Universlty of Manitoba, ln Partîal Fulfiìlment - MSpace at the ...

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suggest¡ng that dysreph¡sm resul ts from di iation and rupture of a
previous ly closed neura l tube.
Gardner maintains that dilation of the closed neural tube could
êccount for hydrocepha I us, encepha locel e, hydromye I i a, syr ì ngomye loce I e
and the Arnold-chiarl malformatîon. Dilation and rupture of the neural
tube,followed by varying degrees of heal ing could account for exencephaly"
anencephaly, mye I omen i ngoce I e , meningocele, spína bifìda occulta, distematomyelia,
anterior spina bifida and various neuro-enteric connections.
2.4.4 AbnormAL-:Lrain G rowth
Because of the íntact hindbrain and well developed eyes and craníal
nerves' several authors have argued that anencephaly results from degeneratÎon
with¡n a fully-formed braïn.
Frazer (1921-22) suggested that ¡nadequate flexion of the enlarging
braîn shears off the major arteries at the base of the brain, producing
ischemic necrosîs and sloughing of brain tissue and the ovérlyíng cranial
vault.
2.\.5 Ab¡orEl *spinal Fl ex ion
Browne (1934; 1967) maintained that a variety of malformatíons,
including spina bifida, were produced by embryoníc compress-ion in uteto-
He suggested that rtundue spatial pressurerr might cause hyperflexion
of the primitive trunk and trinterfere w¡th the fusing oi the ridge
which should form the spinal canalr'.
2.\.6 Primary Vqscular Defects_
Anencephalîcs typically show a dÍsorganîzed network of sinusoîds
and anomalous pêttern of larger vessels ãt the exposed brain surface,
combined with relatively normal development of brainstem and midbraín.