Birthmarks: Vascular and Pigmented Lesion Classification

Overview / Definition Birthmarks, also known as nevi, are skin lesions that are present at birth or appear shortly thereafter. They can be broadly classified into two main categories: vascular lesions, which are formed from blood vessels, and pigmented lesions, which are formed from melanocytes. These lesions vary significantly in appearance, location, and clinical significance. Epidemiology Birthmarks are prevalent in the pediatric population, with estimates suggesting that they occur in approximately 10-12% of newborns. Vascular birthmarks are more common than pigmented types, with hemangiomas being the most prevalent vascular lesion. Capillary malformations, such as port-wine stains, have a prevalence of about 0.3% in newborns. Congenital melanocytic nevi occur in about 1% of infants. Pathophysiology / Mechanism The pathophysiology of birthmarks varies between vascular and pigmented types. Vascular lesions arise from abnormal proliferation of blood vessels: Hemangiomas involve endothelial cell proliferation, leading to a mass of blood vessels. Port-wine stains are caused by a permanent dilation of capillaries. In contrast, pigmented lesions develop from an abnormal accumulation of melanocytes: Congenital melanocytic nevi result from the migration and proliferation of melanoblasts during embryogenesis. Acquired nevi occur due to sun exposure and genetic predisposition. Clinical Presentation Birthmarks present in various forms and can be classified based on their clinical appearance: Vascular lesions: Hemangiomas: Raised, red or purple lesions that may grow rapidly during the first year of life. Port-wine stains: Flat, pink to deep red lesions that do not regress and can be associated with syndromes. Pigmented lesions: Congenital melanocytic nevi: Brown or black lesions present at birth, varying in size. Acquired nevi: Common moles that develop in childhood and adolescence. Diagnosis / Workup The diagnosis of birthmarks is primarily clinical, based on the appearanc