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A lesion is any damage or abnormal change in the tissue of an organism, usually caused by
disease A disease is a particular abnormal condition that negatively affects the structure or function of all or part of an organism, and that is not immediately due to any external injury. Diseases are often known to be medical conditions that a ...
or
trauma Trauma most often refers to: *Major trauma, in physical medicine, severe physical injury caused by an external source *Psychological trauma, a type of damage to the psyche that occurs as a result of a severely distressing event *Traumatic inju ...
. ''Lesion'' is derived from the Latin "injury". Lesions may occur in plants as well as animals.


Types

There is no designated classification or naming convention for lesions. Since lesions can occur anywhere in the body and the definition of a lesion is so broad, the varieties of lesions are virtually endless. Generally, lesions may be classified by their patterns, their sizes, their locations, or their causes. They can also be named after the person who discovered them. For example, Ghon lesions, which are found in the lungs of those with
tuberculosis Tuberculosis (TB) is an infectious disease usually caused by '' Mycobacterium tuberculosis'' (MTB) bacteria. Tuberculosis generally affects the lungs, but it can also affect other parts of the body. Most infections show no symptoms, ...
, are named after the lesion's discoverer, Anton Ghon. The characteristic
skin lesion A skin condition, also known as cutaneous condition, is any medical condition that affects the integumentary system—the organ system that encloses the body and includes skin, nails, and related muscle and glands. The major function of th ...
s of a
varicella zoster virus Varicella-zoster virus (VZV), also known as human herpesvirus 3 (HHV-3, HHV3) or ''Human alphaherpesvirus 3'' (taxonomically), is one of nine known herpes viruses that can infect humans. It causes chickenpox (varicella) commonly affecting chil ...
infection are called ''
chickenpox Chickenpox, also known as varicella, is a highly contagious disease caused by the initial infection with varicella zoster virus (VZV). The disease results in a characteristic skin rash that forms small, itchy blisters, which eventually scab ...
''. Lesions of the teeth are usually called
dental caries Tooth decay, also known as cavities or caries, is the breakdown of teeth due to acids produced by bacteria. The cavities may be a number of different colors from yellow to black. Symptoms may include pain and difficulty with eating. Complicat ...
.


Location

Lesions are often classified by their tissue types or locations. For example, a "skin lesion" or a "
brain lesion Neurotrauma, brain damage or brain injury (BI) is the destruction or degeneration of brain cells. Brain injuries occur due to a wide range of internal and external factors. In general, brain damage refers to significant, undiscriminating ...
" 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 The central nervous system (CNS) is the part of the nervous system consisting primarily of the brain and spinal cord. The CNS is so named because the brain integrates the received information and coordinates and influences the activity of all p ...
is called a central lesion, and a lesion in the
peripheral nervous system The peripheral nervous system (PNS) is one of two components that make up the nervous system of bilateral animals, with the other part being the central nervous system (CNS). The PNS consists of nerves and ganglia, which lie outside the brai ...
is called a peripheral lesion. 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 The coronary arteries are the arterial blood vessels of coronary circulation, which transport oxygenated blood to the heart muscle. The heart requires a continuous supply of oxygen to function and survive, much like any other tissue or organ ...
. 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.


Cause and behavior

If a lesion is caused by a
tumor A neoplasm () is a type of abnormal and excessive growth of tissue. The process that occurs to form or produce a neoplasm is called neoplasia. The growth of a neoplasm is uncoordinated with that of the normal surrounding tissue, and persists ...
, it can be classified as ''
malignant Malignancy () is the tendency of a medical condition to become progressively worse. Malignancy is most familiar as a characterization of cancer. A ''malignant'' tumor contrasts with a non-cancerous ''benign'' tumor in that a malignancy is not s ...
'' or ''
benign Malignancy () is the tendency of a medical condition to become progressively worse. Malignancy is most familiar as a characterization of cancer. A ''malignant'' tumor contrasts with a non-cancerous ''benign'' tumor in that a malignancy is not s ...
'' after analysis of a
biopsy A biopsy is a medical test commonly performed by a surgeon, interventional radiologist, or an interventional cardiologist. The process involves extraction of sample cells or tissues for examination to determine the presence or extent of a dise ...
. A benign lesion that is evolving into a malignant lesion is called "premalignant". Cancerous lesions are sometimes classified by their growth kinetics, such as the Lodwick classification, which characterizes classes of bone lesions. Another type is an
excitotoxic In excitotoxicity, nerve cells suffer damage or death when the levels of otherwise necessary and safe neurotransmitters such as glutamate become pathologically high, resulting in excessive stimulation of receptors. For example, when glutamate re ...
lesion, which can be caused by excitatory
amino acids Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although hundreds of amino acids exist in nature, by far the most important are the alpha-amino acids, which comprise proteins. Only 22 alpha am ...
like
kainic acid Kainic acid, or kainate, is an acid that naturally occurs in some seaweed. Kainic acid is a potent neuroexcitatory amino acid agonist that acts by activating receptors for glutamate, the principal excitatory neurotransmitter in the central nervo ...
that kill neurons through overstimulation.


Size and shape

Lesion size may be specified as ''gross'', meaning it is visible to the unaided eye, or '' histologic'', meaning a microscope is needed to see it. 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 A stroke is a disease, medical condition in which poor cerebral circulation, blood flow to the brain causes cell death. There are two main types of stroke: brain ischemia, ischemic, due to lack of blood flow, and intracranial hemorrhage, hemorr ...
. Lesions may also be classified by the shape they form. This is the case with many
ulcers An ulcer is a discontinuity or break in a bodily membrane that impedes normal function of the affected organ. According to Robbins's pathology, "ulcer is the breach of the continuity of skin, epithelium or mucous membrane caused by sloughing o ...
, which can have a
bullseye Bullseye or Bull's Eye may refer to: Symbols * ◎ (Unicode U+25CE BULLSEYE), in the Geometric Shapes Unicode block * (Unicode U+0298 LATIN LETTER BILABIAL CLICK), the phonetic symbol for bilabial click Animals and plants * Bull's Eye, '' Eury ...
or 'target' appearance. A
coin lesion A lung nodule or pulmonary nodule is a relatively small focal density in the lung. A solitary pulmonary nodule (SPN) or coin lesion, is a mass in the lung smaller than three centimeters in diameter. A pulmonary micronodule has a diameter of less th ...
as seen in an X-ray has the appearance of a coin sitting on the patient's chest.


Research using lesions

Brain lesions may help researchers understand brain function. 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. ''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 the researcher wishes to study. As such,
transcranial magnetic stimulation Transcranial magnetic stimulation (TMS) is a noninvasive form of brain stimulation in which a changing magnetic field is used to induce an electric current at a specific area of the brain through electromagnetic induction. An electric pulse gener ...
is often used in cognition and neuroscience-related tests to imitate the effect.


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 The hippocampus (via Latin from Greek , 'seahorse') is a major component of the brain of humans and other vertebrates. Humans and other mammals have two hippocampi, one in each side of the brain. The hippocampus is part of the limbic syste ...
in object recognition and object recency.Albasser, Amin, Lin, Iordanova, Aggelton. Evidence That the Rat Hippocampus Has Contrasting Roles in Object Recognition Memory and Object Recency Memory


Notable lesions


See also

*
Ablation Ablation ( la, ablatio – removal) is removal or destruction of something from an object by vaporization, chipping, erosive processes or by other means. Examples of ablative materials are described below, and include spacecraft material for ...


References


External links

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