programmed with various image acquisition protocols and
have features to facilitate intravascular catheter navigation.
Fixed imaging systems provide larger imaging elds and
magnication capabilities, which provide high resolution
8 • Imaging for the Evaluation and Treatment of Vascular Trauma 97
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imaging of the vessels of interest (Fig. 8.5). Centers that
have invested in xed imaging suites in the OR (i.e., hybrid
ORs) also have a more extensive inventory of catheters,
guidewires, and other endovascular supplies, and accessory
equipment.
Patient Care Following Angiography
Removal of arterial catheters and sheaths should be done
by trained personnel following correction of coagulation abnormalities. Use of percutaneous arterial closure
devices may decrease the time to hemostasis, but closure
device use should be considered contraindicated if there
has been a break in sterile technique. The presence of
foreign material in or on the vessel wall (e.g., suture, collagen plug) increases the risk of subsequent infection at
the vascular access site.
16
The arterial access site and the extremity in which the
access was obtained should be monitored for evidence of
injury following sheath removal. Access site and distal
extremity examinations should look for signs of bleeding, neurologic change, or other complications. Of note,
embolic or thrombotic complications appear to be more
common after emergency endovascular procedures for
trauma, as hypercoagulability from shock and performing
procedures without systemic heparin may increase the
risk of pericatheter thrombosis. Postprocedure laboratory
tests should include serum creatinine and hemoglobin
measurements.
Patients who have had interventions for hemorrhage
control or ischemia require careful observation to ensure
that there has been sustained technical success. Such
patients should be serially monitored with physical examination. Objective and quantiable measures of technical
success of the endovascular procedure, such as ankle/brachial index, are particularly useful to identify unexpected
changes in limb perfusion. In some situations, repeat measurements of hematocrit should be performed to ensure
the absence of bleeding.
Stent grafts placed for traumatic aortic injury are evaluated with intraoperative imaging, but postoperative pulse
Fig. 8.5 (A) Arch aortogram (left anterior oblique projection). (B) Selective left subclavian arteriogram. Digital subtraction arteriography provides better vascular definition. In this example, the aorta is uninjured,
but blunt trauma has resulted in occlusion of the left axillary artery
(arrow), which is best demonstrated with selective catheterization and
direct contrast injection into the left subclavian artery.
checks in the upper and lower extremities are needed to
conrm that there has not been coverage of the left subclavian artery or infolding of the graft resulting in distal
ischemia. CT angiography is generally used for endograft
imaging and surveillance in the days and weeks following placement. It is important to note that for many endovascular therapies, postprocedure noninvasive imaging
with duplex ultrasound is sufcient to conrm patency of
treated segments. Because duplex scans are inexpensive,
avoid the use of contrast, and do not expose patients to
radiation, they are also appropriate for long-term surveillance applications.
Complications
Inadequate hemostasis at the arterial puncture site leads
to bleeding and hematoma, and any communication
between the access artery and adjacent vein can result in
an arteriovenous stula. An intimal ap, distal embolization, or de novo thrombosis at the arterial access site can
lead to varying degrees of limb ischemia with or without
neurologic decit. As such, vascular access sites should be
carefully assessed for the presence of ecchymosis, a mass,
or bruit; and the distal limb should be examined for signs
of ischemia.
ULTRASOUND
Ultrasound imaging has many advantages.17 It is noninvasive, inexpensive, and increasingly available for pointof-care examinations. It can be used to image numerous
organs or regions of interest. It can also be used for the evaluation of late complications of vascular injury. Good image
quality, a selection of imaging modes and processing features, and a range of transducer options are now available
with most ultrasound systems. Imaging without the use
of ionizing radiation allows ultrasound systems to be used
without concern for patient or provider radiation exposure.
The introduction of compact systems for POCUS has
made it possible to perform examinations in prehospital
locations (including austere or remote environments), as
well as in a range of clinical settings (including emergency
rooms, ORs, and intensive care settings). Early generations
of compact, portable ultrasound systems were substantially
inferior to the larger, heavier, full-featured systems used by
radiology departments and vascular laboratories. However,
evolution of beam-forming and image-processing technologies narrowed the capability and quality gap between
compact, highly portable devices and traditional high-end
systems. As such, size and mass of ultrasound systems has
continued to decrease, making for smaller devices and less
expensive systems. As a result, use of POCUS for trauma has
become increasingly common.
