Neuro Flashcards
What is rhombencephalosynapsis.
Name 2 imaging features and 1 association
Definition: congenital/developmental agenesis/hypogenesis of the cerebellar vermis, and dorsal fusion of the cerebellar hemispheres, dentate nuclei and cerebellar peduncles
Imaging features:
- as above
- diamond/keyhole shaped 4th ventricle on axial imaging
- horizontal cerebellar folia
- may have hydrocephalus (secondary to aqueductal stenosis)
Associations:
- VACTERL
Broadly describe cerebellar hypoplasia and vermian dysgenesis types/distribution, and name 2 associations
Reduction in volume in the cerebellum (may be global or focal), with normal shape, and stable over time. Can be primarily vermian, global, unilateral, ± brainstem involvement.
Morphology
- Vermian hypoplasia/aplasia
- Dandy-Walker
- Rhombencephalosynapsis
- Global cerebellar hypoplasia
- Genetic abnormalities and syndromes
- CMV infection, prenatal drug exposure, prematurity
- Cerebellar and brainstem involvement
- Pontocerebellar hypoplasia (PCH), Joubert syndrome
- Unilateral hypoplasia
What are the types of schizencephaly and list 2 associated abnormalities
“Transmantle” (aka ext from cortical surface of brain to the ventricles - ie pia to ependyma) cleft lined by grey-matter (GM)
- Open lip - cleft has clear CSF space separating 2 sides
- Closed lip - no clear CSF space, cleft walls closely opposed (better prognosis)
Associations:
* Associated abnormalities
* GM heterotopia adjacent to cleft
* Contralateral polymicrogyria
* Absent septum pellucidum (esp if bilateral clefts)
* Septo-optic dysplasia
Reactions of Neurons to Injury
Morphology
ACUTE Neuronal Injury (“Red Neurons”)
- Spectrum of changes that accompany acute CNS hypoxia/ischemia or
other acute insults.
- Earliest morphological marker of neuronal cell death (12-24 hrs post irreversible insult).
The morphologic features consist of:
- shrinkage of the cell body
- pyknosis of the nucleus
- disappearance of the
nucleolus
- Loss of Nissl substance, with intense eosinophilia of the cytoplasm.
SUBACUTE ANF CHRONIC neuronal injury (“degeneration”):
- Due to progressive disease (neurodegenerative diseases (Alzheimer’s/Amyotrophic lateral Sclerosis).
- Histology:
*Cell loss, often selectively involving functionally related
groups of neurons
*Reactive gliosis.
At an early stage, the
cell loss is difficult to detect; the associated reactive glial
changes are often the best indicator of neuronal injury. For
many of these diseases, there is evidence that cell loss occurs
via apoptotic death.
AXONAL REACTION
- Change in cell body during axon regeneration
- Best seen in anterior horn cells when cut
- Increased protein synthesisassociated
with axonal sprouting. This is reflected in enlargement and
rounding up of the cell body, peripheral displacement of the
nucleus, enlargement of the nucleolus, and dispersion of Nissl
substance from the center to the periphery of the cell (central
chromatolysis).
**Neuronal damage may be associated with a wide range of
subcellular alterations in the neuronal organelles and cytoskel-
eton.
- Neuronal inclusions may occur as a manifestation of
aging, when there are intracytoplasmic accumulations of complex lipids (lipofuscin), proteins, or carbohydrates.
- Abnormal cytoplasmic deposition of complex lipids and other substances also occurs in genetically determined disorders of metabolism in which substrates or intermediates accumulate
Viral infection can lead to abnormal intranuclear inclusions, as
seen in herpetic infection (Cowdry body), cytoplasmic inclu-
sions, as seen in rabies (Negri body), or both nucleus and
cytoplasm as in cytomegalovirus infection.
Some degenerative diseases of the CNS are associated with
neuronal intracytoplasmic inclusions, such as neurofibrillary
tangles of Alzheimer disease and Lewy bodies of Parkinson
disease; others cause abnormal vacuolization of the perikaryon
and neuronal cell processes in the neuropil (Creutzfeldt-Jakob
disease
Key Concept - Cellular Pathology of the CNS
Cellular Pathology of the Central Nervous System
■ Each cellular component of the nervous system has a
distinct set of patterns of response to injury.
■ Neuronal injury commonly results in cell death, either by
apoptosis or necrosis. Loss of neurons that is difficult to
detect without formal quantification may still contribute to
dysfunction.
■ Astrocytes show morphologic changes including hypertrophy of the cytoplasm, accumulation of intermediate filament protein (GFAP), and hyperplasia.
■ Microglia, the resident monocyte-lineage population of the
CNS, proliferate and accumulate in response to injury.
Cerebral Oedema
Cerebral edema (more precisely, brain parenchymal
edema) is the result of increased fluid leakage from blood
vessels or injury to various cells of the CNS.
