2. Congenital Malformations: Failure to Migrate Flashcards
Prologue:
The brain is said to form how?
Inside out
will eventually make up the cortex = birthed from a thick slurry surrounding the fetal ventricles = “proliferative neuroepithelium”
“pit” - Periventricular pit = cells make the climb to the cortex
Act 1: Proliferation
Before climbing, the neuro-glial cells are born into (molded by) the darkness of teh periventricular Lazarus pit.
Divide into additional stems cells = symmetric fashion = later to asymmetric proliferation (1 stem cell splits into 1 stem cell and 1 differentiated cell - Glial or Neuron
= process continues for several cycles and cells receive the signal to undergo apoptosis = they expect on of us in
Number of neuronse = frequence and number of symmetric / asymmetric divisions by stem cells
Disturbance = either too many, too few, or improperly differentiated neurons
Act II: Migration
(RISE)
From the periventricular pit of despair = cells will make the climb = chemical signals and structural cells guide them to freedom =
they climb in 6 waves =
1st wave = forms “pre-plate”
2nd wave = forms “cortical plate”
younger cells always move past the older ones = more superficial in the final position (hence the idea “inside out” or “outside last”)
Disturbance = undermigration, overmigration, or ectopic neurons
Act III Organization =
At this point you may think the cells have given everything to the cortex, and they don’t owe them anymore.
But, they haven’t given everything… not yet.
There is still the process of cortical folding
(gyrification).
The process depdnes heavily on the first two steps
Speed of cortex expansion (relative to the deep white matter) is the key for brain folding.
Proper expansion = right number of cells (act 1) migrated to right order (Act II).
Additional mechanism:
Continued differentiation into structural cell type = organize into:
Horizonal/vertical columns = create underlying cytoarchitexture = for function and structure
Disturbance = ABSENCE or EXCESSIVE Number of folds
Failure to Proliferate (Act I): Hemimegalencephaly
Cause: Failure in the normal neuronal differentiation in the involved hemisphere - “abnormal mixutre of normal tissues” - which defines the hamartoma.
Combo:
1. Dilated ventricle
2. Mismatched hemisphere size
Rassmussen’s Encephalitis
Small side = Big ventrilce = atrophy
Vs
Hemimegalencephaly (Big side = Big ventricle
Dyke-Davidoff-Masson (Cerebral Hemi-Atrophy)
This is another zebra that can look a lot like Rasmussen encephalitis
- but also has weird unilateral skull thickening and expanded sinuses.
Failure to Migrate / Proliferate: Lissencephaly-Pacliygyria Spectrum and Friends
The pathologies related to abnormal migration are best thought of along a spectrum ranging from agyria (no gyri) to pachygyria (flat gyri) to band heterotopias
Lissencephaly “Classic” Type I
Smooth Surface, Thick Cortex
Colpocephaly is common
“FIgure of 8” shaped brain = shallow vertical Sylvian fissure
Double cortex band heterotopia
Associated with seizure disorders.
Gyral pattem is normal (or mildly simplified).
Subcortical band of heterotopic gray matter
Lissencephaly “Cobblestone” Type 2
Overmigration = mor layer of cortex
Most commonly It is commonly located adjacent to the Sylvian fissures
Cobblestoned Cortex (variable in size / location) Associated with congenital muscular dvstrophv. and retinal detachment -
“muscle- eye-brain disease”
Periventricular Nodular Heterotopia
“Failed migration”
Heterotopias follow grey matter on all sequences & do NOT enhance.
Subependymal tubers of TS are
usually brighter on T2 relative to grey
matter and may also be calcified.