B-mode imaging provides a two-dimensional (2-D) gray
scale representation of tissue in the scan plane. Blood
is hypoechoic. The lumen of vessels will appear dark on
B-mode imaging. Real-time imaging can demonstrate
dynamic features of vessels, including the pulsatile expansion of arteries and collapsibility of patent veins if external
pressure is applied with the probe (scan head) during the
examination (Table 8.3). The resolution of B-mode ultra-
sound is related to transducer frequency and the depth
of the imaged structure. Resolution decreases with the
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Table 8.3 Ultrasound Findings With Common Vascular Injuries
Lesion B-Mode Image Color Doppler Pulsed Doppler Notes
Arterial stenosis
Arterial occlusion
Pseudoaneurysm
Arteriovenous fistula• Hematoma may be present near
Venous thrombosis • Vein does not collapse with
•
Flap may be visualized in
superficial vessels
•
Echogenic material may be
visualized in lumen
•
Hypoechoic area extrinsic to
artery
•
Moving blood may be directly
visualized in pseudoaneurysm
due to increased echogenicity
of rouleaux aggregate
site of injury
probe compression
•
Echogenic material in vein
lumen
•
Color aliasing (speckled
pattern)
•
No color filling in
occluded segment
•
Proximal or distal collaterals may be seen
•
Flow extrinsic to artery
•
Alternating red and blue
color (yin-yang pattern)
•
Color aliasing
•
Tissue bruit (speckling
overlying tissue)
•
Absence of flow
•
No augmentation with
distal limb compression
•
Increase in peak systolic velocity (velocity ratio ≥ 2.0)
•
Spectral broadening
•
Absent flow or preocclusive
thump
•
Damped waveform distal to
occluded segment
•
Bidirectional to-fro flow in
pseudoaneurysm or its arterial
connection
•
High-velocity jet at arterial
injury
•
Spectral broadening
•
Pulsatile flow pattern and
increased velocity in outflow
vein
•
Absence of flow
•
•
•
•
•
•
•
Intimal flap
Extrinsic compression
Spasm
Distal pulse absent
Arterial Pressure Index
<0.90
Extravasation from
actively bleeding vessel
may not be seen with
ultrasound
Calf veins may be difficult to visualize
use of lower-frequency transducers, which are used for
the examination of deeper structures. When supercial
anatomic features are evaluated with high-frequency
transducers, details of vessel walls can be seen, including
atherosclerotic plaque, dissection, or intimal ap. Conversely, use of B-mode ultrasound as a stand-alone modality may be insensitive for detection of vascular injury when
deeper vessels are evaluated. In these instances, the only
abnormal B-mode nding may be a hematoma in proximity to the vascular injury. Patient discomfort or agitation, or
the presence of wounds, external xators, or dressings, may
limit ultrasound examinations for trauma.
Duplex ultrasound scanning (DUS), adding Doppler
ow detection to the B-mode image, increases the utility of
diagnostic vascular ultrasound. Flow information from a
specic point of interest is displayed by the pulsed Doppler
ow velocity waveform. Color ow duplex scanning displays areas with ow in color overlying the B-mode image
of anatomy. Color ow imaging assigns colored (rather
than gray scale) pixels in regions where moving tissue
(e.g., blood) returns a Doppler-shifted echo. The color ow
display provides information about the location of the ow,
its direction, and its velocity. In addition, a speaker provides an audio output of the Doppler signal (see Table 8.3).
With experience, users can learn to recognize characteristic “signatures” of abnormal ow, including higher pitch
with elevated velocities; abrupt blunted signal proximal to
an occlusion; course sound with spectral broadening from
turbulence; or continuous low-resistance, diastolic ow
associated with an arteriovenous stula.
