Validation of the Fetal Lamb Model of Spina Bifida

Allogenic umbilical cord-derived mesenchymal stromal cells improve motor function in prenatal surgical repair of myelomeningocele: An ovine model study

OBJECTIVE

To investigate the effects of an adjuvant allogenic umbilical cord mesenchymal stromal cell (UC-MSC) patch applied during fetal surgery on motor and sphincter function in the ovine MMC model.

DESIGN

MMC defects were surgically created at 75 days of gestation and repaired 14 days later.

POPULATION

Ovine MMC model: fetal lambs.

METHODS

We compared lambs that received a UC-MSC patch with a control group of lambs that received an acellular patch.

MAIN OUTCOME MEASURES

Clinical neurological assessment was performed at 2 and 24 hours of life and included determination of the Sheep Locomotor Rating scale (SLR), which has been validated in the ovine MMC model. Electrophysical examinations, spine scans and histological analyses were also performed.

RESULTS

Of the 13 operated lambs, nine were born alive: five had of these had received a UC-MSC patch and four an acellular patch. At 24 hours of life, lambs in the UC-MSC group had a significantly higher score (14 versus 5, P = 0.04). Amyotrophy was significantly more common in the control group (75% versus 0%, P = 0.02). All the lambs in the control group and none of those in the UC-MSC group were incontinent. No significant differences were observed between the UC-MSC and control groups in terms of the presence of spontaneous EMG activity, nerve conduction or spinal evoked potentials. In the microscopic examination, lambs in the UC-MSC group had less fibrosis between the spinal cord and the dermis (mean thickness, 453 versus 3921 μm, P = 0.03) and around the spinal cord (mean thickness, 47 versus 158 μm, P < 0.001). Examination of the spinal cord in the area of the MMC defect showed a higher large neuron density in the UC-MSC group (14.5 versus 5.6 neurons/mm2, P < 0.001). No tumours were observed.

CONCLUSIONS

Fetal repair of MMC using UC-MSC patches improves motor and sphincter function as well as spinal preservation and reduction of fibrosis.

Thalamic connectivity topography in newborns with spina bifida: association with neurological functional level but not developmental outcome at 2 years

Spina bifida affects spinal cord and cerebral development, leading to motor and cognitive delay. We investigated whether there are associations between thalamocortical connectivity topography, neurological function, and developmental outcomes in open spina bifida. Diffusion tensor MRI was used to assess thalamocortical connectivity in 44 newborns with open spina bifida who underwent prenatal surgical repair. We quantified the volume of clusters formed based on the strongest probabilistic connectivity to the frontal, parietal, and temporal cortex. Developmental outcomes were assessed using the Bayley III Scales, while the functional level of the lesion was assessed by neurological examination at 2 years of age. Higher functional level was associated with smaller thalamo-parietal, while lower functional level was associated with smaller thalamo-temporal connectivity clusters (Bonferroni-corrected P < 0.05). Lower functional levels were associated with weaker thalamic temporal connectivity, particularly in the ventrolateral and ventral anterior nuclei. No associations were found between thalamocortical connectivity and developmental outcomes. Our findings suggest that altered thalamocortical circuitry development in open spina bifida may contribute to impaired lower extremity function, impacting motor function and independent ambulation. We hypothesize that the neurologic function might not merely be caused by the spinal cord lesion, but further impacted by the disruption of cerebral neuronal circuitry.

Duration of fetoscopic spina bifida repair does not affect the central nervous system in fetal lambs

BACKGROUND

Prenatal spina bifida aperta repair improves neurologic outcomes yet comes with a significant risk of prematurity and uterine scar-related complications. To reduce such complications, different fetoscopic techniques, for example, with varying numbers of ports, are being explored. This has an effect on the duration of the procedure, potentially affecting central nervous system development. Both the condition and anesthesia can affect the central nervous system, particularly the hippocampus, a region crucial for prospective and episodic memory. Previous animal studies have shown the potential influence of anesthesia, premature delivery, and maternal surgery during pregnancy on this area.

