Neural-Dural Transition at the Thoracic and Lumbar Spinal Nerve Roots: A Histological Study of Human Late-Stage Fetuses

Abstract

Epidural blocks have been used extensively in infants. However, little histological information is available on the immature neural-dural transition. The neural-dural transition was histologically investigated in 12 late-stage (28–30 weeks) fetuses. The dural sheath of the spinal cord was observed to always continue along the nerve roots with varying thicknesses between specimens and segments, while the dorsal root ganglion sheath was usually very thin or unclear. Immature neural-dural transitions were associated with effective anesthesia. The posterior radicular artery was near the dorsal root ganglion and/or embedded in the nerve root, whereas the anterior radicular artery was separated from the nearest nerve root. The anterior radicular artery was not associated with the dural sheath but with thin mesenchymal tissue. The numbers of radicular arteries tended to become smaller in larger specimens. Likewise, larger specimens of the upper thoracic and lower lumbar segments did not show the artery. Therefore, elimination of the radicular arteries to form a single artery of Adamkiewicz was occurring in late-stage fetuses. The epidural space was filled with veins, and the loose tissue space extended ventrolaterally to the subpleural tissue between the ribs. Consequently, epidural blocks in infants require special attention although immature neural-dural transitions seemed to increase the effect.

Cervical nerve roots and the dural sheath: a histological study using human fetuses near term

“…We agree with their conclusion, with the exception of the DRG of the second cervical nerve. The thoracic DRG is located less than 1 mm from the dural sac, and therefore it is often adjacent to the dural pocket [3]. In contrast, we found that the cervical DRG was never adjacent to the pocket in frontal sections and the dural sac was not included in sagittal sections showing the cervical DRG.…”

“…The thoracolumbar nerve roots would likely be affected by mechanical stress caused by the marked difference in growth rates between the spinal cord and the vertebral column [ 3 ]. Therefore, long nerve roots would be necessary for adaptation to the delayed and marked growth of the vertebral column, leading to development of the cauda equina [ 2 ].…”

“…Modified from Cho et al Biomed Res Int 2016 Mar 16 [Epub]. http://dx.doi.org/10.1155/2016/8163519 [ 3 ].…”

“…At the thoracolumbar level, frontal sections demonstrate multiple spinal nerve roots with long longitudinal courses through the epidural space [2,3]. Using frontal sections from human fetuses near term, we have previously shown that Original Article https://doi.org/10.5115/acb.20.081 pISSN 2093-3665 eISSN 2093-3673 the posterior nerve root often has a tortuous epidural course resembling a string of beads at the thoracolumbar level [3], whereas a straight anterior root is usually accompanied by a radicular artery in this region (Fig. 1).…”

Suboccipital myodural bridges revisited: Application to cervicogenic headaches

“…Histological investigation of soft tissues in such large fetuses has several advantages: (1) the fascial configuration is the same as or similar to that in adults in most regions of the body; (2) pathological changes in the fascia, such as adhesion and thickening with inflammation, are minimal or absent; (3) preparation of tissue sections is much easier than for adult specimens because of the smaller size of the structures and minimal degree of calcification. We have also used fetal specimens for investigation of the neurodural junction in the thoracic spinal cord (Cho et al, 2016). Moreover, we have become familiar with the topographical anatomy of the atlanto-occipital region through our recent study of a temporary disk-like structure appearing at the median atlanto-axial joint (Sakanaka et al, 2019).…”