A model for in utero endoscopic treatment of myelomeningocele

Dural substitutes for spina bifida repair: past, present, and future

PURPOSE

The use of materials to facilitate dural closure during spina bifida (SB) repair has been a highly studied aspect of the surgical procedure. The overall objective of this review is to present key findings pertaining to the success of the materials used in clinical and pre-clinical studies. Additionally, this review aims to aid fetal surgeons as they prepare for open or fetoscopic prenatal SB repairs.

METHODS

Relevant publications centered on dural substitutes used during SB repair were identified. Important information from each article was extracted including year of publication, material class and sub-class, animal model used in pre-clinical studies, whether the repair was conducted pre-or postnatally, the bioactive agent delivered, and key findings from the study.

RESULTS

Out of 1,121 publications, 71 were selected for full review. We identified the investigation of 33 different patches where 20 and 63 publications studied synthetic and natural materials, respectively. From this library, 43.6% focused on clinical results, 36.6% focused on pre-clinical results, and 19.8% focused on tissue engineering approaches. Overall, the use of patches, irrespective of material, have shown to successfully protect the spinal cord and most have shown promising survival and neurological outcomes.

CONCLUSION

While most have shown significant promise as a therapeutic strategy in both clinical and pre-clinical studies, none of the patches developed so far are deemed perfect for SB repair. Therefore, there is an opportunity to develop new materials and strategies that aim to overcome these challenges and further improve the outcomes of SB patients.

State of the art in translating experimental myelomeningocele research to the bedside

Myelomeningocele (MMC), the commonest type of spina bifida (SB), occurs due to abnormal development of the neural tube and manifest as failure of the complete fusion of posterior arches of the spinal column, leading to dysplastic growth of the spinal cord and meninges. It is associated with several degrees of motor and sensory deficits below the level of the lesion, as well as skeletal deformities, bladder and bowel incontinence, and sexual dysfunction. These children might develop varying degrees of neuropsychomotor delay, partly due to the severity of the injuries that affect the nervous system before birth, partly due to the related cerebral malformations (notably hydrocephalus-which may also lead to an increase in intracranial pressure-and Chiari II deformity). Traditionally, MMC was repaired surgically just after birth; however, intrauterine correction of MMC has been shown to have several potential benefits, including better sensorimotor outcomes (since exposure to amniotic fluid and its consequent deleterious effects is shortened) and reduced rates of hydrocephalus, among others. Fetal surgery for myelomeningocele, nevertheless, would not have been made possible without the development of experimental models of this pathological condition. Hence, the aim of the current article is to provide an overview of the animal models of MMC that were used over the years and describe how this knowledge has been translated into the fetal treatment of MMC in humans.

Modern fetal surgery-a historical review of the happenings that shaped modern fetal surgery and its practices

The history of fetal surgery is one of constant evolution. Over the last 50 years, fetal surgery has progressed from a mere idea to an internationally respected innovative field of surgery. This article aims to provide a historical review of how the enterprise of maternal-fetal surgery came to be its modern version. This review is less focused on the history of specific therapies for a relatively small number of conditions, and more on how the whole field of maternal-fetal surgery evolved. The various internal and external influences that steered the field's evolution are discussed in chronologic order. Since the start of modern fetal surgery in the 1980s, large paradigm shifts have characterized the growth of the field as a whole. Innovative interventions are now based on physiologic manipulation as opposed to simple anatomic repair, fetoscopy has become the more frequently preferred surgical approach, and rigorous scientific evaluation with randomized controlled trials is now the standard expected by the community. In a very similar fashion to when the field first began in the early 1980s, recently community's leaders have risen to protect the integrity of maternal-fetal surgery by publishing ethical guidelines for innovation and clinical practice. This incredible history of innovation, rigorous science and ethical contemplation is the foundation on which modern maternal-fetal surgery rests.

