British Journal of Radiology 74 (2001),328-330 © 2001 The British Institute of Radiology
Identification of vertebral arteries on CT of the chest
E Oh, MD,
D J Quint, MD and
B H Gross, MD
Department of Radiology, University of Michigan Medical Center, Ann Arbor, MI 48109, USA
Correspondence: Douglas J Quint, MD, B1D520, Neuroradiology, Box 30, Radiology, University of Michigan Medical Center, 1500 East Medical Center Drive, Ann Arbor, MI 48109-0030, USA
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Abstract
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Knowledge of the superior mediastinal course of the vertebral arteries is important for radiologists who evaluate chest CT, particularly in the setting of trauma, when planning a percutaneous interventional procedure or for pre-operative planning. Our aim was to determine how often the vertebral arteries could be identified on chest CT studies. Contrast enhanced chest CT studies from 100 consecutive patients were reviewed, with specific attention to the vertebral arteries in the superior mediastinal and thoracic outlet regions. The left vertebral artery was identified in 85 patients and the right vertebral artery in 76 patients. Non-visualization of a vertebral artery was usually owing to proximal venous occlusion with extensive collateral vessels in the expected location of the vertebral arteries, local lymphadenopathy, poor contrast bolus technique or local beam hardening artefact. Radiologists need to alert surgeons planning resection of mass lesions in this region to the location of the vertebral arteries. It is also important to note that a vertebral artery was not identified on chest CT in 24% of patients.
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Introduction
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Imaging of the aorta and the great vessels by CT has been extensively investigated. CT imaging of the great vessels in the setting of trauma has recently received attention [1, 2]. Some authors advocate dedicated CT angiography of the great vessels of the neck in specific cases of neck trauma [3]. However, the appearance of the vertebral arteries on a standard chest CT has not previously been described to our knowledge. As it is important in the setting of acute or old trauma, or in pre-operative planning, to know the exact location of the superior mediastinal portion of the vertebral arteries, the purpose of this study was to describe the normal CT appearance of the vertebral arteries on standard chest CT, including their frequency of visualization in a clinical population.
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Materials and methods
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100 consecutive helical chest CT studies performed over a 6-week period were retrospectively reviewed by a thoracic radiologist (BHG) and a neuroradiologist (DJQ) in consensus. All studies were performed on a GE Helical Advantage CT unit (GE Medical Systems, Milwaukee, WI) and utilized bolus administration of iv contrast medium by power injection. Three different protocols were utilized depending on the clinical indication for each study. Dedicated imaging of the chest only was performed using 5 mm collimation and a pitch of 1:1.7. Intravenous contrast medium was injected at an infusion rate of 1.5 ml s-1 for a total of 75 ml with imaging initiated 35 s after the beginning of contrast medium injection. Images were prospectively reconstructed and photographed at 7 mm thickness. If scanning also included the abdomen, the chest images were again obtained with 5 mm collimation and a pitch of 1:1.7. Intravenous contrast medium was then injected at an infusion rate of 3 ml s-1 for a total of 150 ml, with imaging initiated 25 s after the beginning of contrast medium injection. Images were again prospectively reconstructed and photographed at 7 mm thickness. If imaging of the chest, abdomen and pelvis was performed, the chest images were obtained with 10 mm collimation and a pitch of 1:1. Intravenous contrast medium was injected at an infusion rate of 3 ml s-1 for a total of 150 ml, with imaging initiated 25 s after the beginning of contrast medium injection. Soft tissue windows were reviewed for all studies, with a window width of 450 Hounsfield units and a level of 20. All imaging was performed to include the lung apices. As all scans were performed with a field ofview to include the entire chest, the thoracic location of both vertebral arteries was included inevery case. However, no specific landmark wasutilized to determine the start location of each imaging sequence. A variable amount of the lower neck was therefore included in these CT examinations.