Use and interpretation of vascular ultrasound is integral
to the training of surgeons. The Registered Physician in
Vascular Interpretation (RPVI) credential of the Alliance
for Physician Certication and Advancement (APCA) is a
prerequisite for vascular surgery board certication. Vascular ultrasound may be useful for trauma care, even if vascular specialty expertise is not available. Most radiologists
have training in general ultrasound, and many general and
trauma surgeons have skills with the use of POCUS. Measurements of vessel size (detection of aneurysms), detection
of arterial or venous ow, assessment for deep-vein patency,
mapping of supercial veins, and other simple evaluations
can be learned without extensive formal training. Providers may seek voluntary certication for POCUS competency
through professional societies or the Point-of-Care Ultrasound Certication Academy (an APCA spin-off) https://
www.pocus.org.
Indications
Focused assessment with sonography for trauma (FAST)
can be a part of the secondary survey of the injured patient,
used to identify pericardial effusion and hemoperitoneum.
The extended FAST (eFAST) includes ultrasound assessment
of both thoraces looking for pneumothorax or hemothorax.18 Although not typically included in a FAST examination, ultrasound can also conrm endotracheal tube
positioning and can provide an indication of intravascular
volume by evaluating ventricular lling and the dimensions
of the inferior vena cava. A practical aspect of POCUS is its
ability to be repeated over time to conrm initial impressions or to show trends.
Ultrasound is of particular utility in evaluation of
neck
19,20
and extremity vessels
21,22
following trauma due
to their relative supercial location. Dissection, stenosis,
thrombosis, and arteriovenous stula can all be demonstrated using this imaging modality. Because duplex is
safe, inexpensive, and noninvasive, it is especially useful
to conrm a normal physical examination in patients who
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have extremity injury mechanisms associated with a risk
of vascular injury, including penetrating trauma, posterior knee dislocation, hyperextension, and supracondylar
fracture (Fig. 8.6).
In the absence of hard signs, the presence of an extremity vascular injury can be excluded with a combination of
physical examination and noninvasive pressure measurement to calculate the injured extremity index (IEI). Using
continuous-wave Doppler, this cuff occlusion technique
measures the systolic blood pressure in the injured limb and
compares it to the cuff occlusion pressure in the uninjured
contralateral limb.23 An IEI of less than 0.90 suggests that
a ow-limiting arterial stenosis or occlusion is present. DUS
complements the measurement of the IEI; however, in the
absence of clinically evident ischemia or bleeding, with a
normal IEI, there is little risk in delaying the duplex scan by
several hours or even days.
When minor vascular injuries are detected, most may be
managed nonoperatively with expectation of spontaneous
healing. Injuries with low risk of late complications include
intimal injuries (intimal ap) that are associated with less
than 50% stenosis. The absence of a pressure gradient
across the injured segment (i.e., a normal injured extremity
index) or a duplex nding of peak systolic velocity increased
by less than a factor of two suggest the absence of a hemodynamically signicant injury. The noninvasive nature
of duplex allows for serial examinations to conrm that a
given injury has healed over time.
Severely injured patients are at risk for venous thrombosis and pulmonary embolism.
24,25
The presence of signicant
injury causes thrombophilia (a procoagulant condition).
DUS is the diagnostic test of choice for the detection of venous
thrombosis of the extremities. New unilateral limb swelling
is the best clinical sign that predicts deep vein thrombosis
(DVT), but clinical evaluation alone lacks the sensitivity or
specicity. Thus, duplex scanning to evaluate for DVT is indicated when there are signs or symptoms of DVT, or to screen
for DVT in asymptomatic high-risk patients.
POCUS with probe compression to see if the popliteal
and common femoral veins collapse under manually
applied pressure can serve as a quick screening test. With
this basic bedside maneuver, one can accurately identify
major proximal limb DVT.26 To diagnose iliac vein thrombosis, nonocclusive DVT, limited segmental DVT, or calf
vein thrombosis, a complete examination should be performed by a vascular technologist. If limited thrombosis
(e.g., isolated calf vein DVT) is observed and is not treated
with anticoagulation, repeat duplex examination 5 to 7
days later may be used to look for proximal thrombus
progression.
Intraoperatively, ultrasound can be useful for localization of vessel injuries (Fig. 8.7) and for evaluation of
technical results after repair of vascular trauma. DUS can
identify defects that may lead to early thrombosis or late
complications including abnormalities of the intima at
the site of vascular clamp placement (i.e., clamp injury).
