Lesion

Key takeaways

Lesion belongs to biology; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Lesion to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Lesion from memory before moving on to harder problems.

Reference excerpt

A lesion is any damage or abnormal change in the tissue of an organism, usually caused by injury or diseases. The term lesion is derived from the Latin laesio, meaning "injury". Lesions may occur in plants and animals.

Location Lesions are often classified by their tissue types or locations. For example, "skin lesions" or "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. 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 which side of the heart is affected and the diameter of the artery in which they form.

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". 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 lesion, which can be caused by excitatory amino acids like kainic acid 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, such as a small area of the brain that has turned to fluid following a stroke. 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 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, so damage to the tissue should be minimal.

Research with humans Humans with brain lesions are often 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 is often used in cognition and neuroscience-related tests to imitate the effect.

Research with animals Using animal subjects gives researchers the ability to study lesions in specific body parts, 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.

Types There is no designated classification or naming convention for lesions. Because lesions can occur anywhere in the body and their definition is so broad, the varieties of lesions are virtually endless. Generally, lesions may be classified by their patterns, sizes, locations, or 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, are named after the lesion's discoverer, Anton Ghon. The characteristic skin lesions of a varicella zoster virus infection are called chickenpox. Lesions of the teeth are usually called dental caries, or "cavities".

Notable lesions

Illustrations

Worked examples

Example 1 — a first encounter with Lesion

Start with the simplest possible case. Write down what Lesion claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In biology, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Lesion before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Lesion ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Lesion

In research: Lesion appears in biology research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Lesion in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Lesion is common in secondary-school and first-year university syllabi. It links to neighbouring topics Anatomical pathology, Lesions, Medical signs, so understanding it makes those chapters shorter.
In everyday life: Look for Lesion outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

How to study Lesion in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Lesion means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Lesion out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Lesion in simple terms?

A lesion is any damage or abnormal change in the tissue of an organism, usually caused by injury or diseases. The term lesion is derived from the Latin laesio, meaning "injury".

Why does Lesion matter?

Because it connects several biology ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Lesion?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Lesion.