Myelomeningocele¶

Definition¶

Myelomeningocele is the most common and most severe form of open spinal dysraphism. It consists of herniation of the spinal cord (neural placode), nerve roots, and meninges through a posterior bony defect, forming a sac that is not covered by skin. It is the most common congenital anomaly of the central nervous system and the most common cause of paraplegia in children.

Associated Anomalies¶

Chiari II malformation — Present in virtually 100% of myelomeningocele patients. The hindbrain herniates through the foramen magnum.
Hydrocephalus — Develops in 80–90% of cases, usually requiring shunt placement
Syringomyelia — Common
Tethered cord — The cord is tethered at the repair site
Segmentation anomalies — Hemivertebra, block vertebra

Imaging Findings¶

Prenatal Ultrasound¶

Open posterior bony defect with protruding sac containing neural elements
"Lemon sign" — Frontal bone scalloping of the fetal skull
"Banana sign" — Curved cerebellum from Chiari II malformation
Ventriculomegaly

MRI (Postnatal)¶

Spinal — Neural placode extending into the meningeal sac through a wide posterior bony defect. Low-lying conus. Tethered cord at the repair site after surgery.
Brain — Chiari II malformation (cerebellar tonsils and vermis herniated below the foramen magnum, small posterior fossa, beaked tectum), hydrocephalus

CT¶

Wide posterior spina bifida
Laminar defects often spanning multiple levels
Associated vertebral anomalies

Clinical Pearl

Virtually every myelomeningocele patient has an associated Chiari II malformation — this is so consistent that if Chiari II is absent, the diagnosis of myelomeningocele should be questioned. After surgical repair, MRI surveillance is needed to monitor for re-tethering of the cord, syringomyelia, and shunt malfunction.

Key Points¶

Most common and most severe form of open spinal dysraphism
Neural placode herniates through posterior defect — not covered by skin
Chiari II malformation present in virtually 100%
Hydrocephalus in 80–90%
Prenatal ultrasound: lemon sign + banana sign + open spinal defect
Lifelong MRI surveillance for re-tethering, syringomyelia, and hydrocephalus

References¶

Karsonovich T, Alruwaili AA, Das JM. Myelomeningocele. In: StatPearls. Treasure Island (FL): StatPearls Publishing; 2024. Available from: https://www.ncbi.nlm.nih.gov/books/NBK546696/
Adzick NS, Thom EA, Spong CY, et al. A randomized trial of prenatal versus postnatal repair of myelomeningocele. N Engl J Med. 2011;364(11):993-1004. PMID: 21306277.
Trapp B, de Andrade Lourenção Freddi T, de Oliveira Morais Hans M, et al. A Practical Approach to Diagnosis of Spinal Dysraphism. RadioGraphics. 2021;41(2):559-575. PMID: 33449837.
Kumar J, Afsal M, Garg A. Imaging spectrum of spinal dysraphism on magnetic resonance: A pictorial review. World J Radiol. 2017;9(4):178-190. PMID: 28529681.
Nagaraj UD, Bierbrauer KS, Zhang B, Peiro JL, Kline-Fath BM. Hindbrain Herniation in Chiari II Malformation on Fetal and Postnatal MRI. AJNR Am J Neuroradiol. 2017;38(5):1031-1036. PMID: 28279990.
George E, MacPherson C, Pruthi S, et al. Long-Term Imaging Follow-up from the Management of Myelomeningocele Study. AJNR Am J Neuroradiol. 2023;44(7):861-866. PMID: 37385677.
Myelomeningocele. Radiopaedia.org. Available from: https://radiopaedia.org/articles/myelomeningocele-1