- Email: [email protected]
Anatomic and radiologic analysis of the atlantal part of the vertebral artery
Journal of Clinical Neuroscience 16 (2009) 675–678
Contents lists available at ScienceDirect
Journal of Clinical Neuroscience journal homepage: www.elsevier.com/locate/jocn
Neuroanatomical Study
Anatomic and radiologic analysis of the atlantal part of the vertebral artery Sahika Liva Cengiz a,*, Aynur Cicekcibasi b, Demet Kiresi c, Yalcın Kocaogullar a, Onur Cicek a, Alper Baysefer a, Mustafa Buyukmumcu b a
Neurosurgery Department, Selçuk University, Meram Faculty of Medicine, A/5 Meram Akyokusß 42080, Konya, Turkey Anatomy Department, Selçuk University, Meram Faculty of Medicine, Konya, Turkey c Radiology Department, Selçuk University, Meram Faculty of Medicine, Konya, Turkey b
a r t i c l e
i n f o
Article history: Received 19 February 2008 Accepted 27 May 2008
Keywords: Cadaver External landmarks Horizontal part Paramedian suboccipital craniectomy Posterior fossa surgery Third segment of the vertebral artery Vertebral artery
a b s t r a c t The horizontal third segment (V3h) of the vertebral artery (VA) in 7 cadavers (14 sides) was dissected and the anatomical measurements recorded. Measurements from 24 healthy individuals (48 sides) were taken for comparison using multislice CT scanning. The distance between the medial tip of the VA V3h and the line passing through the mid point of the posterior tuberculum of the atlas was marked as length A. The distance between the medial tip of the VA V3h and the point penetrating the dura mater was classified as length B. The angle between these lines was the alpha (a) angle. Measurements were taken when the head was in a neutral position, as well as in maximum right and left rotation, extension and flexion. In cadavers, the mean a angle (±S.D.) was 82.42 ± 10.34° and 83.21 ± 10.81° on the right and left side, respectively. On multislice CT scanning, the mean a angle was 81.64 ± 10.15° on the right and 83.77 ± 10.65° on the left. These angles varied with the position of the head. Ó 2008 Elsevier Ltd. All rights reserved.
1. Introduction
2. Methods
A potential hazard of the far lateral approach in a posterior fossa craniectomy is injury to the horizontal third segment (V3h) of the vertebral artery (VA), located in the superior aspect of the atlas. The VA is classically divided into four parts: its origin (from the subclavian artery in the root of the neck) to the sixth cervical vertebra (first part); its course through the foramina transversaria of the sixth to the first cervical vertebrae (cervical/second part); from the foramen transversarium of the atlas vertebra to its passage through the dura mater at the foramen magnum (suboccipital/ third part); and its course within the cranium to the pontomedullary border (intracranial/fourth part).1–12 The V3h portion of the VA lies close to the floor of the posterior fossa and damage to the VA may be fatal.13,14 Therefore, before attempting surgery at the posterior fossa and craniocervical junction, a thorough anatomical study of the path of the VA is mandatory. Here, we describe the normal anatomy and variations, as well as the surgical approach needed to expose the VA V3h segment, with the intention of developing a safe and effective technique for the far lateral approach in a posterior fossa craniectomy.
