Developmental study of leptomeningeal glioneuronal heterotopia.

The timing of the appearance of leptomeningeal glioneuronal heterotopia (LGH) and its immunohistochemical development were examined on autopsied brains ranging from 12 to 43 weeks of postmenstrual age. LGH appeared at 20 weeks postmenstrual age and its incidence gradually increased until 28-31 weeks. All patients with trisomy 13 who were older than 34 weeks postmenstrual age had LGH. Glial fibrillary acidic protein-positive glial processes appeared earlier in the subpial layer of brainstems in patients with trisomy 13 than in the controls without LGH, and protruded along the perforating vessels into the leptomeninges; therefore, LGH may be formed from the midfetal period and develop with an increase of subpial glial processes along perforating vessels.