Morphologic analysis of the neuromuscular development of the anorectal unit in fetal rats with retinoic acid induced myelomeningocele.

The Children's Center for Fetal Research, Children's Hospital of Philadelphia, The University of Pennsylvania School of Medicine, Abramson Research Center, Room 1116B, 3615 Civic Center Boulevard, Philadelphia, PA 19104-4318, USA.
Neuroscience Letters (Impact Factor: 2.06). 02/2008; 430(2):157-62. DOI: 10.1016/j.neulet.2007.10.048
Source: PubMed

ABSTRACT To investigate whether myelomeningocele (MMC) is associated with a global neuromuscular maldevelopment of the lower gastrointestinal (GI) tract and anorectum, the distribution and staining intensity of non-neuronal (alpha-smooth-muscle-actin), neural crest cell (NCC, [Hoxb5]), and neuronal markers (PGP-9.5, synaptophysin, neurotubulin-beta-III) within the distal colon, rectum, and anal sphincters were analyzed by immunohistochemistry and Western blot in rat fetuses with retinoic acid (RA) induced MMC. At term (E22), no gross-morphological differences of the anorectal unit of OIL (n=21) MMC (n=31), and RA-exposed-non MMC (RA, n=19) fetuses were found. Smooth muscle cells were evenly distributed within the muscle layers of the rectum and the internal anal sphincter in OIL, MMC, and RA fetuses. Density and staining intensity of NCC and mature enteric neurons within the myenteric plexus of the distal colon and rectum and innervation pattern within anal sphincters in MMC fetuses were analogous to RA and OIL controls. Normal smooth muscle and myenteric plexus development of the rectum and normal innervation of the anal sphincters and pelvic floor suggests that MMC is not associated with a global neuromuscular maldevelopment of lower GI structures in this short-gestational model.

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    ABSTRACT: Formerly, the disastrous cluster of neurologic deficits and associated neurogenic problems in patients with myelomeningocele (MMC) was generally thought to solely result from the primary malformation, i.e., failure of neurulation. Today, however, there is no doubt that a dimensional additional pathogenic mechanism exists. Most likely, it contributes much more to loss of neurologic function than non-neurulation does. Today, there is a large body of compelling experimental and clinical evidence confirming that the exposed part of the non-neurulated spinal cord is progressively destroyed during gestation, particularly so in the third trimester. These considerations gave rise to the two-hit-pathogenesis of MMC with non-neurulation being the first and consecutive in utero acquired neural tissue destruction being the second hit. This novel pathophysiologic understanding has obviously triggered the question whether the serious and irreversible functional loss caused by the second hit could not be prevented or, at least, significantly alleviated by timely protecting the exposed spinal cord segments, i.e., by early in utero repair of the MMC lesion. Based on this intriguing hypothesis and the above-mentioned data, human fetal surgery for MMC was born in the late nineties of the last century and has made its way to become a novel standard of care, particularly after the so-called “MOMS Trial”. This trial, published in the New England Journal of Medicine, has indisputably shown that overall, open prenatal repair is distinctly better than postnatal care alone. Finally, a number of important other topics deserve being mentioned, including the necessity to work on the up till now immature endoscopic fetal repair technique and the need for concentration of these extremely challenging cases to a small number of really qualified fetal surgery centers worldwide. In conclusion, despite the fact that in utero repair of MMC is not a complete cure and not free of risk for both mother and fetus, current data clearly demonstrate that open fetal–maternal surgery is to be recommended as novel standard of care when pregnancy is to be continued and when respective criteria for the intervention before birth are met. Undoubtedly, it is imperative to inform expecting mothers about the option of prenatal surgery once their fetus is diagnosed with open spina bifida.
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    ABSTRACT: This article narrates the thrilling story of how the pathogenetic understanding of myelomeningocele was fundamentally revised during the last decades and how these new insights, in particular the "two-hit hypothesis," have prepared the terrain for human fetal surgery. Formerly, the devastating cluster of neurologic and neurogenic problems was mainly attributed to the primary malformation, that is, failure of neurulation. At present, there is solid evidence that in early gestation the nonneurulated spinal cord functions well, but suffers from progressive traumatic and degenerative damage in later gestation because it is openly exposed to the amniotic cavity. There is no doubt that the secondary, in utero acquired spinal cord destruction is mainly responsible for the disastrous and irreversible peripheral neurologic deficit present at birth, and there is no doubt either that timely prenatal protective coverage can potentially arrest these deleterious dynamics and preserve neurologic function. Also, tethering of the cord within and constant outflow of cerebrospinal fluid from the lesion are seen as the driving forces behind the Chiari II malformation and consequent ventriculomegaly. Untethering and watertight sealing of the lesion reverses hindbrain herniation and lowers the risk for a relevant hydrocephalus. This article then details how human fetal surgery started in the late 1990s and follows the evolution from the pioneer case studies via the first case series providing encouraging results to the ground breaking Management of Myelomeningocele Study Trial, published in The New England Journal of Medicine in February 2011 by Adzick et al, that has, for the first time, generated unequivocal evidence that patients with prenatal repair do significantly better than those with postnatal care only. Finally, this review looks at several other critical issues, including the hitherto immature endoscopic approach to fetal repair, some future directions of research and clinical practice, and also utters a plea for concentration of these equally rare and complex cases to a few truly qualified centers worldwide. The conclusion derived from all data existing today is that maternal-fetal surgery, although not a cure and not free of risks, represents a novel standard of care for select mothers and their fetuses suffering from one of the most ruinous nonlethal congenital malformations.
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