Seven cadavers (14 sides), with no history of craniocervical pathology, and 24 healthy individuals (48 sides), who were anatomically normal, were examined. The procedures were based on the guidelines of Selçuk University’s Ethical Committee on the Care and Use of Cadaveric Specimens. All of the healthy individuals who took part in the study were volunteers and were notified of the potential implications of radiation exposure. Dissections of the left and right V3h segments of the VA were performed in all cadavers. Each cadaver was placed in a prone position. The head was slightly extended in the neutral position, as the position of the head can greatly influence the structures that the surgeon will encounter. A midline incision was made through the inion and foramen magnum. After the blunt dissection of the trapezius, splenius capitis, and semispinalis capitis muscles, the suboccipital trigonum was exposed. The V3h portion of the VA was measured using an electronic caliper and goniometer. All length measurements were in centimeters. The distance between the medial tip of the VA V3h and the line passing through the mid point of the posterior tuberculum of the atlas was recorded as length A. When the head was in the neutral position (N), length A was labelled as NAR on the right (R) side and NAL on the left (L) side (Table 1). The distance between the medial tip of the VA V3h and the point penetrating the dura mater was recorded as length B. When the head was in the neutral position, length B was defined as NBR on the right side and NBL on
* Corresponding author. Tel.: +90 33 2223 6449; fax: +90 33 2223 6181. E-mail address: [email protected] (S.L. Cengiz). 0967-5868/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.jocn.2008.05.033
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S.L. Cengiz et al. / Journal of Clinical Neuroscience 16 (2009) 675–678
Table 1 Descriptive statistics of the atlantal horizontal third part of the vertebral artery in cadavers and healthy individuals
Cadavers (n = 7) Healthy individuals (n = 24)
NAR (cm)
NBR (cm)
NaR (°)
NAL (cm)
NBL (cm)
NaL (°)
p
1.67 ± 0.18 1.76 ± 0.24
0.81 ± 0.16 0.78 ± 0.75
82.42 ± 10.34° 81.64 ± 10.15°
1.67 ± 0.24 1.72 ± 0.26
0.84 ± 0.18 0.91 ± 0.22
83.21 ± 10.81° 83.77 ± 10.65°
>0.05 >0.05
Significant difference was defined as (p < 0.05). NAR, NAL: N = neutral position of the head. Length A = the distance (cm) between the medial tip of the horizontal portion (V3h) of the vertebral artery (VA) and the line passing through the mid point of the posterior tuberculum of the atlas. Length A was labelled as NAR on right (R) side and NAL on left (L) side. NBR, NBL: Length B = the distance between medial tip of VA V3h and the point penetrating the dura mater. Length B was defined as NBR on right side and NBL on left side. Alpha (a) angle = angle between these two lines, NaR = the a angle on the right side, with head in neutral position, NaL = the a angle on the left side, with head in neutral position.
the left side (Table 1). The angle between these two lines was defined as the alpha (a) angle (Table 1). Due to the stiffness of the cadavers, as well as the deep location and inaccessibility of the VA, there was slight error in the measurements. To minimize error rates, repeated measurements of each individual at different times were taken using a goniometer. To determine whether the a angle changed with the position of the head, measurements were taken when the head was placed in neutral, in maximum right and left rotations, and in maximum extension and flexion positions, using multislice CT scanning (Fig. 1). 2.1. Radiologic procedure The same measurements were also taken in 24 healthy individuals (48 sides) (see Supplementary Fig. 1). All of the participants were volunteers, and were informed about the potential implications of radiation exposure encountered during the study. Similarly, as with the cadavers, measurements of each individual were taken repeatedly at different times, so as to minimize the rate of error. For each group, the data obtained when the head was in the neutral position were compared bilaterally with: Group I (n = 6), the maximum right rotation of the head (see Supplementary fig. 2); Group II (n = 6), the maximum left rotation; Group III (n = 6), the maximum extension, and Group IV (n = 6), the maximum flexion. Spinal CT angiography (CTA) was performed using a 64-detector row helical scanner (Sensation 64; Siemens, Germany). After 100 mL of non-ionic contrast material was administered through an antecubital vein at a rate of 5 mL/s, CTA was performed from the lower half of the posterior fossa to the C3/4 level (acquisition protocol: gantry speed per rotation, 0.5 s; collimation, 0.75; 120 kV; 120 mAs). A bolus-tracking technique was employed and the scan started when the contrast material reached the common carotid arteries. When the Hounsfield units in the preset lumen of the
Fig. 1. The mean alpha (a) angle of healthy individuals, left (L, square) and right (R, diamond) sides in all positions. Ext = measurements with maximum extension of the head, Flex = measurements with maximum flexion of the head, Lrot = measurements with maximum left rotation of the head, Neutr = neutral head position, Rrot = measurements with maximum right rotation of the head. This figure is available in colour at www.sciencedirect.com.