Validation of the Fetal Lamb Model of Spina Bifida

A randomized trial demonstrated that fetal spina bifida (SB) repair is safe and effective yet invasive. New less invasive techniques are proposed but are not supported by adequate experimental studies. A validated animal model is needed to bridge the translational gap to the clinic and should mimic the human condition. Introducing a standardized method, we comprehensively and reliably characterize the SB phenotype in two lamb surgical models with and without myelotomy as compared to normal lambs. Hindbrain herniation measured on brain magnetic resonance imaging (MRI) was the primary outcome. Secondary outcomes included gross examination with cerebrospinal fluid (CSF) leakage test, neurological examination with locomotor assessment, whole-body MRI, motor and somatosensory evoked potentials; brain, spinal cord, hindlimb muscles, bladder and rectum histology and/or immunohistochemistry. We show that the myelotomy model best phenocopies the anatomy, etiopathophysiology and symptomatology of non-cystic SB. This encompasses hindbrain herniation, ventriculomegaly, posterior fossa anomalies, loss of brain neurons; lumbar CSF leakage, hindlimb somatosensory-motor deficit with absence of motor and somatosensory evoked potentials due to loss of spinal cord neurons, astroglial cells and myelin; urinary incontinence. This model obtains the highest validity score for SB animal models and is adequate to assess the efficacy of novel fetal therapies.

Fetal surgery: a critical review

Therapeutic fetal surgical procedures are predicated upon the ability to make an accurate fetal diagnosis. The earliest open fetal surgical procedures were introduced in the 1960s to treat Rh isoimmunisation. They were introduced when it became possible to predict impending fetal demise. Open procedures were abandoned when percutaneous approaches proved superior. The introduction of fetal ultrasound allowed the diagnosis of other congenital anomalies, some being amenable to fetal interventions. Open fetal surgical procedures were initially utilised, with significant maternal morbidity. For some anomalies, percutaneous approaches became favoured. In general, all of these procedures involved significant risks to the mother, to save a baby that was likely to die before or shortly after birth without fetal intervention. Fetal repair for myelomeningocele was a "sea change" in approach. The same maternal risks were taken to improve the quality of life of the affected fetus, not save its life. The completion of the "MOMs Trial" has occasioned a "tsunami" of centres in North America applying this approach. Others are attempting percutaneous repairs, with mixed results. This paper reviews the history of fetal surgery, focusing on the themes of the tension between accurate diagnosis and prognosis and open versus "minimally invasive" approaches.

Evaluation and Management of Lumbosacral Myelomeningoceles in Children

OBJECTIVE

Myelomeningoceles are the common form of open neural tube defects that are usually associated with neurological deficits. Many techniques of repair and methods of prevention have been proposed with respect to the size of defect and the neurological condition of patient. The aim of this study was to report our experience on the management of lumbosacral myelomeningoceles in children.

MATERIALS AND METHODS

We retrospectively analysed the data of 36 paediatric cases of surgically lumbosacral myelomeningocele treated in our department between 1998 and 2013. Twenty (56%) patients were female and sixteen were male, with a mean age of 4 months (ranged between 0 and 24 months). All patients had neurological deficits in the preoperative period. Computed tomography was performed in 33 (92%) patients and magnetic resonance imaging in 15 (42%) patients in the preoperative period. Repair of the myelomeningocele and closure of the skin defect were performed in all patients. The mean follow-up period was 36 months.

RESULTS

Thirty (83%) patients were operated for hydrocephalus and 10 (28%) patients were re-operated for tethered cord syndrome during the follow-up period. Neurological worsening was not observed in any patient while cerebrospinal fluid fistula was detected in 2 patients.

CONCLUSION

Surgical treatment using appropriate microsurgical techniques is crucial for lumbosacral myelomeningoceles in children. Early surgical intervention with close follow-up will improve the neurological condition of the patients.

Fetal Myelomeningocele Closure: Technical Considerations

Myelomeningocele (MMC) is one of the most common serious congenital malformations. Typically this condition has been treated with closure of the MMC defect shortly after birth. In general, surgery for MMC aims to provide a multilayered closure to provide protection to the neural elements, prevent leakage of spinal fluid and reduce infection risks. A randomized controlled trial, the Management of Myelomeningocele Study (MOMS), has shown that closure during the fetal period can be performed relatively safely and can result in significant benefit to the child. Whereas the surgical technique of prenatal closure of an MMC defect is similar to a postnatal closure, there are some important technical differences. The goal of this paper is to describe the technique of fetal closure of MMC defects, highlight the unique steps that are needed for this surgery and delineate some potential pitfalls.

Experimental models of spinal open neural tube defect and Chiari type II malformation

INTRODUCTION

Experimental animal models are essential for investigation of the pathoembryogenesis, pathophysiology, and management strategy of spinal open neural tube defect (ONTD) and its associated anomalies including Chiari type II malformation. Genetic, chemical/nutrient, and surgical models have been widely used for a variety of purposes. The aim of this article is to review the representative animal models of spinal ONTD and associated Chiari type II malformation with respect to their advantages and disadvantages.