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Normal anatomy
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The vertebral arteries usually arise from the posterosuperior aspects of the proximal subclavian arteries and enter the transverse foramina of the cervical vertebrae above the level of C7 (at C6 level in more than 95% of subjects). They extend cephalad through these foramina transversaria to the C1 level. The vertebral arteries then turn posteromedially above the C1 lamina and pass medial to the superior portions of the lateral masses of C1. After coursing through the ligaments at the foramen magnum (the posterior atlanto-occipital membrane), the vessels pierce the dura and arachnoid to enter the paramedullary subarachnoid space and then join anterior to the pontomedullary junction to form the basilar artery. The left vertebral artery is the same size or larger than the right vertebral artery in approximately 75% of patients [4]. However, the right vertebral artery has been reported to be larger than the left in 32% of patients [5].
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Results
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The left vertebral artery was seen in 85 of 100 (85%) patients. The artery was visualized for an average cephalocaudal distance of 2.5 cm and could be followed to the most cephalic image of the chest CT study in 69 of 85 (81%) studies. Its average diameter was 3 mm.
The right vertebral artery was seen in 76 of 100 (76%) patients. The artery was visualized for an average of 2.2 cm and could be followed to the most cephalic image of the chest CT study in 58 of 76 (76%) studies. Its average diameter was also 3 mm.
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Discussion
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The vertebral arteries were seen in the majority of patients, 85% on the left and 76% on the right (Figure 1
), and could usually be followed for over 2 cm, often to the most superior image of these dedicated chest CT studies. The most common reason for non-visualization of a vertebral artery was the presence of extensive collateral vessels, which usually occurred in the presence of proximal venous occlusion (Figure 2). This accounted for approximately 75% of the cases of non-visualization. Additional reasons for non-visualization, accounting for approximately 24% of the cases, included poor contrast bolus, "streak artefact" from the shoulders and extensive lymph node enlargement with secondary distortion of the normal anatomy.
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Figure 1. Normal vertebral arteries. The vertebral arteries (arrows, b–d) are well-seen bilaterally arising from the posteromedial aspects of the subclavian arteries (arrowheads, a). a–d are serial sections extending cephalad from the level of the subclavian arteries. a, subclavian arteries; t, trachea; e, oesophagus.
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Figure 2. Non-visualization of vertebral arteries. Extensive collateral veins (arrowheads) due to superior mediastinal obstruction obscure the expected location of the vertebral arteries. Arrow, expected location of the left vertebral artery; t, trachea; e, oesophagus.
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Although the angiographic literature indicates that the left vertebral artery is the same size or larger than the right in approximately 75% of patients [4], there was no detectable size difference in our study. This is not surprising given the small size of the vessels and the relatively poor spatial resolution of CT in comparison with cut-film angiography, the gold standard for the imaging determination of vessel size. Additionally, our sample size was small and probably insufficient to detect minimal size differences.
As utilization of CT and CT angiography increases, it is important for radiologists to be aware of the course of the thoracic portions of the vertebral arteries on chest CT. Neck and superior mediastinal trauma, often owing to motor vehicle accidents, is a common occurrence. Knowledge of the normal location and appearance of a vertebral artery may help in the evaluation of gross bleeding or a penetrating injury to this region. When there is a history of trauma, the possibility of post-traumatic pseudoaneurysm or fistula in this region may also require consideration. Knowing the exact location of the vertebral arteries when performing percutaneous superior sympathetic ganglia blocks is important to avoid placement of the needle into a vertebral artery (Figure 3). Finally, knowing that the vertebral arteries may not be identified in up to 24% of patients on chest CT examinations may be useful for determining the need for additional imaging.
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Figure 3. Sympathetic block via a percutaneous approach. Contrast medium (arrow) injected along with the anaesthetic agent extends to the expected location of the left vertebral artery. t, trachea; e,oesophagus.
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Received for publication April 14, 2000.
Revision received September 18, 2000.
Accepted for publication October 5, 2000.
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References
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Abstract
Introduction