OBJECTIVE

This study aimed to compare the effects of 2- vs 3-port fetoscopic spina bifida aperta repair in the fetal lamb model using neuron count of the hippocampus as the primary outcome.

STUDY DESIGN

Based on the hippocampal neuron count from previous lamb experiments, we calculated that we required 5 animals per group to achieve a statistical power of ≥ 80%. A spina bifida aperta defect was developed in fetal lambs at 75 days of gestation (term: 145 days). At 100 days, fetuses underwent either a 2-port or 3-port fetoscopic repair. At 143 days, all surviving fetuses were delivered by cesarean delivery, anesthetized, and transcardially perfused with a mixture of formaldehyde and gadolinium. Next, they underwent neonatal brain and spine magnetic resonance imaging after which these organs were harvested for histology. Hippocampus, frontal cortex, caudate nucleus, and cerebellum samples were immunostained to identify neurons, astrocytes, microglia, and markers associated with cell proliferation, myelination, and synapses. The degree of hindbrain herniation and the ventricular diameter were measured on magnetic resonance images and volumes of relevant brain and medulla areas were segmented.

RESULTS

Both treatment groups included 5 fetuses and 9 unoperated littermates served as normal controls. The durations for both skin-to-skin (341±31 vs 287±40 minutes; P=.04) and fetal surgery (183±30 vs 128±22; P=.01) were longer for the 2-port approach than for the 3-port approach. There was no significant difference in neuron density in the hippocampus, frontal cortex, and cerebellum. In the caudate nucleus, the neuron count was higher in the 2-port group (965±156 vs 767±92 neurons/mm2; P=.04). There were neither differences in proliferation, astrogliosis, synaptophysin, or myelin. The tip of the cerebellar vermis was closer to the foramen magnum in animals undergoing the 2-port approach than in animals undergoing the 3-port approach (-0.72±0.67 vs -2.47±0.91 mm; P=.009). There was no significant difference in the ratio of the hippocampus, caudate nucleus, or cerebellar volume to body weight. For the spine, no difference was noted in spine volume-to-body weight ratio for the lower (L1-L2), middle (L3-L4), and higher (L5-L6) levels. Compared with controls, in repaired animals, the cerebellar vermis tip laid closer to the foramen magnum, parietal ventricles were enlarged, and medulla volumes were reduced.

CONCLUSION

In the experimental spina bifida fetal lamb model, a 2-port repair took 40% longer than a 3-port repair. However, there was no indication of any relevant morphologic differences in the fetal brain.

A comprehensive workflow and its validation for simulating diffuse speckle statistics for optical blood flow measurements

Diffuse optical methods including speckle contrast optical spectroscopy and tomography (SCOS and SCOT), use speckle contrast (κ ) to measure deep blood flow. In order to design practical systems, parameters such as signal-to-noise ratio (SNR) and the effects of limited sampling of statistical quantities, should be considered. To that end, we have developed a method for simulating speckle contrast signals including effects of detector noise. The method was validated experimentally, and the simulations were used to study the effects of physical and experimental parameters on the accuracy and precision of κ . These results revealed that systematic detector effects resulted in decreased accuracy and precision of κ in the regime of low detected signals. The method can provide guidelines for the design and usage of SCOS and/or SCOT instruments.

Neuroprotection is improved by watertightness of fetal spina bifida repair in the sheep model

OBJECTIVES

A contributing factor to unsuccessful prenatal spina bifida aperta (SBA) repair via an open approach may be incomplete neurosurgical repair causing persistent in-utero leakage of cerebrospinal fluid (CSF) and exposure of the fetal spinal cord to amniotic fluid. We aimed to investigate the neurostructural and neurofunctional efficacy of watertight prenatal SBA repair in a validated SBA fetal lamb model.

