Clinical Manifestations
Hemorrhage and tissue ischemia are the main clinical manifestations of vascular trauma. Symptoms of lower limb vascular injuries can be described as hard or soft signs. Hard signs include arterial bleeding, loss of pulse, expanding hematoma, bruit or thrill, and signs of ischemia, and indicate the need for immediate surgical intervention [
5]. The classic 6P syndromes defined as paresthesia, pulselessness, paralysis, pain, pallor, and poikilothermia can diagnose damage to lower limbs arteries.
Soft signs include a history of prehospital blood loss, diminished pulse, moderate hematoma, proximity to a large vessel or bony injury, and ipsilateral neurologic deficit, and indicate the need for further diagnostic imaging [
11,
12,
43]. It is important to underline that negative clinical exams do not rule out vascular trauma, especially in the calf, where low blood compensation can masquerade the vessel injury[
11,
12,
44].
Ultrasound
Ultrasound (US) is widely used in the setting of trauma, and peripheral vascular examination may detect features of vascular injuries such as luminal narrowing, intramural hematoma, flaps, posttraumatic stenosis, the” yin-yang” sign characteristic of pseudoaneurysm and acute occlusion [
11,
12,
48,
49]. The use of Color Doppler increase ultrasound accuracy and has a sensitivity up to 94% [
11,
12,
50]. US has several limits in the diagnosis of peripheral vascular injuries with a certain false negative rate. Ultrasound is operator-dependent and requires experienced staff, and more importantly cannot access some areas due to bony structures, open wounds, large hematomas, bulky dressing, or splints [
11,
12,
51]. Moreover, high BMI and subcutaneous emphysema negatively impact ultrasound examination [
11,
12,
52].In penetrating trauma, ultrasound is not sensible enough to rule out vascular injuries [
52,
53,
54]. Generally, Doppler US and the ankle-brachial pressure index (ABPI) are associated with a substantial false negative rate and inter-observer variability[
15,
33,
42] so they are not routinely used to rule out vascular injuries, instead positive US may obviate CTA [
52,
55].
MDCTA or CTA
Digital Subtraction Angiography (DSA) is considered the gold standard in peripheral vascular injuries, allowing diagnosis and treatment, however, the technological progress of Multidetector Computed Tomography (MDCT) scanners makes MDCT with CT Angiography (CTA) the imaging of choice in evaluating patients with suspected peripheral artery injuries, replacing DSA as first diagnostic step allowing an accurate definition of peripheral vascular injuries and other associated trauma lesions [
11,
12]. Moreover, because vascular limb traumas can occur in isolation or as a part of polytrauma, total body CTA may be performed in a single time, allowing the detection of vascular limbs and other cranial-neck-thoracic-abdominal-pelvic and musculoskeletal injuries. Currently, 85% of patients with multi-system trauma undergo admission whole-body trauma CT [
10,
56]; with simultaneous considerations of extremities and intracavitary injuries[
32,
41,
57].
CT angiography is not indicated routinely in polytraumatized patients, but in the case of risk factors (open fractures, distal tibia fractures, multiple fractures in one extremity, or isolated fractures of the proximal third of the fibula) with at least 1 between hard and soft signs (hard signs: absent distal pulses, pulsatile bleeding, cold/pale limb, expanding hematoma, palpable thrill, audible bruit; soft signs: decreased pulses compared to the contralateral side, any peripheral nerve deficit(s), small local hemorrhage(s), a wound near an artery, non-pulsatile hematoma) [
5,
30,
38,
55,
56,
58] however, in patients with suspected vascular injuries, a negative CTA was also used as rationale for immediate discharge [
59].
CTA Protocol
A specific protocol for a patient suspected limb trauma should be chosen both on the parameters of the scanner and about whether the CTA is acquired alone or as part of a whole-body examination [
5].
The patient is supine positioned feet first. Scanning width and position of the limbs depend on the context: in polytrauma patients, the volume is extended to the lower limbs, with legs at the isocenter to the gantry and feet slightly externally rotated; containment bands are always preferred if injuries allow them and especially in uncooperative patients. The upper limbs involved are imaged in adduction along the flanks, favoring the traumatized side in centering the patient; depending on the size of the patient, one or both upper limbs can be included in this way.
