Imaging anatomy and variation of vertebral artery and bone structure at craniocervical junction

Abstract

The objective of this article is to display the vertebral artery and bone structure at the craniocervical junction (CJVA and C_0-1-2) with three-dimensional CT angiography (3DCTA) and identify their anatomic features and variations. Eighty-eight subjects without pathology of vertebral artery (VA) and C_0-1-2 were selected from head–neck CTA examination. 3D images were formed with volume rendering (VR) and multiplanar reconstruction (MPR). On the 3D images, CJVA and C_0-1-2 were measured, and their variations were observed. CJVA goes along C_0-1-2 with five curves, of which three curves are visibly away from C_0-1-2, one is 0.0–8.3 mm away at the second curve with 0.0–11.2 mm in width, another is 0.0–9.2 mm away at the fourth with 2.8–14.8 mm and the other is 0.0–6.2 mm away at the fifth. Statistical comparisons show that there is no significant difference in the measurements between left and right, and that the curves become smaller and farther away from C_0-1-2 with the increase of age. CJVA is not equal in size, with the biggest in the fourth curve and the smallest in the fifth. Statistical comparison shows the left CJVA is larger than the right in the fifth curve. Variations were found on CJVA in 16 cases and on C₁ in 12 cases. The anatomy and variations of CJVA and C_0-1-2 are complicated. It is of vital significance to identify their anatomic features in clinical practice.

The vertebral artery (VA) goes along the craniocervical junction (CJVA), which includes the bone structures of occipital and first two cervical vertebra (C_0-1-2). The relationship between CJVA and C_0-1-2 is so complicated that it is not quite easy to observe clearly and directly them by regional anatomy and two-dimensional image [1, 2, 9]. Three-dimensional CT angiography (3DCTA) has advantages in showing their related anatomy and pathology [4, 5, 8, 21]. This study is to measure their anatomic relations and observe their variations, and provide anatomic basis for clinical applications.

Materials and methods

General information

In our hospital, from 1 January 2008 to 31 October 2008, CT scanning data of 88 subjects (46 males, 22 females, aged between 17 and 85 years, mean age 50.82 ± 3.56) without pathology on C_0-1-2 (dislocation, fracture, tumor and so on) and VA (calcification, narrow, thrombus, being pressed and so on) were selected from 608 cases of head–neck CT angiography (CTA). 3D images were retrospectively performed to show clearly the structures of CJVA and C_0-1-2.

Materials and equipments

The contrast medium (Omnipaque, 300 mgI/ml) with the total amount of 1.5–2.0 ml/kg was injected in a velocity of 3.0–4.0 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 by Light Speed VCT (64-detector-row).

Scanning method and data processing

After the contrast medium was injected into the forearm vein, spiral CT scan from the neck to head, being delayed for 25 and 45 s, respectively, was automatically carried on for two phases within one breath, with collimation in 0.6 mm, pitch 0.984 or 1.375. The slice thickness was 1.25 mm, and the increment was 0.6 mm. The scanning range is 30–50 cm. The 3D imaging method is volume rendering (VR) together with the techniques of separating, fusing, opacifying and false-coloring (SFOFC) and multiplanar reconstruction (MPR). With satisfactory 3D images, the curves of CJVA were measured in size, height and width of the second, fourth and fifth curves (the size is the diameter of VA, height is the biggest distance from the inner margin of the curve to the C_0-1-2 and the width is the biggest distance of the curve’s open; Figs. 1, 2, 3), and variations were observed. Statistical comparisons were made using t test, first in the bilateral measurements, and then between the measurements of age groups over 60 and below, and the t value and P value were calculated, respectively.

Fig. 1.

VR-3D image view from back to front showing the measurement method of the second curve (H is the height of the curve, and W is the width)

Fig. 2.

VR-3D image view from up to down, showing the measurement method of the fourth curve (H is the height of the curve, and W is the width)

Fig. 3.

MPR-3D image showing the measurement method of the fifth curve (H is the height of the curve)

Results

Anatomy and variations

The anatomy and variations of CJVA and C_0-1-2 were clearly and directly shown in 3D images (Figs. 4, 5, 6). CJVA goes along C_0-1-2, extending from the transverse foramen of C₂ through foramen magnum to basilar artery. There were 72 cases (81.8%) with five curves in the course of CJVA (Fig. 5, 6). In the total of 88 cases, variations of CJVA exist in 16 cases, of which 8 cases were found abnormal course (5 on the left, 2 on the right and 1 on both, Fig. 7), 3 cases abnormal branch (2 on the left and 1 on both, Fig. 8), 4 cases small in size (1 on the left, 3 on the right) and 1 case absence of VA on the right (Fig. 9). Variations of C₁ were found in 12 cases, of which 7 cases were congenital arcuate foramen (Fig. 4), and 5 cases were congenital defects of posterior arch. No variations were found in C₀ or C₂.

Fig. 4.

VR-3D image view from back to front, showing the variation of the congenital arcuate foramen of the atlas vertebra (the white arrow and label)

Fig. 5.

3D image view from back to front with the SFOFC, showing the courses of CJVA with five curves (the white arrow and label) and the fifth curve with an irregular shape whose width is difficult to measure (VC5)

Fig. 6.

The same subject as in Fig. 5, the left lateral view of 3D image with the SFOFC, showing the courses of CJVA with five curves (the white arrow and label) and the fifth curve with an irregular shape whose width is difficult to measure (VC5)

Fig. 7.

3D image view from back to front with the SFOFC, showing the abnormal courses of CJVA (the white arrow and LACVA and RACVA label)

Fig. 8.

3D image view from back to front with the SFOFC, showing the abnormal branch of CJVA (the white arrow and LABVA and RABVA label)

Fig. 9.

3D image view from front to back with the SFOFC, showing the congenital absence of VA (the white arrow and no RVA label)

Course of CJVA

The curves of CJVA are almost arc-shaped except the fifth, with the first curve going through the transverse foramen of C₂, the second going up beside C_1-2, the third going through the transverse foramen of C₁, the fourth going on or above the posterior arch of C₁. The fifth goes forward and through foramen magnum to basilar artery with an irregular shape whose width is difficult to measure (Figs. 5, 6). CJVA is not equal in size. The curved parts slightly expand. The biggest is in the left fourth curve with 5.6 mm in size, and the narrowest is in the right fifth curve with less than 1.0 mm. Statistical comparison shows the left CJVA is larger than the right in the fifth curve (Table 1, P < 0.05).

Table 1.

The mean of the second, fourth and fifth curve of CJVA in size (CCJVA, S) between the left and right (X ± S)

Measuring parameter	Left (60)	Right (60)	t value	P value
Second CCJVA (S, mm)	3.49 ± 0.48	3.24 ± 0.55	2.6528	>0.05
Fourth CCJVA (S, mm)	3.72 ± 0.46	3.51 ± 0.67	2.0991	>0.05
Fifth CCJVA (S, mm)	2.88 ± 0.55	2.41 ± 0.46	5.0772	<0.05

Measurement about CJVA and C_0-1-2

In the total of 88 cases, except 28 case variations of CJVA and C_0-1-2, CJVA of 60 cases with five curves were measured. Statistical comparison shows that the curves become more obvious with the increase of age (smaller open and farther away from C_0-1-2, Table 2). Among the five curves, there are three departures visibly away from C_0-1-2, one is 0.0–8.3 mm away at the second curve with 0.0–11.2 mm in width, another is 0.0–9.2 mm away at the fourth with 2.8–14.8 mm and the other is 0.0–6.2 mm away at the fifth. There is no significant difference in the measurements between left and right (Table 3, P > 0.05).

Table 2.

The mean of the second, fourth and fifth curves of CJVA (CCJVA) in height (H), size (S) and/or width (W) between the subjects over 60 years and below (X ± S)

Measuring parameter		≥60 years (26 × 2a)	<60 years (34 × 2a)	t value	P value
Second CCJVA	H (mm)	2.84 ± 0.49	2.59 ± 0.37	3.0705	<0.05
	W (mm)	5.01 ± 0.83	5.58 ± 1.06	3.3043	<0.05
	S (mm)	3.50 ± 0.53	3.25 ± 0.61	2.3974	>0.05
Fourth CCJVA	H (mm)	4.42 ± 0.96	3.83 ± 0.85	3.5036	<0.05
	W (mm)	7.68 ± 1.73	8.39 ± 1.43	2.3978	>0.05
	S (mm)	3.89 ± 0.60	3.48 ± 0.49	4.0999	<0.05
Fifth CCJVA	H (mm)	3.32 ± 0.85	3.01 ± 0.73	2.2031	>0.05
	S (mm)	3.02 ± 0.45	2.91 ± 0.83	0.9291	>0.05

^a“×2” represents the combined measurements of the left and right

Table 3.

