|Year : 2006 | Volume
| Issue : 4 | Page : 223-226
The course of the V1 segment of the vertebral artery
V Ranganatha Sastry, KY Manjunath
Dept. of Anatomy, St. Johnís Medical College, Bangalore - 560 034, India
K Y Manjunath
Dept. of Anatomy, St. Johnís Medical College, Sarjapur Road, Bangalore - 560 034
Source of Support: None, Conflict of Interest: None
| Abstract|| |
Background: It has become important to know the exact origin and course of the vertebral artery as well as the percentage of the abnormalities of these variations from the point of view of surgery, angiography and in all non-invasive procedures. In decompressive procedures and for subsequent stabilization procedures of the cervical spine, thorough knowledge of the anatomy of the vertebral artery is mandatory to avoid a potentially catastrophic injury to the vertebral artery. Aims of the Study: The present study was aimed at investigating the frequency of occurrence of the variations of the pre-transverse segment of the vertebral artery especially concerning the level of its entry into the foramen transversarium, tortuosity and size in formalin fixed adult cadavers and fetuses with the view of keeping the surgeons alert regarding the frequency of occurrence of these variations in the local subjects. Materials and Methods: The pre-transverse segment of the vertebral artery (V1 segment) was studied in 19 formalin fixed cadavers (6 females and 13 males) and ten formalin fixed newborn fetuses. The total length and the diameter of the V1 segment of the vertebral artery were measured in adult cadavers to the nearest millimeter using a sliding caliper. Variations in the level of entry of the vertebral artery in to the foramen transversarium and also tortuosity of the artery were noted down. Results: The vertebral artery measured a mean length of 4.9 Ī 1.24 cms and a mean diameter of 3.58 Ī1.59 mms. In over 71% of the cases the vertebral artery entered the foramen transversarium at the level of C6. The next highest frequency was C7 (18.42%) and in small percentage of the cases at C5 (5.3%), C4 (2.6%) and C3 (2.6%). The vertebral artery was found to be tortuous in nine cases (23.7%). Conclusions: Data derived from gross anatomical studies serve as an indicator of prevalence of variations within a population group. But it would be safest for the surgeon to investigate each case by a computed tomographic scan before the cervical surgery.
Keywords: Cervical vertebrae, foramen transversarium, vertebral artery
|How to cite this article:|
Ranganatha Sastry V, Manjunath K Y. The course of the V1 segment of the vertebral artery. Ann Indian Acad Neurol 2006;9:223-6
The vertebral artery (VA) is the first and the largest branch of the subclavian artery; arising from its postero-superior aspect, it courses upwards and medially in the scaleno-vertebral triangle (formed in between the longus colli and the scelenus anterior muscles) and enters the foramen transversarium (FT) of the sixth cervical vertebra. This part of the course of the vertebral artery i.e., between its origin from the subclavian artery and its entry in to the foramen transversarium is called as the V1 segment of the artery (or the pretransverse segment).
However the level of entry of the vertebral artery into the foramen transversarium is variable according to the previous studies: according to Rieger and Huber: sixth cervical vertebra - 87.5%; fifth cervical vertebra - 6.6%; fourth cervical vertebra - 0.5%; seventh cervical vertebra - 5.4%; according to Adachi: 4.5, 1.2 and 0.7% at C5, C7 and C4 respectively. «avdar and Arisan have also reported similar percentage of incidence.,,
Apart from the variable levels of entry of the VA other variations like tortuosity and hypoplasia also have been reported in literature.,
In surgery, angiography and in all non-invasive procedures, it is of great importance to know the exact details of the course of the V1 segment of the VA to prevent catastrophic laceration of the VA during the surgical procedures. The present study was undertaken to find out the variations of the V1 segment of the VA in the gross anatomical dissections of cadavers since no similar studies could be traced in the Indian literature.
| Materials and Methods|| |
Observations of the pretransverse segment of the VA were made in 19 formalin fixed adult cadavers (6 females, 13 males; total -38 sides) between 45-70 years of age and ten formalin fixed newborn fetuses (20 sides). None of the adult cadavers showed atherosclerotic changes on gross examination. On each side of the cadaver the course of the VA was cleaned from its origin from the subclavian artery to its entry in to the FT. Variations in the level of entry of the VA in to the FT and also tortuosity of the artery were noted down. The total length and the diameter of the V1 segment of the VA were measured in adult cadavers to the nearest millimeter using a sliding caliper.
| Results|| |
The results did not show any significant side or sex differences. The results of the present study are summarized in [Table - 1][Table - 2]. The details of the observations are given below:
Dimensions of the VA [Table - 1] : The mean length of the V1 segment of the artery does not differ significantly on two sides. Whereas the mean diameter of the VA is slightly smaller on the left side (left: 3.06 Ī 1.25 mm; right: 4.09 Ī 1.78 mm).
Level of entry in to the foramen transversarium [Table - 2] : In over 71% of the cases the VA entered the FT of the C6. The next highest frequency was C7 (18.42%) and in small percentage of the cases of C5, C4 and C3 (5.3, 2.6 and 2.6% respectively) [Figure - 1]A. In all the fetuses dissected the VA entered the FT at the level of C6 only except in one instance of the right side it entered the FT at the level of C7.
