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Myelomeningocele (MMC) is a devastating condition considered the most common non-lethal congenital malformation of the central nervous system, affecting 1 in every 2000 newborns. It is produced by a closure defect in the posterior portion of the vertebral spine in the third week of gestation and can be detected on ultrasound study after the 16th to 18th week of gestation. Spina bifida aperta can lead to motor and sensory neurological deficits, orthopedic deformities, and fecal and urinary incontinence, as well as encephalic anomalies.
All children with MMC present associated Chiari II cerebral malformation, which includes hypoplasia of the posterior cerebral fossa, herniation of the medulla, cerebellar tonsils and vermis through the foramen magnum, structural changes in the skull, and other neuro-anatomic alterations of the brain. Patients with Chiari malformation can develop lower cranial nerve disturbances, including absent gag reflex, neurological alterations of upper limbs, cerebellar problems, and respiratory problems (45%-65%), and up to 30% of patients can die during the first 2 decades of life, mainly because of respiratory failure. Most (85%-90%) develop hydrocephalus and require decompression of the ventricular system.
One of the most plausible theories for the brain abnormalities in these patients is leakage of cerebrospinal fluid (CSF) through the MMC defect. This situation precludes fluid and pressure accumulation within the cranial vesicles, which results in a lack of distension of the embryonic ventricular system and leads to a small posterior fossa, cerebral disorganization, and herniation of the cerebellum.
One of the currently available treatment options during gestation is fetal repair of the MMC defect. Experimental studies found that intrauterine MMC repair in fetal sheep averted the development of Chiari malformation and clinical human trials demonstrate that Chiari malformation can be reversed by means fetal intervention, although there is a high rate of uterine and fetal complications because of the invasiveness of the surgery. Open surgery with neural placode dissection, dural closure and suturing of the spinal defect in a multilayer fashion is the currently available option in selected Centers. The rationale of the surgery is to protect the neural tissue to the progressive chemical damage produced by the contact with amniotic fluid, and also avoid loss of CSF. Fetoscopic approach in a short future will minimize the fetal maternal risk of this fetal intervention
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