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State of the Art 3DCT Angiography Assessment of Upper Extremity Trauma: Pearls, Pitfalls, and Study Design Optimization

Elliot K. Fishman M.D.
Johns Hopkins Hospital

Click here to view this module as a video lecture.

Objectives

Optimize image acquisition, injection technique and processing of 3DCT angiography in upper extremity trauma
Illustrate the various 3DCT angiography findings of vascular trauma of the upper extremity
Discuss pearls and pitfalls

Introduction

Multi-detector computed tomography angiography (MDCTA) is now an essential part of the initial assessment of acutely injured patients and has replaced catheter-based angiography in many institutions worldwide.
Advances in MDCT technology enable high speed simultaneous evaluation of both upper and lower extremities with a single peripheral intravenous power-injected bolus of iodine-based contrast.
Polytrauma MDCT protocols have been developed to integrate MDCTA into multiphasic whole-body trauma MDCT.
Reformation of data rapidly provides high-resolution multi-planar views and three-dimensional reconstructions with minimal motion artifact.

Epidemiology and Etiology

Upper extremity vascular injury in present is 30% of all modern wars and civilian trauma in the U.S.
Arterial injury is present in up to 3.3%, which is a higher incidence than in the lower extremities.
60% are penetrating injuries (e.g., fire arm, stabbing) and 40% are blunt trauma (e.g., motor vehicle accident).
Brachial artery injury (40%) is most common, followed by radial artery (25%), axillary/subclavian artery (20%), and ulnar artery (15%).
35% have associated injuries, including venous injury in 35%, orthopedic injury in 25% and nerve damage in 20%.

Management

Scenarios with so-called hard signs of vascular injury usually require immediate surgical exploration and appropriate treatment, such as repair or bypass:

CT of Upper Extremity Trauma

Top 4 indications for MDCTA

Exclusion of vascular injury in the absence of hard signs.
Determination of injury location, nature, and extent of a vascular injury in the absence of hard signs.
Penetrating injuries with clinical hard signs and uncertain presence or location of arterial injury, such as in delayed presentation, severe bone fracture or soft-tissue injury, chronic vascular disease, and gunshot wounds.
In blunt trauma, owing to the high incidence of associated bone, nerve, and soft-tissue injuries that could contribute to clinical hard signs, thereby obscuring an accurate diagnosis.

The Algorithm

Optimization of MDCT acquisition parameters and low-dose techniques

64+ MDCT provide critical advantages of isotropic and high spatial resolution data acquisition (<0.4 mm), fast image acquisition, increased speed of data reconstruction and real-time postprocessing capabilities.
100-120 mL of intravenous contrast material at a rate of 4-5 mL/sec results in excellent vascular opacification, unless contraindicated.
Appropriate timing is critical for maximum arterial enhancement:
- 40–45 sec delay usually results in optimal middle to late arterial phase.
- Bolus tracking / test bolus may be used, but delay may be most expedient.
- Good venous opacification can be achieved 25–35 sec after the arterial phase
Dual source technology, higher pitch, modified slice thickness, decreased mAs, tube current of 80-100 kV, flash rotation speed and dose reduction algorithms are helpful to minimize radiation exposure.

64 Slice MDCT angiography protocols

Metal artifact reduction

Reducing artifacts from high-density foreign matter:

increasing peak voltage
increasing tube charge
smallest possible collimation
extended display CT scale

The resulting increase in radiation dose, especially from increasing peak voltage, however, needs to be considered.

Artifacts may also be substantially reduced by Dual Energy CT based high energy extrapolation algorithms.

MDCTA versus Digital Subtraction Angiography

Pertinent vascular MDCT angiography anatomy

3D visualization

3D mapping of MDCTA data allows for virtual visual inspection, simulated classic catheter digital subtraction angiogram, provides the capability to display tissue muscle, soft tissues, and bone, and segmentation capabilities for virtual bone removal, which may be required for maximum intensity projection and volume rendering technique.