In the case of isolated limb trauma, the position of the lower limbs is identical, while the positioning of the upper limbs depends on the type of trauma. If possible, the injured upper limb is placed over the head with the palm raised and extended fingers, if not the arm is scanned in a prone position with the upper limb adducted along the flanks. In some severe injured upper limb trauma, the patient may be not able to mobilize the arm and it can be scanned adducted to the body[
57,
60].
All devices that can generate artifacts, such as rings and chains, should be removed before scanning if possible. Pillows and tape can be used to immobilize the upper extremity and fingers as much as possible.
About the contrast agent, the higher the iodine concentration, the better the quality of the study because the higher the density of the vessels.
Vascular venous access is obtained with an angiocath caliber of 18- or 20-gauge adequate for the flow (at least 3 ml/sec), followed by a 40-mL saline flush at the same rate.
The positioning of the intravenous cannula should be chosen concerning the body area to be studied; for evaluating the lower limbs, the venous access should be positioned in the antecubital fossa and on the opposite site of the injured arm to prevent that the dense venous contrast obscures the arterial side. However, in the case of a study of both upper limbs, in the absence of a central venous access, a pedideal venous access could be chosen, which however would not allow the use of high flows[
61].
The amount of contrast agent depends on the patient weight, iodine delivery rate (IDR) and on the length of the scanning duration. The examination starts with a biplane scout topogram to prescribe the scanning range and FOV.
CT scans are acquired in the caudal-cranial direction from the inferior aspect of the aortic arch to the tips of the fingers and in the cranio-caudal direction when the upper limbs are placed above the head [
60].
It is suggested to acquire an unenhanced scan to focus spontaneous hyper densities such as bone fragments and for comparison with the post-contrast acquisitions, to better understand contrast agent distribution. If dual energy CT machine is available, the use of virtual unenhanced scan can be considered as well as iodine maps that may help in the detection of vascular alterations[
62]. Then a multiphasic CT study is suggested with arterial, portal phase with delayed phase acquisition in selected cases[
63].
Arterial scanning delay is determined by automated bolus tracking with the region of interest on the aortic arch for the upper limb examinations or in the whole-body CT examination, and on the abdominal aorta in case of lower limb examinations. Automated bolus tracking is recommended to obtain optimal acquisition timing, particularly in patients with decrease cardiac output.
The venous scan is acquired about 60-70 seconds after the contrast agent injection and is essential to detect venous injuries and bleeding and to differentiate contained vascular injuries from actively bleeding lesions[
64].
Late phase, acquired 180 seconds after the contrast agent injection, offers a further help in detecting late bleeding and solve doubts [
64].
Multiplanar reconstruction, maximum intensity projection (MIP) reconstruction, and volume-rendered (VR) and CTA road maps are extremely useful in the assessment of limbs vascular trauma[
5,
44,
57,
58] (5, 44, 55, 56) and need to be routinely adopted in the post-processing [
60].
CTA Imaging Findings
CTA features of arterial traumas reflect the depth of mural involvement, and they are characterized by different CT findings (
Figure 2) [
5,
65,
66]:
Arterial Transections represents the complete rupture of the vessel, and determines the loss of distal opacification, a massive hematoma and active bleeding [
5] (
Figure 3). Active arterial bleeding is visualized as contrast extravasation in the arterial phase, which enlarges in venous and delayed phases [
67]. In partial transection, the arterial tear involves the three layers of the vessel wall, without affecting the entire vessel’s circumference, distal opacification is appreciable although reduced luminal caliber and opacification can be detected [
5,
55].
Pseudoaneurysm is caused by focal arterial wall tear involving intimal and medial layers, and represents a collection of blood contained only by the adventitia layer or surrounding tissue [
5,
56,
59]. It appears as an outpouching sac with a round and smooth margin in continuity with the arterial adjacent lumen (
Figure 4). Pseudoaneurysm bleeding appears as irregular, lobulated perilesional contrast blush [
65,
68]. Pre-exiting calcification or pseudoaneurysm should be differentiate form active bleeding; delayed phase acquisition can be useful because in active bleeding the contrast extravasation dissipates along tissue planes instead pseudoaneurysm and calcification remain stable [
60,
67].