DISCUSSION

Among them, the surgical model was described in detail because it is familiar to neurosurgeons and it is used for evaluations of prenatal repair of spinal ONTDs. The surgical model also has advantages because it allows quantitative analysis of the lesions. A description of our previous studies on spinal ONTDs using a chick surgical model is presented as an example.

Fetoscopic coverage of experimental myelomeningocele in sheep using a patch with surgical sealant

OBJECTIVE

Assess the feasibility of a fetoscopic patch coverage method for myelomeningocele repair in a sheep model.

STUDY DESIGN

Experimental study. A myelomeningocele-like defect was created in 15 fetal sheep on day 75 of gestation. Six remained untreated, whereas 9 underwent fetoscopic coverage of the defect on day 95 of gestation using an inert patch secured with surgical sealant. Clinical and histological examinations were performed after delivery.

RESULTS

Four valid newborn lambs were obtained in each group. Mean fetoscopic surgical time was 26.9 (SD=7.4)min. All untreated animals had an open lumbar defect with cerebrospinal fluid leakage, paraplegia, urinary incontinence, and Chiari malformation. All treated animals had a closed defect and were able to walk; one had weak bladder control, and another mild Chiari malformation.

CONCLUSION

In a chronic myelomeningocele model in fetal sheep, fetoscopic repair using a sealed patch results in simple, fast, satisfactory neural tube closure and averts neurological damage and Chiari malformation.

Foetal surgery and cleft lip and palate: current status and new perspectives

Now-a-days, high-resolution ultrasound allows an accurate and relatively early diagnosis of congenital malformations. In a limited number of such conditions foetal surgery may be lifesaving. However, premature labour has been the major drawback for open foetal surgery. Recently, improvement of video-endoscopic technology has boosted the development of operative techniques for feto-endoscopic surgery, which has been demonstrated to be less invasive than the open approach. Main clinical application of fetoscopic procedures today is the treatment of feto-foetal transfusion syndrome. Although still in development, feto-endoscopic surgery seems to offer new hope for surgical foetal therapy not only in cases of life threatening conditions. Experimental intrauterine correction of cleft lip and palate (CLP) has been lately performed using the feto-endoscopic approach. This procedure offers two major advantages: first, scarless foetal wound healing and bone healing without callus formation, which would also allow a better/normal maxillary growth, and second, significant decrease of foetal and maternal morbidity. Herein, we report the current status of experimental and clinical foetal surgery and propose possible directions for continuing research to make intrauterine procedures safer. Furthermore, we discuss current knowledge and new perspectives of experimental foetal cleft lip and palate repair, which in the future may lead to such excellent results in the operative treatment of clefts, that less or no secondary corrections and therapies, such as orthodontic, dental, logopedic, etc. would be needed. Only if these conditions can be fulfilled, will we be able to improve substantially our therapy for the human foetus with a cleft lip and palate. In spite of all efforts, however, it must be considered that it may not ever be possible to find the optimal treatment method for this or other craniofacial malformations.

Intrauterine myelomeningocele repair

Preliminary studies have suggested that IUMR reduces the incidence of shunt-dependent hydrocephalus and the severity of the Chiari malformation. An RCT is in progress to confirm these results. Future efforts will revolve around refinement of the procedure with the goal of reducing risk. Robot-assisted surgery holds the promise of achieving this goal. If it is successful. IUMR might well become the standard therapy for myelomeningocele, resulting in a significant reduction in the devastating morbidity associated with this disease.

Fetal intervention for myelomeningocele: effect on postnatal bladder function

PURPOSE

Myelomeningocele is the most common congenital malformation of the central nervous system noted on prenatal ultrasound. Due to its significant postnatal sequelae, treatment in utero could potentially have a profound impact on the newborn. Others have reported fetal surgical techniques for in utero repair of myelomeningocele and its potential benefits on motor and neurological function. We report our urodynamic findings in the newborn after in utero repair of spina bifida in an effort to characterize postnatal bladder function.

MATERIALS AND METHODS

A retrospective review of the fetal surgery database at University of California San Francisco was performed identifying patients with a diagnosis of myelomeningocele. Prenatal surgical repair of myelomeningocele was considered if a normal karyotype was present, no other significant congenital anomalies were evident and gestational age was less than 24 weeks. The spinal defects were in the lumbar or lumbosacral region. All surgery was performed before 24 weeks of gestations.

