Click on Images for Enlarged View
Radiologic Findings: Myelomeningocele of lumbar spine, with neural placode present posterior to enlarged thecal sac. Ventral nerve roots course through CSF-filled sac to exit neural foramina. Tethered spinal cord.
Diagnosis: Myelomeningocele of lumbar spine.
Discussion: A myelomeningocele is a neural tube closure defect. The embryonic neural folds fail to flex and fuse into a tube, which persists as a flat plate, the neural placode. The superficial ectoderm does not disjoin from the neural ectoderm, remaining in a lateral position. Thus the neural placode is not covered with skin. The spinal cord remains tethered to the lesion.
Spinal dysraphism is present, usually extending over 4-6 vertebral levels. Most myelomeningoceles are lumbar, with 70% present below L2.
A myelomeningocele contains nerve roots, and spinal cord within a thecal sac, with herniation through the dysraphic spine, causing the neural placode to be elevated and everted. This differentiates this lesion from a meningocele which contains no neural tissue, and the neural placode remains flush with the surface.
A Chiari II malformation is present with virtually 100% of myelomeningoceles. Other CNS abnormalities that are associated are hydrocephalus (80%), corpus callosum agenesis, hydrosyringomyelia, and diastematomyelia. Non-CNS abnormalities include other vertebral malformations, hip deformities, and bladder/bowel dysfunction.
References:
1. Diagnostic Neuroradiology. Osborn, Anne, 1994.
2. Pediatric Radiology, Blickman, Johan, 1994.
3. Practical Pediatric Imaging. Kirks, Donald, 1991.
Submitted by: