Laminar heterotopia: A rare cause of epilepsy and mental retardation

Subcortical laminar heterotopia also called as band heterotopia or double cortex consists of bilateral extensive plates of heterotopic gray matter located between the cortex and the cerebral ventricles [1]. It is an X-linked disorder (located on Xq22 or Xq21–24) with a dominant inheritance. Laminar heterotopia results from a cortical dysgenesis disorder associated with a defect in neuronal migration [2], affected individuals typically present with mental retardation and epilepsy. The brain malformation is often detected after onset of seizures in childhood. The overwhelming majority of affected patients are females, although rare males have been described.

We report the case of a 16-year-old male patient presented with sudden disturbance of consciousness, complex seizures since the age of ten, moderate mental and intellectual retardation, no consanguinity was noted, and there was no family history of epilepsy or other neurological disorders.

Physical and neurologic examination was normal. Interictal electroencephalograms (EEG) study revealed presence of frequent epileptiform discharges over bilateral parietotemporal regions.

Magnetic resonance imaging brain (Figure 1 and Figure 2) revealed a symmetric band of gray matter paralleling the cortex and subcortical white matter in both cerebral hemispheres. The abnormal band of gray matter displayed similar signal intensity to cortex on all pulse sequences suggestive of band heterotopia, giving a double cortex image. No other structural abnormality was seen on magnetic resonance imaging.

Subcortical band heterotopia was defined as a neurodevelopmental disorder that consists of bilateral and symmetric ribbons of gray matter located in the centrum semiovale between the cortex and ventricular walls, which are separated from both by layers of white matter [3].

Band heterotopia is a rare cortical malformation seen predominantly in females and considered as a mild form of lissencephaly [4]. Patients commonly present with epilepsy and possible delayed milestones and/or mental retardation [5].

The seizure types are highly variable from patient to patient and vary from focal, complex partial to generalized seizures [5]. Although patients with the more severe forms often present during infancy, patients may present at any age from newborn to adulthood. The relative thickness of the heterotopic band correlates with the phenotype and the severity of intellectual disability varies and depends on the thickness of the heterotopic band, patients with thicker bands have more severe mental retardation and seizures [1],[2],[3],[4],[5],[6].

Subcortical band heterotopia may be familial, with X-linked dominant inheritance and results from an early arrest of neuronal migration. There is no specific pattern of EEG findings described in the current literature [7].

On magnetic resonance imaging, it shows the characteristic 3-layer cake called “double cortex,” which is characterized by an extensive linear symmetric circumferential subcortical neuronal heterotopia parallel to the cortical surface. The cortex may be relatively normal or pachygyric [5]. The laminar heterotopic gray matter remains isointese to cortical surface on all sequences and do not enhance after administration of paramagnetic contrast [8].

Neuronal migration disorders, including laminar and nodular (subcortical or periventricular) heterotopia, have been recognized by neuropathologists for many years. The causes of neural migration disorders remain unknown. Vascular and toxic causes have been suspected [9].

Antiepileptic medication corresponding to the symptomatic generalized epilepsy with focalization is the mainstay of treatment for SBH. Antiepileptic drugs should be selected according to each patient’s seizure types. However callosotomy is not capable of eliminating seizures, because of its palliative nature; nevertheless, it would be worth considering for patients with frequent drop attacks [10].

Subcortical laminar heterotopia (SCLH), or “double cortex,” is a cortical dysgenesis disorder associated with a defect in neuronal migration. It is revealed by epilepsy associated or not with psychomotor retardation. Magnetic resonance imaging makes a positive diagnosis, assess the thickness of the heterotopic band, and looks for associated malformations.