Developmental anomalies of the axis are commonly encountered, especially anomalies involving the odontoid process. Anomalies of the posterior elements are uncommon. We describe a unique case of agenesis of posterior elements of C2 with basilar invagination and atlanto-axial dislocation. An obese 8-year-old boy presented with symptoms of cervical myelopathy. Radiological workup revealed a craniovertebral junction anomaly with occipitalised atlas, absent posterior elements of axis, and hypertrophied C3 spinous process. Atlanto-axial instability and basilar invagination was present. Magnetic resonance angiography revealed hypoplastic left vertebral artery. Traction with cervical tongs failed to improve the alignment and symptoms. Anterior trans-oral release, followed by posterior decompression and custom-made instrumentation, was done. The patient recovered completely and was asymptomatic at the end of two years. X-ray and computed tomography scan demonstrated reduction of basilar invagination and maintenance of alignment. This is the first case to be reported of agenesis of posterior elements of axis associated with basilar invagination. One should look for this condition in patients with hypertrophied spinous process of C3. Utilization of hypoplastic pedicle of axis serves as an additional fixation point to increase the stability of the construct.
Developmental anomalies of the axis are commonly encountered, especially anomalies involving the odontoid process [
An 8-year boy presented to the outpatient department with neck pain, progressive imbalance and difficulty in walking, since 6 months duration. On examination, he was found to be obese, with a body mass index of 31.42 kg/m2. He had a low hairline and stiffness of neck movements. Power and sensations in all extremities were normal; however, he had spasticity and exaggerated deep tendon reflexes in all four extremities. The plantar response was extensor. Static and dynamic radiographs of cervical spine revealed mobile AAD, absent spinous process of axis and hypertrophied C3 spinous process (
The computed tomography (CT) scan of cervical spine with 3D reconstruction further illustrated the pathoanatomy of the condition (
Developmental anomalies are common in odontoid process. However, anomalies of posterior elements of axis are uncommon. These include invagination of lamina of axis causing cord compression and absence of posterior elements of axis [
The axis develops from the second spinal sclerotome in three essential stages [
Most of the cases reported till date had varying degrees of anterolisthesis of C2 over C3 [
Being a congenital anomaly, we included MR angiography in the preoperative workup. Angiography revealed hypoplastic left vertebral artery. This had important clinical implications, as we had to be extra cautious while inserting the right-sided screws.
Our patient had a basilar invagination, which was irreducible on cervical traction. Thus, we opted for anterior transoral release of contracted structures, as described by Wang et al. [
Almost all cases of agenesis of posterior elements of C2 have presented with myelopathy, and no asymptomatic cases have been reported in literature [
We present a unique case of absent posterior elements of axis with occipitalised C1, mobile AAD and basilar invagination, presenting as cervical myelopathy. Absent posterior elements of axis is a rare condition. One should look for this condition in patients with hypertrophied spinous process of C3. Close follow up is necessary, and fusion may be considered in patients who develop myelopathy. Careful preoperative evaluation should be done. Angiography must be considered to identify anomalies in vertebral artery. Utilization of hypoplastic pedicle of axis serves as additional fixation point to increase the stability of construct. Further experience is mandatory to formulate an appropriate treatment protocol for this complex anomaly.
Cases have been listed in chronological order of date of publication.
NA, not available; AAD, atlanto-axial dislocation; O–C4, occiput to C4.