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

l2
2.1 ErI0L0rL!! fïE qYs34t!1!!jrArEs
lnvestlgatîon of the etîology of neural defects falls into the two
separate fîelds of Epídemiology and Embryology. Ëp l clem i o log i ca l studies
descrìbe the distribution of defects within a defined population,and
attempt to analyse the factors producing this distrîbution. Embryologîcal
studies involve both human material and experimental lesions in animal
models.
The lack of unÍform termínology to describe the dysraphic conditions._
complicates any review of the I iterature, Host authors exclude the occult
I es ions and refer to:
a) anencephaly, pseuclen cepha I y, cranioschisis, meningocele or menîngoencepha
locele cran ial ly;
b) spîna bifida, rachischisis, meningocele, mye I omen i ngoce I e , myelocystocele,
or myeloceIe caudal ly.
ln addition, the lesions seen in experimental animals may bê called:
a) exencephaly, brain hernia, cleiencephaly, or acleiencephaly cranially;
b) myeloschisis or neuroschisis caudal ly.
2.2 E!_LDExlqror!!êL_gM t Es
2.2.1 lnc idencq
L'arge variations in the estimated incidence of neural malformations
are found in different publ ications. A comparative review of fifteen
hospital seríes (Alter, 19621 showed a frequency per l,OOO.births varying
between :
0.5 and 5.9 for anencephaly
0.2 and ).2 for spina bifida manifesta
0.J and 4.2 for hydrocephalus