Anatomical Study of the Retrodural Space of Okada in the Cervical Region: 3D Micro-CT Findings

The retrodural space of Okada (RSO) is a potential space located posterior to the ligamentum flavum. It can complicate epidural injections owing to its communication with the epidural space and facet joints. The purpose of this study was to clarify the anatomical structures of the cervical RSO and adjacent ligamentous tissues in cadavers. Cervical spine specimens from 15 embalmed cadavers were used for serial sectional dissection, histological verification, and micro-computed tomography (micro-CT) analysis. Micro-CT images of the RSO were acquired after phosphotungstic acid preparation at the C5-7 levels. The RSO was examined meticulously on the basis of its three-dimensional (3D) topography. The 3D shape of the cervical RSO was successfully visualized using micro-CT imaging reconstruction. It had clear anatomical communications with the epidural space, facet joints, and interspinous space. Histological examination confirmed the presence of loose connective tissue within the RSO, which probably facilitates these communications. This cadaveric study demonstrated the 3D shape of the cervical RSO and its communications with adjacent anatomical structures. Further clinical studies are needed to explore the potential implications of these findings for cervical epidural injections.