Paracondylar process and epitransverse process on cone beam computed tomography: a pictorial review based on a serie of 9 patients

Objective: Paracondylar (PCP) and epitransverse processes (ETP) represent rare types of articulations that can occur between the occipital bone and the transverse process of atlas vertebra. Material and methods: Five systematic search strings were conducted on PubMed database on 14.01.2022. The search was conducted by one observer to identify studies on PCP, and on ETP in living patients. Open and close access articles were selected as this topic is infrequently described in the main medical literature. Results: We provided with a pictorial review of 1) Paracondylar tubercle, 2) Unilateral PCP with cylindrical shape, 3) Unilateral PCP with pyramidal shape, 4) Unilateral PCP with lateral joint with transverse process, 5) Unilateral PCP with superior joint and partial fusion with transverse process, 6) Unilateral ETP with neo-condyle and joint with occipital condyle, 7) Unilateral ETP with joint with occipital bone, 8) Unilateral ETP with a bony bridge with lateral mass (ponticulus lateralis), and 9) Bilateral variation: paracondylar mass and ETP. Conclusions: Six figures were found in the selected literature and belong only to articles published in closed access. We provided with additional 41 open access freely available figures. We were first to present CBCT reference figures of: 1) Unilateral paracondylar tubercle, 2) Fusion of PCP with the transverse process of C1, 3) Joint between ETP and the lateral side of occipital condyle, and 4) Presence of bony bridge (ponticulus lateralis) between ETP and the lateral mass of C1. We were also first to describe a bilateral mixt variation with paracondylar mass on one side and ETP on the other side of C1. An open and accessible knowledge support (such as Nemesis journal) is needed to easily find clinical reference CBCT figures of craniocervicofacial bone variations.