The mean of the second, fourth and fifth curve of CJVA (CCJVA) in height (H) and/or width (W) between the left and right (X ± S)

Measuring parameter		Left (60)	Right (60)	t value	P value
Second CCJVA	H (mm)	3.21 ± 0.57	2.89 ± 0.87	1.7126	>0.05
	W (mm)	5.41 ± 1.06	5.05 ± 1.33	1.6393	>0.05
Fourth CCJVA	H (mm)	4.12 ± 0.55	4.31 ± 0.90	1.1889	>0.05
	W (mm)	7.60 ± 1.75	8.04 ± 1.49	1.4829	>0.05
Fifth CCJVA	H (mm)	2.92 ± 0.75	3.05 ± 0.93	0.8431	>0.05

The width of the fifth curve is not measured because of its irregular shape

Discussion

Clinical significance

Because of the complicated course and structure, CJVA and C_0-1-2 cannot be clearly and directly shown by the conventional two-dimensional image. 3DCTA, with the advantages of showing clearly the spatial location and bone marks, can be a valuable means of observing the anatomy and variations of CJVA and C_0-1-2 [10, 12, 17, 22]. It is helpful in observing the size, shape and course of CJVA and in evaluating the blood supply of vertebro-basilar artery. Imaging anatomy can make up of or enrich the content of regional anatomy, and provide reliable basis for the clinical diagnosis and treatment. Identifying anatomy and variations of CJVA and C_0-1-2 is necessary in the choice and plan of surgery and raise the accuracy and safety of operations [6, 10].

Imaging anatomy and the characteristic

The CJVA is accompanied with C_0-1-2 with five curves by 81.8%. It is subject to restriction when going through the transverse foramen of C1 or C2. The second, fourth and fifth curves keep off C_0-1-2. The distance will be helpful for open surgery, percutaneous injections and biopsies on the region. Statistical comparison between the measurements of size in the left and right fifth curve shows that the left is larger than the right; it proves that the blood supply of VA is asymmetry. The curves become smaller and farther away from C_0-1-2 with the increase of age. That is why, for the elder people, the blood of VA flows with more resistance and thus may probably result in vertebro-basilar artery insufficiency and influence normal functions of corresponding organs, such as inner ear, diencephalon, brain stem, cerebellum and so on. These results are not found in any previous reports. Imaging anatomy can show the different surface or deep structure in every direction, and the imaging data can be analyzed and discussed repeatedly [3, 15].

Variations about the CJVA and C_0-1-2

In our study, the abnormal course of CJVA and heteroplasia of C1 are found. These variations are multifarious and unexpected, which may cause VA and C_0-1-2 malfunctions. The variational structure is easily influenced by outside force, such as neck massage and external injury [18–20]. Identification of these variations can prevent potential injured danger, and provide anatomic basis for diagnosis and treatment of the related discord. Ascertaining the variations before operation can enable us to make a reasonable plan of surgery and avoid injure to VA or related structures.

Advantages of 3DCT in anatomy

Satisfactory 3D image of CJVA and C_0-1-2 is the basis for imaging anatomy. With the improvement of CT scanning and imaging technique, the quality of 3D image has been improving continuously and is up to the clinical accurate requirements. Both CJVA and C_0-1-2 can be clearly and directly shown in the same image because of their close relations and the similar density. Certainly, for a clearer observation and measurement their anatomy, we can use the techniques of SFOFC on 3D imaging, as it can show VA or CJVA alone as in DSA image and the C₀, C₁ and C₂ alone as bone specimen [7]. By adjusting the tissue’s CT value threshold and different colors or opacity, 3D images can show the different surface or deep anatomic structure at the same image in every direction, and the imaging data obtained can be analyzed and discussed repeatedly [15]. It is an important method to study the 3D anatomy of bone and blood vessel [4, 11].

Application of imaging anatomy

Showing clearly the anatomy and variations of CJVA and C_0-1-2 is one of the research hotspots in medical imaging. Other imaging examinations such as ultrasound, MRI, conventional angiography or DSA have some defections or shortcomings; they cannot show both CJVA and C_0-1-2 on an image [12–14]. 3DCTA can clearly and directly show not only the anatomy and variations of VA but also its wall calcification and other pathological changes. Moreover, it can differentiate the narrow or blocking of VA and judge the causes, which can be the basis for treatment plans. Abnormal or various C_0-1-2 such as atlantoaxial subluxation or congenital arcuate foramen of the C₁ may result in distortion, narrow of CJVA. Showing the relations between CJVA and C_0-1-2 is a basis for diagnosing abnormality of atlantoaxial joint and CJVA, and can provide the anatomy foundation for the choice of operation [3, 10, 16].

Summary

The anatomy of CJVA and C_0-1-2 is complicated with some unexpected variations. With five curves, CJVA is not equal in size, and statistical comparison shows the left CJVA is larger than the right in the fifth curve. These curves become more obvious with the increase of age. These results give important anatomic basis for the study on the hemodynamics of VA and operation at the craniocervical junction.