Hemiazygos Vein
The hemiazygos vein is seen on chest imaging studies. It is located in the posterior thorax along the left side of the vertebral column. This vessel serves as a collateral pathway in the venous drainage system. When mentioned in radiology reports, it may indicate normal anatomy or abnormal conditions affecting venous return. This article will discuss the hemiazygos vein, its appearance on different imaging modalities, and the clinical significance of any abnormalities of the vein.
What Is the Hemiazygos Vein?
The hemiazygos vein is a blood vessel located in the left side of your chest, running alongside your spine. It collects deoxygenated blood from the left side of your chest wall and delivers it to the azygos vein, which ultimately returns this blood to your heart.
Think of the hemiazygos vein as part of your body’s backup drainage system. While most of your blood returns to your heart through the main highway—the superior and inferior vena cava—the hemiazygos vein serves as an alternate route when needed.
Hemiazygos Vein Anatomy
The hemiazygos vein typically begins near the left kidney and ascends through the chest. Around the level of the 8th or 9th thoracic vertebra, it crosses over to the right side of your spine to join the azygos vein.
This vein has several important connections:
- It receives blood from the lower left intercostal veins (the veins between your ribs)
- It connects with the accessory hemiazygos vein, which drains the upper left chest area
- It often communicates with the left renal vein near your kidney
Understanding these connections helps radiologists interpret findings related to this vessel on imaging studies.
How the Hemiazygos Vein Appears on Imaging
CT Scan Appearance
On CT (computed tomography) scans, the hemiazygos vein appears as a small, tubular structure on the left side of the spine in the posterior chest. When intravenous contrast is used, this vein enhances (appears brighter) during the venous phase. Enlargement of the vein may indicate increased blood flow through this vessel, possibly due to blockage elsewhere in the venous system.
Ultrasound Visualization
While not commonly targeted during routine ultrasound examinations, the hemiazygos vein can sometimes be visualized with specialized techniques. Color Doppler ultrasound can show blood flow direction and velocity within this vessel when needed for specific diagnostic questions.
Common Radiological Findings Involving the Hemiazygos Vein
Hemiazygos Vein Enlargement
Enlargement of the hemiazygos vein is one of the most common abnormal findings involving this vessel. This typically indicates:
- Obstruction of the inferior and superior vena cava
- Blockage in the azygos vein
- Increased pressure in the right side of the heart
- Liver cirrhosis causing portal hypertension
When radiologists note an enlarged hemiazygos vein, they look for associated findings to determine the underlying cause.
Hemiazygos Continuation
Sometimes, a person may have a condition called “hemiazygos continuation,” where the lower portion of the inferior vena cava is absent, and the hemiazygos vein takes over its function. This developmental variation is typically discovered incidentally during imaging for unrelated reasons.
In these cases, the hemiazygos vein appears significantly larger than normal because it’s handling much more blood flow than it typically would.
Collateral Pathway in Vena Cava Obstruction
When the superior or inferior vena cava becomes blocked (due to blood clots, tumors, or other conditions), the body often recruits the hemiazygos vein as an alternate pathway for blood return to the heart. Radiologists look for an enlarged, tortuous hemiazygos vein as evidence of this compensatory mechanism.
Clinical Significance of Hemiazygos Vein Abnormalities
Understanding what hemiazygos vein findings mean can provide important clinical insights:
Cancer Evaluation
Enlarged lymph nodes or tumors in the chest can compress or invade the hemiazygos vein. Radiologists carefully evaluate this vein when staging lung cancer, lymphoma, or other thoracic malignancies.
Heart Failure Assessment
Right-sided heart failure can cause backup pressure in the venous system, leading to enlargement of the hemiazygos vein. This finding may help confirm the diagnosis or indicate the severity of heart failure.
Congenital Anomalies
Variations in the development of the hemiazygos vein can be associated with other congenital anomalies, particularly those involving the development of the inferior vena cava and other major blood vessels.
Interventional Procedures Involving the Hemiazygos Vein
In some cases, the hemiazygos vein becomes important for interventional radiology procedures:
Vascular Access
When traditional vascular access routes are unavailable, interventional radiologists may sometimes use the azygos or hemiazygos system to reach specific areas of the body.
Embolization Procedures
Rarely, abnormal connections involving the hemiazygos vein require embolization—a procedure where materials are introduced to block abnormal blood flow.
When I see an enlarged hemiazygos vein on imaging, it prompts me to look for evidence of inferior vena cava obstruction or right heart dysfunction. This single finding can sometimes be the first clue to a significant underlying condition that might otherwise be missed.
Conclusion
The hemiazygos vein may be a small structure, but its appearance on imaging studies can provide valuable diagnostic information. Abnormalities of this vessel often reflect problems elsewhere. Whether you’re a patient trying to understand your radiology report or a healthcare professional reviewing imaging findings, recognizing the significance of hemiazygos vein abnormalities can help guide appropriate clinical management and further diagnostic workup.
Understanding the normal anatomy and common variations of this vein helps radiologists accurately interpret imaging findings and avoid misdiagnosis. While not often the primary focus of imaging studies, the hemiazygos vein serves as an important anatomical landmark and potential indicator of underlying pathology.
References
- https://radiopaedia.org/articles/hemiazygos-vein?lang=us
- https://pmc.ncbi.nlm.nih.gov/articles/PMC3473485/
- https://www.sciencedirect.com/science/article/pii/S1930043323002741