METHODS

A well-powered superiority study was conducted in the validated SBA fetal lamb model (n = 7 per group). The outcomes of lambs which underwent watertight or non-watertight multilayer repair through an open approach were compared to those of unrepaired SBA lambs (historical controls) at delivery (term = 145 days). At ∼75 days, fetal lambs underwent standardized induction of lumbar SBA. At ∼100 days, they were assigned to an either watertight or non-watertight layered repair group based on an intraoperative watertightness test using subcutaneous fluorescein injection. At 1-2 days postnatally, as primary outcome, we assessed reversal of hindbrain herniation using magnetic resonance imaging (MRI). Secondary proxies of neuroprotection were: absence of CSF leakage at the repair site; hindlimb motor function based on joint-movement score, locomotor grade and Motor Evoked Potential (MEP); four-score neuroprotection scale, encompassing live birth, complete hindbrain herniation reversal, absence of CSF leakage and joint-movement score ≥ 9/15; and brain and spinal cord histology and immunohistochemistry. As the watertightness test cannot be used clinically due to its invasiveness, we developed a potential surrogate intraoperative three-score skin-repair-quality scale based on visual assessment of the quality of the skin repair (suture inter-run distance ≤ 3 mm, absence of tear and absence of ischemia), with high quality defined by a score ≥ 2/3 and low quality by a score < 2/3, and assessed its relationship with improved outcome.

RESULTS

Compared with unrepaired lambs, lambs with watertight repair achieved a high level of neuroprotection (neuroprotection score of 4/4 in 5/7 vs 0/7 lambs) as evidenced by: a significant 100% (vs 14%) reversal of hindbrain herniation on MRI; low CSF leakage (14% vs 100%); better hindlimb motor function, with higher joint-movement score, locomotor grade and MEP area under the curve and peak-to-peak amplitude; higher neuronal density in the hippocampus and corpus callosum; and higher reactive astrogliosis at the SBA lesion epicenter. Conversely, lambs with non-watertight SBA repair did not achieve the same level of neuroprotection (score of 4/4 in 1/7 lambs) compared with unrepaired lambs, with: a non-significant 86% (vs 14%) reversal of hindbrain herniation; high CSF leakage (43% vs 100%); no improvement in motor function; low brain neuron count in both the hippocampus and corpus callosum; and small spinal astroglial cell area at the epicenter. Both watertight layered repair and high (≥ 2/3) intraoperative skin-repair-quality score were associated with improved outcome, but the watertightness test and skin-repair-quality scale could not be used interchangeably due to result discrepancies.

CONCLUSIONS

Watertight layered fetal SBA repair is neuroprotective since it improves brain and spinal-cord structure and function in the fetal lamb model. This translational research has important clinical implications. A neurosurgical technique that achieves watertightness should be adopted in all fetal centers to improve neuroprotection. Future clinical studies could assess whether a high skin-repair-quality score (≥ 2/3) correlates with neuroprotection. © 2022 International Society of Ultrasound in Obstetrics and Gynecology.

Fetal Surgery for Myelomeningocele: Neurosurgical Perspectives

More than 30 years have elapsed since it was recognised that folic acid supplementation could substantially reduce the risk of open neural tube defects (ONTDs). During that time, many countries have adopted policies of food fortification with demonstrable reduction in the incidence of both cranial and spinal ONTDs. Improved prenatal detection and termination has also resulted in a reduction in the number of affected live births. Nonetheless, in the USA about 1500 children, and in the UK around 500 children are born each year with myelomeningocele (MMC) and so the management of MMC and its complications continues to constitute a significant clinical workload for many paediatric neurosurgical units around the world.Until recently, the options available following antenatal diagnosis of MMC were termination of pregnancy or postnatal repair. As a result of the MOMS trial, prenatal repair has become an additional option in selected cases (Adzick et al., N Engl J Med 364(11):993-1004, 2011). Fetal surgery for myelomeningocele is now offered in more than 30 centres worldwide. The aim of this chapter is to review the experimental basis of prenatal repair of MMC, to critically evaluate the neurosurgical implications of this intervention and to describe the technique of 'open' repair, comparing this with emerging minimally invasive alternatives.

The Sheep as a Large Animal Model for the Investigation and Treatment of Human Disorders

Simple Summary

We review the value of large animal models for improving the translation of biomedical research for human application, focusing primarily on sheep.