distal common carotid artery rose by 100, the multidetector (MD) CT scan was triggered automatically after 3 s. The threedimensional (3D) reconstruction took place after the data had been transferred to the workstation. Transverse sections were reconstructed with a section width of 0.5 mm. MD CTA images were processed from the source images obtained using a volume-rendered technique (VRT) algorithm. 2.2. Statistical analysis Computer-assisted data analysis was performed with the help of the Statistical Package for the Social Sciences (v. 13.0) software (SPSS Inc; Chicago, IL, USA). The Mann–Whitney U-test was used in the comparative analysis between the cadavers and healthy individuals (Table 1). In healthy individuals, the Wilcoxon signed ranks test was used when comparing the neutral position to the other positions. Statistical significance was defined as p < 0.05. 3. Results In the cadavers, the mean a angle in the neutral position was 82.42 ± 10.34° on the right side and 83.21 ± 10.81° on the left side. In comparison, the mean a angle (±S.D.) measured using multislice CTA scans in healthy living individuals was 81.64 ± 10.15° on the left side and 83.77 ± 10.65° on the right side (Table 1); however, those angles varied with the position of the head (Fig. 1). In healthy individuals, when measurements in the neutral position were compared to measurements with the head at maximum
Fig. 2. Mean lengths A and B on the left and right side, in all positions. AL = Mean values of length A (cm) (triangle, dashed line) on the left side (the distance between the medial tip of the horizontal portion of the vertebral artery (VA V3h) and the line passing through the mid point of the posterior tuberculum of the atlas), AR = mean values of length A (diamond, solid line) on the right side, BR = mean values of length B (rectangle, solid line) on the right side (the distance between the medial tip of the VA V3h and the point penetrating the dura mater), BL = mean values of length B (cross, solid line) on left side, Ext = measurements with maximum extension of the head, Flex = maximum flexion of the head, Lrot = maximum left rotation of the head, Neutr = neutral position of the head, Rrot = maximum right rotation of the head. This figure is available in colour at www.sciencedirect.com.
S.L. Cengiz et al. / Journal of Clinical Neuroscience 16 (2009) 675–678
left rotation, all values were significantly different (p = 0.03), except for length B on the left side. When the lengths of B in the left and neutral positions were compared to the measurements with the head at maximum left rotation on the left side, the difference was not significant (p > 0.05) (Fig. 2). When comparing the measurements taken in the neutral position to measurements with the head at maximum extension, all values were significantly different (p = 0.03), except for length B on the left side. The length of B in the left and neutral positions compared to the maximum extension of the head on the left side was not significantly different (p > 0.05). When measurements in the neutral position were compared to measurements with the head at maximum flexion, all values were significantly different (p = 0.03), except for the length of B on the left side. As the lengths of B in the left and neutral positions were compared to the maximum flexion of the head on the left side, the difference was not significant (p > 0.05) (Fig. 2). There were no significant differences between length A on the left and right sides in the neutral position and the measurements of maximum right rotation of the head on both sides (p > 0.05). Measurements of length B and the a angle on the left and right sides in the neutral position were compared to measurements of maximum right rotation of the head on both sides. All values were significant (p = 0.03).
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cm on the left. Lang et al. measured the same length as 0.44 cm (0.27–0.60 cm).15 Differences between sexes, and the right and left sides were not significant. Length measurements of the VA between the medial border of V3h and the posterior tuberculum of the atlas in the neutral position (length A) were consistent with the findings of Lang et al.15 We have taken into account the margin of error associated with the measurements due to the stiffness of the cadavers and the difficulty in accessing the VA owing to its deep location. For these reasons, we repeated the same measurements at different times in both cadavers and multislice CT scans to reduce potential error. In conclusion, the V3h section of the VA can be easily identified by performing multislice CT scans pre-operatively. In addition, the measurements taken in cadavers corresponded to the same measurements seen on multislice CT scans. This may provide considerable intra-operative safety when exposing the V3h portion of the VA during a suboccipital craniectomy.
