Estudo de uma nova técnica para criação cirúrgica de um defeito semelhante a meningomielocele em fetos de coelhos A different technique to create of a myelomeningocele-like defect in the fetal rabbit

OBJETIVO: Avaliar a sobrevida fetal usando uma nova técnica cirúrgica para criação de um defeito semelhante a meningomielocele em fetos de coelho. MÉTODOS: Foram utilizadas seis coelhas da linhagem Nova Zelândia que tiveram um defeito espinhal criado em seus fetos no 23° dia de gestação. O defeito foi criado em 19 fetos e a tentativa de correção foi feita em 15 casos (grupo I), 4 fetos permaneceram sem correção (grupo II). No 30° dia de gestação, os fetos foram submetidos a avaliação anátomo-patológica. RESULTADOS: No 30° dia a meningomielocele estava presente em todos os fetos sobreviventes. A sobrevida total foi de 73,68% (14/19), 11 fetos sobreviveram no grupo I, e 3 no grupo II. CONCLUSÃO: A técnica modificada apresenta sobrevida fetal satisfatória, no modelo experimental de criação de defeito espinhal em fetos.PURPOSE: To evaluate fetal survival rate using a modified technique to surgically create a "myelomeningocele-like" defect in the rabbit model. METHODS: Six white New Zealand rabbits had a spinal defect created in their fetuses at 23 days of gestation. The defect was created in 19 fetuses and an attempt to correct it was made in 15 cases (group I), 4 fetuses where left without correction (group II)At 30 days of gestation, fetuses were harvested for anathomo-pathologic evaluation. RESULTS: At 30 days, a "myelomeningocele-like" defect was present in all surviving fetuses. The total survival rate was 73,68% (14/19), 11 fetus survived in group I and 3 in group II. CONCLUSION: The technique modifications including fetal positioning and exposure of its back prior to the incision of the lamina associated to a different technique for miometrium closure offers an alternative and probably safer method to surgically create a spinal defect in the fetal rabbit

Validation of the ovine fetus as an experimental model for the human myelomeningocele defect Validação do feto de ovino como modelo experimental de meningomielocele

PURPOSE: To produce a myelomeningocele-like human defect in the ovine fetus and validate this experimental model in our population. METHODS: A prospective study on 12 pregnant sheep of a crossed Hampshire/Down breed where a spinal defect was surgically created between Day 75 and Day 77 after conception. The technique consisted of a hysterotomy with exposure of fetal hind limbs and tail up to the mid spine. Fetal skin, paravertebral muscles, and 4 posterior spinal arches were excised, exposing the spinal cord. Duramater was opened and the medulla was incised until the medullar canal. Animals were euthanized at 139 days of gestation for fetal evaluation. The central nervous system was submitted to post-mortem magnetic resonance imaging (MRI) and the spine was submitted to pathological examination. RESULTS: The defect was created in 13 fetuses and 5 survived. Mean gestational age at necropsy was 121.6 days (varying from 93 to 145 days). Macroscopically, the defect was present in 4 cases. Microscopy revealed a flattened medulla with disappearance of the medullar canal and disruption of normal medullar architecture with neuronal apoptosis and/or fusion of the piamater and duramater. The MRI showed herniation of the cerebellum into the cervical canal and syringomyelia. CONCLUSIONS: The surgically produced defect mimics the defect found in the human fetus, including the Arnold-Chiari malformation. Post-mortem MRI was used for the first time in our study and proved an excellent alternative for demonstrating the cerebellar herniation. We standardized the technique for creating the defect in our population.<br>OBJETIVO: Produzir um defeito semelhante a meningomielocele humana em feto de ovinos, validando este modelo experimental, em nosso meio. MÉTODOS: Estudo prospectivo com 12 ovelhas de cruzamento das raças Hampshire e Down, onde um defeito na coluna foi criado cirurgicamente com 75 a 77 dias de gestação. A técnica consistiu em histerotomia com exposição das patas traseiras e cauda até a metade da coluna fetal. Foram retirados pele, musculatura paravertebral e 4 arcos vertebrais posteriores, expondo a medula. A dura foi aberta e uma incisão até o canal medular foi realizada. O sacrifício foi realizado com 139 dias de gestação para avaliação fetal. O sistema nervoso central foi submetido a ressonância magnética (REMA) post-mortem e a coluna foi submetida a exame anátomo-patológico. RESULTADOS: O defeito foi criado em 13 fetos e 5 sobreviveram. A idade gestacional média da necropsia foi de 121,6 dias (variando de 93 a 145 dias). Macroscopicamente o defeito estava presente em 4 casos. A microscopia revelou achatamento da medula, com desaparecimento do canal medular e desarranjo da citoarquitetura medular com apoptose neuronal e/ou fusão da pia e dura-máter. A REMA demonstrou herniação do cerebelo para o canal cervical e siringomelia. CONCLUSÕES: O defeito produzido foi muito semelhante à meningomielocele em fetos humanos, levando inclusive à mal-formação de Arnold-Chiari. A REMA post-mortem, utilizada de forma inédita neste estudo, demonstrou ser uma excelente alternativa para demonstrar a presença da herniação do cerebelo. A técnica para produzir o defeito foi padronizada em nosso meio

Biosynthetic cellulose induces the formation of a neoduramater following pre-natal correction of meningomyelocele in fetal sheep A celulose biossintética induz a formação de uma neoduramáter na correção antenatal da meningomielocele em fetos de ovelhas