Abstract

An essential aim of biomedical research is to translate basic science information obtained from preclinical research using small and large animal models into clinical practice for the benefit of humans. Research on rodent models has enhanced our understanding of complex pathophysiology, thus providing potential translational pathways. However, the success of translating drugs from pre-clinical to clinical therapy has been poor, partly due to the choice of experimental model. The sheep model, in particular, is being increasingly applied to the field of biomedical research and is arguably one of the most influential models of human organ systems. It has provided essential tools and insights into cardiovascular disorder, orthopaedic examination, reproduction, gene therapy, and new insights into neurodegenerative research. Unlike the widely adopted rodent model, the use of the sheep model has an advantage over improving neuroscientific translation, in particular due to its large body size, gyrencephalic brain, long lifespan, more extended gestation period, and similarities in neuroanatomical structures to humans. This review aims to summarise the current status of sheep to model various human diseases and enable researchers to make informed decisions when considering sheep as a human biomedical model.

Fetoscopic insufflation of heated-humidified carbon dioxide during simulated spina bifida repair is safe under controlled anesthesia in the fetal lamb

OBJECTIVE

To assess the safety of Partial-Amniotic-Insufflation-of-heated-humidified-CO₂ (hPACI) during fetoscopic spina bifida repair (fSB-repair).

METHOD

A simulated fSB-repair through an exteriorized uterus under hPACI was performed in 100-day fetal lambs (term = 145 days) under a laboratory anesthesia protocol (n = 5; group 1) which is known to induce maternal-fetal acidosis and hypercapnia. Since these may not occur clinically, we applied a clinical anesthesia protocol (n = 5; group 2), keeping maternal parameters within physiological conditions, that is, controlled maternal arterial carbon dioxide (CO2) pressure (pCO₂  = 30 mmHg), blood pressure (≥67 mmHg), and temperature (37.1-39.8°C). Our superiority study used fetal pH as the primary outcome.

RESULTS

Compared to group 1, controlled anesthesia normalized fetal pH (7.23 ± 0.02 vs. 7.36 ± 0.02, p < 0.001), pCO₂ (70.0 ± 9.1 vs. 43.0 ± 1.0 mmHg, p = 0.011) and bicarbonate (27.8 ± 1.1 vs. 24.0 ± 0.9 mmol/L, p = 0.071) at baseline. It kept them within clinically acceptable limits (pH ≥ 7.23, pCO₂  ≤ 70 mmHg, bicarbonate ≤ 30 mm/L) for ≥120 min of hPACI as opposed to ≤30 min in group one. Fetal pO₂ and lactate were comparable between groups and generally within normal range. Fetal brain histology demonstrated fewer apoptotic cells and higher neuronal density in the prefrontal cortex in group two. There was no difference in fetal membrane inflammation, which was mild.

CONCLUSION

Fetoscopic insufflation of heated-humidified CO₂ during simulated fSB-repair through an exteriorized uterus can be done safely under controlled anesthesia.

Complex gastroschisis: a new indication for fetal surgery?

Gastroschisis (GS) is a congenital abdominal wall defect, in which the bowel eviscerates from the abdominal cavity. It is a non-lethal isolated anomaly and its pathogenesis is hypothesized to occur as a result of two hits: primary rupture of the 'physiological' umbilical hernia (congenital anomaly) followed by progressive damage of the eviscerated bowel (secondary injury). The second hit is thought to be caused by a combination of mesenteric ischemia from constriction in the abdominal wall defect and prolonged amniotic fluid exposure with resultant inflammatory damage, which eventually leads to bowel dysfunction and complications. GS can be classified as either simple or complex, with the latter being complicated by a combination of intestinal atresia, stenosis, perforation, volvulus and/or necrosis. Complex GS requires multiple neonatal surgeries and is associated with significantly greater postnatal morbidity and mortality than is simple GS. The intrauterine reduction of the eviscerated bowel before irreversible damage occurs and subsequent defect closure may diminish or potentially prevent the bowel damage and other fetal and neonatal complications associated with this condition. Serial prenatal amnioexchange has been studied in cases with GS as a potential intervention but never adopted because of its unproven benefit in terms of survival and bowel and lung function. We believe that recent advances in prenatal diagnosis and fetoscopic surgery justify reconsideration of the antenatal management of complex GS under the rubric of the criteria for fetal surgery established by the International Fetal Medicine and Surgery Society (IFMSS). Herein, we discuss how conditions for fetoscopic repair of complex GS might be favorable according to the IFMSS criteria, including an established natural history, an accurate prenatal diagnosis, absence of fully effective perinatal treatment due to prolonged need for neonatal intensive care, experimental evidence for fetoscopic repair and maternal and fetal safety of fetoscopy in expert fetal centers. Finally, we propose a research agenda that will help overcome barriers to progress and provide a pathway toward clinical implementation. © 2021 International Society of Ultrasound in Obstetrics and Gynecology.