Tortuosity: The tortuosity was observed in nine cases (23.7%) of the present study. In all the cases the plane of the tortuosity was horizontal [Figure - 1]B.
| Discussion|| |
The vertebral artery has become more and more important since the time Egas Moniz performed the first vertebral angiography in 1933. One of the first surgical approaches to this region was described by Crawford and DeBakey in 1958 for lesions causing ostial stenosis. In addition to angiography, continuous wave Doppler sonography has been the most important tool for the non-invasive investigations of the extra cranial course of the VA for many years.,
In surgery and angiography and also in all non-invasive procedures it is of great importance to know the details of the course of the vessels. Especially for the surgeon, it is equally important to know at which precise location of the subclavian artery the VA originates and in which percentages the real abnormalities can be found.
Matula et al , have divided the variations of the VA according to the source of origin of the VA and secondly the origin from the subclavian artery with respect to its circumference. They found origin of the VA other than the subclavian in 6% of the cases. In our series in all instances the VA originated from the subclavian.
The location of the origin of the VA on the circumference of the subclavian was found to be cranial in 47%, dorsal in 44%, caudal in 6% and ventral in 3% of the cases in the series reported by Matula et al .
Tortuosity and hypoplasia of the V1 segment
Matula et al in their series found in 52.9% of the cases the VA followed a non tortuous path from the origin to the transverse foramen and in 47.2% followed a tortuous path. Further they have classified the tortuosity according to the geometric plane as, transverse (42.5%) and sagittal (30.5%). Curylo et al found the VA course tortuous in 27% of their cases. In the present series the tortuosity was observed in 23.7% of the cases (nine cases) [Figure - 1]B.
Tortuosity of the V1 segment does not have any haemodynamic consequences but the loops of the V1 segments have been reported to cause radicular symptoms by nerve root compressions. Cervical spinal fractures secondary to bony erosions by the close contact with the loop of V1 segment have been reported. Symptomatic loop may be corrected by bypass surgery.,,,,
A hypoplastic artery (diameter < 3.5 mm) was found in 8.6% of the cases studied by Matula et al . In the present series, in five cases VA was hypoplastic (13.16%) [Figure - 1]C.
According to Golueke, Sclafani, Philips, Goldstein, Scalea, Duncan approximately 15% of patients have a hypoplastic VA. In patients with VA asymmetry the left VA is usually found to be larger. In the present series, the VA was found to be symmetrical in four cases and in five cases (three of the right and two of left sides, 13.16%) VA was found to be hypoplastic (2 to 3.5 mms). In two cases of hypoplastic VA of right side and one case of left side the VA of the opposite side measured 7 mms in diameter, i.e., almost twice the size of the hypoplastic VA.
The level of entry in to FT [Figure - 1] A, B, C:
According to the data available from the previous studies the entry of the vertebral artery has a variable level of entry into the foramen transversarium: Rieger and Huber have observed the entry of the VA at the level of sixth cervical vertebra in 87.5%, fifth cervical vertebra in 6.6%, fourth cervical vertebra in 0.5% and seventh cervical vertebra in 5.4%. Adachi in his examination of 1,000 half heads found the VA entering the FT at C5, C7 and C4 in 4.5, 1.2 and 0.7%, respectively. «avdar and Arisan have also reported similar percentage of incidence.,,
Matula et al found level of entry of the VA in to the FT of C6 in 90% in their study. They also found one case each of the VA entering at C4 and C5 and two cases VA entering at the level of C7. Heary et al have reported VA entering into the FT of the C6 in 100% of their series. In our series the VA entered the FT at the level of C6 in 71.1% of the cases in adults and in 95% of the cases in fetuses [Table - 2]. Jackson, Wheeler and Darden have described one case of a left VA entering the FT at C3 level. Only two other reports of VA entering at the level of C3 are of Fujiama, Gluncic., Fazan, Caetano and Filho have described a rare case of the VA of right side originating from the common carotid artery and entering the FT of the axis vertebra (C2).
In our series we found only one case of VA entering the FT at the level of C3 [Table - 3], [Figure - 1]A.
The morphometric data of the VA has utility for both surgical exposure and endovascular approaches to the vessel. According to Matula et al , the length of V1 segment was not reported in earlier studies. They also found that the contorted vessels differ in their diameter significantly than the length with their straight counter part.
Surgical importance of the course of the V1 segment of the VA
Anterior cervical decompression surgery is performed for a variety of reasons. The operative indications for surgery in the cervical region include spondylosis, herniated inter-vertebral disc, tumor, infection and trauma. An understanding of the anatomy of these arteries and the surrounding bony anatomy is essential to prevent iatrogenic VA injuries.
In the presence of an abnormally tortuous VA, using anatomic landmarks to guide decompression may not prevent iatrogenic injury to the VA. Failure to recognize this anomaly during preoperative planning can lead to laceration of the vessel.
Laceration of the VA is a most challenging surgical dilemma during anterior cervical spinal surgery; gaining control of the massive hemorrhage from a ruptured VA is difficult and could possibly result in an uncertain neurological morbidity.
Since no similar study of the V1 segment of the VA by gross anatomical dissections could be found in the Indian literature, the present study was undertaken to find out the frequency of variable point of entry of the VA into the FT and any other variations associated with the V1 segment of the artery in cadavers. As can be seen from the data of the present study the course of the V1 segment of the VA varies considerably from one study to the other [Table - 3]. These variations may have a racial and ethnic basis. A much detailed and extensive study of large number of gross anatomical dissections may be necessary to establish the trend of variations in the local population group. Although data derived from gross anatomical dissections of cadavers can be a useful guideline to the surgeon, it would be safest to perform a preoperative computed tomography scan in each case before planning cervical spine surgery.
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[Figure - 1]
[Table - 1], [Table - 2], [Table - 3]
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