The effects of amniotic fluid on the histopathologic changes of exposed spinal cord in fetal sheep.

BACKGROUND Experimental studies have shown that in myelomeningocele, the primary malformation is neural tissue damage resulting from exposure of neural tissue to amniotic fluid. In this study, the effects of amniotic fluid on histopathologic changes of exposed spinal cord in fetal sheep were evaluated. METHODS In an experimental trial, 10 fetal sheep in two groups containing five subjects (group A) and five shams (group B) were studied. In the sheep at 90 - 100 days of gestation (term: 145 - 150 days) the lumbar skin was incised, paraspinal soft tissues were excised, laminectomy was performed at L2 - L4, and dura matter was opened. In group A, the dura matter was not dorsally closed and thus the spinal cord was left exposed to amniotic fluid, and in group B the skin was immediately closed. The lambs were delivered near term by cesarean section and were assessed clinically and morphologically. RESULTS In group A, all lambs (n=5) had a complete or incomplete flaccid sensorimotor paraplegia and suffered from urine incontinence. Four lambs in this group were stool incontinent. In group B (n=4), only one lamb had paraparesis (P=0.048) and all lambs were urine and stool continent. In group A, all lambs had hypoplastic longitudinal muscles of the rectum but well- developed circular muscles. The anal sphincter muscles did not develop normally. In group B, all lambs had well-developed longitudinal and circular muscles and anal sphincter muscles developed normally (P=0.048). Histopathologic examination of the spinal cords showed edema, focal calcification, fibrosis, and capillary cell proliferation in group A, but in group B such changes were not seen. The number of ganglion cells was significantly higher in group B compared with group A (P<0.0005). CONCLUSION Exposure of spinal cord to amniotic fluid causes structural neural tissue damage that can be prevented by fetal surgery through repairs of myelomeningocele.