DUS can also detect ow-limiting stenosis at the anastomosis of a vascular repair or the presence of intraluminal
thrombus. By detecting these injuries or technical defects
intraoperatively, surgical revision can be performed before
leaving the OR.
Preparation
No specic preparation is needed for most ultrasound
examinations. However, fasting before abdominal DUS
may reduce the amount of bowel gas that obscures the
view of deeply positioned abdominal, retroperitoneal, and
pelvic vessels.
Pitfalls and Danger Points
The hazards related to, or limitations of, ultrasound are
negligible but include:
n Results are operator dependent, requiring a basic knowl-
edge and some technical skill
n Tissue disruption, obesity, or edema may limit imaging
Fig. 8.6 Popliteal artery injury from posterior knee dislocation. A 24-year-old man was involved in a motor vehicle crash, which resulted in posterior disloca-
tion of the right knee. The right foot was pulseless and pale. CT angiography (A, three-dimensional [3-D] reconstruction) and digital subtraction angiography
(DSA) (B, subtracted DSA image; C, nonsubtracted image) show occlusion of the infragenicular (P3) segment of the popliteal artery. This was reconstructed
with a bypass graft from the distal superficial femoral artery to the tibioperoneal trunk. Patency of the vein graft was confirmed at 1-month follow-up with
duplex ultrasound scanning (D) that showed a hyperemic arterial flow pattern (forward flow through mid and late-diastole).
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Intima separated
Aorta
Fig. 8.7 (A) A seat belt–restrained 15-year-old girl injured in a car crash presented with a Chance fracture, a bowel injury, and a right lower extremity
ischemia. Intraoperative ultrasound imaging demonstrates patency of the aorta at the level of the inferior mesenteric artery. (B) The seat belt injury to
the terminal aorta resulted in an extensive intimal tear, which is seen in this intraoperative transverse B-mode image.
from adventitia
n Ultrasound transmission through air is poor; imaging of
intrathoracic structures is limited; and bowel gas may
obscure abdominal and pelvic imaging
n Bowel gas may be increased in nonfasting patients and in
trauma patients who have been ventilated with a mask
before intubation
n Ultrasound transducers should be appropriately disin-
fected to prevent transmission of infectious agents
Strategy
Providers at the point of care can perform vascular-specic
examination or a registered technologist may perform an
ultrasound during the tertiary survey (or at any subsequent step of a patient’s care). Ultrasound can be used as a
screening tool to detect injuries or vascular complications
that are not evident from clinical assessment. Examples of
screening examinations include evaluation of limbs with
“soft” or no signs of vascular injury that sustained trauma
with mechanisms known to injure vessels.
Ultrasound can be used as a diagnostic tool, either alone
or in combination with other testing modalities. Arterial
disruption, intimal dissection or ap, thrombosis, and arteriovenous stula can be denitively diagnosed using ultrasound, especially in the extremities. If DUS is combined
with thorough physical examination, including calculation
of the IEI, additional imaging, such as CTA or angiography
may be unnecessary.
DUS may also be used as a complement to other diagnostic tests or screening maneuvers (e.g., Doppler pressure
measurements and calculation of the IEI). In many cases, if
the initial examination is normal and there is no hard sign
of vascular injury, a more thorough evaluation with DUS
can follow on an elective basis (see Table 8.3).
Ultrasound imaging is also an important tool to guide
real-time certain vascular or endovascular procedures. For example, ultrasound has become the standard
to guide health care providers as they accomplish percutaneous arterial or venous access.
27,28
Ultrasound can also
help with localizing vascular structures or injuries during
an operation to repair a vascular structure or other injuries.
Focal pseudoaneurysms of extremity arteries may be managed with real-time, ultrasound-guided thrombin injection, a technique that is used to treat iatrogenic femoral
artery pseudoaneurysms, but can be used for other arterial
pseudoaneurysms. Finally, ultrasound can be used for the
real-time assessment of surgical outcomes, either during a
procedure (when corrective action can be taken if a technical defect is found) or later, if surveillance is indicated.
