Case Report

Partial agenesis of the posterior arch of the atlas^B

Abstract

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).

^? This article was presented at the Fourth Mediterranean Emergency Medicine Congress (Sorrento, Italy, September 15-19, 2007).

0735-6757/$ - see front matter (C) 2008

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 [1] described an anatomical classifica- tion of posterior arch defects of the atlas:

Type A: failure of posterior midline fusion of the 2 hemiarches

Fig. 1 Lateral cervical radiograph demonstrating partial absence of the posterior arch of the atlas.

118.e4 Case Report

Fig. 2 Cervical CT scan demonstrating aplasia of the posterior arch of the C1 with a persistent posterior tubercle.

Type B: unilateral defect Type C: bilateral defects

Type D: absence of the posterior arch, with persistent posterior tubercle

Type E: absence of the entire arch, including the tubercle.

According to this classification, our case complies with type D given the presence of persistent posterior tubercle.

The type A anomaly is the most frequent form (N95%), and fusion defects of C1 hemiarches can affect 3% to 5% of the population [2].

It is not clear whether this is a hereditary defect, though 2 reports have been documented of cases within a family (mother and children) [1,3]. Incidence among both sexes is similar. In general, the clinical presentation is variable. Patients are most commonly asymptomatic, though the defect can cause chronic cervical pain, headache, and Lhermitte sign [4]. The abnormalities of the posterior arch may be discovered as an incidental asymptomatic finding. Cervical myelopathy is also possible and has been reported in several cases [4-7], especially with types C and D of the Currarino classification, which are both associated with the presence of a posterior osseous fragment.

It appears to be associated with a mobile and isolated posterior arch remnant, which is displaced forward, making contact with the upper cervical cord during extension of the cervical spine. Klimo et al [5] demon- strated this displacement mechanism with fluoroscopy in a 17-year-old patient with sensory loss in the lower limbs and the left arm and Lhermitte sign. Nearly complete resolution of symptoms was achieved after surgical extirpation of the osseous fragment. The mechanism has also been reported in other cases by lateral cervical

radiography in flexion and extension [6]. Sagiuchi et al [4] described the case of a young man with the presence of Lhermitte’s phenomenon while yawning and mild weak- ness in all extremities. The mechanism of spinal cord injury was shown with dynamic cervical multisection- detector CT myelography with sagittal reconstruction. After surgical extirpation, the patient’s symptoms disap- peared completely. Other cases have been reported where symptoms commenced after mild trauma [6-8].

Diagnosis is usually made as a casual finding in asymptomatic patients. In other cases, the defect is observed after lateral cervical radiography after a minor accident [9,10] where the defect can be mistaken for a cervical fracture, for instance, Jefferson’s fracture, in which case, cervical CT can be very useful to differentiate the findings [11]. Magnetic resonance imaging is reserved for cases where any neurologic abnormality is observed or there is a suspicion of myelopathy.

Treatment is normally conservative; surgery indicated when patients present atlanto-axis instability and spinal cord compromise [5,6]. Some authors, however, recommend early surgical intervention in patients with types C and D (with posterior osseous fragment) to avoid accumulative Spinal injury [4,7].

Knowledge of this congenital defect is useful to avoid diagnostic errors, especially in patients with cervical trauma, in which the anomaly can be mistaken for a cervical fracture. In addition, neurologic deficit of any kind must be ruled out in patients presenting the anomaly because they can benefit from effective early surgical intervention.

Carlos Beaumont Caminos MD

Emergency Department, Hospital of Navarra

Pamplona, Navarra, Spain E-mail address: [email protected]

Idoya Zazpe Cenoz MD, PhD

Department of neurosurgery, Hospital of Navarra

Pamplona, Navarra, Spain

Angel Hernandez Galan MD Clint Jean Louis MD Bernabe Fenandez Esain MD

Inmaculada Gimena Ramos MD

Emergency Department, Hospital of Navarra

Pamplona, Navarra, Spain

doi:10.1016/j.ajem.2007.07.022

References

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