Diseases of Nervous System

Fatima Obeidat, MD

I. Patterns Of Injury In the Nervous System

A. Features of Neuronal Injury

1. Red neurons: Within 12 hours of an irreversible ischemic injury, acute neuronal injury becomes evident on H&E stain and characterized by:

a. Shrinkage of the cell body, pyknosis of the nucleus and Loss of Nissl substance

b. Angulated nucleus and disappearance of nucleolus

c. Intense eosinophilia of the cytoplasm

RED NEURONS

2. Specific intranuclear inclusionsa. Neurofibrillary tangles in Alzheimer diseaseb.. Lewy bodies in Parkinson diseasec. Inclusions in viral infections:Example: Nigri bodies in Rabies

Nigri bodies

B. Astrocytes in Injury and repair1.Astrocytes are the principal cells for repair and scar formation in the brain Gliosis:-The astrocytes undergo hypertrophy and hyperplasia in response to injuryI. In early gliosis, astrocytes are called gemistocytes and Characterized by:A. Enlarged nucleus with prominent nucleolusB. Stout ramifying processes extend from the cell

C. The scanty cytoplasm becomes abundant and pinkII. In long standing gliosis ,there will be extensive

formation of astrocytic glial filaments called gliotic scar

III. Chaslin’s gliosis in subpial layer in epilepsy• Note:- Unlike else in the body fibroblasts participate to a

limited extent in healing in brain and in the following situations:

1. Brain abscess2. Penetrating trauma

2. Rosenthal fibers- Are thick elongated , eosinophilic aggregates found

in processes of astrocytes , composed of Large amounts of glial fibrillary acidic protein (GFAP)and Ubiquitin and are prominent in the following:

a. Chronic gliosisb. Pilocytic astrocytoma(inside the tumor) c. In the tissue surrounding:1. Hemangioblastoma2. Craniopharyngioma

Gemistocytes Rosenthal fibers

3. Spinal syrinxd. Alexander’s disease: Activating mutation in GFAP

gene3. Corpora amylacea: - Are spherical laminated bodies composed of

polyglucosan- Most abundant close to pia, around blood vessels

and adjacent to ependymal lining- Their accumulation is associated with aging and in

response to neuronal loss- Stain positive with PAS

Corpora amylacea

C. Microglial cells

- Are bone marrow derived cells- Function as the resident phagocytes of the CNS- Microglial cells take on the appearance of activated

macrophages in areas of1. Demyelination2.Organizing infarct3. Hemorrhage

NotesI. Rod cells : are microglial cells having elongated

nuclei in cases of neurosyphilisII. Microglial nodules: are aggregates of microglial

cells around brain injury (viral infection) such as in HIV encephalitis

II.Neuronophagia: aggregation of microglial cells around and phagocytosing injured neurons such as in poliomyelitis

Microglial Nodules Neuronophagia

D. Ependymal cells- Have limited capacity to regeneration- Once the ependynal surface is broken due to

stretching by ventricular dilatation or inflammation, it is probably not repaired

- Typical ependymal reactions to injury includea. Atrophy and reactive cell loss b. Formation of ependymal discontinutiesc. subventricular gliosis (subventricular glial nodules)

- Which appear as tiny clear granules(granular ependymitis) and best seen in the floor of the fourth ventricle.

II.Edema, Hydrocephalus and Herniation

A. Brain Edema

-Is the accumulation of excess fluid within the brain parenchyma

-There are two main types that may occur together mainly after generalized injury

I. Vasogenic edema- Is the most common type - Affects mainly the white matter- Occurs when the integrity of the blood brain

barrier

is disrupted , allowing fluid to shift from the vascular compartment into the extracellular spaces of the brain and can be

A. Localized in a. Brain tumors either primary or metastatic ( it is

more severe in metastatic brain tumors)- In brain tumors, the blood vessels may be abnormal

with fenestrations in the capillary wallb. Cerebral abscess

Vasogenic edema surrounding glioblastoma

B.. Generalized In late stages of ischemic encephalopathy due to

damage of endothelial cells by ischemiaII. Cytotoxic edema : - An increase in intracellular fluid secondary to

neuronal or glial membrane injury- The extracellular space is reduced - The blood brain barrier is intact - Caused by ischemia to the brain

- it occurs because energy failure disables the Na/K pump system allowing large amounts of sodium accompanied by water to enter the cells

- Mainly affects the gray matter

III. Interstitial Edema:- It occurs in Patients with acute obstructive high

pressure hydrocephalus- Due to damage to the ependymal lining by

stretching - Which leads to an increase in the water content in

the periventricular white matter - It is most pronounced around the frontal and

occipital horns of the lateral ventricles

B. Hydrocephalus :- - Means accumulation of excessive CSF within the

ventricular system as a result of a disturbance in its secretion, circulation or absorption

a. Most commonly due to impaired flow or resorption of CSF

b. Overproduction of CSF, seen in choroid plexus papilloma is only rarely causes hydrocephalus.

Types of hydrocephalusI.Non-communicating hydrocephalus

(obstructive): - It occurs when a lesion impedes the free passage of the CSF from the ventricles to the subarachnoid space, causing dilatation of the portion of the CSF pathway that lies proximal to the obstructions; Causesa. Obstructive hydrocephalus affecting the lateral

ventricles only may be caused by colloid cyst of the third ventricle

Or intraventricular hemorrhage or suprasellar tumors invaginating the anterior part of the third ventricle

b. Obstruction of the posterior end of the third ventricle and aqueduct may be due to aqueductal stenosis or tumors of the pineal region

c. Lesions obstructing the fourth ventricle such as ependymoma

d. Lesions of the cerebellum such as medulloblastioma may produce sufficient distorsion of the the fourth ventricle

e. Obstruction of the outlet of the fourth ventricle at level of formaina of Lushcka and Magendiemay result from acute inflammatory exudate related to meningitis, sarcoidosis

II. Communicating hydrocephalus, : - Refers to the abnormality in which there is free

passage of CSF from within the ventricular system into the subarachnoid space

-Causesa. Defects in the subarachnoid space such as fibrosis in

leptomeningeal infection and hemorrhage from saccular aneurysms

B. Defects in absorption of CSF at the arachnoid granulations such as

1. congenital deficiency of arachnoids' granulation2. Increased cerebral venous pressureC. Overproduction of CSF by choroid plexus

papillomaD. Idiopathic

QUIZ

•MENTION NAMES OF THE LAYERS OF THE NEOCORTEX