Fact-sheet: Heterotopic gray matter


Updated on 08/14/2020 at 10:10 AM

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Definition

Heterotopias correspond to groups of cells belonging to normal tissue but located in an inappropriate position.
During the fetal period, neurons migrate from the periventricular germinal zone to the cortex.
These heterotopias result from arrest of migration.

Three types of heterotopic gray matter can be identified on imaging, with subependymal nodular heterotopia being the most common.

  • Subependymal nodular neuronal heterotopia
  • Subcortical nodular neuronal heterotopia
  • Laminar neuronal heterotopia

Frequent association with lissencephaly.

Clinical features

  • Drug-resistant epilepsy
  • Asymptomatic

CT

Irregularities of the surface of a lateral ventricle.

MRI

The lesions are isointense to cortex on all sequences, particularly on FLAIR.
There is no enhancement after gadolinium injection.

  • Subependymal nodular form: islands of heterotopic gray matter appearing as nodules, visible from the subependymal regions to the subcortical regions.
  • Laminar neuronal form: band of heterotopic neurons separated from the cortex by a thin band of white matter, giving a double cortex appearance

Diffusion tensor imaging shows a fractional anisotropy value intermediate between that of the cortex and that of the basal ganglia, consistent with arrest along the migration pathway of neurons from the periventricular region toward the cortex.

Search for associated abnormalities in malformative syndromes.

Management

  • Surgical resection of the epileptogenic zone in cases of drug resistance.

Differential diagnosis

  • Tuberous sclerosis of Bourneville: this entity shows enhancement after injection and calcifications.