Innominate Vein
The innominate vein, also known as the brachiocephalic vein, is an important blood vessel in the upper chest that can sometimes be mentioned in radiology reports. This article explains what the innominate vein including how it appears on various imaging studies and what abnormalities may be noted.
What Is the Innominate Vein?
The innominate vein is a large blood vessel formed by the joining of the internal jugular vein and the subclavian vein. There are two innominate veins – the right and left. They meet to form the superior vena cava, which carries deoxygenated blood back to the heart.
The term “innominate” literally means “without a name,” though today most medical professionals prefer the more descriptive term “brachiocephalic vein” (meaning it relates to both the arm and head). The left innominate vein is longer than the right and traverses horizontally across the upper chest, passing in front of the major arteries that emerge from the heart.
Innominate Vein on Different Imaging Modalities
CT Scan Appearance
On computed tomography (CT) scans, the innominate veins appear as tubular structures in the upper chest. When intravenous contrast is used, these veins can become bright white, making them easily identifiable. Radiologists can assess their size, patency (openness), and relationship to surrounding structures.
MRI Visualization
Magnetic resonance imaging (MRI) offers excellent soft tissue contrast that can clearly demonstrate the innominate veins without radiation exposure.
Ultrasound Findings
Ultrasound can provide real-time visualization of the innominate veins, especially in children and thin adults. The sonographer typically places the transducer at the base of the neck or upper chest to view these vessels. Normal blood flow appears blue or red on Doppler ultrasound, depending on the direction of flow relative to the transducer.
Chest X-ray Limitations
The innominate veins are not directly visible on standard chest X-rays. However, significant enlargement or abnormalities of these veins may cause subtle changes in the mediastinal contour (the central part of the chest containing the heart and major blood vessels).
Common Abnormalities of the Innominate Vein
Thrombosis (Blood Clots)
Innominate vein thrombosis appears on imaging as filling defects within the vein. The affected vein may be enlarged and the surrounding tissues may show inflammatory changes. This condition often relates to central venous catheters, pacemaker wires, or other devices placed within the vein.
Compression Syndromes
The left innominate vein can become compressed between the sternum (breastbone) and the aortic arch, a condition known as innominate vein compression syndrome. On imaging, this appears as narrowing of the vein with potential collateral vessel formation (new blood vessels that develop to bypass the obstruction).
Congenital Variations
Anatomical variations of the innominate veins are relatively common. These include abnormal positioning, duplication, or even absence of one of the veins. These variations are important to identify before certain surgical procedures, particularly those involving the placement of central venous catheters.
Tumor Involvement
Masses in the mediastinum (the central compartment of the chest) may compress, displace, or even invade the innominate veins. Lymphoma, thymoma, and lung cancer are common culprits. Imaging may show narrowing or occlusion of the vein with possible collateral vessel formation.
Importance in Medical Procedures
The innominate veins serve as important landmarks during many medical procedures. They are common sites for central venous catheter placement, which appears on imaging as a tube-like structure within the vessel lumen. Surgeons operating in the chest and neck area must be aware of these vessels to avoid inadvertent injury.
When to Be Concerned About Innominate Vein Findings
Not all innominate vein abnormalities require treatment. Many congenital variations cause no symptoms and are simply noted in the radiology report. However, certain findings warrant further investigation:
- Complete blockage of the vein
- Significant compression causing symptoms
- Evidence of tumor invasion
- Thrombus (blood clot) formation
- Abnormal dilation or aneurysm
Diagnostic Approaches for Innominate Vein Issues
When abnormalities of the innominate vein are detected, your doctor may recommend additional tests. Contrast venography, where dye is injected directly into the vein and X-rays are taken, provides detailed images of blood flow through the vessel. CT venography combines the benefits of CT scanning with contrast injection for more complete evaluation.
Conclusion
The innominate vein plays an important role in returning blood from the head, neck, and upper limbs to the heart. Abnormalities in this vessel need prompt diagnosis and treatment in some cases. Modern imaging techniques allow for detailed visualization of the innominate veins and can identify various pathologies affecting these important structures. Understanding what these findings mean on your radiology report can help you have more informed discussions with your doctor.
References
- https://www.ncbi.nlm.nih.gov/books/NBK544339/
- https://my.clevelandclinic.org/health/body/23466-brachiocephalic-vein
- https://radiopaedia.org/articles/brachiocephalic-vein?lang=us