Hyperammonemic Encephalopathy

• Low-lying spinal cord terminating at the level of L5
• Associated T1/T2 hyperintense mass measuring 14 x 12 x 12 mm with signal suppression on STIR. This mass extends from the neural placode posteriorly through a spinal canal defect into the posterior paraspinal soft tissues
• Sacral spinal dysraphism

• Lipomyelocele

• Neural tube defects can be complicated to understand and distinguish
• Try thinking about them in groups of conditions resulting from failures of different steps of neurulation (see below diagrams):
  • Normal neurulation occurs during the third and fourth weeks of gestation as the neural tube forms within and then separates from the ectoderm

• • • Failed closure and failed separation of the neural tube from the ectoderm results in open neural tube defects (i.e. defects with no skin covering), including:
      • Myelomeningocele – the meningeal lining and the neural placode extend beyond the skin surface
      • Myelocele – the neural placode remains flush with skin surface

• • • Premature disjunction results in closed neural tube defects (i.e. defects with skin covering) where mesodermal elements are interposed within an incompletely closed neural tube that separates from the ectoderm, including:
      • Lipomyelomeningocele – lipoma-placode interface located outside of the spinal canal
      • Lipomyelocele – lipoma-placode interface located inside of the spinal canal
      • Meningocele – meningeal lining herniates through a spinal canal defect without herniation of neural elements
      • Terminal myelocystocele – syringocele herniates into a meningocele

• • • Incomplete disjunction results in a closed neural tube defect with a persistent dermal sinus attached to the neural tube
      • May have associated intradural dermoid or epidermoid lesions

• • • Additional disorders of abnormally located mesodermal elements can result in intradural lipomas without associated dural defects
• This case is an example of a lipomyelocele because there is an intact skin covering, a fatty mass extending through a spinal canal defect, and the lipoma-placode interface is located within the spinal canal

Images