CT Angiography for Diagnosing Thoracic Outlet Syndrome and Decreased Blood Flow to the Arm
CTA of the upper extremity is highly effective for diagnosing thoracic outlet syndrome and decreased blood flow to the arm, providing excellent visualization of arterial compression and stenosis with sensitivity and specificity of 90-100% compared to conventional angiography. 1
Diagnostic Capabilities of CTA for Thoracic Outlet Syndrome
- CTA effectively evaluates arterial compression in thoracic outlet syndrome by visualizing indentation of the anterior wall of the subclavian artery as it passes around the anterior scalene muscle and displacement of subclavian vessels 2
- CTA should be performed in both neutral and elevated arm positions to assess for dynamic arterial compression, which is essential for diagnosing arterial thoracic outlet syndrome (aTOS) 2, 1
- Arterial stenosis can be precisely quantified as a percentage reduction of cross-sectional area or diameter of the artery, providing objective measurements of compression 2
- CTA shows good correlation with operative findings and results of decompression, making it valuable for surgical planning 2
Technical Considerations for Optimal Imaging
- Sagittal reformation of data is crucial for accurate assessment of arterial compression, as axial slices alone can lead to underestimation of stenosis in 43% of cases (versus only 10% with sagittal reformations) 2, 1
- Volume-rendered images are preferred over surface displays with 3D shading, as the latter can overestimate stenosis in 16% of cases (versus 7% with volume rendering) 2, 1
- A multislice CT scanner with collimation of 0.6 mm and reconstruction slice thickness between 0.5-1.0 mm is recommended for upper extremity CTA 1
- Non-ionic iodinated contrast agent (≥350 mg/mL) using a power injector (≥4 mL/s) provides optimal vessel visualization 1
Advantages Over Other Imaging Modalities
- CTA provides simultaneous analysis of both vascular structures and surrounding anatomy, allowing assessment of potential causes of arterial compromise such as cervical ribs, fibromuscular bands, or muscular hypertrophy 2, 1
- Unlike conventional angiography, CTA is non-invasive and doesn't carry the risks associated with catheterization, while still providing detailed vascular information 2, 1
- CTA has largely replaced conventional angiography as the reference standard for arterial imaging in many institutions 1
- Compared to MRA, CTA offers faster acquisition times, which is beneficial for symptomatic patients who may have difficulty maintaining positions during longer imaging sequences 2, 1
Clinical Applications Beyond Diagnosis
- CTA is valuable for post-intervention assessment to evaluate vessel patency and complications such as restenosis, occlusion, or aneurysm formation 2, 1
- For patients undergoing surgical treatment for thoracic outlet syndrome, CTA can evaluate interval changes in the thoracic outlet and assess adequate decompression 2
- In patients with arterial thoracic outlet syndrome presenting with acute limb ischemia, early diagnosis with CTA is crucial as delayed thoracic outlet decompression is associated with increased risk of recurrent thromboembolic events 3
- CTA can identify subclavian artery pathology including stenosis, aneurysm formation, mural thrombus, or distal emboli that may require surgical intervention 4
Potential Limitations and Pitfalls
- Heavily calcified atheromatous disease can limit the ability to interpret CT images 1
- Timing of contrast administration is critical to avoid venous contamination or inadequate arterial opacification 1
- For venous thoracic outlet syndrome (VTOS), CT venography (CTV) would be more appropriate than CTA 5
- Patients with renal dysfunction may have contraindications to iodinated contrast agents used in CTA 1
CTA of the upper extremity provides comprehensive assessment of vascular anatomy and pathology, making it an excellent choice for diagnosing thoracic outlet syndrome and decreased blood flow to the arm. Its ability to visualize both vascular structures and surrounding anatomy in multiple planes offers significant advantages for diagnosis and treatment planning.