The Nævi and Ichthyosis

Abstract

A naevus is a congenital vascular or pigmentary growth in the skin. The lesion results from a deposit of embryonic tissue and the evidence may not become apparent until later in life. The lesions develop from both the ectoderm and mesoderm. There are two main groups: (1) the vascular group due to hyperplasia of the blood or lymph vessels, and (2) the nonvascular group composed of epidermal or connective tissue elements. The vascular naevi may originate from (1) blood vessels (hæmangioma), or from (2) the lymphatics (lymphangioma). The melanocytes in pigmented naevi are now believed to be neurogenic in origin and to come from the neural crest.