Technique
The hand-held transducer (probe) transmits ultrasound
energy and receives reected echoes. Because air has high
acoustic impedance, a water-based gel is used for acoustic
coupling between the transducer and the skin for routine
applications, but blood or saline irrigation are suitable coupling media during intraoperative use. A transducer that
is appropriate for the depth and the location to be evaluated is selected. Deeper structures require the use of lower
ultrasound frequencies (1 to 5 MHz). High-frequency transducers (6 to 12 MHz) provide better imaging resolution
but with limited imaging depth. Transducer elements can
be mounted in a curved or linear array to create a sector
or boxlike image. Phased array transducers can provide a
compact footprint, with a sector-like scan. Probes designed
specically for intraoperative use may have a T-shaped or
“hockey-stick” design to facilitate use in the operative eld.
Transducers are typically designed to operate over a range
of frequencies (broadband) for greater versatility and better
imaging. Specics of transducer design vary among manufacturers and systems used.
Vessels in the neck and extremities can be imaged
directly. Because air in the lungs and viscera interferes with
ultrasound transmission, ultrasound imaging to evaluate
for truncal vascular injury is limited. Subcostal and parasternal views or “windows” allow for evaluation of the
heart and pericardial sac, but the thoracic aorta cannot
be visualized with a transthoracic approach. The presence
of intraabdominal uid (i.e., blood) on a FAST examination is indirect evidence of vascular disruption or solid
organ parenchymal injury. Direct vascular examination
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of intraabdominal vessels is seldom performed in the acute
phases of trauma evaluation and management (i.e., not
part of the FAST).
Vascular access is facilitated with routine use of ultrasound for venous and arterial punctures. When ultrasound
is used for procedural guidance or intraoperative assessment, the transducer is placed in a sterile sleeve. Acoustic
coupling gel needs to be placed inside the sleeve, with no air
gap or bubbles between the transducer face and the inner
portion of the sleeve. Sterile gel is used on the eld. An 18- or
21-gauge needle can be seen with ultrasound as it is directed
through the soft tissues into the vessel lumen. Needles with
a stippled surface may be more echogenic and easier to visualize with B-mode ultrasound. Imaging the vessel in a longitudinal scan plane allows the site of vascular entry to be
selected, while changing to a transverse image ensures that
vessel entry is precisely at the 12 o’clock position. Ultrasound imaging can also conrm intraluminal positioning of
catheters and guidewires once access is achieved.
Some ultrasound applications such as transesophageal
echocardiography (TEE) used to evaluate the thoracic aorta,
require specialized capabilities.
1,29
TEE in the setting of
trauma requires endotracheal intubation for airway control. Intraoperative TEE may provide the initial diagnosis of
BTAI for patients who have been brought directly to the OR
for surgical stabilization, bypassing the CT scanner. Intravascular ultrasound (IVUS) is an invasive technology requiring vascular access, catherization of a target vessel, and
introduction of an imaging catheter over a guidewire. The
aorta can be evaluated with an 8-French IVUS catheter over
a 0.035-inch wire. Although IVUS is not appropriate as a
screening test, it can provide detailed morphologic information to guide the choice of an appropriately sized endograft
for treatment of BTAI (Fig. 8.8).30 IVUS allows real-time
imaging and diameter measurements in both systole and
diastole while the patient is on the OR table. Routine use of
IVUS prior to TEVAR for BTAI is recommended, as CTA mea-
Fig. 8.8 Intravascular ultrasound (IVUS) evaluation of aortic pseudoaneurysm. An endovascular graft was used to treat a 51-year-old woman
who was found to have a pseudoaneurysm of the infrarenal aorta found
after a roll-over accident while using a riding lawnmower. The abnormal
segment is shown on the digital subtraction angiography (DSA) image (A).
IVUS was used to measure the dimensions of the aorta at the left renal
vein (B), to assess the aneurysmal segment (C), and to evaluate the distal
abdominal aorta (D), proximal to the bifurcation.
surements may underestimate the diameter of the aorta if
the CTA was performed in the setting of intravascular hypovolemia.
