Variations of atlas ... Kavakli et al
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atlas is concave and elongated, joint with the
corresponding occipital condyle. Sometimes the
articular surface is divided into 2-facet.
present study, a complete subdivision of the joint
surface was observed in 11 atlases (12.8%) (
Figure 2). Prescher
found this variation in 28 out
of 200 atlases (14%): 7.5% on the right, 2% on the
left, 4.5% bilateral. In the literature, the frequency
of the bipartite superior joint surface was reported
That this variation develops
from 2 sources, namely, the proatlas and C1
segment, may explain its origin.
symptoms and disturbances caused by facies
articularis superior bipartita atlantis have not been
reported. However, it may be mistaken for fractures
Processus infratransversarius atlantis. This is
a bony extension emerging from the transverse
process in caudal direction.
In the present study,
this structure was observed in different localization
with a frequency of 1.2-7% in variable lengths
Figure 3). Clinically, this variation may represent
symptomatic disturbances at the craniocervical
Patients with symptomatic variations of
the craniocervical junction often complain of pain in
the neck region or at the back of the head or they
suffer from vertigo or disturbances in balance.
Principal mechanisms of symptoms are mechanical
compression of nervous and vascular structures,
marked instability or in contrast, elevated rigidity.
Arthrotic formations simulating variants:
Corona atlantis peridentalis. In the present study,
arthritic formation, corona atlantis peridentalis or
"coulisse of the atlas" termed by Prescher,
arcus anterior atlantis was found in 8 cases (9.3%),
corresponding to the "coulisse of the dens" (
& 4). Lombardi
reported that these formations
might be partly attributed to the occipital vertebra.
He also observed that the patients in his series were
free of any physical disturbances attributable to the
In conclusion, the findings from our study
generally agree with those of the previous. The only
difference was that ponticulus posterior was
observed with a low frequency on the right, only
perhaps encountered by chance. It might even be
peculiar to the population living in the area. Our
results for processus infratransversarius atlantis,
arthrotic formation and corona atlantis peridentalis,
will also be compared with those of further works
for our literature survey failed to find any data
concerning them in other populations.
Acknowledgment. The authors would like to thank
Assoc. Prof. Hassan Boynukara who made the necessary
correction of the English grammar.