Chapter 17 Flashcards
How do neural tube defects arise?
From incomplete closure of the neural tube (neural plate invaginates early in gestation to form the neural tube, which runs along the cranial-caudal axis of the embryo. The wall of the neural tube forms the CNS tissue, the hollow lumen forms the ventricles and spinal cord canal, and the neural crest forms the peripheral nervous system)
Associated with low folate levels
How are neural tube defects detected in utero?
Elevated alpha fetoprotein (AFP) levels in the amniotic fluid and maternal blood
Anencephaly (absence of the skull and brain) results in what clinical finding?
Maternal polyhydramnios (since fetal swallowing of amniotic fluid is impaired)
What is the most common cause of hydrocephalus in newborns?
cerebral aqueduct stenosis (between 3rd and 4th ventricle)
Describe the flow of CSF
Produced by the choroid plexus lining the ventricles, flows into the lateral ventricles and then into the 3rd ventricle via the interventricular foramen of Monro
From the 3rd to 4th via the cerebral aqueduct
From the 4th ventricle into the subarachnoid space via the foramine of Magendie and Luschka
What is a Dandy-Walker malformation?
Congenital failure of the cerebellar vermis to develop presenting as a massively dilated 4th ventricle (posterior fossa) with an absent cerebellum (accompanied by hydrocephalus)
What is a Arnold-Chiari Malformation?
Congential downward displacement of the cerebellar vermis and tonsils through the foramen magnum causing obstruction of the CSF flow resulting in hydrocephalus
What is a syringomyelia?
Cystic degeneration of the spinal cord arising with trauma or in association with a type I Arnold Chiari Malformation (usually at C8-T1)
How might a syringomyelia present?
Presents as sensory loss of pain and temp with sparing of fine touch and position sense in the upper extremities due to involvement of the anterior white commissure of the spinothalamic tract with sparing of the dorsal columns
Syrinx expansion can result in involvement of other spinal tracts leading to:
Muscle atrophy and weakness with decreased muscle tone and impaired reflexes due to damage to lower motor neurons of the anterior horn
Horner syndrome with ptosis, miosis, and anhidrosis due to disruption of the lateral horn of the hypothalamospinal tract
How does poliomyelitis cause disease?
Damage to the anterior horns due to poliovirus presenting with lower motor neuron signs including flaccid paralysis with muscle atrophy, fasciculations, weakness with decreased muscle tone, impaired reflexes, and negative Babinski sign
What is Werdnig-Hoffman Disease?
A variant of spinal muscular atrophy- inherited degeneration of the anterior motor horn (AR) presenting as floppy baby (death occurs within a few yrs of birth)
What is amyotrophic lateral sclerosis (ALS)?
Degenerative disorder of upper AND lower motor neurons of the corticospinal tract with atrophy and weakness of the hands as an early sign (lack of sensory impairment distinguishes ALS from syringomyelia)
Mostly sporadic in middle aged adults
What is a known cause of one form of inherited amyotrophic lateral sclerosis (ALS)?
Zinc-copper superoxide dismuatase (SOD1) mutation- causes free radical injury to neurons
What is Friedreich-Ataxia?
What causes Friedreich-Ataxia?
AR due to expansion of an unstable trinucleotide repeat (GAA) in the frataxin gene (frataxin is needed for mitochondrial iron regulation; loss results in buildup with free radical damage)
Presents in early childhood, and pts are wheelchair bound within a couple yrs at most
What is the major association of Friedreich-Ataxia?
hypertrophic cardiomyopathy
What is meningitis?
Inflammation of the leptomeninges (meninges layers: dura, arachnoid, and pia; the pia and arachnoid are collectively called the leptomeninges)
What are the most common causes of meningitis by age?
Neonates: GBS, E. Coli, and Listeria
Adults: N. meningitis, S. pneumo
Coxsackievirus
Fungi (immunocompromised)
How long can neurons survive without glucose?
Undergo necrosis within 3-5 minutes
What are the major etiologies of global cerebral ischemia?