31
Complications
Ultrasound is safe, noninvasive, and not associated with
direct risk of complications. The primary hazards associated with diagnostic ultrasound are the risks of interpretation errors. Without attention to cleaning and disinfection,
ultrasound equipment can be a potential vector for transmission of health care–associated infection.32 Tissue heating is negligible with diagnostic ultrasound applications,
and there is essentially no risk of injury in typical clinical
applications.
(EDs) found CT use increased by 330% between 1996 and
2007.33 The availability and convenience of CT scanning
has reduced reliance on FAST imaging in the emergency
departments.
34
CT is routine for the evaluation of injuries to the brain,
face, chest, abdomen, and pelvis, as well as spine and skeletal
injuries. Routine single-pass, whole-body computed tomography (WBCT, or “pan scan”) has been advocated by some
for its high diagnostic yield and potential to identify missed
injuries.35 The alternative of a more targeted use to avoid
unnecessary health care costs and radiation-exposure risks
may be more appropriate for most patients, though. From
the standpoint of vascular trauma, contrast-enhanced CTA
can reliably conrm and characterize clinically evident
COMPUTED TOMOGRAPHY
Computed tomography (CT) is the workhorse imaging technology in contemporary emergency medicine and trauma
care including vascular trauma. Multidetector CT (MDCT)
with high-speed helical scanning has reduced imaging
times to minutes. The availability of CT scanning is nearly
ubiquitous, even in relatively austere locations on the battleeld. Data from a US survey of nearly 100 million patients
who underwent CT scanning in emergency departments
problems (e.g., occluded extremity vessel with ischemia), as
well as detect subclinical injuries (e.g., asymptomatic arterial injuries or minor BAI) (Fig. 8.9).
36
Magnetic resonance imaging (MRI) and magnetic resonance angiography (MRA) may be used as alternatives to CT
and CTA, with the potential advantages of avoiding CT artifacts and radiation exposure. However, MRI is not as readily available and has slower image acquisition times. There
are also a greater number of contraindications for the use
of MRI, including the presence of metallic implants. Also
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of practical importance, there are many pieces of medical
equipment that are not compatible with use in the presence
of a strong magnetic eld and thus cannot accompany a
patient during an MRI scan.
Indications
The indications for CTA are broad. Any patient with a
known or suspected vascular injury may be a candidate for
CTA, though CTA may not be needed if there is sufcient
information from clinical assessment (i.e., hard signs of vascular injury). Other noninvasive imaging modalities may
sufce to make the correct diagnosis of vascular injury and
may allow for appropriate management.
Indications for CTA of the head and neck after blunt or
penetrating trauma include unexplained or incongruous
central or lateralizing neurological decit. This modality
is also indicated for complex facial or mandible fractures,
Fig. 8.9 Mid-shaft humerus fracture with brachial artery disruption.
Long bone fractures, such as this mid-shaft humerus fracture, can result in
intimal disruption and arterial occlusion, as seen in the three-dimensional
(3-D) rendering of the CT angiography (A) and the maximum intensity
projection (B).
penetrating injuries to the neck (zones I, II, and III), cervical
spine or spinal cord injuries, and thoracic injuries. CTA for
suspected arterial injuries of the neck without initial indications for immediate operation allows characterization of
lesions, such as partial or complete occlusion, pseudoaneurysm, intimal flap, dissection, and arteriovenous fistula (Fig. 8.10).37 With the same examination, CT provides
information about the cervical soft tissues, the aerodigestive
tract, the spinal canal, and the spinal cord. In cases of penetrating injuries, the bullet or fragment trajectories and the
locations of fragments may be assessed.
The most common indication for thoracic CTA for
trauma is evaluation of known or suspected BTAI, usually
in the setting of high-energy deceleration injuries. CTA of
the chest is also useful in the setting of penetrating trauma
with possible great vessel injury. Chest x-ray ndings that
suggest BTAI or other vascular injury include a widened
mediastinum, an apical cap, and a displacement of the trachea, left main bronchus, or nasogastric tube. However, a
normal chest x-ray does not exclude BTAI.
BTAI has been characterized based on ndings on CTA as
follows: type I, intimal ap; type II, intramural hematoma;
type III, pseudoaneurysm; and type IV, aortic disruption.7
This grading scheme separates those patients who may be
managed without an operation (type I), from those with
more severe injuries (types II, III, and IV), who require operative or endovascular treatment.