CT of Upper Extremity Trauma

MDCTA of vascular injury

Findings of arterial injuries include:

Hematoma
Active extravasation
Vasospasm
Stenosis
External compression
Occlusion
Intimal injury and dissection
Arteriovenous fistulas
Pseudoaneurysm formation

Active extravasation

Active extravasation is caused by disruption of all layers of the vessel wall, which can be partial or involve the entire circumference of the vessel. MDCTA is helpful for the differentiation of ongoing hemorrhage versus hematoma without active bleeding.

Clotted hematomas without active hemorrhage are typically hyperdense and show no signs of iodine-contrast accumulation.

Acute hemorrhage is demonstrated by the accumulation of iodine contrast material inside a hematoma or in soft tissues.

MDCTA is especially helpful in differentiating active hemorrhage of peripheral arterial branches, which may be treated with conservatively from active hemorrhage of a major artery, which are more likely to require surgery.

Illustration demonstrates active arterial extravasation with disruption of all layers and partially clotted hematoma. CT of Upper Extremity Trauma

Active extravasationSoft tissues

MDCTA and 3DCT images following stab wound trauma of the left chest demonstrate an arterial extravasation (red arrows) of the left pectoralis major of a small branch of the thoracoacromial. The axillary artery is intact (yellow arrows).

Active extravasationSoft tissues

Active extravasationSmall arterial branches

MDCTA and 3DCT images following blunt chest trauma demonstrate a soft tissue hematoma involving the left latissimus dorsi muscle (red arrow) with small foci of active hemorrhage originating from branches of the circumflex scapular artery (yellow arrows). Data were acquired with elevated left arm.

Active extravasationSmall arterial branches

Active extravasationSmall arterial branches

3D CTA images following gun shot injury of the proximal left upper extremity demonstrates the bullet entry (red arrow) and focal active arterial extravasation of a branch of the profunda brachii artery (yellow arrows).

Active extravasationSmall arterial branches

Active extravasationSmall arterial branches with soft tissue laceration

3D CTA images of a mangled right upper extremity* demonstrate a soft tissue laceration of the elbow region with active arterial extravasation (red arrows) of branches of the profunda brachii artery (yellow arrows).

* defined as high energy transfer and/or crush injury resulting in some combination of injuries to artery, bone, tendon, nerve and/or soft tissue

Active extravasationSmall arterial branches with soft tissue laceration

Active extravasationTransection

MDCTA and 3DCT images following penetrating injury of the right axillary region demonstrate active hemorrhage originating from the axillary artery (yellow arrows) with no apparent contrast enhancement distally (red circles), representing a surgically proven transection.

Active extravasationTransection

Active extravasationTransection

3D CTA images of a mangled upper extremity* show soft tissue laceration (yellow arrow) and underlying traumatic transection of the proximal brachial artery (red arrow) with absent blood flow distally.

* defined as high energy transfer and/or crush injury resulting in some combination of injuries to artery, bone, tendon, nerve and/or soft tissue

Active extravasationTransection

Pseudoaneurysm

Pseudoaneurysm is caused by incomplete disruption of the layers of the arterial wall. The occurrence of a pseudoaneurysm may be delayed or it may manifest as a contained hematoma during the healing phase of a vascular injury.

Illustration demonstrates incomplete disruption of the arterial wall and the sequence of development of a pseudoaneurysm (box).

Pseudoaneurysm

3D MDCTA image in a patient following gun short trauma shows a comminuted fracture of the right scapula (yellow arrow) and a traumatic pseudoaneurysm of the right axillary artery (right arrow) in the trajectory of the bullet.

Pseudoaneurysm

3D MDCTA images in a patient after nail gun injury of the left elbow region demonstrates a pseudoaneurysm of a small branch of the radial artery (arrows).

Vascular occlusion and spasm

Luminal narrowing and occlusion can be due to severe vasospasm, dissection, injury of the intima with thrombus formation, and external compression.

Post-traumatic vasospasm presents as reactive, transient luminal narrowing. In cases of vasospasm, signs of arterial insufficiency resolve over time.

