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Brain Lesions (Lesions on the Brain) (cont.)

Brain Lesions Causes

From the above description of brain lesion types, it is evident that the different types are arranged, in general, according to different mechanisms that lead to brain cell changes which produce various brain lesions. The causes, however, can be further categorized. The following is a list of causes containing more specific subsets and descriptions:

  • Trauma: penetrating or blunt. Blunt trauma may be further subdivided to include with or without skull fracture. Trauma results in damaged or destroyed brain tissue with immediate and/or delayed (hours to days, usually) symptoms.

  • Infectious: Brain lesions caused by a wide variety of pathogenic agents ranging from viruses, bacteria, fungi, and parasites. Some may develop symptoms quickly over hours to days (such as in viral and bacterial meningitis) or over many years (such as in the parasitic infection Cysticercosis).

  • Malignant: Malignant brain lesions subtypes are termed "primary" if they arise from the brain tissue cells (such as gliomas and medulloblastomas) and "secondary" if they originate in other body organs and spread (metastasis) to the brain (such as lung, breast, and colon cancers). Secondary brain lesions are more common than primary brain lesions. Some lesions develop fairly fast (weeks to months), while others may develop more slowly. In addition, malignant lesions are often graded, which means they are assigned a number (I, II, II or IV) based on their appearance under a microscope. Grade I tumors are less aggressive and tend to grow and spread more slowly, while grade IV tumors are the highly aggressive and tend to grow and spread more rapidly.

  • Benign (non-cancerous): Brain lesions composed of abnormally growing cells which are non-cancerous (though a rare few may contain some cancer cells, mainly grade I). They may cause symptoms if they become large and compress other normal brain tissue or interfere with the blood supply to the brain. They usually develop slowly (for example, meningiomas).

  • Vascular: Three subtypes of vascular brain lesions exist; 1) arteriovenous malformations (weak vascular areas that may leak or burst, causing blood to leak into brain tissue), 2) abnormal growth of vessels in the brain (hemangioblastomas associated with von Hippel-Lindau disease), and 3) the most frequently encountered vascular problem, strokes (also termed cerebral vascular accidents or CVA's). Most strokes are caused by clots (about 85%) which cause brain cell damage or death by reducing or cutting off the blood supply to areas of the brain. Except for the long-term development of diseases like von Hippel-Lindau, vascular brain lesions generally produce symptoms within minutes to hours.

  • Genetic: Errors in human DNA or certain DNA sequences in the genetic makeup of some individuals can lead to brain lesions, such as neurofibromatosis or familial British dementia. Most of these lesions develop over years.

  • Immune: The individual's immune system mistakenly attacks and attempts to destroy brain tissue components, such as myelin (a sheath surrounding nerve cells). The resulting scar tissue can be seen in multiple sclerosis, for example. These types of lesions usually progress in development over years.

  • Brain cell death or malfunction: The cause of certain brain lesions, like those seen with Parkinson's disease, are due in part to the malfunction and death of brain cells that produce dopamine. However, the underlying cause may be related to genetics, toxic exposures, or various other combinations of potential causes. Development usually progresses over years.

  • Plaques (deposits of substances in brain tissue): Deposits of materials such as Lewy bodies, amyloid plaques, and neurofibrillary tangles or bundles in brain tissue are associated with several diseases, most notably Alzheimer's disease. However, it is not clear whether the deposits are the primary cause or if they are the secondary results of an underlying (and as of yet) unidentified cause. Development usually progresses over years.

  • Ionizing radiation: X-rays, gamma rays and other types of radiation, when intense enough or if acquired sequentially in high levels, can disable and destroy brain cells, as well as other cell types.

Many brain lesions may have more than a single cause and are often associated with multiple risk factors, which some researchers believe may be the cause, although a direct link to the risk factor(s) is often difficult or unlikely to be proven by researchers.

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