Appendix A. Supplementary data Supplementary data associated with this article can be found, in the online version, at doi:10.1016/j.jocn.2008.05.033. References
4. Discussion The atlantal part of the VA is deeply buried at the craniocervical junction, which is an area where numerous lesions can be found. Therefore, a thorough study of its anatomic structure may make surgical interventions less complicated. Information regarding the microsurgical anatomy of the atlantal part of the VA is sparse.2,3,14–17 According to Abd El-Bary et al., the VA third segment (V3) enters the transverse foramen of Cl, where it runs in a vertical, slightly anterior direction.16 Just above the transverse foramen of C1, the artery changes direction dorsally and runs further in the sagittal plane. In most cases, this change of direction is associated with an acute angle, but in some cases, the change is in a posteromedial direction. The artery then changes its direction again and runs transversely above the posterior arch of Cl.16 The course of the VA V3 is divided into three portions: a vertical portion between the transverse processes of C2 and C1; a horizontal portion (V3h) in the groove of the posterior arch of the atlas; and an oblique portion where it leaves this groove and travels up to the dura mater.18,19 At the end of the groove, the height of the posterior arch of the atlas increases like a step. Thereafter, the VA runs in a superomedial direction to the dura mater of the foramen magnum. The junction between the second and third portion of the V3 is sometimes called the genu of the VA.20–22 Anatomical studies have shown that the left VA is larger, smaller or equal in size to the right VA in 45%, 21% and 34% instances, respectively.23 Although the VA V3 anatomy is documented,2,3,14–17 no information is available regarding the angle of the VA where it penetrates the dura mater. This study draws attention to the surgical dangers of the far lateral approach in a suboccipital craniectomy. In our study, the range of values for the a angle as it passed through the dura mater varied, the greatest difference being when the head was in maximum flexion compared to neutral flexion. During the flexion of the neck, the VA glides superiorly and anteriorly relative to the posterior arch, and this is most likely to occur at the level of the lateral masses of the atlas rather than at more caudal sites in the neck.24 In cadavers, the median measurements (±.S.D.) of length B of the VA (from its entrance into the transverse foramen of the atlas to its passage through the dura mater) in the neutral position were 0.81 ± 0.16 cm on the right and 0.84 ± 0.18
1. Buckenham TM, Wright IA. Ultrasound of the extracranial vertebral artery. Br J Radiol 2004;77:15–20. 2. Cacciola F, Phalke U, Goel A. Vertebral artery in relationship to C1–C2 vertebrae: an anatomical study. Neurol India 2004;52:178–84. 3. Cokkeser Y, Naguib MB, Kizilay A. Management of the vertebral artery at the craniocervical junction. Otolaryngol Head Neck Surg 2005;133:84–8. 4. George B, Cornelius J. Vertebral artery: surgical anatomy. In: Spetzler RF, editor. Operative Techniques in Neurosurgery. 1st edn. Philadelphia: W.B. Saunders; 2001. p. 168–81. 5. Güvençer M, Men S, Naderi S, et al. The V2 segment of the vertebral artery in anterior and anterolateral cervical spinal surgery: a cadaver angiographic study. Clin Neurol Neurosurg 2006;108:440–5. 6. Lu J, Ebraheim NA. The vertebral artery: surgical anatomy. Orthopedics 1999;22:1081–5. 7. Macchi C, Giannelli F, Cecchi F, et al. The inner diameter of human intracranial vertebral artery by color Doppler method. Ital J Anat Embryol 1996;101:81–7. 8. Hayward R. Posterior fossa craniotomy: an alternative to craniectomy. Pediatr Neurosurg 1999;31:330. 9. Hinse P, Thie A, Lachenmayer L. Dissection of the extracranial vertebral artery: report of four cases and review of the literature. J Neurol Neurosurg Psychiatry 1991;54:863–9. 10. Abou Madawi A, Solanki G, Casey AT, et al. Variation of the groove in the axis vertebra for the vertebral artery. Implications for instrumentation. J Bone Joint Surg (Br) 1997;79:820–3. 