Widespread symmetrical subcortical band heterotopia.

A 47 year-old woman with normal neurological examination and normal intelligence developed medically refractory seizures at the age of 13 years. Over time, six distinct types of partial seizure were identified: left cheek myoclonus, forced tongue movements followed by lower extremity thrashing movements, left arm numbness and tingling, rising epigastric sensation, visual distortion, and graying of left superior quadrant vision. Each type could occur as a simple partial seizure, evolve to a complex partial seizure, or evolve to a secondarily generalized tonic-clonic seizure. Surface and subdural electroencephalographic studies confirmed independent seizure onsets from frontal, temporal and occipital lobes. Magnetic resonance imaging (MRI) examinations at our own institution and at another epilepsy centre in the remote past were reported as normal (images no longer available for review). She underwent repeat MRI examination as part of a comprehensive re-evaluation (Figure 1). The MRI revealed a thin band of heterotopic grey matter paralleling the cortex closely on all sequences. This heterotopic grey matter was symmetrically distributed in the frontal, parietal, and occipital lobes. There was no other malformation. Subcortical band heterotopia (SBH) is a disorder of neuronal migration that may be considered a forme fruste of classic Xlinked lissencephaly. It is attributed to a defect in the production of doublecortin, a protein that stabilizes microtubules1. Doublecortin is encoded by the DCX gene on the X chromosome1. Females with a DCX mutation demonstrate functional mosaicism due to X-inactivation1. Consequently, neuronal precursors with normal DCX expression migrate to the cortex, while cells with mutant gene expression fail to migrate, giving rise to SBH1. Males with a DCX mutation can only produce abnormal doublecortin and so develop the X-linked form of classic (type 1) lissencephaly1. Different mutations of the DCX gene range in severity, with large deletions resulting in a more severe phenotype than single base pair substitutions2. The imaging appearance of SBH was first described in 1989 by Barkovich et al3. In this series of five patients, the band of heterotopic grey matter was described as thick, and its margins did not parallel the infolding of the overlying cerebral cortex3. Even so, the abnormality had not been recognized at first reading in three of the five patients, because of its diffuse and