PURPOSE: The aim of this study was to compare the effectiveness of two dura-mater substitutes, namely human acellular dermal matrix (HADM) and biosynthetic cellulose (BC), in repairing, in utero, surgically-induced meningomyelocele (MMC) in fetal sheep. METHODS: A neural tube defect was created at 74-77 days gestation in 36 fetal sheep. They were divided into 3 groups, the control group that did not receive pre-natal corrective surgery, and the other two groups that received corrective surgery using HADM (Group A) or BC (Group B). Both materials were used as a dura-mater substitutes between the neural tissue and the sutured skin. Correction was performed at gestation day 100 and the fetuses were maintained in utero until term. Sheep were sacrificed on gestation day 140. The fetal spine was submitted to macro and microscopic analysis. At microscopy, adherence of the material to the skin and neural tissue was analyzed. RESULTS: In the initial phase (pilot), experimentally-induced MMC was performed on 11 fetuses and 4 survived (37%). In the second phase (study), 25 fetuses received surgery and 17 survived (68%). In the study group, 6 fetuses did not undergo repair (control group), 11 cases were submitted to corrective surgery (experimental group) and one fetal loss occurred. Of the surviving cases in the experimental group, 4 constituted Group A and 6 in Group B. Macroscopically, skin and underlying tissues where easily displaced from the BC in all cases it was used; in contrast, HADM adhered to these tissues. To compare the adherence, 4 cases from Group A and 4 in Group B were studied. We observed adherence, host cell migration and vessel proliferation into the HADM all sections from Group A and this aspect was not present in any cases in Group B (p < 0.05). In Group B, we also observed that a new fibroblast layer formed around the BC thus protecting the medulla and constituting a "neoduramater". CONCLUSION: The use of BC seems to be more adequate as a dura-mater substitute to cover the damaged neural tissue than HADM. It seems promising for use in the in utero correction of MMC because to does not adhere to neural tissue of superficial and deep layers ("tethered spinal cord"). Thus, BC minimizes the mechanical and chemical intrauterine damage to the spinal medulla.<br>OBJETIVO: Estudar os efeitos do emprego de dois materiais consideravelmente diferentes quanto à origem e custo na correção intra-uterina da meningomielocele criada experimentalmente em feto de ovino. MÉTODOS: Em 36 fetos de ovinos foi criado um defeito aberto de tubo neural, com 75 de dias de gestação. Os casos foram divididos em três grupos: o controle onde o defeito não foi corrigido, grupo corrigido A onde o material utilizado para cobrir a medula exposta foi a matriz dérmica humana acelular (MDHA) e o grupo corrigido B onde o material foi a celulose biossintética (CB). Após a correção realizada com 100 dias, os fetos eram mantidos intra-útero até o termo da gestação. Os sacrifícios foram realizados com 140 dias e a coluna fetal era submetida à análise macro e microscópica onde foi observada a aderência dos materiais à pele, medula ou tecido nervoso remanescente. RESULTADOS: Na fase inicial (piloto), 11 fetos foram operados e 4 sobreviveram (37%). Na segunda fase (estudo) 25 fetos foram operados e 17 sobreviveram (68%). No grupo de estudo, 6 fetos não foram submetidos à correção (grupo controle), 11 casos foram corrigidos e ocorreu 1 perda fetal. Do total de 10 casos, 4 constituíram o grupo A e 6, o grupo B. À macroscopia observou-se deslizamento da pele e tecidos subjacentes sobre a CB em todos os casos onde ela foi empregada e isto não ocorreu em nenhum dos casos onde a MDHA foi utilizada. Para comparar a aderência, foram considerados 4 casos do grupo A e 4 do grupo B. A aderência, caracterizada pela migração de células do hospedeiro e proliferação de vasos para dentro da MDHA, foi observada em 100% dos casos do grupo A e em nenhum caso no grupo B (p < 0,05). No grupo B observou-se formação de uma camada de fibroblastos ao redor do material, protegendo a medula, caracterizando a formação de uma "neoduramater". CONCLUSÃO: A utilização da película de celulose biossintética parece ser mais adequada como substituto de dura-máter para cobertura e proteção do tecido nervoso que a matriz dérmica humana acelular. Ela parece promissora na correção intra-uterina da meningomielocele, evitando a aderência do tecido nervoso aos planos superficiais ("medula presa") minimizando os efeitos deletérios do ambiente intra-uterino sobre a medula espinhal

Validation of the ovine fetus as an experimental model for the human myelomeningocele defect: a pilot study

Objective: To produce a myelomeningocele-like human defect inthe ovine fetus and validate this experimental model in ourpopulation. Methods: A prospective study on 12 pregnant sheep ofa crossed Hampshire/Down breed where a spinal defect wassurgically created between day 75 and day 77 after conception.The technique consisted of a hysterotomy with exposure of fetalhind limbs and tail up to the mid spine. Fetal skin, paravertebralmuscles, and 4 posterior spinal arches were excised, exposingthe spinal cord. Duramater was opened and the medulla was inciseduntil the medullar canal. Animals were euthanized at 139 days ofgestation for fetal evaluation. The central nervous system wassubmitted to post-mortem magnetic resonance imaging (MRI) andthe spine was submitted to pathological examination. Results:The defect was created in 13 fetuses and 5 survived. Meangestational age at necropsy was 121.6 days (varying from 93 to145 days). Macroscopically, the defect was present in 4 cases.Microscopy revealed a flattened medulla with disappearance ofthe medullar canal and disruption of normal medullar cellarchitecture with neuronal apoptosis and/or fusion of the piamaterand duramater. The MRI showed herniation of the cerebellum intothe cervical canal and syringomyelia. Conclusions: The surgicallyproduced defect mimics defects in the human fetus, including theArnold-Chiari malformation. Post-mortem MRI was used for thefirst time in our study and proved an excellent alternative fordemonstrating the cerebellar herniation. We standardized thetechnique for creating the defect in our population