Partial agenesis of the posterior arch of the atlas
We report the case of a 54-year-old woman who
presented at the emergency department complaining of
cervical pain with no irradiation to superior extremities after
a low-energy traffic accident. Physical examination was
unremarkable, except for tenderness on percussion of
cervical spinous process and pain with flexion and extension
of the neck. A lateral cervical radiograph showed a
congenital malformation (partial agenesis of the posterior
arch of the atlas). Congenital defects of the posterior arch are
not frequent, and their incidence is not well known.
Currarino et al (Am J Neuroradiol 1994;15:249) described
an anatomical classification of posterior arch defects of the
atlas with 5 different types. These defects of the posterior
arch of the atlas may be discovered incidentally because
patients are generally asymptomatic, though chronic
cervical pain and even myelopathy can occur. Treatment is
normally conservative, but surgery may be indicated when
patients present spinal cord compromise.
A 54-year-old woman presented at the emergency
department complaining of cervical pain with no irradiation
to upper limbs after a low-energy traffic accident (fall in a
public bus due to an abrupt halt). She had a personal history of
hypothyroidism and type 2 diabetes mellitus in treatment with
levothyroxin and insulin, respectively. Her physical exam-
ination was unremarkable, except for tenderness on percus-
sion of cervical spinous process and pain, especially with
flexion and extension of the neck. No strength or sensory loss
in the upper extremities was evident, and normal osteotendi-
nous reflexes were present. A lateral cervical radiograph was
taken, showing a congenital abnormality with partial absence
of the posterior arch of the atlas (Fig. 1).
Nonsteroid anti-inflammatory drugs (NSAIDs) were
prescribed, and rest with cervical collar was advised.
Cervical computed tomography (CT) was performed show-
ing the posterior arch anomaly with a persistent posterior
tubercle (Fig. 2).
She was referred for physiotherapy to alleviate cervical
pain, and 2 months later, she had improved though
occasionally had mild discomfort. Magnetic resonance
imaging was not performed because no signs of spinal cord
affectation were observed.
Congenital anomalies of the posterior arch of the atlas are
not frequent, and their incidence is not well known. They
range from partial clefts to total agenesis of the posterior
arch. Currarino et al  described an anatomical classifica-
tion of posterior arch defects of the atlas:
Type A: failure of posterior midline fusion of the
Fig. 1 Lateral cervical radiograph demonstrating partial absence
of the posterior arch of the atlas.
This article was presented at the Fourth Mediterranean Emergency
Medicine Congress (Sorrento, Italy, September 15-19, 2007).
0735-6757/$ – see front matter © 2008 Elsevier Inc. All rights reserved.
American Journal of Emergency Medicine (2008) 26, 118.e3–118.e5