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General Pathology 601 for Dental Students Nervous System
Nitya Ghatak, MD
Objectives | Terms | Basic Pathologic Reactions Etiology & Pathology Selected Diseases Objectives
Other Important Terms Basic Pathologic Reactions of Neural Tissue Regardless of the cause, destruction of neural tissue is followed by mononuclear phagocytes mostly derived from peripheral blood. Unlike many other organs, neurons and their processes in the CNS do not regenerate adequately. However, the peripheral nerves are capable of regeneration, under favorable conditions. Introduction to Basic Pathological Processes The basic pathologic processes affecting the nervous system are similar to those causing damage to other organs. However, because of the highly specialized structure and functions of the nervous system, the lesions caused by vascular insufficiency, infections, trauma, and tumors, among other causes, have special clinical and prognostic significance. The brain is often severely affected by general metabolic disorders, as well as by various toxic agents and nutritional deficiencies. In addition, nervous system diseases, such as multiple sclerosis and Alzheimer's disease, have an etiology and pathogenesis which are not known. The goal of these two lectures is to provide essential information about the basic pathologic reactions of neural tissue, and basic information about the etiology and pathology of the following:
Brief information about clinical approaches for these conditions is also provided. Cells of The Nervous System and Their Pathologic Reactions
1. Increased Intracranial Pressure Because of the rigid encasement of the brain by the skull, an increased volume of the intracranial contents (space occupying lesions), under various conditions, gives rise to increased pressure, which may prove fatal. Some of the common causes of increased intracranial pressure are:
Brain edema accompanies other brain lesions and enhances intracranial pressure resulting in displacement of the brain from one intracranial compartment to another, a condition called herniation.
Brain injury represents the most serious consequence of head trauma responsible for a major portion of the fatalities in automobile accidents. Several types of lesions are seen:
The brain is particularly vulnerable to deprivation of oxygen. The entire brain may suffer from hypoxia in circumstances such as cardiac or respiratory failure, shock, carbon monoxide poisoning. Usually, hypoxia affects large neurons in many areas of the brain. The irreversibly damaged neurons appear shrunken with bright pink cytoplasm and pyknotic nuclei. Pathologic changes in the brain secondary to vascular abnormality occur in two forms: InfarctionDue to vascular occlusion from a thrombosis or embolism; the most common predisposing cause of thrombosis is atherosclerosis of the major arteries (carotid and vertebral) and their large branches. The embolic materials are usually derived from the heart or carotid arteries in the neck. The part of the brain supplied by the occluded artery becomes infarcted. In the early stage, the infarcted area appears pale and soft. Within several weeks to months the infarcted area is converted to a cystic cavity. Microscopically, the early changes consist of coagulative necrosis followed by the removal of the necrotic debris by macrophages derived from peripheral blood monocytes. The infarcts caused by embolic occlusion are often hemorrhagic. Hemorrhage Another type of spontaneous hemorrhage, mostly in the subarachnoid space, occurs as a result of ruptured aneurysms arising at the junction of the major arteries at the base of the brain. They are called berry or saccular aneurysms. These outpouchings of the arterial walls occur at the sites of congenitally deficient smooth muscle and elastic layers. The clinical features and prognosis of various vascular lesions of the brain depend on the anatomic location, extent and the nature of the lesions. A cerebral infarction involving large area of a hemisphere is usually not fatal in the short run; but the patient is left with a major deficit, usually hemiplegia. Intracerebral hemorrhage in general, carries poor prognosis. Rupture of saccular aneurysms is a serious condition. However, early diagnosis and surgical treatment may be life saving. The brain is vulnerable to infections by various pathogenic organisms such as bacteria, virus, fungi and protozoa. Infections predominantly involve the meninges with variable extension of the brain tissue resulting in leptomeningitis. Sometimes, infections primarily affect the brain parenchyma; for example brain abscess, tuberculoma, viral encephalitis.
Tumors of the CNS account for about 9% of all primary neoplasms and comprise a diverse group in patients of all ages. The biological behavior of these tumors differs in many ways, from that of tumors in other organs. It is important to note that histologically benign tumors may be fatal. Classification and Nomenclature of CNS Tumors:
Common primary brain tumors
7. Selected Diseases of the Nervous System 1. Alzheimer's Disease--degenerative; the major cause of dementia in the elderly; main pathologic change is generalized atrophy of brain with neurofibrillary tangles and senile plaques in many parts of the brain; although it has recently become the subject of intense investigation, the cause remains unknown. 2. Multiple Sclerosis--chronic; often disabling; onset in young adulthood in most cases; the pathology is characteristic and consists of sharply demarcated areas of demyelination in the CNS with special predilection for the optic nerve and periventricular region; the cause is not known, although, it is generally thought to be immunologically mediated. 3. Parkinson's Disease--relatively common disorder in the middle-aged and elderly; the major pathologic changes are seen in the pigmented neurons of the substantia nigra in the midbrain; neurons in this area contain intracytoplasmic inclusions called Lewy bodies. 4. Amyotrophic Lateral Sclerosis (ALS)--fatal; selective degeneration of motor neurons.5. Wernicke's Disease--thiamine deficiency usually seen in alcoholic patients; there are focal lesions in the hypothalamus and brain stem; alcohol also adversely affects the nervous system in several other ways. Digital Legends for Labs 601 Home | Syllabus | Differential Diagnosis Updated September 5, 2007
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