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Fig. 1b. Anencephalic Craniorhachischisis

This type is similar to the preceding, but has an associated involvement of the vertebral column and a characteristic change in the position of the head. The vertebral arches have failed to unite in a varying degree. The open spinal canal may reach from the base of the cranium to any level of the vertebral column, and this defect frequently occupies the middle third of the surface of the back. The external covering or roof of the canal is structurally the same as the thin covering of the anencephalic cranium. This membrane is continuous with the surrounding skin of the back, but is distinctly marked off from it. It is a meningeal-like membrane and not epidermal in structure. In many of these cases the canal is so widely open and the membrane is so transparent that the roots of the spinal nerves are easily seen passing to the intervertebral foramina. In some cases, however, the spinal cord is completely absent and no nervous structure is seen through the roof.

The vertebral column in these cases is abnormally shortened and bent so that the head is drawn backward with the face directed upward. The convexity of the curvature of the column in many of these iristaiices is most acute in the lumbar region producing an exaggerated posterior prominence of the gluteal regions. Fourteen cases of this type of anencephalus were encountered in the series (24.5 per cent).

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Links: Fig 1. Anencephalus types | Fig 1a. anencephalic acranius | Fig 1b. anencephalic craniorhachischisis | Fig 1c. microcephalic acrauius | Fig 1d. microcephalic craniorhachischisis | Fig 1e. exocephalic acranius | Fig 16. anencephalic and normal fetuses | Historic Embryology Papers | Neural Abnormalities | Folic Acid and Neural Tube Defects | Skull Development


Nañagas JC. A comparison of the growth of the body dimensions of anencephalic human fetuses with normal fetal growth as determined by graphic analysis and empirical formulae. (1925) American J. Anatomy. 455-494.

Cite this page: Hill, M.A. (2024, April 17) Embryology Nanagas1925-fig01b.jpg. Retrieved from

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© Dr Mark Hill 2024, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G

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