11. Al-Mefty O. Petrosal approach to clival tumors. In: Sekhar LN, Janecka IP, editors. Surgery of Cranial Base Tumors. 1st edn. New York: Raven Press; 1993. p. 307–15. 12. Arnautovic´ KI, al-Mefty O, Pait TG, et al. The suboccipital cavernous sinus. J Neurosurg 1997;86:252–62. 13. Yoshida M, Neo M, Fujibayashi S, et al. Comparison of the anatomical risk for vertebral artery injury associated with the C2-pedicle screw and atlantoaxial transarticular screw. Spine 2006;15:13–7. 14. Tubbs RS, Johnson PC, Shoja MM, et al. Foramen arcuale: anatomical study and review of the literature. J Neurosurg Spine 2007;6:31–4. 15. Lang J, Kessler B. About the suboccipital part of the vertebral artery and the neighboring bone–joint and nerve relationships. Skull Base Surg 1991;64:64–71. 16. Abd el-Bary TH, Dujovny M, Ausman JI. Microsurgical anatomy of the atlantal part of the vertebral artery. Surg Neurol 1995;44:392–401. 17. Arnautovic´ KI, Al-Mefty O, Pait TG, et al. The microsurgical anatomy of the suboccipital vertebral artery and its surrounding structures. Oper Tech Neurosurg 2002;5:1–10. 18. Thiel HW. Gross morphology and pathoanatomy of the vertebral arteries. J Manipulative Physiol Ther 1991;14:133–41. 19. Bruneau M, Cornelius JF, George B. Anterolateral approach to the V2 segment of the vertebral artery. Neurosurgery 2005;57:262–7. 20. Yamaki K, Saga T, Hirata T, et al. Anatomical study of the vertebral artery in Japanese adults. Anat Sci Int 2006;81:100–6. 21. Mawera G, Hillen B. Topographical relations of the vertebral arteries in the human neck: an anatomical study. Cent Afr J Med 2001;47:81–3.
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22. Huang MJ, Glaser JA. Complete arcuate foramen precluding C1 lateral mass screw fixation in a patient with rheumatoid arthritis: case report. Iowa Orthop J 2003;23:96–9. 23. Cakmak O, Gurdal E, Ekinci G, et al. Arcuate foramen and its clinical significance. Saudi Med J 2005;26:1409–13.
24. Tubbs RS, Shoja MM, Shokouhi G, et al. Simultaneous lateral and posterior ponticles resulting in the formation of a vertebral artery tunnel of the atlas: case report and review of the literature. Folia Neuropathol 2007;45:43–6.
Contents lists available at ScienceDirect
Journal of Clinical Neuroscience journal homepage: www.elsevier.com/locate/jocn
Neuroanatomical Study
Anatomic and radiologic analysis of the atlantal part of the vertebral artery Sahika Liva Cengiz a,*, Aynur Cicekcibasi b, Demet Kiresi c, Yalcın Kocaogullar a, Onur Cicek a, Alper Baysefer a, Mustafa Buyukmumcu b a
Neurosurgery Department, Selçuk University, Meram Faculty of Medicine, A/5 Meram Akyokusß 42080, Konya, Turkey Anatomy Department, Selçuk University, Meram Faculty of Medicine, Konya, Turkey c Radiology Department, Selçuk University, Meram Faculty of Medicine, Konya, Turkey b
a r t i c l e
i n f o
Article history: Received 19 February 2008 Accepted 27 May 2008
Keywords: Cadaver External landmarks Horizontal part Paramedian suboccipital craniectomy Posterior fossa surgery Third segment of the vertebral artery Vertebral artery
a b s t r a c t The horizontal third segment (V3h) of the vertebral artery (VA) in 7 cadavers (14 sides) was dissected and the anatomical measurements recorded. Measurements from 24 healthy individuals (48 sides) were taken for comparison using multislice CT scanning. The distance between the medial tip of the VA V3h and the line passing through the mid point of the posterior tuberculum of the atlas was marked as length A. The distance between the medial tip of the VA V3h and the point penetrating the dura mater was classified as length B. The angle between these lines was the alpha (a) angle. Measurements were taken when the head was in a neutral position, as well as in maximum right and left rotation, extension and flexion. In cadavers, the mean a angle (±S.D.) was 82.42 ± 10.34° and 83.21 ± 10.81° on the right and left side, respectively. On multislice CT scanning, the mean a angle was 81.64 ± 10.15° on the right and 83.77 ± 10.65° on the left. These angles varied with the position of the head. Ó 2008 Elsevier Ltd. All rights reserved.
