Myelomeningocele versus myeloschisis: comparison of brain development and need for CSF diversion

How hydrocephalus rates and brain development differ between myelomeningocele (MMC; with overlying sac) and myeloschisis (without overlying sac) is poorly understood. In this study, the authors compare rates of and age at CSF diversion as well as brain anatomy in patients with MMC and myeloschisis after prenatal and postnatal repair.

Demographic and clinical data were retrospectively collected from open spinal dysraphism patients who underwent prenatal or postnatal repair between 2015 and 2024 at Washington University in St. Louis. The need for and timing of permanent CSF diversion and brain imaging characteristics on the first postnatal MRI examination were compared by lesion type (myeloschisis vs MMC). The following imaging characteristics were examined: ventricular anatomy; corpus callosum, massa intermedia, tectum, and septum pellucidum morphology; the presence of gray matter heterotopias; hindbrain herniation; and medullary kinking/compression/displacement below foramen magnum.

A total of 98 patients (48% female, 88% Caucasian) were included. There were 21 (21%; 9 prenatal repair, 12 postnatal repair) myeloschisis and 77 (79%; 29 prenatal repair, 48 postnatal repair) MMC patients with similar distribution of lesion levels (p = 0.115). After both prenatal (relative risk [RR] 2.17, 95% CI 1.14-5.62) and postnatal (RR 1.33, 95% CI 1.07-1.65) repair, more patients with myeloschisis than MMC required CSF diversion. Those with prenatally repaired MMC (median 94 days, range 15-154 days) underwent CSF diversion earlier than those with myeloschisis (median 210 days, range 13-357 days) (Hodges-Lehmann Δ114, 95% CI 2-226). However, this was no longer significant after adjusting for fetal atrial diameter, the presence of hindbrain herniation, and medullary compression (β = 75 days, 95% CI -78 to 229). There were minimal differences in brain imaging characteristics except for an increased presence of hindbrain herniation (4 [44%] myeloschisis patients vs 6 [21%] MMC patients; Δ23.8, 95% CI -11.9 to 59.4) and a decreased presence of posterior fossa crowding (2 [22%] myeloschisis patients vs 15 [52%] MMC patients; Δ30.3, 95% CI 3.0-62.1) in patients with myeloschisis versus MMC that was repaired prenatally.

Patients with myeloschisis have an increased need for CSF diversion after both prenatal and postnatal repair compared to those with MMC, which may be a consequence of increased rates of hindbrain herniation. The timing of CSF diversion after prenatal repair occurs later in patients with myeloschisis, which may be a consequence of lower rates of medullary compression. These findings suggest that there may be differences in pathophysiology between lesion types and may help with patient counseling.