Allografts for Skin Closure during In Utero Spina Bifida Repair in a Sheep Model

Objectives: Use of off-label tissue graft materials, such as acellular dermal matrix (ADM), for in utero repair of severe spina bifida (SB), where primary skin layer closure is not possible, is associated with poor neurological outcomes. The cryopreserved human umbilical cord (HUC) patch has regenerative, anti-inflammatory, and anti-scarring properties, and provides watertight SB repair. We tested the hypothesis that the HUC is a superior skin patch to ADM for reducing inflammation at the repair site and preserving spinal cord function. Methods: In timed-pregnant ewes with twins, on gestational day (GD) 75, spina bifida was created without a myelotomy (functional model). On GD 95, repair was performed using HUC vs. ADM patches (randomly assigned) by suturing them to the skin edges. Additionally, full thickness skin closure as a primary skin closure (PSC) served as a positive control. Delivery was performed on GD 140, followed by blinded to treatment neurological assessments of the lambs using the Texas Spinal Cord Injury Scale (TSCIS) for gait, proprioception, and nociception. Lambs without spina bifida were used as controls (CTL). Ex vivo magnetic resonance imaging of spines at the repair site were performed, followed by quantitative pathological assessments. Histological assessments (blinded) included Masson’s trichrome, and immunofluorescence for myeloperoxidase (MPO; neutrophils) and for reactive astrocytes (inflammation) by co-staining vimentin and GFAP. Results: The combined hind limbs’ TSCIS was significantly higher in the HUC group than in ADM and PSC groups, p = 0.007. Both ADM and PSC groups exhibited loss of proprioception and mild to moderate ataxia compared to controls. MRI showed increased pathological findings in the PSC group when compared to the HUC group, p = 0.045. Histologically, the meningeal layer was thickened (inflammation) by 2–3 fold in ADM and PSC groups when compared to HUC and CTL groups, p = 0.01. There was lower MPO positive cells in the HUC group than in the ADM group, p = 0.018. Posterior column astrocyte activation was increased in ADM and PSC lambs compared to HUC lambs, p = 0.03. Conclusion: The HUC as a skin patch for in utero spina bifida repair preserves spinal cord function by reducing underlying inflammation when compared to ADM.

Preliminary Results of a Reverse Thermal Gel Patch for Fetal Ovine Myelomeningocele Repair

BACKGROUND

Prenatal surgical closure of Myelomeningocele (MMC) is considered part of the current age armamentarium. Clinical data has demonstrated the need for innovative patches to maximize the benefits and decrease the risks of this approach. Our team has developed a minimally invasive reverse thermal gel (RTG) patch with cellular scaffolding properties. Here, we demonstrate the initial gross and microscopic histological effects of this RTG patch in the fetal ovine model of MMC.

MATERIALS AND METHODS

A fetal ovine MMC defect was created at 68-75 days gestation, RTG patch application or untreated at 100-103 days, and harvest at 135-140 days. The RTG was applied to the defect and secured in place with an overlay sealant. Defect areas underwent gross and microscopic analysis for inflammation and skin development. Brains were analyzed for hindbrain herniation and hydrocephalus.