RESULTS

Fetal surgery to correct myelomeningocele was performed in 6 patients. All patients were born premature at 32 weeks of gestation or less. Videourodynamics performed at age 1 month in 4 patients indicated decreased bladder capacity for weight, increased detrusor storage pressures and significant post-void residual. Hydronephrosis was demonstrated in 4 patients on renal/bladder ultrasound, and moderate vesicoureteral reflux was seen in 3.

CONCLUSIONS

Patients with spinal bifida treated in utero appear to have the same changes in urodynamic parameters and anatomical abnormalities in the urinary tract as other children with spinal defects who have undergone standard postnatal care. In utero treatment of spinal bifida may expose the newborn to the effects of prematurity. The long-term effects on bladder function in the fetus after in utero repair of myelomeningocele remain unknown. A randomized controlled trial is necessary to evaluate long-term bladder function as well as other outcome variables in this experimental approach to patients with myelomeningocele.

Endoscopic coverage of fetal myelomeningocele in utero

OBJECTIVE

Our goal was to evaluate the safety and efficacy of minimally invasive surgery for the coverage of myelomeningocele in utero.

STUDY DESIGN

Women in the mid-second trimester of a pregnancy complicated by fetal myelomeningocele were offered an experimental procedure designed to prevent ongoing exposure of the spinal cord to the intrauterine environment. The procedure consisted of maternal laparotomy while the patient was under both general and epidural anesthesia, with exposure of the gravid uterus. Endoscopic ports were placed for camera and operating instruments. Amniotic fluid was removed and replaced with carbon dioxide. The fetus was then positioned and a maternal split-thickness skin graft was placed over the exposed spinal cord or neural elements. The skin graft and a covering of Surgicel Absorbable Hemostat were attached with fibrin glue prepared from autologous cryoprecipitate.

RESULTS

Four fetuses with open myelomeningocele underwent endoscopic coverage of the spinal lesion between 22 weeks 3 days and 24 weeks 3 days of gestation. One infant, delivered by planned cesarean section at 35 weeks' gestation after demonstration of fetal lung maturity, is almost 3 years old. A second infant was delivered by cesarean section at 28 weeks after preterm labor and is now almost 6 months old. Both survivors manifest only mild motor and somatosensory deficits. One fetus who was delivered 1 week after operation after development of amnionitis died in the delivery room of extreme prematurity. The final fetus died intraoperatively from abruptio placentae.

CONCLUSION

Minimally invasive fetal surgery appears to constitute a feasible approach to nonlethal fetal malformations that result in progressive and disabling organ damage.

Initial studies of holmium:YAG laser creation of spinal defects in fetal rabbits: model for urologic effects of myelomeningocele

Myelomeningocele (MMC) is characterized by paraplegia and incontinence, often necessitating surgery. Current models of MMC in sheep and primates create a spinal defect long after anomalous neural tube closure ordinarily occurs. An ideal model of MMC would allow creation of the defect at the earliest age in a low-cost species with a short gestation. We present a method utilizing the holmium laser to create spinal defects in rabbits in utero for the study of the pathophysiology and repair of MMC. Pregnant rabbits of 22 to 23 days' gestational age were prepared and draped in sterile fashion for laparotomy under general anesthesia. The abdomen was opened, and both uterine horns were inspected. Double opposing pursestring sutures were placed to secure the chorioamniotic membranes over the fetal lumbar spine. Amniotic fluid was removed with a needle and saved. Electrocautery was used to open the uterus within the pursestring suture, exposing the fetal dorsum. The spine was exposed by laser dissection of the fetal dorsal musculature. Posterior laminectomy was accomplished with laser incisions of each side of the spinous process, leaving the underlying dura and cord exposed. The pursestring was then cinched, amniotic fluid was returned, and the uterus and trocar sites were closed. Cesarian section was performed at 30 to 31 gestational days, and the pups were examined and then humanely sacrificed for histologic evaluation of the lesion. The rabbit is an inexpensive species with a short gestation (33-35 days), and four or more fetuses may be operated on per litter, with the remainder serving as controls. Utilization of minimally invasive techniques including holmium:YAG laser dissection facilitates creation of spinal defects at an early age in this small-animal model.