lesion

A lesion is a localized area of tissue that has been altered by injury, disease, or a pathological process. The term is broad and does not specify a diagnosis; it simply denotes an abnormality in structure or function. The word derives from Latin laesio, meaning damage or injury, and is used in many medical specialties to describe visible changes on the surface or within organs.

Lesions may be classified by appearance, such as skin lesions like macules, papules, vesicles, ulcers, or by underlying process, including traumatic, infectious, inflammatory, neoplastic, ischemic, vascular, or congenital conditions. They can be external, as in dermatology, or internal, such as a brain lesion, liver lesion, or pulmonary lesion. Some lesions are benign, others may be precancerous or malignant; imaging and histopathology help determine this.

Diagnosis commonly involves clinical examination plus imaging techniques (ultrasound, CT, MRI) and, when indicated, tissue sampling for histopathology. In radiology, the term lesion denotes an area of altered density or signal that warrants further evaluation, rather than a definitive diagnosis.

Management depends on the underlying cause and may range from observation and medical therapy to biopsy, surgical excision, or radiation and chemotherapy for malignant lesions. Prognosis varies with the type, location, and etiology of the lesion.