RESULTS

The untreated fetus (n = 1) demonstrated an open defect lacking tissue coverage, evidence of spinal cord injury, increased caspase-3, Iba1 and GFAP in spinal cord tissues, and hindbrain herniation and ventricular dilation. RTG treated fetuses (n = 3) demonstrated defect healing with well-organized dermal and epidermal layers throughout the entire healed tissue area overlaying the defect with minimal inflammation, reduced caspase-3, Iba1 and GFAP in spinal cord tissues, and no hindbrain herniation or ventricular dilation.

CONCLUSION

An RTG patch applied to MMC defects in fetal sheep promoted skin coverage over the defect, was associated with minimal inflammation of the spinal cord tissues and prevented brain abnormalities. The present findings provide exciting results for future comprehensive radiological, functional, and mechanistic evaluation of the RTG.

A preliminary investigation of high retinoic acid exposure during fetal development on behavioral competency and litter characteristics in newborn rats

Myelomeningocele (MMC) is the most common and severe type of spina bifida in which the developing spine and neural tube fail to close during prenatal development. This typically results in a small portion of the lower spinal cord and meninges protruding from the back of the individual, accompanied by severe motor and sensory deficits. In rats, retinoic acid (RA) exposure in high doses during fetal development has been shown to induce morphologic and clinical symptoms similar to humans with MMC. The aim of the current study was to examine litter characteristics and sensorimotor function in MMC-affected rat pups. Pregnant rats were gavage-fed 2 ml olive oil or all-trans RA (40, 45, 50 mg/kg) on gestational day 11. Pups underwent behavioral testing on postnatal day 2. Litter characteristics and newborn sensorimotor function varied across RA doses. Pups prenatally exposed to 45 and 50 mg/kg RA weighed significantly less than olive oil and 40 mg/kg RA pups. Litters exposed to 45 mg/kg RA suffered significantly higher mortality rates compared to other groups. Additionally, bladder function was significantly impaired in pups exposed to 40 mg/kg RA. Sensorimotor function findings demonstrated that for most behavioral assessments there was not a significant difference between control and RA-exposed subjects. However, pups treated with 40 mg/kg RA showed increased facial wiping, suggesting a hyper-responsiveness to sensory stimuli. Overall, the findings of the current study provide evidence for a model to examine litter characteristics and behavioral effects as well as morphology.

Validation of a high-fidelity training model for fetoscopic spina bifida surgery

Open fetal surgery for spina bifida (SB) is safe and effective yet invasive. The growing interest in fetoscopic SB repair (fSB-repair) prompts the need for appropriate training. We aimed to develop and validate a high-fidelity training model for fSB-repair. fSB-repair was simulated in the abdominal cavity and on the stomach of adult rabbits. Laparoscopic fetal surgeons served either as novices (n = 2) or experts (n = 3) based on their experience. Technical performance was evaluated using competency Cumulative Sum (CUSUM) analysis and the group splitting method. Main outcome measure for CUSUM competency was a composite binary outcome for surgical success, i.e. watertight repair, operation time ≤ 180 min and Objective-Structured-Assessment-of-Technical-Skills (OSATS) score ≥ 18/25. Construct validity was first confirmed since competency levels of novices and experts during their six first cases using both methods were significantly different. Criterion validity was also established as 33 consecutive procedures were needed for novices to reach competency using learning curve CUSUM, which is a number comparable to that of clinical fSB-repair. Finally, we surveyed expert fetal surgeons worldwide to assess face and content validity. Respondents (26/49; 53%) confirmed it with ≥ 71% of scores for overall realism ≥ 4/7 and usefulness ≥ 3/5. We propose to use our high-fidelity model to determine and shorten the learning curve of laparoscopic fetal surgeons and retain operative skills.

Effects of Maternal Abdominal Surgery on Fetal Brain Development in the Rabbit Model

INTRODUCTION

Anesthesia during pregnancy can impair fetal neurodevelopment, but effects of surgery remain unknown. The aim is to investigate effects of abdominal surgery on fetal brain development. Hypothesis is that surgery impairs outcome.