CT scanning of the abdomen and pelvis is an established
modality for the evaluation of blunt trauma. Standard
imaging protocols are often employed, but contrastenhanced CTA provides additional information for the
evaluation of suspected vascular injuries that may not
have been clinically apparent (Fig. 8.11). In addition, the
vascular injuries may be associated with other injury patterns. For example, patients with truncal vascular injuries
may have associated spine or spinal cord injury, or injury
to the viscera or solid organs.
38
The indications for CTA for the evaluation of extremity
trauma are similar to those for conventional arteriography.
However, the availability and diagnostic accuracy of CTA
has made it the imaging modality of choice for extremity trauma in most centers.39 Adding extremity CTA to an
Fig. 8.10 Carotid artery dissection from blunt trauma. Images from a CT scan done to evaluate a 25-year-old man who was severely beaten about the head
and neck. Axial reconstruction (A) demonstrates dissection flap in the cervical portion of the left internal carotid artery, dilation of the segment, and luminal
irregularity (yellow arrow). Coronal display of maximum intensity projection facilitates visualization of pseudoaneurysm (B, yellow arrow), with proximal and
distal irregularity. The 3-D rendering (C) shows the vasculature and bony anatomy together.
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A
Fig. 8.11 Traumatic renal artery occlusion. Chest and abdominal injuries were sustained by a 14-year-old boy who was thrown from a motor bike traveling
35 miles per hour. (A) CT scan with contrast demonstrates left renal artery occlusion – likely from dissection (yellow arrow). The right kidney (R) is enhanced
with contrast, but no contrast appears in the left kidney (L). (B) Color flow duplex scanning of the kidneys demonstrates flow in arcuate arteries and veins in the
right kidney (top) but no flow in the left kidney (bottom). (C) Normal pulsed Doppler arterial waveforms can be obtained from the right kidney (top), but only
slow velocity venous flow can be detected in the left renal hilum (bottom).
already-planned scan of the chest, abdomen, and pelvis
adds little time, and provides detailed information useful in
the polytrauma patient. Studies of CTA in the evaluation of
extremity vascular trauma have shown high rates of sensitivity and specicity (90% to 100%).
40
Preparation
Reliable IV access is needed for contrast administration.
Planning the sequence of imaging may help limit the volume of iodinated contrast agents (by limiting multiple diagnostic imaging procedures). Avoiding hypovolemia is also
recommended to reduce the risk of CIN. As experienced
clinicians are aware, transporting critically ill or injured
patients to an imaging suite is associated with risks. This
may require suspension of specic therapies and may initiate a transition of care. Additionally, movement of a seriously injured patient to the CT scan area and scanning
table may result in interruption of cardiovascular monitoring and may increase the risk of displacement of lines or
tubes. Thus, coordination and planning are needed anytime
patients are moved to the CT scanner from the resuscitation
room, OR, or intensive care unit.
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Pitfalls and Danger Points
Risks associated with CTA are similar to conventional arteriography but without the risks of arterial catheterization.
CTA hazards include:
n CIN
n Anaphylactic reaction to contrast
n Contrast extravasation outside of the vein
n Late effects of exposure to ionizing radiation (cancer)
n Venous injuries may be missed if single-phase acquisi-
tion is performed
n Diagnostic (interpretation) errors
n Imaging limitations due to artifact
n Movement of the patient from a treatment area to the CT
imaging suite
From a population-based perspective, the risk of radiation exposure from diagnostic CT scans is considerable.
However, on an individual basis, radiation-associated risks
are low and usually not major considerations in the context of a potentially life- or limb-threatening injury. The
most practical way to keep radiation exposures as ALARA
in trauma care is to perform only those studies needed for
patient management. Routine CT imaging for low-risk
injury mechanisms is discouraged. This is particularly
important for children, as they are at greater lifetime risk
for cancer due to radiation exposure.41 Since 2006, the
“Image Gently Alliance” (https://www.imagegently.org),
which began as a committee of the Society for Pediatric
Radiology, has advocated to decrease radiation doses to
children, primarily through more selective use of imaging,
but also by the use of dose-limiting imaging protocols and
up-to-date equipment.
