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Original article

Three-dimensional CT angiography study on the relations between the vertebral artery and atlantoaxial joint

DUAN, Shao-yin; LÜ, Shao-mao; YE, Feng; LIN, Qing-chi; CHEN, Liao-bin

Editor(s): WANG, De

Author Information
doi: 10.3760/cma.j.issn.0366-6999.2009.08.007
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Abstract

The vertebral artery (VA) is an important source of brain blood supply. It goes along the atlantoaxial joint (AAJ) with curves or loops and forms the so-called atlantoaxial segment vertebral artery (ASVA). Research on the ASVA or AAJ have been conducted,1-6 but there is no research on the relationship between the ASVA and AAJ with three-dimensional CT angiography (3DCTA), a new imaging method with the advantages of showing blood vessels and bone or joints clearly and directly.7-9 Our study was to observe with 3DCTA the course of the ASVA and describe its relationship to the AAJ from the view of clinical imaging anatomy, and to provide an anatomical basis for related research.

METHODS

General information

In our hospital, from January 1st 2005 to April 30th 2008, CT scanning data of 68 subjects (46 males, 22 females, aged between 16 years and 82 years, mean age 32.2±2.5 years) without pathology of the AAJ and VA were selected from head-neck CT angiography (CTA). The 3D images were retrospectively performed in order to show clearly the structures of the AAJ and ASVA.

Materials and equipment

The contrast medium (Omnipaque, 300 mgI/ml) with a total amount of 1.5 ml/kg-2.0 ml/kg was injected at a velocity of 3.0 ml/s-4.0 ml/s with a pressure injector (MCT-plus, PGH. or Stellant, USA). The multi-detector-row spiral CT scanner (MDCT) and the Advantage Workstation 4.2 with 3D imaging software (GE company, USA) were used in 15 cases by Light Speed16 (16-MDCT) and in 53 by Light Speed VCT (64-MDCT).

Scanning method and data processing

After the contrast medium was injected into the forearm vein, spiral CT scans of the head and neck, delayed for 25 seconds and 45 seconds respectively, were carried out automatically for 2 phases within one breath, with collimation at 0.625 mm, pitch 0.984 or 1.375, slice thickness 1.25 mm and increment 0.6 mm. The scanning range was 30 cm-50 cm. The imaging method was volume rendering (VR) together with techniques of separating, fusing, opacifying and false-coloring (SFOF). In satisfactory 3D images, the ASVA, AAJ and their interrelations were observed and/or measured, including the course and size of the ASVA, and the biggest distance from the AAJ to the 2nd and 4th curves of the VA (namely the biggest perpendicular distance from the inner margin of the 2nd curve to the outer edge of the AAJ, and the ante-outer margin of the 4th curve to the hind-outer margin of the posterior arch of the atlas (Figures 1 and 2).

Figure 1.
Figure 1.:
3D image of the ASVA and AAJ view from front to back: showing the measurement method of MD2ndCA (the 2D measurement in 3.9 mm, the white arrow).Figure 2. The same subject as Figure 1. 3D image of the ASVA and AAJ view from down to up: showing the measurement method of MD4thCA (the 2D measurement in 8.6 mm and 8.6 mm, the white arrow).Figure 3. 3D image of the ASVA and AAJ view from back to front: showing the courses of the ASVA with 5 curves (the white arrow and label).Figure 4. The same subject as in Figure 3, the left lateral-view of the 3D image of the ASVA and AAJ: showing the courses of the ASVA with 5 curves (the white arrow and label).Figure 5. With the techniques of SFOF, the 3D image of the ASVA and AAJ view from back to front: showing the courses of the ASVA and the congenital arcuate foramen of the atlas vertebra (the white arrow and label).Figure 6. The same subject as in Figure 5, the right lateral-view of the 3D image of the ASVA and AAJ: showing the courses of the ASVA and the congenital arcuate foramen of the atlas vertebra (the white arrow and label).Figure 7. With the techniques of SFOF, the 3D image of the ASVA and AAJ view from back to front: showing the abnormal branch and courses of the ASVA (the white arrow and AVA label) and the congenital thinness of the VA (the white arrow and LVA label).Figure 8. The same subject as in Figure 7: the course of the ASVA can be seen through bone (the white arrow and LVA label). Figure 9. With the techniques of SFOF, the 3D image of the ASVA and AAJ view from back to front: showing the congenital defects of the posterior arch of the atlas (the two white arrows).Figure 10. The same subject as in Figure 9: by deleting C2, the 3D image shows C1 with the congenital defects of the posterior arch (the white arrow) and the course of the ASVA can be seen through bone.

Statistical methods

Statistical comparisons were made about the bilateral measurements with t or x2 test, and the t or x2 and P value were calculated respectively.

RESULTS

Examination and imaging techniques

Satisfactory 3D images were obtained with the scanning and imaging parameters in our study. The ASVA and AAJ were clearly and directly shown in the high quality images, and satisfied the requirements of our study. 3D imaging together with the techniques of SFOF is helpful to improve the ability to show their structures and interrelations (Figures 3-6).

Course of the ASVA and its variations

In the total of 68 cases, the course of the ASVA, extending from the transverse foramen of C2 to the foramen magnum, was clearly observed, in which 60 cases (88.2%) were found to have five curves in the course of the ASVA and 8 had variations. The five curves were arc-shaped, with the 1st going through the transverse foramen of C2, the 2nd going up beside the joint, the 3rd going through the transverse foramen of C1, the 4th going on the posterior arch of C1 and the 5th going forward to the foramen magnum (Figures 3 and 4). In the 8 variations, an abnormal course or branch was found in 4 cases at the left 3rd or 4th curves, not going through the transverse foramen of C1 after going out from that of C2, but going into the spinal canal and upward directly to the 5th curve of the ASVA. In the other 4 cases, the ASVA was found to be small in size or partly absent on the right (Figures 7 and 8).