1. Introduction
2. Methods
A potential hazard of the far lateral approach in a posterior fossa craniectomy is injury to the horizontal third segment (V3h) of the vertebral artery (VA), located in the superior aspect of the atlas. The VA is classically divided into four parts: its origin (from the subclavian artery in the root of the neck) to the sixth cervical vertebra (first part); its course through the foramina transversaria of the sixth to the first cervical vertebrae (cervical/second part); from the foramen transversarium of the atlas vertebra to its passage through the dura mater at the foramen magnum (suboccipital/ third part); and its course within the cranium to the pontomedullary border (intracranial/fourth part).1–12 The V3h portion of the VA lies close to the floor of the posterior fossa and damage to the VA may be fatal.13,14 Therefore, before attempting surgery at the posterior fossa and craniocervical junction, a thorough anatomical study of the path of the VA is mandatory. Here, we describe the normal anatomy and variations, as well as the surgical approach needed to expose the VA V3h segment, with the intention of developing a safe and effective technique for the far lateral approach in a posterior fossa craniectomy.
Seven cadavers (14 sides), with no history of craniocervical pathology, and 24 healthy individuals (48 sides), who were anatomically normal, were examined. The procedures were based on the guidelines of Selçuk University’s Ethical Committee on the Care and Use of Cadaveric Specimens. All of the healthy individuals who took part in the study were volunteers and were notified of the potential implications of radiation exposure. Dissections of the left and right V3h segments of the VA were performed in all cadavers. Each cadaver was placed in a prone position. The head was slightly extended in the neutral position, as the position of the head can greatly influence the structures that the surgeon will encounter. A midline incision was made through the inion and foramen magnum. After the blunt dissection of the trapezius, splenius capitis, and semispinalis capitis muscles, the suboccipital trigonum was exposed. The V3h portion of the VA was measured using an electronic caliper and goniometer. All length measurements were in centimeters. The distance between the medial tip of the VA V3h and the line passing through the mid point of the posterior tuberculum of the atlas was recorded as length A. When the head was in the neutral position (N), length A was labelled as NAR on the right (R) side and NAL on the left (L) side (Table 1). The distance between the medial tip of the VA V3h and the point penetrating the dura mater was recorded as length B. When the head was in the neutral position, length B was defined as NBR on the right side and NBL on
* Corresponding author. Tel.: +90 33 2223 6449; fax: +90 33 2223 6181. E-mail address: [email protected] (S.L. Cengiz). 0967-5868/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.jocn.2008.05.033
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S.L. Cengiz et al. / Journal of Clinical Neuroscience 16 (2009) 675–678
Table 1 Descriptive statistics of the atlantal horizontal third part of the vertebral artery in cadavers and healthy individuals
Cadavers (n = 7) Healthy individuals (n = 24)
NAR (cm)
NBR (cm)
NaR (°)
NAL (cm)
NBL (cm)
NaL (°)
p
1.67 ± 0.18 1.76 ± 0.24
0.81 ± 0.16 0.78 ± 0.75
82.42 ± 10.34° 81.64 ± 10.15°
1.67 ± 0.24 1.72 ± 0.26
0.84 ± 0.18 0.91 ± 0.22
83.21 ± 10.81° 83.77 ± 10.65°
>0.05 >0.05
Significant difference was defined as (p < 0.05). NAR, NAL: N = neutral position of the head. Length A = the distance (cm) between the medial tip of the horizontal portion (V3h) of the vertebral artery (VA) and the line passing through the mid point of the posterior tuberculum of the atlas. Length A was labelled as NAR on right (R) side and NAL on left (L) side. NBR, NBL: Length B = the distance between medial tip of VA V3h and the point penetrating the dura mater. Length B was defined as NBR on right side and NBL on left side. Alpha (a) angle = angle between these two lines, NaR = the a angle on the right side, with head in neutral position, NaL = the a angle on the left side, with head in neutral position.
