LM 3.1: Perinatal/Neurodevelopmental Pathology Flashcards
what causes congenital brain malformations?
- genetics
- nutrition = folic acid deficiency
- disease = diabetes
- toxins = alcohol, smoking
- infections = rubella, toxoplasmosis, CMV, sphilis
- radiation
- unknown
what are the embryological stages of the CNS?
7 days = implantation
22-28 days = neural tube formation
4-8 weeks = organogenesis of the brain and brainstem
8 weeks-birth = migration of cells; neuroblasts
10 weeks = CNS susceptible to destructive lesions
20 weeks on = myelination
how is the neural tube formed?
the neural plate of the embryo rolls up in the middle into a tube
there’s two openings = anterior and posterior neuropore
the anterior neuropore will close and become the brain while the posterior will close and become the spinal cord (sometimes this doesn’t happen properly and you end up with things being messed up)
during what period of gestation can you get neural tube defects?
22-28 days
what are the two anterior neuropore defects?
- anencephaly
- encephalocele
these have to do with the brain because the anterior neuropore is what closes to form the brain
what are the 3 posterior neuropore defects?
- myeloeningocele
- meningocele
- spina bifida
these have to do with the spinal cord because the posterior neuropore is what closes to form the end of the spinal cord
what is anencephaly?
anterior neuropore defect
normal from the eyes down but the whole top of the head is missing and basically all the brain is missing too
the skull is missing because the brain induces the development of the dura and skull so all you have is skin and hair on the top of the head
what is encephalocele?
anterior neuropore defect
a skull defect leads to the brain growing out of the skull covered only by skin and hair
so the brain is growing outside the skull like there’s literally a whole extra head looking thing sticking outside the head….
what happens is that brain formed normally but the skull didn’t finish forming so there was a hole in the skull that the brain just grew out of….
the surgeon can go put the brain back in and if not a big part of the brain is sticking out usually the kids are fine
what is a meningocele?
posterior neuropore defect
open bone that leads to a cystic, skin covered lesion on the back that contains meningeal elements only
what is a myelomeningocele?
posterior neuropore defect
cystic, skin covered lesion on the back that contains meningeal elements AND neural elements –> spinal cord is involved too
what is spina bifida?
posterior arches of the vertebrae are missing
so relatively speaking this isn’t that bad because everything else is normal
over time patients might have back pain but other than that they can have normal life
what is the chiari type 2 malformation?
- hydrocephalus = ventricle is way too big
- widened foramen magnum which causes the cerebellum to go down into the spinal canal because the opening is too wide! this is a downward herniation of the cerebellar vermis and medulla
- notch in cervical spinal cord
we don’t really understand why or how this happens or the order of how it happens..
what is organogenesis?
the formation of all the brain structures
this happens after the neural plate folds into the neural tube and now you have the anterior neuropore that’s going to become the brain
so now that you have a neural tube, you make a telencephalon, diencephalon, mesencephalon, myelecephalon etc. –> these go on to make the thalamus, hypothalamus, pons, etc.
when do the cerebral lobes form?
10 weeks
when do the midline structures of the brain form?
16 weeks
ex. corpus collasum
which disorders can occur during organogenesis?
organogenesis = 4-8 weeks
- holoproscencephaly
- agenesis of the corpus callosum
- olfactory aplasia
what is holoproscencephaly?
a disorder that can occur during organogenesis
a failure of the cerebrum to divide into two hemisphere and you just have one hemisphere
so it looks like the frontal lobes are just one frontal lobe because the brain never finished dividing
babies with this can grow up and lead a relatively good life but there is some cognitive impairment
what happens when there’s agenesis of the corpus callosum?
on top of the corpus callosum there’s supposed to be the singulate gyrus but without the corpus callosm it doesn’t develop
surprisingly this isn’t that bad and people are fine without it!
what happens with agenesis of the olfactory tracts?
there’s no gyri rectus; instead there’s sulci crossing the midline – this is because the gyrus rectus is induced by the olfactory tract
there’s also no cranial nerve 1
this just means the person can’t smell
what happens during cell migration?
so at this point you have your brain and spinal cord and they have all their structures like the thalamus and cerebellum etc. and now you just need to fill it with cells!
the cells are born by the ventricle surface and the neuroblasts migrate to the outer surface of the cerebrum by migrating up the radial glia
so as all their neuroblasts migrate you start to see sulci and gyri to form because there’s so many neuroblasts that the folds form to fit them all in
a variety of things can go wrong at this stage like the cells could just not migrate at all
what are the various disorders of cell migration?
