Late rupture of a myelomeningocele sac devoid of neural placode associated with good functional outcome 2 years after postnatal repair: illustrative case.

BACKGROUND: Neurological deficits in myelomeningocele are driven by a three-hit paradigm: primary myelodysplasia, intrauterine chemotoxic amniotic fluid exposure, and mechanical traction on the neural placode. How sac integrity and rupture timing influence these progressive pathophysiological hits remains poorly understood. OBSERVATIONS: A neonate presented with a prominent S1 myelomeningocele sac that remained intact until approximately 35 weeks' gestation. Rather than a distinct neural placode, postnatal repair at 36+3 weeks revealed a hairpin loop of functional nerve roots within the myelomeningocele sac that entered and exited via the dorsal defect. A mild Chiari type II malformation was identified only on postnatal imaging. Following postnatal repair, the child demonstrated not only excellent lower extremity motor function as expected, but also excellent urinary sphincter function with no hindbrain herniation or ventriculomegaly 2 years postrepair. LESSONS: This case illustrates a possible "best of both worlds" clinical scenario in which the persistent hydrostatic pressure of the intact sac protected against early hindbrain herniation and direct toxicity, while the structural absence of a neural placode within the sac reduced mechanical stretch injury. Finally, rupture of the myelomeningocele sac only in late gestation minimized chemical toxicity to neural elements. Overall, this case highlights the multifaceted and varied nature of myelomeningocele pathophysiology. https://thejns.org/doi/abs/10.3171/CASE26739.