Morphogenesis of the epidural space in humans during the embryonic and early fetal periods.

The development of the epidural space was studied on 51 series of sections from embryos and early fetuses aged from four to 13 weeks using histological and embryological methods for plastic and graphic reconstruction. We found that three stages can be discriminated in the development of the epidural space: I) the primary epidural space (embryos of 16-31 mm crown-rump length (CRL); II) reduction of the primary epidural space (embryos of 35-55 mm CRL); and III) the secondary epidural space (embryos of 60-70 mm CRL and fetuses of 80-90 mm CRL). The morphogenesis of the primary epidural space is determined by the formative influence of the spinal cord and its dura mater, while that of the secondary epidural space is determined by the walls of the vertebral canal. In the spinal cord-dura mater of the spinal cord-vertebral canal correlation system, the latter two components, subjected to the inducing influence of the first, determine the morphogenesis of the epidural space via a system of morphogenetic correlations. The correlational relationships are apparent as time-linked connections between the rudiment of the dura mater of the spinal cord and the vertebral canal, resulting in the stage-by-stage formation of the epidural space in the ventrodorsal and craniocaudal directions. These same morphogenetic correlations also determine the staging of the development of the epidural space.

[Characteristics and distribution of normal human epidural fat]. / Características y distribución de la grasa epidural humana normal.

Epidural fat provides sufficient cushion for the pulsatile movements of the dural sac, protects nerve structures, facilitates the movement of the dural sac over the periosteum of the spinal column during flexion and extension, and forms a pharmacologic reservoir of lipophilic substances. We review epidural fat and related structures, including their development during the fetal period when the epidural space is filled by undifferentiated loose, areolar mesenchymal tissue that surrounds the dural sac. In the adult, epidural fat has a continuous distribution and follows a certain metameric pattern. It is located mainly on the dorsal side of the epidural space, where it is organized in triangular capsules joined to the midline of the ligamentum flavum by a vascular pedicle. We consider the distribution of epidural fat in the axial and sagittal planes; its presence in the anterior, lateral and posterior epidural space; its presence in the cervical, thoracic and lumbar portions of the spinal column; and its characteristics and variations according to differing body habits and sex. Finally, we speculate on the possible anesthetic implications of epidural fat in terms of the pharmacokinetics of drugs injected into the epidural space and the tasks of locating the epidural space and inserting an epidural catheter during anesthetic procedures.

Características y distribución de la grasa epidural humana normal / Characteristics and distribution of normal human epidural fat

La grasa epidural (GE) permite un adecuado almohadilladode los movimientos pulsátiles del saco dural, protegea estructuras nerviosas, y facilita el deslizamientodel saco dural sobre el periostio del canal vertebraldurante los movimientos de flexo-extensión, formandoun reservorio farmacológico de sustancias lipofílicas.Revisamos la GE y las estructuras anatómicas relacionadas;su desarrollo en el feto donde el espacio epidural(EE) está ocupado por un tejido laxo, areolar,mesenquimatoso indiferenciado organizado a todo alrededordel saco dural. En el adulto, la GE epidural tieneuna distribución discontinua y responde a un patróndeterminado, con una topografía metamérica, localizadaprincipalmente en la parte posterior del EE, donde estáorganizada en paquetes de forma triangular que estánadheridos a la línea media del ligamento amarillo por unpedículo vascular.Evaluamos su distribución en los planos axiales ysagitales, su presencia dentro del EE anterior, lateral yposterior; en la porción cervical, torácica y lumbar de lacolumna; sus características y variaciones según los diferenteshábitos corporales y sexo. Por último, se planteanhipótesis sobre posibles implicaciones anestésicas quepodría tener la GE en la farmacocinética de las sustanciasinyectadas dentro del EE, en aspectos de la localizacióndel EE y en la ubicación de catéteres epiduralesdurante la realización de anestesias epidurales

Epidural fat provides sufficient cushion for the pulsatilemovements of the dural sac, protects nerve structures,facilitates the movement of the dural sac over theperiosteum of the spinal column during flexion andextension, and forms a pharmacologic reservoir of lipophilicsubstances.We review epidural fat and related structures, includingtheir development during the fetal period when theepidural space is filled by undifferentiated loose, areolarmesenchymal tissue that surrounds the dural sac. In theadult, epidural fat has a continuous distribution andfollows a certain metameric pattern. It is located mainlyon the dorsal side of the epidural space, where it is organizedin triangular capsules joined to the midline of theligamentum flavum by a vascular pedicle.We consider the distribution of epidural fat in theaxial and sagittal planes; its presence in the anterior,lateral and posterior epidural space; its presence in thecervical, thoracic and lumbar portions of the spinalcolumn; and its characteristics and variations accordingto differing body habits and sex. Finally, we speculate onthe possible anesthetic implications of epidural fat interms of the pharmacokinetics of drugs injected into theepidural space and the tasks of locating the epiduralspace and inserting an epidural catheter during anestheticprocedures

The human lumbar anterior epidural space: morphological comparison in adult and fetal specimens.

