Bovine meroanencephaly and gastroschisis: a macro and microscopic study.

Summary Congenital malformations correspond to one of the maincauses of embryonic loss during the gestational process. Theyresult from interaction of several factors such as multifactorheredity, chromosomal and genetic alterations and environ-mental agents; however, unknown aetiology also can be pres-ent. In this article, we have used 10 embryos, from a frigorificarea of Dracena, SP, Brazil, which were fixed in Bouin solutionfor a macro- and micro-scopic description. We could verify thepresence of an encephalic tissue mass on the embryos dorsalcranial area, resulting from the non-formation of part of thecranial cap and from the non-closing of cephalic neuroporeand consequent neuroepithelial cells disorganization. In theabdominal area, the embryos did not show the complete fusionof the body lateral pleats during the abdominal wall forma-tion, and the liver extruded into the amniotic cavity withoutinvolvement of the intestine. Introduction The anencephaly is a congenital malformation arising from anabnormal neurulation, resulting in the absence of neural pleatsfusion and neural tube formation on the encephalon area(Moore and Persaud, 2004). So, it is the more common lethalform of central nervous system (CNS), where the foetus atterm can be still born or live for some hours or days (Urdanetaand Eliexer, 1988; Ramirez-Espitia et al., 2003). Already, thegastroschisis is a congenital anomaly of the abdominal wall,resulting in a defect next to the median plane ventral to theabdomen, presenting an extrusion of the viscera without theumbilical cord involvement. The viscera make a protrusion inthe amniotic cavity being bath by the amniotic fluid (Mooreand Persaud, 2004; Oyachi et al., 2004).Poswillo (1976) and Hendricks et al. (1988) have related thata normal embryological development depends on two mainphenomena: genetic instructions to the morphogenesis andability of the tissues to complete the general metabolic process,which requires that the cells survive and replicate themselves.The normal and abnormal developments occur so that thesystems and organs are formed and stabilized till the finaldifferentiation is completed, depending on the genetic instruc-tions until a cellular plane more capable in the formation oftissues conducting the general metabolic functions that areessentials to the cell survival.Persaud (1990), Behrman et al. (1996) and Moore andPersaud (2004) have suggested that a teratogen is any agentcapable to produce a congenital anomaly or to increase ananomaly incidence in the population. Environmental factors,such as infections and drugs, can simulate genetic conditionswhen they affect two or more sons of normal parents, being theorgans the more sensitive embryos parts during the fastdifferentiation period. However, Borges-Oso´rio and Robinson(2001) have complemented that the main teratogenic effectsand teratogens include the radiations, the viruses, the drugsand the maternal diseases, and that the effect of these agentsdepends on several factors, such as exposition time to theteratogen, dosage of the teratogen, maternal genotype, geno-type and susceptibility of the embryo, enzymatic activity of thefoetus, integrations between teratogens and their specificity.Moore et al. (2002) have related that in the meroanenceph-aly or anencephaly in humans, the posterior encephalonappears like a vascular-spongy mass (angiomatous stroma) inthe cranial base, having a symmetrical absence in the skullabove the orbitals (Urdaneta and Eliexer, 1988; Jacobson,1992; Moore and Persaud, 2004).Crossman and Neary (2002) in their studies have added thatthe cerebral general architecture is altered, the hemispheresbeing developed beneath the telencephalic invagination areaand the diencephalic duct borders that covered them, that isthe nervous tissue is not covered by osseous nor by cutaneousformation (ectoderm). Muller and ORahilly (1991) havestudied the development of anencephalic embryos comparedwith control embryos and have verified that many parts of theCNS are limited, occurring an evident specialization in thecerebral hemispheres, presenting two open areas, being thesefrom the tail to the superior medulla and from the thoracicvertebrae to the lumbar one. The lateral ventricles were notclearly limited and connected through the median plane; therewas a reduction of the choroid plexus in small spaces of thecerebral hemispheres.