A lesion is any area of abnormal or damaged tissue in your body. It can be as minor as a small scrape on your skin or as serious as a tumor in an organ. Lesions show up anywhere: on the skin, in the brain, on blood vessels, in the liver, along the spine. Common examples include wounds, ulcers, sores, cysts, abscesses, and tumors. A lesion can be benign (not cancerous) or malignant (cancerous), which is why doctors take the word seriously even when the cause turns out to be harmless.
Types of Skin Lesions
Skin lesions are the most visible and most common type. Doctors sort them into categories based on how they look and feel:
- Macules are flat, discolored spots smaller than 10 mm. They sit flush with the skin surface, so you can see them but can’t feel a raised edge. Freckles and flat moles are macules.
- Papules are small raised bumps, also under 10 mm. Unlike macules, you can feel them when you run a finger across the skin. A pimple is a papule.
- Nodules are firm lumps that extend deeper into the skin or the tissue underneath it. They’re larger than papules and often feel solid to the touch.
- Vesicles are small fluid-filled blisters under 10 mm. A chickenpox blister or a cold sore is a vesicle.
Larger versions of these exist too. A flat discolored area bigger than 10 mm is called a patch. A raised, fluid-filled blister bigger than 10 mm is a bulla. These size distinctions help doctors communicate precisely about what they’re seeing.
Lesions Inside the Body
Internal lesions form in organs, blood vessels, and the central nervous system. You can’t see or feel most of them directly, which is why they’re typically found through imaging. Contrast-enhanced CT scans are one of the most common first-line tools for detecting internal lesions, especially in the liver, because the way a lesion absorbs contrast dye reveals important clues about what it is. MRI is widely used for the brain and spine.
A surprising number of internal lesions are discovered by accident. When doctors scan you for one problem, they sometimes spot something unrelated. These incidental findings are far more common than most people realize. About 22% of brain MRIs and 22% of spine MRIs reveal an unexpected lesion. Chest CT scans turn up incidental findings in roughly 45% of cases. Most of these are benign. An adrenal gland lesion found by accident, for example, is almost always harmless and simply monitored with a follow-up scan at three to six months, then annually for a year or two.
Brain Lesions and Their Effects
Brain lesions deserve their own discussion because their symptoms depend heavily on location. A lesion in one part of the brain can cause completely different problems than a lesion a few centimeters away.
The frontal lobe controls planning, attention, and movement. Lesions here can cause mood swings, difficulty finding words, weakness on one side of the body, or loss of your sense of smell. Temporal lobe lesions affect how you process sound and understand language. Parietal lobe lesions can cause numbness, tingling, confusion between left and right, or difficulty writing and doing math.
Lesions in the occipital lobe, which handles vision, can lead to blindness that originates in the brain rather than the eyes, an inability to see color, or difficulty recognizing faces. Cerebellum lesions affect coordination and balance, causing dizziness, tremors, slurred speech, or double vision. Brainstem lesions are particularly serious because the brainstem controls heart rhythm, breathing, and blood pressure.
Common causes of brain lesions include multiple sclerosis, lupus, infections (bacterial, fungal, or parasitic), strokes, and traumatic brain injuries like concussions.
What Causes Lesions to Form
Lesions develop through a handful of core mechanisms, and understanding these helps explain why treatment varies so widely.
Inflammation is one of the most common drivers. In autoimmune diseases like multiple sclerosis, the immune system attacks healthy tissue and creates areas of damage. The body sends immune cells to the site, which release compounds that break down the protective coating around nerve fibers. In a related condition called neuromyelitis optica, antibodies trigger a chain reaction involving the complement system (part of your immune defense) that destroys cells in the spinal cord and optic nerves.
Infection is another major trigger. Bacteria, viruses, fungi, and parasites can all damage tissue and create lesions at the site of infection. These range from a skin abscess caused by staph bacteria to brain lesions caused by a fungal infection.
Reduced blood flow, or ischemia, starves tissue of oxygen. This is what happens during a stroke: a blocked blood vessel cuts off blood supply and the affected brain tissue dies, forming a lesion. Swelling in tissue can also compress tiny blood vessels and indirectly cause the same kind of damage.
Physical trauma creates lesions through direct mechanical force. A cut, a burn, or a concussion all produce areas of damaged tissue. And abnormal cell growth, whether benign or malignant, creates lesions that can press on surrounding structures and cause symptoms even when they aren’t cancerous.
Benign vs. Malignant Lesions
The most important question about any lesion is whether it’s benign or malignant. The distinction comes down to four characteristics: how organized the cells look, how fast they grow, how they grow, and whether they spread.
Benign lesions are made of well-organized cells that closely resemble normal tissue. They grow slowly, expand outward in a contained way (often surrounded by a capsule), and stay put. A lipoma, which is a soft lump of fat under the skin, is a classic benign lesion.
Malignant lesions look disorganized under a microscope. Their cells are abnormal in size and shape, they divide rapidly, and they invade surrounding tissue without any capsule to contain them. The defining trait of malignancy is metastasis: the ability to spread to distant parts of the body through the blood or lymphatic system. Pathologists look for specific red flags like an unusually high ratio of nucleus to cell size, irregular nuclear shapes, and areas of dead tissue within the lesion.
When doctors can’t determine whether a lesion is benign or malignant based on imaging alone, they take a biopsy, removing a small sample of tissue for examination under a microscope. For many incidental findings, though, the appearance on imaging is distinctive enough that a biopsy isn’t needed, and the lesion is simply monitored over time to confirm it isn’t changing.
How Lesions Are Treated
Treatment depends entirely on the type, location, cause, and severity. A small benign skin lesion like a mole may need no treatment at all. A cyst that’s causing discomfort might be drained or surgically removed. Infected lesions like abscesses typically need antibiotics, and sometimes drainage.
For inflammatory lesions caused by autoimmune conditions, the goal is controlling the immune response. This usually means medications that reduce inflammation and slow the disease process, which can prevent new lesions from forming and limit damage from existing ones.
Malignant lesions are treated based on cancer type and stage, with approaches that range from surgical removal to radiation and systemic therapies. Benign tumors that press on important structures, like a brain tumor causing vision problems, may also require surgical removal even though they aren’t cancerous.
Internal lesions found incidentally and deemed likely benign are often managed with watchful waiting: periodic imaging to make sure they aren’t growing or changing. This approach spares you unnecessary procedures while keeping a safety net in place.