Background: Ossified lesions of the upper cervical spine behind the dens may cause cervical myelopathy. We investigated the prevalence of ossified lesions in patients with ossification of the posterior longitudinal ligament in order to clarify the characteristics of these patients.

Methods: Fifty-six consecutive patients with ossification of the posterior longitudinal ligament in the cervical spine were included in the study. Multidetector computed tomography images of the whole spine were made. Ossified lesions of the upper cervical spine were defined as ossified lesions behind the dens as seen on axial computed tomography images. The prevalence of ossified lesions at the first cervical level was analyzed. The clinical and radiographic parameters were compared between the patients with ossified lesions at the first cervical level and the patients without such lesions.

Results: Fourteen patients (25%) had ossified lesions of the upper cervical spine. The continuous type of ossification of the posterior longitudinal ligament in the lower cervical spine was common and the segmental type was rare in this group as compared with the types of ossification in the group without ossified lesions at the first cervical level. The patients with first cervical level ossification more frequently had ossification of the posterior longitudinal ligament in the thoracic and/or lumbar spine, compared with the patients without upper cervical ossification. One patient had cervical myelopathy as a result of the upper cervical ossified lesion.

Conclusions: Computed tomography imaging demonstrated the presence of ossified lesions behind the dens in 25% of patients with subaxial ossification of the posterior longitudinal ligament. These upper cervical ossified lesions were commonly seen in patients with multiple-level ossification of the posterior longitudinal ligament. When upper cervical ossified lesions cause severe narrowing of the spinal canal, they should be considered a potential cause of cervical myelopathy.

Level of Evidence: Diagnostic Level IV. See Instructions to Authors for a complete description of levels of evidence.