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

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the mid-polnts of the defects were found to lie essentially between
somltes 21 and.31, correspondi.ng to future vertebral levels of T.4 to S.2.
ln the 12 day expêrimental embryos rÌrost lesions of spina biflda manifesta
were lndeed centered at the lumbar r.egion. Those lylng at more caudal levels
may have been nye I odysp I as ias , rather than myeloschisls, though the two
defects were dlfficul t to distinguish.
The less serious defects of spina bifida occulta in 12 day embryos,
were mainly locâted in the cervical and upper thoracic regions, and showed
very llttle overlap w¡th sp¡na blflda manifesta.
A slmllar d¡stríbutlon of lesions emerges from the study of human
dysraphism. 0f 601 dysraphic infants admitted to hospital and examined
by radlology and necropsy, skeletal defects lay mainly în the lumbar and
sacral reglons. The low incidence of cranial and uppercervical defects
was probably due to abortîons and stiltbirths caused by associated anencephaly.
Skeletal defects at the cervico-thorac¡c and lumbo-sacral areas
were quite local ized, but bony lesions ¡n the thoraco-lumbar regîon and
those involving anencephaìy were more extensive. This suggest that there
are two types of dysraphic lesions in man - major defects (anencephaly and
thoraco-lumbar. spína bifida) and more minor defects in other regions (Barson,
1970') .
- Rump defeòts observed in the chick embryos may be compared to sacral
agenesîs in man, which varies in severity from loss of coccygeal sêgments
to partíal reductîon of the.sacrum or even absence of all sacral and lumbar
vertebrae. Extensîve sacral agenesis may be accompanied by neurological
involvement and anal or genito-urlnary defects (Blumel et al., '|959; Russel I
and Altken, 1963). ÌJhereês rumplessness is one of the commones t spontaneous