A lesion is any localized damage or abnormal alteration of tissue in a living organism, resulting from disease, injury, developmental anomaly, or other processes. The word derives from the Latin laesio, meaning "injury." Lesions can be apparent to the naked eye (gross lesions) or detectable only by microscopy, and they occur in animals, humans and plants. In clinical practice the term often serves as a neutral descriptor until a specific diagnosis—such as infection, trauma, or neoplasm—is established. Medical resources commonly use the term to describe sites needing further assessment.
Types and appearance
Lesions are described by their shape, size, depth and tissue involved. In dermatology, for example, common morphological categories include:
- macule and patch (flat discolorations)
- papule and plaque (raised solid areas)
- nodule and tumor (deeper or larger masses)
- ulcer and erosion (loss of surface tissue)
- cyst (fluid- or semi-solid-filled cavity)
Beyond appearance, clinicians classify lesions by cause: traumatic, infectious, inflammatory, vascular, degenerative, congenital or neoplastic (benign or malignant).
Diagnosis and management
Evaluation begins with history and physical examination, noting onset, progression and symptoms. Imaging (X-ray, CT, MRI, ultrasound), laboratory tests and tissue sampling (biopsy) help determine the lesion's nature. Treatment addresses the underlying cause and may range from observation and medical therapy to surgical removal. Prognosis depends on location, extent and etiology; for instance, a small benign skin lesion differs markedly from a malignant brain lesion in potential outcomes.
Lesions in plants follow similar descriptive principles and can indicate infections, nutrient deficiencies, or environmental damage. Understanding the lesion's context is essential for accurate diagnosis, appropriate management and communication between clinicians, pathologists and researchers.