For arm pain and paresthesia, should I get a Computed Tomography Angiography (CTA) of the thorax or the upper extremity?

CTA Thorax is the Preferred Imaging Choice for Arm Pain and Paresthesia

For arm pain and paresthesia, CTA thorax is the most appropriate initial imaging study rather than CTA upper extremity, as it provides comprehensive evaluation of the thoracic outlet structures and central vessels that are most likely causing these symptoms.

Rationale for CTA Thorax Selection

• CTA thorax specifically evaluates the chest and thoracic outlet, including central vessels as well as subclavian and axillary arteries and veins, which are the key structures involved in thoracic outlet syndrome that commonly presents with arm pain and paresthesia 1, 2
• CTA upper extremity protocols are designed to evaluate the entire limb peripherally to the wrist, which extends beyond what's needed for thoracic outlet assessment and may miss central pathology 1, 2
• The American College of Radiology distinguishes between these protocols, noting that CTA thorax is tailored for thoracic outlet evaluation while CTA upper extremity is for peripheral limb assessment 1, 2

Clinical Presentation Considerations

• Patients with thoracic outlet syndrome often present with symptoms of ipsilateral upper-extremity edema, pain, paresthesia, and functional impairment, which matches your clinical presentation 1
• Unilateral swelling indicates an obstructive process at the level of the brachiocephalic, subclavian, or axillary veins, which are best visualized with CTA thorax 1
• Neurogenic thoracic outlet syndrome (nTOS) can cause arm pain and paresthesia due to compression of the brachial plexus, which CTA thorax can help evaluate by demonstrating anatomical narrowing 1

Technical Protocol Considerations

• CTA thorax for thoracic outlet syndrome should be performed in both neutral and stressed positions to demonstrate dynamic compression 1, 2
• The protocol should include thin-section CT acquisition timed with arterial enhancement, with multiplanar reformations and 3D renderings 1, 2
• Scan acquisition typically uses contralateral antecubital IV injection with either empiric scan delay or bolus tracking over the ascending aorta 1

Advantages of CTA Over Other Modalities

• CTA offers volumetric (3D) imaging, enabling extensive image post-processing to create a detailed arterial road map 3
• CTA provides simultaneous analysis of both vascular structures and surrounding anatomy, allowing for comprehensive assessment of potential causes of arterial compromise 3, 4
• The sensitivity and specificity of CTA for detection of significant stenoses are 90% to 100% when compared with conventional angiography 3, 4

Common Pitfalls to Avoid

• Reliance on axial slices alone can lead to underestimation of stenosis in 43% of cases, while sagittal reformations reduce this to only 10% 3
• Heavily calcified atheromatous disease can limit the ability to interpret CT images 2, 3
• Timing of contrast administration is critical to avoid venous contamination or inadequate arterial opacification 3

Alternative Considerations

• If thoracic outlet syndrome is suspected but CTA is contraindicated, MRI with MRA would be an alternative choice, particularly for neurogenic TOS where definition of the brachial plexus is required 1
• Ultrasound duplex Doppler can be useful for initial screening but has limitations in visualizing deeper vessels and the central thoracic outlet 1, 3

By selecting CTA thorax over CTA upper extremity for arm pain and paresthesia, you'll receive the most comprehensive evaluation of the potential vascular and anatomical causes of your symptoms, focusing on the thoracic outlet region where most pathology causing these symptoms originates.