Bladder changes after several coverage modalities in the surgically induced model of myelomeningocele in lambs

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.

Early investigations into improving bowel and bladder function in fetal ovine myelomeningocele repair

INTRODUCTION

Fetal myelomeningocele (MMC) repair improves lower extremity motor function. We have previously demonstrated that augmentation of fetal MMC repair with placental mesenchymal stromal cells (PMSCs) seeded on extracellular matrix (PMSC-ECM) further improves motor function in the ovine model. However, little progress has been made in improving bowel and bladder function, with many patients suffering from neurogenic bowel and bladder. We hypothesized that fetal MMC repair with PMSC-ECM would also improve bowel and bladder function.

METHODS

MMC defects were surgically created in twelve ovine fetuses at median gestational age (GA) 73 days, followed by defect repair at GA101 with PMSC-ECM. Fetuses were delivered at GA141. Primary bladder function outcomes were voiding posture and void volumes. Primary bowel function outcome was anorectal manometry findings including resting anal pressure and presence of rectoanal inhibitory reflex (RAIR). Secondary outcomes were anorectal and bladder detrusor muscle thickness. PMSC-ECM lambs were compared to normal lambs (n = 3).

RESULTS

Eighty percent of PMSC-ECM lambs displayed normal voiding posture compared to 100% of normal lambs (p = 1). Void volumes were similar (PMSC-ECM 6.1 ml/kg vs. normal 8.8 ml/kg, p = 0.4). Resting mean anal pressures were similar between cohorts (27.0 mmHg PMSC-ECM vs. normal 23.5 mmHg, p = 0.57). RAIR was present in 3/5 PMSC-ECM lambs that underwent anorectal manometry and all normal lambs (p = 0.46). Thicknesses of anal sphincter complex, rectal wall muscles, and bladder detrusor muscles were similar between cohorts.

CONCLUSION

Ovine fetal MMC repair augmented with PMSC-ECM results in near-normal bowel and bladder function. Further work is needed to evaluate these outcomes in human 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.

Antenatal biological models in the characterization and research of congenital lower urinary tract disorders

Congenital lower urinary tract disorders are a family of diseases affecting both urinary storage and voiding as well as upstream kidney function. Current treatments include surgical reconstruction but many children still fail to achieve urethral continence or progress to chronic kidney disease. New therapies can only be achieved through undertaking research studies to enhance our understanding of congenital lower urinary tract disorders. Animal models form a critical component of this research, a corner of the triangle composed of human in-vitro studies and clinical research. We describe the current animal models for two rare congenital bladder disorders, posterior urethral valves (PUV) and bladder exstrophy (BE). We highlight important areas for researchers to consider when deciding which animal model to use to address particular research questions and outline the strengths and weaknesses of current models available for PUV and BE. Finally, we present ideas for refining animal models for PUV and BE in the future to stimulate future researchers and help them formulate their thinking when working in this field.

A Decade of Experience with the Ovine Model of Myelomeningocele: Risk Factors for Fetal Loss

INTRODUCTION

The ovine model is the gold standard large animal model of myelomeningocele (MMC); however, it has a high rate of fetal loss. We reviewed our experience with the model to determine risk factors for fetal loss.

METHODS

We performed a retrospective review from 2009 to 2018 to identify operative factors associated with fetal loss (early fetal demise, abortion, or stillbirth). Operative risk factors included gestational age at operation, operative time, reduction of multiple gestations, amount of replaced amniotic fluid, ambient temperature, and method of delivery.

RESULTS

MMC defects were created in 232 lambs with an overall survival rate of 43%. Of the 128 fetuses that died, 53 (42%) had demise prior to repair, 61 (48%) aborted, and 14 (11%) were stillborn. Selective reduction of multiple gestations in the same uterine horn was associated with increased fetal demise (OR 3.03 [95% CI 1.29-7.05], p = 0.01). Later gestational age at MMC repair and Cesarean delivery were associated with decreased abortion/stillbirth (OR 0.90 [95% CI 0.83-0.90], p = 0.03, and OR 0.37 [95% CI 0.16-0.31], p = 0.02), respectively.

CONCLUSION

Avoiding selective reduction, repairing MMC later in gestation, and performing Cesarean delivery decreases the rate of fetal loss in the ovine MMC model.