Polygonal deformation of the dural sac in lumbar epidural lipomatosis: anatomic explanation by the presence of meningovertebral ligaments.

BACKGROUND AND PURPOSE In patients with epidural lipomatosis, axial lumbar spine CT and MR images occasionally reveal a geometric, polygonal or stellar, shape of the dural sac. The purpose of this study was to define the anatomic structures responsible for this radiologic appearance. We hypothesized that meningovertebral ligaments could anchor the dura mater to the osteofibrous walls of the spinal canal and account for the geometric deformation of the dural sac. METHODS The epidural spaces were examined in 15 adult cadaveric and seven aborted fetal lumbar spines. For macroscopic studies, 70 adult vertebral segments were separated and dissected by removing the extradural fat. For microscopic examination, axial histologic sections were obtained from 35 fetal and five adult undissected vertebral segments. RESULTS Meningovertebral ligaments were observed in the median, paramedian, and lateral aspects of the anterior and posterior epidural spaces of both adult and fetal lumbar spines. These ligaments anchor the outer surface of the dura mater to the osteofibrous walls of the lumbar canal. They may form an irregular longitudinal septum partitioning the epidural space. Histologic examination demonstrated the fibroelastic composition of these ligaments and suggested their possible perivascular morphogenetic origin. CONCLUSION The morphologic and topographic features of the meningovertebral ligaments explain the polygonal, stellar, or Y-shaped deformation of the dural sac observed on axial CT and MR images in patients with lumbar epidural lipomatosis.