Variants in the structure and topography of the superior margin of the epidural space of the human spinal cord.

Variants in the structure of the upper margin of the epidural space at sites of transition from the dura mater of the spinal cord to the dura mater of the brain were studied. Stereoepidurographic (88 observations) and corrosion studies (49 observations) identified four levels for the position of the upper margin of the anterior section (intracranially located, lower edge of the occipital bone, bodies of C1 and C2) along with five levels for the posterior section (occipital bone, occipital bone-arch of C1, C1, C1-C2, C2) of the epidural space. Variants on the shape of the upper margin of the anterior (falciform, oval, and dentate in the frontal plane; pointed, flexed spurs, pointed slits, and olive-shaped in the sagittal plane) and posterior (collar-shaped, oval, and bidentate forks with prongs of equal length and forks with prongs of unequal lengths) sections of the epidural space arose as a result of asymmetry in the attachment of the upper sections of the sac of the dura mater of the spinal cord to the walls of the vertebral canal. Weak areas of the upper wall of the epidural space (sites of transition from the dura mater of the spinal cord to the dura mater of the brain, paravasal capsule of the vertebral artery, the area of the first intervertebral foramen) were seen.