A rare case of split cord malformation type II with concomitant myelocystocele: illustrative case.

backgroundSplit cord malformation (SCM) and myelocystocele (MC) are rare forms of spinal dysraphism arising from aberrant embryogenesis at distinct developmental stages. Although both lesions share embryological origins, their concomitant occurrence is exceedingly uncommon. OBSERVATIONS: The authors report the first case of a type II SCM coexisting with an MC in an infant. The patient underwent microsurgical detethering and repair of the MC. Postnatal postoperative MRI revealed a type II SCM of the thoracolumbar spine. At 17 months, the patient demonstrated neurological symptoms consistent with spinal cord tethering and was brought back to the operating room for a complex detethering procedure with the assistance of the plastic surgery team and intraoperative neurophysiological monitoring. At the 2-year follow-up, the patient demonstrated stable spinal anatomy and improved functional outcomes. Genetic testing identified a variant in the GLI2 gene, suggesting a potential role for midline developmental gene perturbations in complex dysraphic syndromes. LESSONS: This case expands the spectrum of closed spinal dysraphism, highlighting that errors in gastrulation and secondary neurulation can co-occur. Comprehensive preoperative imaging, high-resolution postnatal MRI, multidisciplinary coordination, and consideration of genetic evaluation are essential when managing complex spinal dysraphism. Awareness of such rare lesion combinations informs both surgical planning and developmental understanding of spinal cord malformations. https://thejns.org/doi/10.3171/CASE26552.