Focal Cortical Dysplasia

Focal cortical dysplasia (FCD) is a type of malformation caused by abnormalities of cortical development and one of the most common causes of intractable epilepsy in children. Other malformations of cortical development include pachygyria, polymicrogyria, and hemimegalencephaly, all of which, unlike focal cortical dysplasia, are associated with diffuse abnormal gyration.

Histopathological Subtypes

Two types of focal cortical dysplasia have been described based on histopathology. Type I demonstrates dyslamination of the cortical layer on pathology, without dysmporphic neurons or balloon cells. Type IA FCD demonstrates dyslamination (architectural abnormalities), with or without neuronal ectopia. Type IB demonstrates dyslamination plus giant or immature neurons. Patients with type I FCD may or may not have epilepsy. Some may have learning or other cognitive disorders. Patients with Type I FCD who have epilepsy, tend to do better following resection.

Type II (Taylor type) FCD has the dyslamination of type I plus dysmorphic neurons, without or with balloon cells. Type IIA FCD does not have balloon cells, while type IIB does. Balloon cells are large cells that can't decide whether they're neurons or astrocytes. They can be seen in tuberous sclerosis, leading some people to hypothesize that type IIB FCD is a forme fruste of tuberous sclerosis

Imaging

MRI findings can be subtle. It is unclear whether type I FCD can be detected on MRI. In addition, not all type II FCDs are detectable on MRI. Findings on MRI may include

• Focal areas of increased cortical thickness
• Blurring of the gray-white junction
• Increased signal on T2-weighted, PD, or FLAIR images (more likely in balloon cell FCD)
• Extension of cortical tissue with increased signal from the surface to the ventricle (transmantle dysplasia)

Reference

• Palmini A, Najm I, Avanzini G, Babb T, Guerrini R, Foldvary-Schaefer N, Jackson G, Lüders HO, Prayson R, Spreafico R, Vinters HV. Terminology and classification of the cortical dysplasias. Neurology. 2004 Mar 23;62(6 Suppl 3):S2-8.
• Rastogi S, Lee C, Salamon N. Neuroimaging in pediatric epilepsy: a multimodality approach. Radiographics. 2008 Jul-Aug;28(4):1079-95.