Vasogenic
* Caused by ↑ Vascular permeability or disruption of the blood-brain barrier
* Fluid shifts from vascular space Interstitial space of the brain
* Causes
Localised: Inflammatory focus (infection/abscess), Haemorrhage or tumour
Cytotoxic
* Blood brain barrier remains intact
* Due to injury of neuronal, glial or endothelial cells
Causes
* Generalised Hypoxia/ischemia
* Metabolic derangement which alters normal membrane ion gradient
* Can also get Interstitial oedema around Lateral ventricles due to Hydocephalus
Hydrocephalus
Accumulation of excessive CSF in the Ventricular System
Causes
- Impaired flow/resportption
- Excessive production (RARE) - accompanies tumours of the choroid plexus
Consequences:
- Infants: Expansion of head (Increased HC)
- Expansion of Ventricles + Raised ICP
Types
- Non-communicating (obstructive):
Obstructed drainage of ventricle. entricles expand proximal to obstruction
- Communicating: Ventricles communicate with Subarachnoid space - Entire ventricular system enlarges
- Hydrocephalus ex vacuo: COmpensatory expansion of ventricular volume secondary to loss of brain parenchyma
Raised ICP
Causes
- Increased volume of intracranial contents
- Haemorrhage
- Tumour
- Hydrocephalus
- Cerebral Oedema
Types of Herniation
- Subfalcine (cingulate)
CIngulate gyrus displaced under Falx to contralateral side
COmpresses ACA and its branches - Transtentorial/Uncal:
Medial aspect of temporal lobe herniates under the ternorum cerebelli
Can compress CN III or PCA - Tonsillar:
Cerebellar tonsils herniates through Foramen Magnum.
Causes brainstem compression
Cerebral Malformations and Developmental Disorders
■ Malformations may be associated with single gene muta-
tions, larger scale genetic alterations, or exogenous
factors.
■ Overall, the earlier in development a malformation
occurs, the more severe the morphologic and functional
phenotype.
■ Neural tube defects are associated with failure to close or
inappropriate reopening of the developing neural tube; these
range from incidental findings to severe manifestations.
■ Cortical development depends on proper orchestration of
progenitor cell proliferation in the germinal matrix and
migration of progenitors upwards into the developing
cortex. Disruption of these processes can alter the size,
shape, and organization of the brain.
■ Malformations involving the posterior fossa are typically
distinct from those which affect the cerebral
hemispheres
Patterns of Vascular Injury in CNS trauma
Diffuse axonal Injury Morphology
- Diffuse axonal injury is characterized by widespread, often
- asymmetric axonal swellings that appear within hours of the
- injury and may persist for much longer. The swelling is best
- demonstrated with silver impregnation techniques or with
- immunoperoxidase stains for axonally transported proteins,
- such as amyloid precursor protein and α-synuclein. Later,
- increased numbers of microglia areas are seen in damaged
- areas of the cerebral cortex, and subsequently there is degen-
- eration of the involved fiber tracts
Acute Subdural Haematoma morphology
Grossly, acute subdural hematomas appear as a collection
of freshly clotted blood along the brain surface, without exten-
sion into the depths of sulci (Fig. 28-12). The underlying brain
is flattened and the subarachnoid space is often clear. Usually,
venous bleeding is self-limited and the resulting hematoma is
broken down and organized over time.
This most often occurs
in the following sequence:
* Lysis of the clot (about 1 week)
* Growth of fibroblasts from the dural surface into the hema-
toma (2 weeks)
Early development of hyalinized connective tissue (1 to 3
months)
Typically, the organized hematoma is firmly attached by
ingrowing fibrous tissue to the inner surface of the dura and is
free of the underlying arachnoid, which does not contribute to
healing. The lesion can eventually retract as the granulation
tissue matures until only a thin layer of reactive connective
tissue remains (“subdural membranes”). In other cases,
however, multiple recurrent episodes of bleeding occur (chronic
subdural hematomas), presumably from the thin-walled
vessels of the granulation tissue. The risk of repeat bleeding is
greatest in the first few months after the initial hemorrhage.
Spinal Cord Injury
The histologic features of traumatic injury of the spinal cord are
similar to those found at other sites in the CNS. At the level of
injury the acute phase consists of hemorrhage, necrosis, and
axonal swelling in the surrounding white matter. The lesion
tapers above and below the level of injury. In time central
areas of neuronal destruction becomes cystic and gliotic;
cord sections above and below the lesion show secondary
ascending and descending wallerian degeneration, respec-
tively, involving the long white-matter tracts affected at the site
of trauma.
Cerebrovascular Disease - Key Concepts
■ Stroke is the clinical term for acute-onset neurologic defi-
cits resulting from hemorrhagic or obstructive vascular
lesions.
■ Cerebral infarction follows loss of blood supply and can
be widespread or focal, or affect regions with the least
robust vascular supply (boundary zones).
■ Focal cerebral infarcts are most commonly embolic; with
subsequent dissolution of an embolism and reperfusion, a
nonhemorrhagic infarct can become hemorrhagic.
■ Primary intraparenchymal hemorrhages typically are due
to either hypertension (most commonly in white matter,
deep gray matter, or posterior fossa contents) or cerebral
amyloid angiopathy.
■ Spontaneous subarachnoid hemorrhage usually is caused
by a structural vascular abnormality, such as an aneurysm
or arteriovenous malformation.
Saccular Aneurysms
