Paracondylar process of the occipital bone of the skull: a rare congenital anatomical variant.

To cite: Narayanan R, Shankar B, Paruthikunnan S M, et al. BMJ Case Rep Published online: [please include Day Month Year] doi:10.1136/ bcr-2014-205315 DESCRIPTION A 35-year-old male polytrauma patient’s cervical spine was evaluated by CT. Coronal (figure 1), axial (figure 2) and volume rendered (figure 3) CT images showed conical bony protuberances arising from the paracondylar area on both sides of the occiput and extending inferiorly to articulate with the superior aspect of the transverse process of atlas bilaterally. The imaging findings are typical of paracondylar processes. A paracondylar process is a developmental variation owing to incomplete assimilation of proatlas somite into the occiput. It is a rare developmental anomaly with only a few cases reported in the medical literature. It can be unilateral or bilateral and is usually asymptomatic. It is often detected incidentally, as in our case. Large paracondylar processes can sometimes be symptomatic, especially when they fuse or articulate with the transverse process of atlas and limit the atlanto-occipital motion. The process may sometimes act as a shim and manifest as skeletal torticolis. It is in close proximity to the C1 cervical nerve root and can potentially lead to compression and occipitocervical pain. The anomaly is often missed on anteroposterior and lateral cervical radiographs because of superimposed anatomical structures. However, on coronalreformatted CT images, the extent and location of this anomalous bridge is well depicted. A calcified stylohyoid ligament can mimic this anomaly, but is typically a more slender structure and is directed medially.