Differences between Myeloschisis and Myelomeningocele in Patients Undergoing Prenatal Repair of Open Spina Bifida

Introduction: Open spina bifida (OSB) manifests as myelomeningocele (MMC) or myeloschisis (MS). Both lesions theoretically leak cerebrospinal fluid (CSF) and produce different degrees of Chiari II malformation (CHMII). However, it is not entirely clear whether these forms of OSB have different clinical manifestations. This study aimed to evaluate the clinical and/or radiological differences between MS and MMC in patients who underwent prenatal OSB repair. Methods: A total of 71 prenatal repairs were performed with the open technique at the Public Hospital of Rancagua, Chile, between 2012 and 2022. We performed follow-up magnetic resonance imaging (MRI) of fetuses that qualified for prenatal OSB repair surgery. We examined the correlations between various anthropomorphic measurements and clinical and imaging variables, such as the type of lesion and dimensions such as ventricle atrium diameter, degree of severity of CHMII, need for CSF shunt at 12 months, and walking at 30 months. Results: This study included 71 fetuses with OSB for which 38 MRI examinations were analyzed; 61% (43/71) of lesions were MMC and 39% (28/71) were MS. Grade 3 (severe) Chiari II malformations were found in 80% (12/15) of MS and 43% (10/23) of MMC (p 0.05). Fetuses with an atrial diameter less than 13.48 mm had a lower probability of requiring a CSF shunt at 12 months (p 0.05). MMC was associated with a significantly higher frequency of clubfoot at birth (p 0.05), whereas MS was significantly associated with more severe CHMII (p 0.05). Although the correlations were not significant, we observed clear trends that more children with MS required shunts at 12 months and could walk at 30 months compared to children with MMC. Conclusions: MS and MMC are distinct subtypes of OSB. Further studies of larger cohorts that include biomolecular and histological analysis are required to better understand the differences between these lesions. The findings of this study may enable healthcare providers to better advise parents and prepare healthcare teams earlier for the management of patients undergoing prenatal repair of OSB.