The paracondylar process: anatomical relationships and clinical implications

PURPOSE: The paracondylar process (PCP) is a rare and infrequently reported anatomical variant, where the incomplete separation of the lowest occipital sclerotome (proatlas) and uppermost cervical sclerotome results in a complete bony projection that meets with an epitransverse process of the atlas. We report a case that highlights the imaging and anatomical relationships of the PCP, particularly with the vertebral artery (VA), which has been given little attention in literature despite its important symptomatic and neurosurgical implications. CASE PRESENTATION: A 55-year-old male presented with longstanding limitation to neck movement, left‑sided headaches and occasional dizzy spells. Cervical computed tomography (CT) imaging demonstrated a bony strut projecting inferiorly from the skull base, laterally adjacent to the left occipital condyle, articulating with the epitransverse process of C1. Though CT angiography was not performed, close examination of the course of the left vertebral artery on the soft tissue CT windows demonstrated an intimate relationship of the artery coursing immediately medial to the bony process in its V3 segment. We present a three-dimensional reconstruction prepared via segmentation and close reading of the soft tissue CT to illuminate the expected course of the vertebral artery and its' relationship to the PCP. CONCLUSION: This case demonstrates the anatomical and clinical significance of the paracondylar process (PCP), with a particular focus on its relationship with the vertebral artery. Whilst rare, this finding carries important clinical implications if surgical resection is to be contemplated.