Dissection is caused by an intimal tear, resulting into an intimal flap, which can float in the vessel lumen or cause occlusion [
5]; at CT it appears as a semilunar luminal deformation or eccentric stenosis or complete occlusion. Findings in dissection can be subtle but if evident at CT, the intimal flap can be classically seen as a linear flap within the vessel lumen [
5,
65,
69,
70] (
Figure 5).
Luminal narrowing: the vessel wall appears lobulated with eccentric narrowing, it can be the result of extrinsic compression, non-occlusive thrombus, or dissection (
Figure 3).
Vasospasm: it is represented by a concentric, focal and segmental luminal narrowing with smooth margin, caused by the contraction of the arterial wall, as a response to an injury [
5].It can be difficult to differentiate from an intimal tear and occlusion in distal small arteries [
71,
72]. The differential diagnosis between vasospam and dissection often requires DSA for the proper management (
Figure 6).
Arteriovenous fistulas appear as a direct connection between arteries and veins with early venous enhancement in the arterial phase, and communicating channel with the artery can be detected[
67,
68,
70] (
Figure 7).
Figure 3.
CTA, coronal planes, MIP (A), and 3D reconstructions (B). Arterial transections of proximal and medium tracts of right superficial femoral artery. In this patient, it could be noted both the complete loss of opacification of the proximal tract (white arrows) and the lower opacification of the downstream revascularized tract (yellow arrows) of the right superficial femoral artery, with reduced luminal caliber (narrowing).
Figure 3.
CTA, coronal planes, MIP (A), and 3D reconstructions (B). Arterial transections of proximal and medium tracts of right superficial femoral artery. In this patient, it could be noted both the complete loss of opacification of the proximal tract (white arrows) and the lower opacification of the downstream revascularized tract (yellow arrows) of the right superficial femoral artery, with reduced luminal caliber (narrowing).
Figure 4.
CTA, axial planes. Right common femoral artery pseudoaneurysm can be noted (arrow). It appears as an outpouching sac with a round margin in continuity with the arterial adjacent lumen. In this case, imminent signs of rupture of the pseudoaneurysm can be seen, as irregular and lobulated margins and the adjacent hematoma.
Figure 4.
CTA, axial planes. Right common femoral artery pseudoaneurysm can be noted (arrow). It appears as an outpouching sac with a round margin in continuity with the arterial adjacent lumen. In this case, imminent signs of rupture of the pseudoaneurysm can be seen, as irregular and lobulated margins and the adjacent hematoma.
Figure 5.
CTA, axial planes. Right deep femoral artery dissection can be seen (arrow), resulting in a linear flap within the vessel lumen.
Figure 5.
CTA, axial planes. Right deep femoral artery dissection can be seen (arrow), resulting in a linear flap within the vessel lumen.
Figure 6.
CTA, axial planes. Left popliteal arteriovenous fistula: a direct connection between the artery and the vein with early venous enhancement in the arterial phase and communicating channel with the artery can be detected (arrow).
Figure 6.
CTA, axial planes. Left popliteal arteriovenous fistula: a direct connection between the artery and the vein with early venous enhancement in the arterial phase and communicating channel with the artery can be detected (arrow).
Figure 7.
CTA scout (A) and arterial phase, axial planes (B). In this case, the correct positioning with a wide field of view was not possible, causing nondiagnostic examination. When these conditions happen, a second limb acquisition is essential and could be performed by decentralizing the patient on the CT table and focusing the exam on the limb of interest.
Figure 7.
CTA scout (A) and arterial phase, axial planes (B). In this case, the correct positioning with a wide field of view was not possible, causing nondiagnostic examination. When these conditions happen, a second limb acquisition is essential and could be performed by decentralizing the patient on the CT table and focusing the exam on the limb of interest.