the left side (Table 1). The angle between these two lines was defined as the alpha (a) angle (Table 1). Due to the stiffness of the cadavers, as well as the deep location and inaccessibility of the VA, there was slight error in the measurements. To minimize error rates, repeated measurements of each individual at different times were taken using a goniometer. To determine whether the a angle changed with the position of the head, measurements were taken when the head was placed in neutral, in maximum right and left rotations, and in maximum extension and flexion positions, using multislice CT scanning (Fig. 1). 2.1. Radiologic procedure The same measurements were also taken in 24 healthy individuals (48 sides) (see Supplementary Fig. 1). All of the participants were volunteers, and were informed about the potential implications of radiation exposure encountered during the study. Similarly, as with the cadavers, measurements of each individual were taken repeatedly at different times, so as to minimize the rate of error. For each group, the data obtained when the head was in the neutral position were compared bilaterally with: Group I (n = 6), the maximum right rotation of the head (see Supplementary fig. 2); Group II (n = 6), the maximum left rotation; Group III (n = 6), the maximum extension, and Group IV (n = 6), the maximum flexion. Spinal CT angiography (CTA) was performed using a 64-detector row helical scanner (Sensation 64; Siemens, Germany). After 100 mL of non-ionic contrast material was administered through an antecubital vein at a rate of 5 mL/s, CTA was performed from the lower half of the posterior fossa to the C3/4 level (acquisition protocol: gantry speed per rotation, 0.5 s; collimation, 0.75; 120 kV; 120 mAs). A bolus-tracking technique was employed and the scan started when the contrast material reached the common carotid arteries. When the Hounsfield units in the preset lumen of the
Fig. 1. The mean alpha (a) angle of healthy individuals, left (L, square) and right (R, diamond) sides in all positions. Ext = measurements with maximum extension of the head, Flex = measurements with maximum flexion of the head, Lrot = measurements with maximum left rotation of the head, Neutr = neutral head position, Rrot = measurements with maximum right rotation of the head. This figure is available in colour at www.sciencedirect.com.
distal common carotid artery rose by 100, the multidetector (MD) CT scan was triggered automatically after 3 s. The threedimensional (3D) reconstruction took place after the data had been transferred to the workstation. Transverse sections were reconstructed with a section width of 0.5 mm. MD CTA images were processed from the source images obtained using a volume-rendered technique (VRT) algorithm. 2.2. Statistical analysis Computer-assisted data analysis was performed with the help of the Statistical Package for the Social Sciences (v. 13.0) software (SPSS Inc; Chicago, IL, USA). The Mann–Whitney U-test was used in the comparative analysis between the cadavers and healthy individuals (Table 1). In healthy individuals, the Wilcoxon signed ranks test was used when comparing the neutral position to the other positions. Statistical significance was defined as p < 0.05. 3. Results In the cadavers, the mean a angle in the neutral position was 82.42 ± 10.34° on the right side and 83.21 ± 10.81° on the left side. In comparison, the mean a angle (±S.D.) measured using multislice CTA scans in healthy living individuals was 81.64 ± 10.15° on the left side and 83.77 ± 10.65° on the right side (Table 1); however, those angles varied with the position of the head (Fig. 1). In healthy individuals, when measurements in the neutral position were compared to measurements with the head at maximum
Fig. 2. Mean lengths A and B on the left and right side, in all positions. AL = Mean values of length A (cm) (triangle, dashed line) on the left side (the distance between the medial tip of the horizontal portion of the vertebral artery (VA V3h) and the line passing through the mid point of the posterior tuberculum of the atlas), AR = mean values of length A (diamond, solid line) on the right side, BR = mean values of length B (rectangle, solid line) on the right side (the distance between the medial tip of the VA V3h and the point penetrating the dura mater), BL = mean values of length B (cross, solid line) on left side, Ext = measurements with maximum extension of the head, Flex = maximum flexion of the head, Lrot = maximum left rotation of the head, Neutr = neutral position of the head, Rrot = maximum right rotation of the head. This figure is available in colour at www.sciencedirect.com.