Low perfusion (e.g. atherosclerosis)
Acute decrease in blood flow (e.g. cardiogenic shock)
Chronic hypoxia (e.g. anemia)
Repeated episodes of hypoglycemia (e.g. insulinoma)
The clinical features of global cerebral ischemia are based on duration and magnitude of the insult. Explain
Mild ischemia results in transint confusion with prompt recovery, while severe ischemia results in diffuse necrosis (can cause vegetative state)
What are the most susceptible cells to ischemic injury?
Pyramidal neurons of the cerebral cortex (layers 3,5,6) leading to laminar necrosis
Pyramidal neurons of the hippocampus (long term memory)
Purkinje cells in the hippocampus
What is the definition of an ischemic stroke?
Regional ischemia of the brain resulting in focal neurologica deficits lasting 24+ hrs (less than 24 hrs= TIA)
What are the major types of ischemic stroke?
Thrombotic (atheroscleosis typically occurs at branch pts.; results in a pale necrosis)
Embolic stroke (most commonly from the left heart (a fib)- results in a hemorrhagic infarct at the cortex periphery)
Lacunar stroke
Describe Lacunar strokes
Occurs secondary to hyaline arteriolosclerosis, a complication of HTN
Ischemic stroke leads to _____ necrosis
liquefactive
Describe the main histo findings of an ischemic stroke based on time
Eosinophilic change in the neuron cytoplasm (red neurons) at 12 hrs
Necrosis (24 hrs), infiltation by neutrophils (days 1-3), and microglial cells (days 4-7 days), gliosis (2-3 weeks)
Describe the progression of intracerebral hemorrhage
Bleeding into brain parenchyma classically due to ruputre of Charcot-Bouchard microaneurysms of the lentriculostriate vessels (complication of HTN) and most commonly in the BASAL GANGLIA
Presents as severe HA, N/V, and eventual coma
An LP of a suspected subarachnoid hemorrhage would show what?
xanthochromia (yellow hue due to bilirubin)
How is MS diagnosed?
MRI reveals plaques
LP showing increased lymphocytes, increased immunoglobulins with oligoclonal IgG bands on electrophroesis, and myelin basic protein
What are some morphological findings of Alzheimer Disease?
Cerebral atrophy with narrowing of gyri, widening of sulci, and dilation of the ventricles
Neuritic plaques- extracellular core comprised of AB amyloid with entangled neuritic processes
Neurofibrillary tangles- intracellular aggregates of fibers composed of hyperphosphorylated tau protein
Neurofibrillary tangles
Neurofibrillary tangles
Describe glioblastoma multiforme
A malignany, high-grade tumor of astrocytes (most common primary malignant CNS tumor in adults)
usually arises in the cerebral hemispheres, and classically crosses the corpus callosum (butterfly lesion)
How is the histo of glioblastoma multiforme described?
regions of necrosis surrounded by tumor cells (pseudopalisading) and endothelial cell proliferation
GFAP positive; poor prognosis
What is a meningioma?
Benign tumor of arachnoid cells (most common benign CNS tumor in adults; more common in women)
look for a dural tail
Meningioma- described as a whorling pattern
psammoma bodies may be present
Describe schwannomas
Benign tumor of Schwann cells (often at the cerebellopontine angle and involving CN VII or VIII)
S-100 positive
Bilateral with NF-2
Describe oligodendrocytes
Malignant tumor of oligodendrocytes; imaging reveals a calcified tumor in white matter usually involving the frontal lobe (may cause seizures)
Fried-egg appearance on biopsy
What is a pilocytic astrocytoma?
A benign tumor of astrocytes (most common CNS tumor of children; usually arising in the cerebellum)
Imaging reveals a cystic lesion with a mural lobule
Biopsy of a pilocytic astrocytoma would classically show what?
Rosenthal fibers, thick eosinophilic processes of astrocytes
GFAP positive
The histo of medulloblastoma classically shows what?
small, round blue cells and possibly Homer-Wright rosettes
What is an ependymoma?
Malignant tumor of ependymal cells (usually in children) most commonly in the 4th ventricle
Perivascular pseudorosettes are a classic biopsy findings
