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A lesion is any damage or abnormal change in the tissue of an organism, usually caused by disease or trauma. Lesion is derived from the Latin laesio "injury".^[1] Lesions may occur in plants as well as animals.

Types

There is no designated classification or naming convention for lesions. Because the definition of a lesion is so broad, the varieties of lesions are virtually endless. Although most frequently found in the mouth, on the skin, and in the brain, or anywhere where a tumor may occur,^{[citation needed]} lesions can occur anywhere in the body that comprises soft tissue or osseous matter. Generally, lesions may be classified by their patterns, their sizes, their locations, or their causes. Lesions are sometimes also named after the person who discovered them. Some lesions have specialized names, such as Ghon lesions in the lungs of tuberculosis victims, which is named after the lesion's discoverer.^[1] The characteristic skin lesions of a varicella zoster virus (VZV) infection are called chickenpox. Lesions of the teeth are usually called dental caries.

Location

Lesions are often classified by their tissue types or locations. For example, a "skin lesion" or a "brain lesion" are named for the tissue where they are found. If there is an added significance to regions within the tissue - such as in neural injuries where different locations correspond to different neurological deficits - they are further classified by location. For example, a lesion in the central nervous system is called a central lesion, and a lesion in the peripheral nervous system is called a peripheral lesion^[1] A myocardial lesion results from damage to the heart muscle, and a coronary lesion is a subtype that describes a lesion in the coronary arteries. Coronary lesions are then further classified according to the side of the heart that is affected and the diameter of the artery in which they form.^[2]

Cause and behavior

If a lesion is caused by a tumor it can be classified as malignant or benign after analysis of a biopsy. A benign lesion that is evolving into a malignant lesion is called "premalignant."^[1] Cancerous lesions are sometimes classified by their growth kinetics, such as the Lodwick classification, which characterizes classes of bone lesions.^[3] Another type of lesion is excitotoxic lesions, which can be caused by excitatory amino acids like kainic acid, which kill neurons through over-stimulation.

Size and shape

Lesion size may be specified as gross or histologic depending on whether they are visible to the unaided eye or require a microscope to see. A space-occupying lesion, as the name suggests, has a recognizable volume and may impinge on nearby structures, whereas a non space-occupying lesion is simply a hole in the tissue, e.g. a small area of the brain that has turned to fluid following a stroke.^[1]

Lesions may also be classified by the shape they form, as is the case with many ulcers, which can have a bullseye or 'target' appearance. A coin lesion is identifiable in an X-ray as appearing like a coin sitting on the chest of the patient.^[1]

Research using lesions

Lesions may be useful to researchers in understanding how the components of the brain produce cognition. Research involving lesions relies on two assumptions: that brain damage can affect different aspects of cognition independently, and that a locally damaged brain functions identically to a normal brain in its "undamaged" parts.^[4]

Sham lesion is the name given to a control procedure during a lesion experiment. In a sham lesion, an animal may be placed in a stereotaxic apparatus and electrodes inserted as in the experimental condition, but no current is passed, and therefore damage to the tissue should be minimal.

Research with humans

Humans with brain lesions are often the subjects of research with the goal of establishing the function of the area where their lesion occurred.

A drawback to the use of human subjects is the difficulty in finding subjects who have a lesion to the area which the researcher wishes to study.

Research with animals

Using animal subjects gives researchers the ability to lesion specific areas in the subjects, allowing them to quickly acquire a large group of subjects. An example of such a study is the lesioning of rat hippocampi to establish the role of the hippocampus in object recognition and object recency.^[5]

Notable lesions

See also

• Ablation

References

External links