is any abnormality in the tissue of an organism (in layman's terms, "damage"), usually caused by disease or trauma. Lesion
is derived from the Latin word laesio
which means injury
Because the definition of a lesion is so broad, the varieties of lesions are virtually endless. They are subsequently classified by their features. If a lesion is caused by a tumor
A tumor or tumour is commonly used as a synonym for a neoplasm that appears enlarged in size. Tumor is not synonymous with cancer...
it will be classified as malignant
Cancer , known medically as a malignant neoplasm, is a large group of different diseases, all involving unregulated cell growth. In cancer, cells divide and grow uncontrollably, forming malignant tumors, and invade nearby parts of the body. The cancer may also spread to more distant parts of the...
. Lesions may be classified by the shape they form, as is the case with many ulcers, which can have a bullseye
The bullseye, or bull's-eye, is the centre of a target , and by extension the name given to any shot that hits the bullseye...
or 'target' appearance. Their size may be specified as gross
depending on whether they are visible to the unaided eye or require a microscope to see.
An additional classification that is sometimes used is based on whether or not a lesion occupies space. A space-occupying lesion
, as the name suggests, occupies space 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, previously known medically as a cerebrovascular accident , is the rapidly developing loss of brain function due to disturbance in the blood supply to the brain. This can be due to ischemia caused by blockage , or a hemorrhage...
Some lesions have specialized names, like the Gohn lesions
in the lungs of tuberculosis victims. The characteristic skin lesions of a varicella-zoster virus (VZV) infection are called chickenpox
Chickenpox or chicken pox is a highly contagious illness caused by primary infection with varicella zoster virus . It usually starts with vesicular skin rash mainly on the body and head rather than at the periphery and becomes itchy, raw pockmarks, which mostly heal without scarring...
. Lesions of the teeth are usually called dental caries
Dental caries, also known as tooth decay or a cavity, is an irreversible infection usually bacterial in origin that causes demineralization of the hard tissues and destruction of the organic matter of the tooth, usually by production of acid by hydrolysis of the food debris accumulated on the...
Finally, lesions are often classified by their location. For example, a 'skin lesion' or a 'brain lesion'.
Lesions are caused by any process that damages tissues. Lesions can also be caused by metabolic processes, like an ulcer or autoimmune activity, as in the case with many forms of arthritis
Arthritis is a form of joint disorder that involves inflammation of one or more joints....
Lesions are sometimes intentionally inflicted during neurosurgery
Neurosurgery is the medical specialty concerned with the prevention, diagnosis, treatment, and rehabilitation of disorders which affect any portion of the nervous system including the brain, spine, spinal cord, peripheral nerves, and extra-cranial cerebrovascular system.-In the United States:In...
, such as the carefully placed brain lesion used to treat epilepsy
Epilepsy is a common chronic neurological disorder characterized by seizures. These seizures are transient signs and/or symptoms of abnormal, excessive or hypersynchronous neuronal activity in the brain.About 50 million people worldwide have epilepsy, and nearly two out of every three new cases...
and other brain disorders. (See Ablative brain surgery
Ablative brain surgery is the surgical ablation by burning or freezing of brain tissue to treat neurological or psychological disorders. The lesions it causes are irreversible....
Note that lesions are not limited to animals or humans; damaged plants are said to have lesions.