ASVA related to AAJ

The ASVA ascends along the AAJ with curves, which slightly expand, with the biggest diameter of 5.6 mm in the 4th curve. The size of the ASVA was basically symmetrical in 12 cases (12/68, 17.65%), with the left bigger than the right in 46 cases (46/68, 67.65%) and smaller in 10 cases (10/68, 14.71%). Statistical comparison shows that the left ASVA is larger than the right (x2=39.343, P <0.05). Along the course of the ASVA, there are two departures away from the AAJ, one in the 2nd curve of 0.0 mm-5.4 mm away from the side of the joint, and the other in the 4th of 2.6 mm-9.2 mm away from the posterior arch of C1. There is no significant difference in the means of distance from the 2nd or 4th curve to the AAJ between the left and right (Table).

Table
Table:
Distance from the 2nd or 4th curve of the ASVA to AAJ between left and right (mean±SD, mm)

AAJ and variations

All the 3D images clearly showed the structure of the atlas or epistropheus as bone specimens, one of which was separately observed by deleting the other one. It allowed repeated measurement of the C1 or C2 related to the ASVA from various directions. In the 68 cases, there were 12 cases of variations in the AAJ, namely 7 cases of congenital arcuate foramen of C1 and 5 cases of congenital defects of the posterior arch of C1 (Figures 9 and 10).

DISCUSSION

Significance of this study

As there are curves or loops in the course of the ASVA and complicated structures in the AAJ, a conventional two-dimensional image cannot directly show their interrelations. 3D imaging has the advantages of showing the anatomic structure with spatial location accurately, the global view clearly and the bone marks definitely.9-12 3D imaging together with the techniques of SFOF can show C1, C2 and the ASVA respectively and improve the ability to evaluate their interrelations. 3D anatomy data of the ASVA and AAJ can make up and enrich the research contents of regional anatomy of the VA and AAJ. By showing the ASVA related to the pedicle of C2, and to the lateral mass of C1, the anatomical basis can be provided for the choice and plan of surgery. It helps to raise the safety of operations.13,14

Feasibility and advantages of 3D imaging techniques

In our study, satisfactory 3D images of the ASVA and AAJ were obtained from the scanning data of the routine head-neck CTA. With the fast scan of CT and the improvements in processing software, the quality of 3D images are improving continuously, such that 3D imaging has ascended to a new stage with a wider application field. VR is one of the 3D imaging techniques extensively applied in recent years. By adjusting the CT value threshold and different colors or opacity of the object observed, VR-3D imaging can clearly and directly show both the ASVA and AAJ in the same image.15,16 Certainly, for clearer 3D images of the VA and AAJ, we can use the techniques of SFOF to show the VA or ASVA alone as in a DSA image and the atlas or epistropheus alone as a bone specimen.17 Furthermore, CT scanning data can be used more than once and 3D images can be observed and analyzed repeatedly; thus the high accuracy of imaging diagnosis can be assured.16

Anatomical characteristics and variation

The ASVA is accompanied by the AAJ with 5 curves for 88.2% of its length. Its size on the left is larger than on the right. The results are basically consistent with the literatures.1,18-20 The ASVA is subject to restriction when it goes through the transverse foramen of C1 or C2. The 2nd and 4th curve slightly keep off the AAJ structure with an arc shape. In our study, the distance from the 2nd or 4th curve to the AAJ was measured. A statistical comparison shows that there is no significant difference between the distance on the left and right. These results are not found in any previous reports. 3DCTA can clearly show the abnormal course of the ASVA and the heteroplasia of C1 or C2, which may result in a change of VA blood flow, and are easily influenced by outside force, such as neck massage or external injury and so on.11,19 Early identification of these variations can provide the basis for surgical operations and other treatments.

Clinical value

The curves of the ASVA exist in order to adapt to head-neck movement mainly performed by the AAJ. With increase in age, the curves become more obvious and the ASVA wall likely calcifies, and blood flow has higher resistance, which probably leads to vertebro-basilar artery insufficiency and influences the normal functioning of corresponding organs such as the inner ear, diencephalon, brain stem and cerebellum, etc.1,3,7,18,20 Clear demonstration of the ASVA and AAJ is one of the research hotspots in medical imaging, of which ultrasound, MRI, conventional angiography or DSA have defects or shortcomings.8,21-23 3DCTA can show wall calcification and narrowing of the VA, and identify their length and site, based on which we can provide prevention measures in order to decrease the incident rate of cerebral infarction and improve prognosis. Abnormality or variation of the AAJ, such as atlantoaxial subluxation or congenital arcuate foramen, may result in VA distortion, narrowing and being pressed, which may affect the blood flow of the VA. 3DCTA can clearly and directly show the pathologies and variations of the ASVA and AAJ, and provide an important basis for diagnosing and managing abnormalities of the AAJ and ASVA.12,22-25

Summary

With the development of spiral CT, 3D imaging is increasingly applied in medical practice. 3DCTA can globally and directly identify the relations between the ASVA and AAJ, and provide detailed 3D anatomical data, which are the bases for diagnosing and treating the disorders of the AAJ and ASVA.

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Keywords:

vertebral artery; atlantoaxial joint; computed tomography; X-ray; image processing; computer-assisted

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