Meningeal relationships to the spinal nerves and rootlets: a gross, histological, and radiological study with application to intradural extramedullary spinal tumors

Introduction: Juxtapositional tumors of the spinal nerve roots have been noted to not only interact with the roots at various vertebral levels, but also differ among patients. Therefore, the aim of the current study was to elucidate the potential for variation among the relationships of the meningeal layers at different nerve levels.Methods: In 20 unembalmed adult cadavers and five fetal specimens, the spinal nerve roots from the cervical, thoracic, and lumbar regions were harvested with their associated meningeal layers and subjected to microdissection, histological analysis, or radiological imaging using 9.4-T MRI.Results: As the nerve rootlets passed from the cord, they received their root sheath covering from the pia. After crossing the subarachnoid space to reach the apertures in the dura, they received two additional looser sheaths, an outer from the dura and an inner from the arachnoid. The pia mater always ended proximal to the arachnoid, and the pia and arachnoid layers extended more distally along the roots with caudal descent. Although the dorsal and ventral roots generally exited through separate dural openings, a single dural opening was also observed, often in the lower spinal regions. Thin intradural septations almost always separated the dorsal and ventral rootlets. The left and right sides frequently differed within individuals.Conclusions: On the basis of our study, variations of the meninges surrounding the spinal nerve roots are common, but themes do exist. Such data support surgical observations of the different interactions between tumors in these regions with surrounding neural tissues.