Morphological Study of the Foramen
Transversarium of the Atlas Vertebra among
Egyptian Population and Its Clinical Significance
Joseph N Aziz* and Michel Morgan
Department of Anatomy, Cairo University, Egypt
Submission: February 20, 2018; Published: March 15, 2018
*Corresponding author: Joseph N Aziz, Department of Anatomy, Faculty of Medicine, Cairo University, Egypt, Email: email@example.com
How to cite this article: Joseph N Aziz, Michel Morgan. Morphological Study of the Foramen Transversarium of the Atlas Vertebra among Egyptian
Population and Its Clinical Significance. Anatomy Physiol Biochem Int J: 2018; 4(4): 555642. DOI: 10.19080/APBIJ.2018.04.555642.
Background:Foramina transversaria are characteristic bony features of the cervical vertebra, they are located on the transverse process
of cervical vertebrae. These foramina are of anatomical importance as they provide bony passages for several anatomical structures namely
vertebral artery, vertebral vein and sympathetic nerves. They have known to exhibit variations with regard to size, shape and may even
absent, incomplete or duplicated.
Objective:This study aim to investigate the morphology and variations of foramina transversaria of the human atlas vertebrae and to
point out the clinical importance of these variations.
Material and methods:135 atlas vertebrae of Egyptian origin were studied. They were available in the dissecting room of the anatomy
department, Faculty of Medicine, Cairo University. Each vertebra was studied morphologically for the presence of various shapes of foramen
transversarium, presence or absences of any morphological anomaly like accessory foramen or incomplete foramen.
Results: Four shapes were noted. Type 1 (rounded) was predominant 54.1%, type 2 (oval) less prominent 29.6%, type 3 (irregular)
10.4% and type 4 (quadrangular) 5.8%. Double foramina were founded in 23 vertebras, incomplete foramina in 9 vertebras and accessory
incomplete foramina were seen in 12 vertebras.
Conclusion: The morphological knowledge of this type of variation is clinically important because the course of the vertebral artery
may be distorted in such condition. It may be compressed leading to some neurological symptoms or even hearing disturbances. Also, the
knowledge of this type of variation is important for the neurosurgeon during posterior surgical approaches of cervical spine. It is also useful
for radiologist during CT and MRI scan.
The atlas is a ring of bone and consists of a pair of lateral
masses connected by a short anterior arch and a long posterior
arch. The transverse processes projects laterally from the lateral
masses and longer than that of other cervical vertebrae except
the seventh . Marking the transverse processes, the foramen
transversaria (FT) which are located on the transverse process
and are cardinal features of cervical vertebrae . FT transmits
the vertebral vascular bundle (vertebral artery, and veins)
and the sympathetic plexus which accompanies the vessels.
Derangements of these structures in their course because of
narrowing or deformation of the foramina, or osteophytes
impinging on them, have been extensively investigated by many
authors. The importance of such disturbances to these vital
vessels and nerves is obvious. Embryologically, FT is the result
of the special formation of the cervical transverse processes.
It is formed by a vestigial costal element fused to the body
and the originally true transverse process of the vertebra; the
vertebral vessels and nervous plexus are caught between the
bony parts. The FT is closed laterally by the “costotransverse
bar”, a plate of bone interconnecting the rib element to the
original transverse process (Figure 1). Generally, any variations
in the FT may affect the vital structure i.e. vertebral artery
entrapment that may cause vertebrobasilar insufficiency. The
knowledge of these variations is important for surgeons and
radiologist for interpreting CT and MRI scans . From the
surgical point of view, study of the FT is of great value to the
neurosurgeons for posterior approaches of cervical spines .
These foramina exhibit variations in their shape, size, number
and even presence or absence. Morphometry and anomalous
variations are important to the neurosurgeons in determining the etiology, side predilection and vascular variations in the
atlanto-occipital region .
There is correlation between the atlas morphology with
head and neck posture . Thus, the presence of other bony
variations, as well as the prevalence of neck syndromes and
injuries necessitates the study of the atlas transverse foramina.
The recognition of this variation provides safety and efficiency
for the posterior approaches of cervical spine . From the
clinical point of view, occipital neuralgia is usually unilateral and
has a characteristic shock like pain lasting for a short duration
indicative of neural origin . The pain is confined to the
dermatome of the nerve root at the lower occipital region of scalp
and upper neck. Compression of the nerve root by an abnormal
course of vertebral artery has been reported in the literature.
Bony abnormalities at the craniovertebral junction can cause
occipital headache due to abnormal course of vertebral artery
and joint instability [8,9].
Dried 135 atlas vertebrae of Egyptian origin and of adult
size and unknown sex were obtained from the Dissecting room
of dental students, department of Anatomy, Cairo University,
Faculty of Medicine, for the present study. Broken or incomplete
atlases were excluded from the study. The vertebrae were
examined for the presence or absence of foramina, double
foramina and incomplete foramina. The side and shapes of the
foramina also noted. The shapes of the foramina were classified
into four categories using the criteria by Taitz et al. .
According to the shape and direction of the main diameter, the
transverse foramina were classified into four types; (they were
studied as seen in an A-P direction where the anterior arch
facing the examiner).