- agyria
- pachygyria
- heterotopias
- polymicrogyria
what is agyria?
a disorder of neuroblast migration where no cells migrate at all
so you end up with no gyri at all and you have a smooth brain….
what is pachygyria?
a disorder of cell migration where some of the migrate
what is heterotopias?
a disorder of cell migration where the neuroblasts get half way and they quit so they end up in the wrong place
there’s collections of grey matter in the middle of the brain! that’s not right!! the neuroblasts just never made it to the cerebral cortex they only got half way
this can cause seizures; sometimes you can remove the heterotopia if it’s small enough
what is polymicrogyria?
a disorder of cell migration where there is a failure of normal culmination of cell migration
so the neurons got to the surface but couldn’t figure out how to make gyri so it’s just a hot mess
the gyri look super wrinkly and are divided into lots of little gyri….
patients with this condition are usually normal if it’s focal but if it’s complete polymicrogyria there there is extensive neurologic deficits
this is because this happened before the functions of the brain were assigned so the brain just assigned the functions to part of the brain that was normal
which conditions are classified as early destructive lesions?
- porencephaly
- schizencephaly
- hydranencephaly
these happen from 10-25 weeks of gestation
something is wrong with the vasculatory system and the brain is destroyed because it’s basically an intrauterine stroke and without macrophages (because they haven’t developed yet) the brain liquifies and goes away
what is porencephaly?
hole in the brain
what is schizencephaly?
schizm in the brain
what is hydranencephaly?
basically no brain, just meninges
if you hold the baby skull up to light it’s empty
what are examples of late destructive lesions?
- germinal matrix hemorrhage
- choroid plexus hemmorrhage
- parenchymal hemorrhage
- periventricular leucomalacia
they happen after the 25th week
what is a germinal matrix hemorrhage?
a late destructive lesions
the most metabolically active and vascular part of the brain is the germinal matrix because the neuroblasts are being made here!
if there’s hemorrhages in the germinal matrix it could rupture into the ventricle and kill the baby
what is a choroid plexus hemorrhage?
a late destructive lesions
it’s a hemorrhage in the choroid plexus which resides in the ventricles and forms CSF
so if it’s hemorrhaging then it could rupture and kill the baby
what is periventricular leucomalacia?
“soft white matter”
there are little infarcts in the white matter
in the adult it’s the grey matter that have the highest oxygen demands but in the fetus this isn’t true and there isn’t much going on in the cortex; it’s usually the germinal matrix or migrating cells that have the highest oxygen need
so you’re more likely to get a white matter infarct which surrounds the ventricles
which things qualify as birth trauma?
- tearing of the tentorium (not that bad)
- linear tears of white matter (not that bad because no axonal pathways yet)
- tears of the spinal cord and cerebellar peduncles (these are bad)
what does a baby’s brain look like with Down Syndrome?
Camera lucida drawings are where you trace out the projections of individual neurons
in a normal brain there’s lots of projections but in a down’s brain, these projections are very simple and there’s less synapses
- small brain
- reduced dendritic complexity
- premature and severe alzheimer disease (they all get it and in their 30s!)
what is hydrocephalus?
something blocked the flow of CSF so it’s backed up in the ventricles and they greatly expand and you get a baby with a ginormous head
the most common place is the cerebral aqueduct
in a baby it’s sort of okay because the skull isn’t fused so the skull just expands…..however with an older person or kid the brain will just get smashed against the skull and that’s bad
what are the causes of hydrocephalus?
- aqueduct of sylvius obstruction
- arachnoid granulations = the last thing the CSF does once it exits into the subarachnoid space then goes back to the brain and is resorbed into the sinus is susceptible to blockage
- tumors
- increased CSF flow (rare)
- compensatory to brain atrophy (like with aging)
what causes delayed myelination in babies?
it’s a response to almost any chronic insult like poor nutrition, chronic disease or GI problems
no long term sequelae if you can fix the primary problem the baby will eventually catch up
