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Myelomeningocele


KEY FACTS

Terminology

  • Posterior spinal defect lacking skin covering → neural tissue, cerebrospinal fluid (CSF), and meninges exposed to air

  • Synonyms: Meningomyelocele, open spinal dysraphism, spina bifida aperta, spina bifida cystica

Imaging

  • Lumbosacral (44%) > thoracolumbar (32%) > lumbar (22%) > thoracic (2%)

  • Preoperative: Posterior spinal defect lacking skin covering → neural tissue, CSF, and meninges exposed to air

  • Postoperative: Dysraphism, low-lying cord/roots, postoperative skin closure changes

Top Differential Diagnoses

  • Dorsal meningocele

  • Closed (occult) spinal dysraphism

  • Postoperative pseudomeningocele

Pathology

  • Failure of neural tube closure at 3-4 weeks

    • Placode may be segmental or terminal

  • Association with maternal folate deficiency or abnormal folate metabolism

  • Usually accompanied by multiple neurological and orthopedic complications

Clinical Issues

  • Can be diagnosed (MR, ultrasound), treated in utero

  • Stable neurological deficits expected following closure

  • Hydrocephalus and tethered cord determine prognosis for deterioration

  • Neurological deterioration → imaging

    • Cord retethering most common spinal cause of delayed deterioration

    • Other = dural ring constriction, cord ischemia, syrinx

  • Chiari 2 malformation is most common cause of death in meningomyelocele patients

Diagnostic Checklist

  • Low-lying cord on MR does not always equate to clinical tethering

Sagittal graphic shows ballooning of meninges through dysraphic spinal defect, with low-lying cord
terminating in the red neural placode
. Axial insert shows origin of spinal roots from ventral placode and protrusion of meninges and placode through dysraphic posterior elements
.

Sagittal T1WI MR shows a large unrepaired lumbosacral myelomeningocele sac
protruding through a posterior dysraphic defect. Neural elements are seen protruding into the sac
.

Sagittal T2WI MR shows typical posterior fossa Chiari 2 malformation changes. The large myelomeningocele lumbosacral sac
has not been surgically repaired, and it protrudes dorsally through a large posterior dysraphic defect.

Axial T1WI MR of unrepaired lumbosacral myelomeningocele confirms an exophytic meningeal sac
and extension of dysplastic neural elements
through the osseous spinal dysraphic defect into the myelomeningocele.

TERMINOLOGY

Synonyms

  • Meningomyelocele (MMC), open spinal dysraphism (OSD), spina bifida aperta, spina bifida cystica

Definitions

  • Posterior spinal defect lacking skin covering → neural tissue, CSF, and meninges exposed to air

IMAGING

General Features

  • Best diagnostic clue

    • Wide osseous dysraphism, low-lying cord/roots, postoperative skin closure changes

  • Location

    • Lumbosacral (44%) > thoracolumbar (32%) > lumbar (22%) > thoracic (2%)

  • Size

    • Small → large, depending on extent of neural tube defect

  • Morphology

    • Exposed CSF sac + neural elements protrude through wide dorsal dysraphism

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