METHODS

Pregnant rabbits were randomized at 28 days of gestation to 2 h of general anesthesia (sevoflurane group, n = 6) or to anesthesia plus laparoscopic appendectomy (surgery group, n = 13). On postnatal day 1, neurobehavior of pups was assessed and brains harvested. Primary outcome was neuron density in the frontal cortex, and secondary outcomes included neurobehavioral assessment and other histological parameters.

RESULTS

Fetal survival was lower in the surgery group: 54 versus 100% litters alive at birth (p = 0.0442). In alive litters, pup survival until harvesting was 50 versus 69% (p = 0.0352). No differences were observed for primary outcome (p = 0.5114) for surviving pups. Neuron densities were significantly lower in the surgery group in the caudate nucleus (p = 0.0180), but not different in other regions. No differences were observed for secondary outcomes. Conclusions did not change after adjustment for mortality.

CONCLUSION

Abdominal surgery in pregnant rabbits at a gestational age corresponding to the end of human second trimester results in limited neurohistological changes but not in neurobehavioral impairments. High intrauterine mortality limits translation to clinical scenario, where fetal mortality is close to zero.

Preclinical stem cell therapy in fetuses with myelomeningocele: A systematic review and meta-analysis

OBJECTIVE

We performed a systematic review to summarize the efficacy and safety of in utero stem cells application in preclinical models with myelomeningocele (MMC).

METHODS

The study was registered with PROSPERO (CRD42019160399). We searched MEDLINE, Embase, Web of Science, Scopus and CENTRAL for publications articles on stem cell therapy in animal fetuses with MMC until May 2020. Publication quality was assessed by the SYRCLE's tool. Meta-analyses were pooled if studies were done in the same animal model providing similar type of stem cell used and outcome measurements. Narrative synthesis was performed for studies that could not be pooled.

RESULTS

Nineteen and seven studies were included in narrative and quantitative syntheses, respectively. Most used mesenchymal stem cells (MSCs) and primarily involved ovine and rodent models. Both intra-amniotic injection of allogeneic amniotic fluid (AF)-MSCs in rat MMC model and the application of human placental (P)-MSCs to the spinal cord during fetal surgery in MMC ovine model did not compromise fetal survival rates at term (rat model, relative risk [RR] 1.03, 95% CI 0.92-1.16; ovine model, RR 0.94, 95% CI 0.78-1.13). A single intra-amniotic injection of allogeneic AF-MSCs into rat MMC model was associated with a higher rate of complete defect coverage compared to saline injection (RR 16.35, 95% CI 3.27-81.79). The incorporation of human P-MSCs as a therapeutic adjunct to fetal surgery in the ovine MMC model significantly improved sheep locomotor rating scale after birth (mean difference 5.18, 95% CI 3.36-6.99).

CONCLUSIONS

Stem cell application during prenatal period in preclinical animal models is safe and effective.

Fetal surgical intervention for myelomeningocele: lessons learned, outcomes, and future implications

Fetal myelomeningocele (fMMC) closure (spina bifida aperta) has become a care option for patients that meet inclusion criteria, but it is clear that fetal intervention, while improving outcomes, is not a cure. This review will: (1) focus on the rationale for fMMC surgery based on preclinical studies and observations that laid the foundation for human pilot studies and a randomized controlled trial; (2) summarize important clinical outcomes; (3) discuss the feasibility, efficacy, and safety of recent developments in fetal surgical techniques and approaches; and (4) highlight future research directions. Given the increased risk of maternal and fetal morbidity associated with prenatal intervention, accompanied by the increasing number of centres performing interventions worldwide, teams involved in the care of these patients need to proceed with caution to maintain technical expertise, competency, and patient safety. Ongoing assessment of durability of the benefits of fMMC surgery, as well as additional refinement of patient selection criteria and counselling, is needed to further improve outcomes and reduce the risks to the mother and fetus. WHAT THIS PAPER ADDS: High-quality prospective studies are needed to broaden the indication for fetal surgery in the general myelomeningocele population. Innovative minimally invasive approaches have had promising results, yet lack comprehensive and robust experimental or clinical evaluation. Important information to help families make informed decisions regarding fetal surgery for myelomeningocele is provided.