Observations on the caudal end of the spinal cord

Abstract

The development of the structural pattern of the lower sacral and coccygeal segments of the spinal cord in human, rabbit and monkey embryos and fetuses has been studied. The changes observed in serial sections from above downward are outlined, beginning with typical sections through the lower sacral cord. Among the changes, other than diminution in size of the spinal cord and reduction in size of the lower spinal nerves, there i s a gradual disappearance of the posterior funiculus. As this occurs the gray matter appears to spread dorsally and the central canal widens. The gray matter becomes reduced in size and the lateral funiculus extends farther dorsally. A little lower down, the gray matter of the alar plate is reduced further in size and there is corresponding enlargement of the central canal. This enlargement constitutes the terminal ventricle. The spinal cord rapidly becomes smaller as both the fibers and the gray matter are diminished. In some specimens, fibers decussate dorsal to the lower end of the terminal ventricle. Little remains of the lower end of the spinal cord except the ependymal wall of the central canal and the surrounding fiber bundles. The shape and size of the lower end of the central canal is subject to variations.In the lower part of the spinal cord a longitudinal bundle on each side is formed by fiber contributions from the anterior horn cells in the basal plates. This bundle contributes fibers to the fifth sacral and the first and second coccygeal nerves. It is designated the sacrococcygeal fasciculus.The general structural plan and development of the human spinal cord are described i n current textbooks of anatomy and embryology (Goss, '59; Romanes, '64; Arey, '65; Hamilton et al., '62; Patten, '46; Streeter, '12). However, certain aspects of the development and structure of the lower end of the spinal cord have not been adequately investigated or described. This paper is concerned mainly with the structural pattern of this region and the changes that take place in this pattern during the first few months of human development. MATERIALS AND METHODSThis study i s based on the serial sections of human embryos and fetuses which were stained with neurological methods. They include the protargol method of Bodian ( ' 3 6 ) , the silver gelatin method of Pearson and Whitlock ('49) and other methods developed in this laboratory by the authors. The material used in this study includes human specimens whose crown-rump lengths (CRL) range from 8 m m to 130 mm. Also included for study are rabbit and monkey embryos which had been sectioned serially and stained with silver methods. OBSERVATIONSThe caudal end of the spinal cord in the human embryo and fetus tapers into a cone-shaped structure which constitutes in the adult the conus medullaris and the filum terminale. The spinal nerves in lumbar and upper sacral levels are large compared with the lower sacral and coccygeal spinal nerves which become progressively smaller from above downward. The dorsal roots of these nerves diminish more ...

Clinical anatomy of the coccyx: A systematic review

“…In a histological study of 15 adult cadavers, the filum terminale externum was found to have a mean length of 8 cm, mean width of 1 mm, and consisted largely of fibrous tissue containing smooth muscle, blood vessels, and peripheral nerves with occasional ganglia (Tubbs et al,2005). The latter may be remnants from second and third coccygeal nerves present in the fetus (Pearson and Sauter,1971).…”

The Human Central Canal of the Spinal Cord: A Comprehensive Review of its Anatomy, Embryology, Molecular Development, Variants, and Pathology

“…Choi, et al noted that the ependyma-lined central canal of the filum terminale forms a cystic dilatation at the lower end of the conus medullaris to become the ventriculus terminalis of the spinal cord [3]. Similarly, enlargement of the canal was reported by Pearson and Sautter in their observations on the caudal end of the spinal cord [4]. They reported the gray matter of the alar plate was reduced in size with the corresponding enlargement of the central canal, which constituted the terminal ventricle.…”

“…Derived from the primitive neural tube, the central canal encompasses an internal system of cerebrospinal fluid (CSF) cavities that include the cerebral ventricles, aqueduct of Sylvius, and fourth ventricle [1]. Uniformly elliptical in shape throughout most of the cord, variations exist in the morphology of the caudal central canal, including dilatation [3-4], forking [5-6], and outpouchings [6-7]. The function of the adult human central canal is not yet well understood [7].…”

Anatomical and Histological Analysis of a Complex Structure Too Long Considered a Simple Ligament: The Filum Terminale

“…1 Vacuolization and apoptotic phenomena 2,23,29 are responsible for the dedifferentiation of this structure that is redifferentiated into fibrous tissue. 1,4,5 Microscopic examination of human fetal SC reveals GC, ependymal and neuroblastic or neuronal cell bodies that are or not subjected to degenerative processes. 1,24,30 Subsequently, the adult FT is likely to contain the same tissue elements as the SC.…”

“…The development of the Filum Terminale (FT) results from the dedifferentiation of the caudal part of the embryonic and fetal Spinal Cord (SC). [1][2][3][4] After birth, the FT connects the Conus Medullaris (CM) and the coccygeal periosteum. 5 More precisely, the intradural FT (iFT) is the cranial portion of the FT that lies between the CM and the DS, while the extradural FT (eFT = Ligamentum Coccygeale), constitutes the caudal portion of the FT, thus linking the Dural Sac (DS) and the coccyx.…”