Objective: To evaluate the fetal survival rate using a modified technique to surgically create a ‘myelomeningocele-like’ defect in a rabbit model. Methods: Six white New Zealand rabbits had a spinal defect created in their fetuses at 23 days of gestation. At 30 days of gestation, the fetuses were harvested for anatomo-pathologic evaluation. Results: The defect was created in 19 fetuses and an attempt to correct it was made in 15 cases (group I), and 4 fetuses where left without correction (group II). 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 technical modifications, including fetal positioning and exposure of its back prior to the incision of the lamina, associated with a different technique for myometrium closure, offer an alternative and probably safer method to surgically create a spinal defect in the fetal rabbit.

Objective: To study the correction of a ‘myelomeningocele-like’ defect in fetal rabbits. Methods: Twelve pregnant rabbits had a spinal defect surgically created in 40 of their fetuses at 23 days of gestation. Immediate repair was performed in 30 fetuses (group I), and 10 remained uncorrected (group II). After 30 days, the fetuses were harvested and the anatomopathological aspects where compared using Fisher’s exact test. Results: Three different techniques to apply a cellulose graft were used for correction in 8 (technique A), 7 (technique B), and 15 animals (technique C), but only one (technique C) was successful. The survival rate at 30 days was 66.7% (10/15) in group I and 80% (8/10) in group II. A ‘myelomeningocele-like’ defect was present in all fetuses in group II, while in group I the defect was successfully repaired in 80% of the surviving fetuses (p < 0.01). Conclusion: The surgically created spinal defect was successfully repaired, and also the fetal rabbit could be established as a model for the study of intrauterine correction of a myelomeningocele-like defect.

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. Key words: Fetus. Meningomyelocele. Spinal dysraphism. Prenatal care. Cellulose. Animal experimentation. Sheep. RESUMOObjetivo: 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 ma...

Objective: To develop a new endoscopic approach to the correction of a myelomeningocele-like defect in fetal sheep. Methods: The fetuses of 9 pregnant ewes, with an average gestational age of 115 days, were subjected to a 3.0 × 2.0 cm removal of the skin over the lumbar spine, performed through hysterotomy. The uterus was closed, and three 5-mm endoscopic cannulas, without valve mechanisms, were inserted. In the pilot phase (2 animals), we initially worked exclusively in the amniotic fluid space. In the study phase, we partially withdrew the fetus from the amniotic fluid to completely expose its back. By simply allowing air to enter the amniotic cavity (without gas injection), a working space was created using a uterine lift device. The skin around the defect was dissected, and a biosynthetic cellulose material was applied to cover the area. A continuous suture of the skin was performed to completely hide the material. Results: The combined air/fluid space allowed the skin to be successfully closed in 6 out of 7 cases in the study phase. All fetuses were alive at the end of the procedures. Time to complete the endoscopic part of the procedure fell from 3 to 1 h by the end of this series. Premature birth occurred in 2 of the 4 cases allowed to continue with the pregnancy. Conclusion: A new gasless fetoscopic surgery technique was developed as an alternative to current techniques used for fetal endoscopic surgery.

Purpose: To develop a simplified technique for antenatal correction of a meningomyelocele -like defect in fetal sheep to allow direct skin closure. Methods: A spinal defect was surgically created at 75 days of gestation in the fetuses of 36 pregnant sheep, 23 survived the surgery. At 102 days gestation, the defect was corrected in 14 cases (9 were left untreated). Skin surrounding the defect was dissected below the dermis to permit its edges to be approximated and sutured, without interposing any material to its edges. An interface material intended to protect the neural tissue from skin adhesion was used and the skin defect was completely closed over it. Pregnancy was allowed to continue up to 138 days gestation, the fetuses were submitted to macroscopic and microscopic analysis. Results: The defect was successfully corrected in 90.9% in the experimental group, and spontaneous closure occurred in 22.3% in the control group (p < 0.05). The survival rate after the creation and correction of the defect was 63.4% and 78% respectively. Conclusion: This simplified technique was successful in the correction a meningomyelocele-like defect, in the fetal sheep. Key words: Surgery. Fetal Therapies. Meningomyelocele. Spinal Dysraphism. Disease Models, Animal. Sheep. RESUMOObjetivo: Desenvolver uma técnica simplificada de correção pré-natal de defeito semelhante à mielomeningocele em fetos de ovelha permitindo um fechamento direto da pele. Métodos: Um defeito espinhal foi cirurgicamente criado com 75 dias de gestação, em 36 fetos de ovelha, 23 sobreviveram à cirurgia. Após 102 dias de gestação, o defeito foi corrigido em 14 casos (9 não foram tratados). A pele em volta do defeito foi dissecada abaixo da derme para permitir a aproximação direta das bordas através de sutura, sem a interposição de nenhum material entre a pele. Um material de interface foi colocado entre o tecido neural exposto e a pele, com o objetivo de evitar a adesão da medula à pele, que foi completamente fechada sobre o defeito. A gravidez foi mantida até 138 dias, os fetos foram submetidos a análises macroscópicas e microscópicas. Resultados: O defeito foi corrigido em 90.9% no grupo experimental, e o fechamento espontâneo ocorreu em 22.3% no grupo controle (p < 0.05). A taxa de sobrevivência após a criação do defeito e posteriormente a sua correção foi de 63,4% e 78%, respectivamente. Conclusão: Esta técnica simplificada teve sucesso na correção do defeito semelhante à mielomeningocele em feto de ovelha. Descritores: Cirurgia. Terapias Fetais. Meningomielocele. Disrafismo Espinal. Modelos Animais de Doenças. Ovinos.

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.

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