MDCT Protocol and Reporting
MDCT exam acquisition in peripheral vascular trauma can be challenging. In isolated limb trauma, CTA of lower or upper limbs can be acquired with specific protocol, taking into account that optimal acquisition of upper limbs in traumatic patients can be difficult and not optimal because of the limitation to raise both arms owing to injury. Bolus tracking, fixed delays, and test injection are recommended, and test injection is recommended. A fixed delay of 20-30 sec in healthy patients has been proposed in order to image both upper and lower limbs [
60,
66]adequately. In polytraumatized patients, an adequate examination of the upper and lower limbs can be challenging, and 8% of extremity trauma CTA have been reporting nondiagnostic [
66] due to early scan timing for body trauma assessment. With a second contrast arterial bolus and with the advent of dual source, the midcalf and forearm can be reimaged with the same bolus and minimal venous opacification interference [
65,
73]. It’s preferable to use a wide-field-of view that includes both limbs, which helps the radiologist to assess vascular trauma by comparing the two sides and to determine technique equivocal findings due to distal nonenhancement for early scan timing[
72]. Other factors that may negatively influence CTA diagnostic accuracy are artifacts related to beam hardening from hardware, ballistic fragments, and debris [
73]. Mechanism of trauma should be taken into account, especially in penetrating gunshot injuries, to adopt higher peak kilovoltage and tube current, narrow collimation and iterative protocol in order to reduce artifacts[
5].
CTA reporting should include description of arterial damage with its location and length, degree of stenosis (>50% luminal caliber) and level of restitution [
68]. The precise determination of the length between the transition point of a normal artery and an abnormal artery can be difficult to assess, especially in the case of a long non opacified segment. The accuracy in determining the extension of vascular lesion can be underestimated due to adjacent soft tissue [
5,
74]. In penetrating trauma wound tracks or ballistic fragments within 5 mm of a neurovascular bundle must be considered suggestive of vascular injury [
75].
Madhuripan et al. [
67] proposed a systematic approach to CTA, that can be useful in clinical practice. The exam should be first evaluated to assess the quality of vessel opacification. MIP (maximum intensity projection) are useful for a first and fast primary assessment of exam quality and major findings. MPR and 3D images provide a global view of findings and, if possible, the comparison of both limbs could be helpful in pointing out the lesion that should be conformed on axial images. Each vessel should be examined on axial images carefully for caliber, wall alteration, opacification, and extravasation. Meticulous assessment of major vessels run-off is relevant and major branches need to be followed along their course. Particularly attention should be given to perforators in both upper and lower limbs especially in penetrating trauma. Smaller branches opacification of arches of hands and feet is variable and vascular damage should be rule out in case of distal ischemia and no proximal vascular damage. Postprocessing workstation can be used with vascular optional tools to aid the diagnosis. Assessment of nonvascular structures should be carried out in standard and bone windows (fractures, hematomas, soft tissue, lacerations, foreign bodies). Incidental findings should be reported [
67].
CTA Pitfalls
Correct positioning with a wide field of view is essential but not always possible, causing nondiagnostic examination[
76] (
Figure 7). A second limb acquisition could be performed by decentralizing the patient on the CT table and focusing the exam on the limb of interest
Distal poor opacification may occur if adequate flow if not obtained or for delays due to cardiac output, in the latter situation bolus tracking may be helpful [
66].Non optimal opacification especially of distal arteries may be avoided with a second contrast bolus or with a second acquisition immediately after the first arterial phase. In penetrating trauma or in case of severe compressing hematomas, a delayed phase may be acquired to determine late extravasation[
76].
Motion artifacts should be avoided immobilizing the patients [
66]. Streak artifacts from metallic fragments could determine CT diagnostic inaccuracy (
Figure 8), the iterative filter should be applied in order to reduce these artifacts and distal vessels should be carefully examined [
66]. In comminuted fracture, radiologists must pay attention to individuating active bleeding among bony fragments, comparing the unenhanced and arterial phases. Satisfaction errors should be avoided because 12% of patients presents concomitant multiple vascular injuries [
7,
38,
60,
66,
67,
70,
76,
77,
78,
79].