Of note, overall radiation dose may be decreased with the
initial performance of a quality CTA, as its high diagnostic
yield may obviate the need for other radiographic studies.
Technology advances (detector design, image-processing
systems) have decreased radiation dose and other procedure-specic changes (adjustments in tube current [mA],
tube potential [kVp], gantry rotation time, helical pitch) can
further limit exposure. Other pitfalls of CTA include sources
of artifact that can degrade image quality or one's ability to
interpret the image.
During the evaluation of a trauma patient, motion can
also degrade image quality, creating black or white bands,
dark spots, loss of resolution, or anatomic distortion. Strategies to reduce motion artifact include fast scanning, gating
(e.g., to reduce motion artifact from the cardiac cycle), tube
alignment, corrective reconstruction, and postprocessing
techniques. The presence of high-density foreign materials
can also be problematic. Metal can create streak artifacts
by causing the detectors to operate in a nonlinear response
region, and even small fragments can create a star-pattern
artifact. Patient body habitus also affects image quality with
more image distortion occurring in larger patients.
Performance of a CT scan relies on geometric precision
and measurement quality. Inaccurate geometry, inaccurate
alignment of the x-ray tube with the detectors, or incorrect
data can produce artifacts and blurring that limit spatial
resolution. Detector calibration errors and balance can also
occur, detracting from image quality. Artifacts caused by
equipment malfunction can be eliminated by regular preventive maintenance and timely repairs.
Beam attenuation is proportional to the average attenuation coefcient in each volume element (voxel). Resolution
may be degraded when tissues with different absorption
densities are in the same voxel. Partial-volume effects are
minimized by the use of thin sections or “cuts” and by the
selection of a section that lies in the center of the object of
interest for attenuation measurements. Beam-hardening
artifacts result from preferential absorption of low-energy
photons from the x-ray beam. The effect may be pronounced
in areas of high attenuation, such as bone. Specic to CTA,
inadequate vascular opacication due to delayed contrast
medium transit times in patients in shock may render CT
angiography (arterial or venous) nondiagnostic. Timing
delays may be most problematic for CTA of distal vessels or
for more central venous structures.
Strategy
CT scanning has become nearly ubiquitous in the management of the severely injured patient, with demonstrated
efcacy for detection of occult injuries and characterization
of known injuries. Standard imaging protocols detect most
vascular injuries, but dedicated CT angiographic studies are
often needed to better characterize some patterns of vascular
trauma, especially those to medium- and smaller-siz ed vessels.
Technique
CT angiography is performed in targeted regions with
IV contrast infusion. A typical contrast bolus volume is
100 mL, with an infusion rate of 4 mL/s. The imaging delay
is typically estimated, but most systems will time the arterial phase acquisition with bolus tracking, starting when
the contrast arrives at a preselected region of interest. A
technologist performs CT scans, typically with predened
protocols. The technologist positions the patient, administers contrast materials, prepares and operates the CT scan
equipment, then sends image data in Digital Imaging and
Communications in Medicine (DICOM) format to the picture archiving and communication system (PACS).
Conventional CT displays show the density of the imaged
tissue (the degree to which x-rays are attenuated) in gray
scale. CT densities are measured in Hounseld units (HU),
which range from −1024 to +3071. As the human eye can
discern only 30 to 40 gray scale levels, the image display
can be varied to include HU ranges across a small or broad
window, centered on a particular level of interest.
Modern MDCT scanners have isotropic resolution, with all
three dimensions of the individual image volumes (voxels)
being the same (X = Y = Z). Because of this, the CT dataset
can be considered a three-dimensional (3-D) representation of the image volume scanned, and these data can be
displayed in several ways. Postprocessing of the volumetric
imaging data from CTA can greatly facilitate image interpretation. Some postprocessing may be done automatically,
but technologists, radiologists, and other clinicians are able
to manipulate the dataset to yield the views and projections
of specic diagnostic interest. Postprocessing techniques can
create 2-D or 3-D images.
The use of dual energy levels (kVp) during imaging can
facilitate removal of bone from images or can help distinguish
calcium from contrast-enhanced blood.42 The thickness
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