Heterotopic Gray Matter

KEY FACTS

TERMINOLOGY

• Heterotopia (HTP)

• Arrested/disrupted migration of groups of neurons from

periventricular germinal zone (GZ) to cortex

IMAGING

• Ectopic nodule or ribbon, isointense with gray matter on

every MR sequence

• Periventricular, subcortical/transcerebral, molecular layer

• Periventricular HTP located next to periventricular white

matter (GZ of cerebral mantle) but not in corpus callosum

(fiber tract) or next to basal ganglia (GZ of ganglionic

eminence)

• Variable: From tiny to huge, isolated to diffuse

• Thin-slice, high-definition 3D acquisition, heavily weighted

T1 provides optimal contrast and definition

• Large nodular HTP: Often thinned, polymicrogyric-looking

overlying cortex

TOP DIFFERENTIAL DIAGNOSES

• Tuberous sclerosis

• "Closed-lip" schizencephaly

• Tumors

PATHOLOGY

• Periventricular nodular HTP often genetic when diffuse

○ FLNA gene commonly involved (required for cell

migration to cortex) on Xq28

• Band HTP: Mild form of type 1 (classic) lissencephaly

(agyria/pachygyria/double cortex)

○ Predominantly posterior lissencephaly/band HTP:

Deletion LIS1 located on 17p13.3

○ Predominantly anterior lissencephaly/band HTP:

Deletion DCX = double cortin on Xq22.3-q23

(Left) Axial T2WI MR in a 6-

year-old girl with refractory

epilepsy shows massive right

posterior subcortical

heterotopia (HTP) containing

cortex-like GM, WM,

cerebrospinal fluid spaces ſt,

and blood vessels ﬇. The

mass may suggest a tumor,

but the hemisphere is small.

Note the thin overlying cortex.

(Right) Axial DTI color FA map

(same patient) depicts the

complete disorganization of

WM in and around nodular

subcortical HTP ﬇. Red, R-L;

green, A-P; blue, S-I fiber

orientation. Other hues imply

intermediate directions.

(Left) Axial 3D T2WI MR shows

subcortical band heterotopia

in a 12-year-old boy. The

symmetric HTP ﬇ lies below

an intermediate layer of WM

ſt. It is thicker posteriorly st,

in keeping with LIS1 mutation

(autosomal recessive). The

overlying cortex looks

essentially normal. (Right)

Axial T1WI MR in the same

patient coregistered with

magnetoencephalography

(MEG) shows that the MEG

spikes (triangles) originate

from HTP, yet both the HTP

and overlying cortex

participate in the

epileptogenic loop.

Trauma, and Stroke

Brain: Pathology-Based Diagnoses: Malformations,

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