Dissection may present as narrowing of the vessel lumen and may not be differentiated with certainty on MDCTA.

In such cases, catheter-based angiography may be helpful and close clinical follow-up is indicated. MDCTA follow-up may be helpful for further differentiation as well.

Illustrations of arterial vasospasm (left) and arterial dissection (right) with inlay schemes demonstrating the similarity of the appearance of the contrast opacified lumen. Vascular occlusion and spasm

Vascular occlusion

3D CTA images of a mangled forearm show a large soft tissue laceration (red arrow) and underlying traumatic occlusion of the ulnar artery (yellow arrow) without distal reconstitution. There radial artery (blue arrow) is preserved.

Vascular occlusion

Vascular occlusion

3D CTA images following blunt trauma of the right elbow region show a filling defect in the right ulnar artery (arrows) with distal reconstitution of the vessel. Surgical exploration demonstrated disruption of the intima with thrombus formation.

Vascular occlusion

Spasm

3D CTA images of a mangled left forearm show a soft tissue laceration (red arrow) and segmental narrowing of the ulnar artery (yellow arrow) and radial artery (blue arrows) with distal reconstitution due to severe vasospasm, which resolved over time.

Spasm

Early venous contrast opacification

Early venous contrast opacification can be an indirect sign of a traumatic arteriovenous fistula or can be due to trauma-related hyperemia. Arteriovenous fistulas are abnormal communications with shunting of blood from an artery to a vein that occur after simultaneous damage of the two adjacent vessels. Common causes include penetrating trauma from gunshot and stab wound.

Illustrations of an arteriovenous gunshot injury with resulting fistula and abnormal shunting of arterial blood (arrow) into the vein (blue vessel) explaining early venous contrast opacification.

Associated injury

3D CTA image of a penetrating trauma of the left shoulder demonstrates active hemorrhage (arrow) originating from the cephalic vein.

3D CTA image of a mangled right forearm demonstrates a comminuted ulnar shaft fracture (arrow).

Associated injury

Rib Fractures

Pearls

Multiphasic protocols improve the detection and definitive characterization of contrast extravasation and frequently differentiate arterial and venous hemorrhage.
Maximum intensity projection images alone may result in failure to detect subtle lesions like arterial dissection and require correlation with the source images.
Differentiation of severe vascular spasm from occlusion may be difficult by CTA.
In cases of significant penetrating and blunt trauma to the large arteries of the proximal extremities, MDCTA has shown sensitivities of 90-100% and specificities of 98.7-100%.
An advantage of 3D mapping is the ability to display the information in a format that not only simulates a classic catheter angiogram (digital subtraction), but also the capability to display tissue in addition to the vasculature, including muscle, soft tissues, and bone.
MIP and volume rendering technique (VRT) may require segmentation with bone removal. VRT is especially valuable when opaque foreign matter is present.

Pitfalls

A variety of factors may obscure or mimic vascular injury on MDCTA including inadequate arterial enhancement due to timing of contrast injection, motion artifacts, inadequate positioning, streak artifacts, dense calcifications, and similar density of vessel and bone.
Venous injuries may be missed on a single phase study or in the absence of late phase images.
Use of a high-resolution kernel is optimal for evaluating the bones; however, the high-resolution algorithms are suboptimal for vascular reconstruction or 3D mapping and reconstruction with a second dataset may improve interpretation.
Metal fragments can cause beam-hardening artifacts and potentially “create” pseudolesions or hide subtle lesions.

Summary

MDCTA allows for rapid, non-invasive and accurate diagnosis of arterial and associated injuries in upper extremity trauma.
Individualized injection protocols ensure highest diagnostic image quality. Several strategies are available to reduce radiation exposure.
3D visualization techniques will improve the radiologist’s ability to identify the various signs and patterns of vascular injury and will help to demonstrate and communicate pertinent findings.
By demonstrating the extent, location, and type of injury, MDCTA aids in the characterization of vascular injury and helps to determine the appropriate management.