Terminal myelocystocele and the chiari connection: a case-based review with a novel pathophysiological hypothesis

Terminal myelocystocele (TMC) is rare form of closed neural tube defect (NTD), accounting for approximately 4-8% of occult spinal dysraphisms. It is defined by cystic dilatation of the distal central canal herniating through a posterior spina bifida, typically covered by intact skin. Frequently associated with multisystem malformations, its pathogenesis remains debated, with theories involving disordered secondary neurulation, abnormal cerebrospinal fluid (CSF) dynamics, and failed disjunction between ectodermal layers.

We present the case of a male neonate with a lumbosacral mass identified at birth. Magnetic resonance imaging (MRI) revealed a 50 mm TMC associated with a separate meningocele, syringomyelia, scoliosis, butterfly vertebra, and Chiari II malformation. Surgical correction at 2 weeks of age included detethering of the spinal cord, partial cyst wall resection, and dural patch closure under intraoperative neurophysiological monitoring. The postoperative course was uneventful, and at 3-month follow-up the patient remained neurologically stable with normal developmental milestones.

This case underscores the clinical and radiological hallmarks of TMC, as well as the importance of early surgical intervention to prevent progressive neurological deterioration. MRI remains the diagnostic gold standard and guides surgical planning. We introduce a novel hypothesis drawing parallels with Chiari malformations, suggesting that fibrous bands and altered CSF hydrodynamics may contribute to cyst enlargement and clinical decline. A multidisciplinary approach and improved understanding of these mechanisms are crucial to optimize outcomes and refine management strategies.