The atlas stands as the first cervical vertebra,
being articulated with the occipital bone above and the axis vertebra below.
It has the shape of a ring and 2 arches.
The anterior arch is short and articulates with the dens of the axis vertebra,
while the posterior arch bears a groove on its surface for the vertebral artery and the dorsal ramus of the first cervical spine nerve.
The vertebra has 2 transverse processes,
which form a foramen transversarium,
crossed by the vertebral artery and also 2 lateral masses,
which articulate with the occipital condyles and form an ellipsoid type of synovial joint.
Fig. 1: Atlas, first cervical vertebra - anatomy
References: www.wikipedia.org
After its exit from the transverse foramina,
the vertebral artery passes over the posterior arch of the atlas,
forming a groove called the vertebral artery sulcus,
which varies in size and can sometimes be very deep,
located on the posterolateral margin of the posterior arch of the atlas.
Fig. 3: Vertebral artery - lateral view
References: www.wikipedia.org
Inferiorly and posteriorly to the posterior arch of the atlas,
the posterior occipital ligament is attached.
It is connected above with the posterior margin of the foramen magnum and appears as a broad,
but thin ligament.
Its lateral divisions,
the oblique atlanto-occipital ligaments,
create with the vertebral artery sulcus an opening for the vertebral artery and the suboccipital nerve.
Fig. 2: Median sagittal section through the occipital bone and first three cervical vertebrae.
References: www.wikipedia.org
Variants and asymptomatic deviations from the normal vertebral anatomy are often confusing.
This is the reason they have to be studied carefully to insure an adequate differentiation from a pathological process.
If anomalous ossification occurs,
a bony arch - named ponticulus posticus - bridges the sulcus,
encloses the foramen arcuate and through this,
the vertebral artery and the subocccipital nerve pass.
Fig. 5: CT 3D reconstruction of cervical spine, lateral view - complete unilateral ponticulus posticus (blue arrow)
Ponticulus posticus is a possible cause of posterior circulation ischemia,
cervicogenic headache,
vertigo,
neck pain,
discopathy.
This condition had not been a matter of concern for physicians until its surgical significance in the insertion of screws in the lateral mass of the atlas was reported.
Our interest for this anatomic variant was stimulated by its incidental appearance in various lateral cervical spine examinations.
This study`s purpose was to determine occurrence,
varieties,
distribution by age and sex of ponticulus posticus in a Radiology Ambulatory Care Service from Cluj-Napoca.