The whole 135 dried vertebrae, used for this study, were
examined for the presence or absence of foremen transversaria
and the presence of accessory or incomplete foramen. The
following results were recorded: Double foramina were observed
in 23 vertebrae (17.7%) 7 on the left and 13 on the right and 3 on both sides. The accessary foramina were present on the posterior
root of the transverse process in 10 cases while in 13 cases the
foramina were observed at the posterior arch (Figure 3-5). Some
accessory foramina were too small. Incomplete foramina were
observed in 9 vertebrae (6.9%), 4 on right 3 on left 2 bilateral
(Figure 6). Also, in 6 vertebrae (4.6%) incomplete accessory
foramina were observed with different shape semicircular,
hemi circular and U shape in Figure 7 with 2 on the left 3 on
right 1 bilateral (Table 1). Study of the shape of the foramina
transversaria based on the anteroposterior and mediolateral
measurements showed four different shapes; type 1 (rounded)
was predominant 54.1%, type 2 (oval) less prominent 29.6%,
type 3 (irregular) 10.4% and type 4 (quadrangular) 5.8%.
As one of the three bony components of the cranio-vertebral
junctions the atlas constitutes a clinically significant entity
mainly because of importance of its grooves and foramina in the
region of posterior and lateral margin . Transverse foramen
of atlas has been studied in terms of shape, morphometry
and presence or absence in Kenyans . In the current study,
the shapes of the foramen transversarium were categorized
into four different categories, rounded 54.1%, oval 29.6%,
irregular 10.4% and quadrangular 5.8%. In atlas vertebrae, true
transverse process is represented by a thick posterior bar in
intrauterine life, which fuses eventually with thin anterior bar
developed in third – fourth year of life from ventrolateral aspect
of articular pillar and thus completes the formation of FT. Hence
in atlas, the foramen transversarium is formed by fusion of anterior and posterior bars as they pass around the position of
vertebral artery at the age of 3-4 years . The variable shape of
foramen transversarium as observed in the current study were
categorized on the basis of their plane and maximal medio lateral
dimension in coronal plane . The variable shapes of foramina
have been known to have a correlation with the tortuosity and
size of vertebral artery, which is inturn dependent subsequent
on loading forces and stresses in the neck .
It has been observed that in some cases the accessory FT was
too small compared with the original FT. Thus smaller foramen
was explained by absence of vertebral artery or a variation where
the artery runs along the transverse process without entering
the foramen . The current study found double foramina in
23 vertebrae (17.6%). Several authors have reported double or
triple foramina in cervical vertebrae without specific reference to
the atlas. These variations are possibly linked with duplication of
the vertebral artery. However, occurrence of multiple transverse
foramina may not necessarily reflect vertebral artery variations,
as one foramina may be occupied by veins and nerves. The cause
for this variation in cervical vertebrae without specification to
atlas was attributed to fusion of two costal elements with the
transverse process . Moreover, these variations may be
attributable to possible genetic differences and also carrying
heavy loads on the head, which has been associated with various
bony bridges on the atlas vertebrae .
In this study, incomplete transverse foramina were also found
in 9 vertebrae (11%), it could be explained on the base of erosion
of bones as the age advances. However, the age of the bones was
difficult to assess because of lack of information about age related
changes in most of these studies. Also, incomplete accessory
transverse foramina were also found in 6 vertebrae (4.6%),
most of them mainly located at the posterior root. However,
the age of the bones was difficult to assess because of lack of
information about age related changes in most of these studies.
It is reported that tortuosity of the vertebral artery may cause
bony erosion, or impede complete formation of the transverse
foramen [12,13] Developmental changes could account for the
anomaly observed. Other explanations of incomplete foramina
are tensions and stress applied to bones by the running vessels
through foramina with relatively free movements of the cervical
spine . Furthermore, the natural tortuosity of vertebral
artery may cause bony destruction which could be minimal
leading to bony bridge or sever . Accordingly, the shape of
incomplete foramina in the current study is semicircular, hemi
circular and U shape (Table 2).
From the current study, it could be suggested that variations
of the foramina can be useful for estimating changes or variations
of vessels this runs concurrently with previous literature .
The occurrence of incomplete transverse foramina in atlas
should be noted by radiologist, as these can be confused with
other anomalies . On the other hand, some authors have
noticed that the vertebral artery covers about two thirds of the
minimal diameter and more than half of maximal diameter of
the transverse foramen . Moreover, it has been suggested
that the preponderance of osteophytes on lateral margins of
FT could lead to narrowing of mediolateral diameter leading
to compression of vertebral artery and its dissection .
Hence it can be assumed that oval shape FT oval 29.6% with
anteroposterior diameter greater than mediolateral diameter
had minimal risk of vertebral artery compression syndrome.
Also, it is well known that any narrowing of FT may result in
formation of atheromatous plaques in vertebral artery which
may result in thrombosis/emboli /reflex spasm predisposing to
vertebrobasilar insufficiency .
The study has revealed existence of many variations in the
transverse foramina of atlas among Egyptian. The data provided
in the present study is helpful in interpretation of radiographic
features of atlanto-occipital region, as well as surgical access.
Also, this suggests that defects in the FT of the atlas vertebrae
may be included in the cervicovertebral junction anomaly, when
anomalous can cause occipital headache. So that, neurosurgeons
should be aware of such variations while operating at the level
of first cervical vertebra so as to prevent accidental injury of the
vertebral artery and thereby preventing any neurological deficit.
On the other hand, radiologists must also be aware of this fact
in order to correctly interpret the radiograph or CT scan or MRI
image of the cranio-vertebral region.