To increase our understanding of the clinical anatomy of the epidural space, the human lumbar anterior epidural space was studied morphologically and developmentally. Histological transverse sections of human lumbar spines were taken at the level of the intervertebral disc and the vertebral body in adult specimens and in fetuses aged 13, 15, 21, 32 and 39 weeks (menstrual age). At 13 weeks, connective tissue filled the epidural space. The dura mater was attached anteriorly to the posterior longitudinal ligament (PLL). The PLL was attached to the vertebral body beside the midline, whereas it adhered to the posterior edge of intervertebral disc. The anterior internal vertebral venous plexus was located anterolaterally and anteromedially. The vertebral canal was lined with connective tissue that differentiated in a periosteum in contact with the ossification centers. At 15 weeks, the PLL was composed of deep and superficial layers. At 21 weeks, the attachment between the dura mater and PLL was ligament-like at the level of the vertebral body. At 32 weeks, the dura mater was adherent to the superficial layer of PLL. At 39 weeks, groups of adipocytes were identified, and the dura mater was attached to the PLL by some ligaments. There were many more similarities between the adult and the 39-week fetus. In conclusion, some differences in the anatomy of the epidural space exist at each fetal stage studied. The structures of the epidural space are already formed in the fetus of 13 weeks, but they differentiate progressively within the connective tissue.

Extradural endodermal cyst of posterior fossa: case report, review of the literature, and embryogenesis.

OBJECTIVE AND IMPORTANCE: Posterior fossa endodermal cysts are rare. They are located in the midline, in ventral or ventrolateral locations, or intrinsic to the neural axis. Accordingly, various theories of embryogenesis have been proposed. We report the first case of an extradural, dorsolaterally situated endodermal cyst. CLINICAL PRESENTATION: An adult male patient presented with a short history of headache and cerebellar ataxia. Neuroimaging revealed an extra-axial cystic posterior fossa mass. INTERVENTION: An entirely extradural cyst was found and was totally excised. Immunohistochemistry confirmed the diagnosis of endodermal cyst. CONCLUSION: The extradural, dorsal location of the endodermal cyst suggests gaps at the cranial end of the notochord causing ectodermal-endodermal adhesions during early gastrulation and the persistence of endodermal remnants in the dorsal mesenchyme of the blastemal cranium. The literature is reviewed, and proposed theories of embryogenesis are discussed.

Development of the lumbar and sacral vertebral canal in utero.

STUDY DESIGN: This study analyzed the development of the lumosacral vertebral canal and dural sac in human fetus. A collection of fetuses and embryos was used to assess the development of different parameters of the spinal canal. OBJECTIVES: The data were analyzed for the dynamics of the development and also compared with mean adult spinal parameters. SUMMARY OF BACKGROUND DATA: Transversely sectioned specimens and nonsectioned specimens free of abnormalities were selected from the Boyd Collection of human embryos and fetuses. METHODS: The sections were photographed alongside a micrometric scale, and the nonsectioned specimens were scanned by magnetic resonance imaging. The films were computer analyzed for spinal and dural parameters. The error of the measurements was assessed. RESULTS: The most rapid growth period of the spinal canal parameters is between 18-36 weeks' gestation. After 30 weeks of intrauterine life, the upper lumbar canal grows faster than the lower lumbar region. The distal end of the dural sac begins to rise from S5 after 14 weeks. CONCLUSIONS: At the end of intrauterine growth, the interpedicular diameter of the spinal canal from L1 to L4 is 70% of the adult size, however, at L5, the canal is only 50% mature at birth. Therefore, if there is growth impairment in early infancy, the upper lumbar region is partially protected in contrast with the L5 level.

The epidural ligaments during fetal development.

The topography of the developing epidural ligaments in man was investigated by dissecting 12 fetuses ranging from 60-310 mm in CR length. It was found that in a 60 mm CR length fetus, the epidural space is occupied by an ubiquitous connective tissue which in longer fetuses becomes reduced into topographical structures. Posterior, lateral and anterior ligaments could be identified. The atlantodural and the sacral ligaments appear to be permanent ligaments anchoring the dural sac, whereas most of the dorsal ligaments become resorbed during the development of the fetus. These ligaments may be responsible for the compression of the nerve root that occurs when the dural sleeve and the contained nerve root are stretched over a protrusion (e.g. a protruded disc).