S.L. Cengiz et al. / Journal of Clinical Neuroscience 16 (2009) 675–678
left rotation, all values were significantly different (p = 0.03), except for length B on the left side. When the lengths of B in the left and neutral positions were compared to the measurements with the head at maximum left rotation on the left side, the difference was not significant (p > 0.05) (Fig. 2). When comparing the measurements taken in the neutral position to measurements with the head at maximum extension, all values were significantly different (p = 0.03), except for length B on the left side. The length of B in the left and neutral positions compared to the maximum extension of the head on the left side was not significantly different (p > 0.05). When measurements in the neutral position were compared to measurements with the head at maximum flexion, all values were significantly different (p = 0.03), except for the length of B on the left side. As the lengths of B in the left and neutral positions were compared to the maximum flexion of the head on the left side, the difference was not significant (p > 0.05) (Fig. 2). There were no significant differences between length A on the left and right sides in the neutral position and the measurements of maximum right rotation of the head on both sides (p > 0.05). Measurements of length B and the a angle on the left and right sides in the neutral position were compared to measurements of maximum right rotation of the head on both sides. All values were significant (p = 0.03).
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cm on the left. Lang et al. measured the same length as 0.44 cm (0.27–0.60 cm).15 Differences between sexes, and the right and left sides were not significant. Length measurements of the VA between the medial border of V3h and the posterior tuberculum of the atlas in the neutral position (length A) were consistent with the findings of Lang et al.15 We have taken into account the margin of error associated with the measurements due to the stiffness of the cadavers and the difficulty in accessing the VA owing to its deep location. For these reasons, we repeated the same measurements at different times in both cadavers and multislice CT scans to reduce potential error. In conclusion, the V3h section of the VA can be easily identified by performing multislice CT scans pre-operatively. In addition, the measurements taken in cadavers corresponded to the same measurements seen on multislice CT scans. This may provide considerable intra-operative safety when exposing the V3h portion of the VA during a suboccipital craniectomy.
Appendix A. Supplementary data Supplementary data associated with this article can be found, in the online version, at doi:10.1016/j.jocn.2008.05.033. References
4. Discussion The atlantal part of the VA is deeply buried at the craniocervical junction, which is an area where numerous lesions can be found. Therefore, a thorough study of its anatomic structure may make surgical interventions less complicated. Information regarding the microsurgical anatomy of the atlantal part of the VA is sparse.2,3,14–17 According to Abd El-Bary et al., the VA third segment (V3) enters the transverse foramen of Cl, where it runs in a vertical, slightly anterior direction.16 Just above the transverse foramen of C1, the artery changes direction dorsally and runs further in the sagittal plane. In most cases, this change of direction is associated with an acute angle, but in some cases, the change is in a posteromedial direction. The artery then changes its direction again and runs transversely above the posterior arch of Cl.16 The course of the VA V3 is divided into three portions: a vertical portion between the transverse processes of C2 and C1; a horizontal portion (V3h) in the groove of the posterior arch of the atlas; and an oblique portion where it leaves this groove and travels up to the dura mater.18,19 At the end of the groove, the height of the posterior arch of the atlas increases like a step. Thereafter, the VA runs in a superomedial direction to the dura mater of the foramen magnum. The junction between the second and third portion of the V3 is sometimes called the genu of the VA.20–22 Anatomical studies have shown that the left VA is larger, smaller or equal in size to the right VA in 45%, 21% and 34% instances, respectively.23 Although the VA V3 anatomy is documented,2,3,14–17 no information is available regarding the angle of the VA where it penetrates the dura mater. This study draws attention to the surgical dangers of the far lateral approach in a suboccipital craniectomy. In our study, the range of values for the a angle as it passed through the dura mater varied, the greatest difference being when the head was in maximum flexion compared to neutral flexion. During the flexion of the neck, the VA glides superiorly and anteriorly relative to the posterior arch, and this is most likely to occur at the level of the lateral masses of the atlas rather than at more caudal sites in the neck.24 In cadavers, the median measurements (±.S.D.) of length B of the VA (from its entrance into the transverse foramen of the atlas to its passage through the dura mater) in the neutral position were 0.81 ± 0.16 cm on the right and 0.84 ± 0.18
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