Nevus

Overview
  • A nevus, known as a "mole", is a common benign neoplasm of pigment-forming cells, termed "nevocytes" whose cell of origin is likely the melanocyte. Nearly all individuals display a handful of nevi.
Morphology
  • Gross Morphology
    • Nevi appear as well-demarcated flat macules or raised papules with a light to dark brown color. Those present in the dermis may appear blue. Nevi are typically symmetric in shape, display a regular border, and are uniformly colored throughout. Suspicion should be directed toward those thta do not fit this description or appear clearly different from a patients other nevi.
  • Histological Morphology
    • Nevi are histologically categorized based on their location within the skin. "Junctional Nevi" are those present at the bottom of rete ridges within the epidermis at the level of the dermo-epidermal junction. "Intradermal Nevi" are completely enclosed within the dermis while "Compound Nevi" span the epidermis and dermis.
    • Nevocytes typically grow in nests and bundles. Their morphology changes as they grow down into the dermis with superficial cells being rounder, producing pigment, and possessing a clear cytoplasm while deeper cells become more spindle-shaped and lose pigment production. This histological "maturation" is an important characteristic which distinguishes nevi from melanoma, the most important disease in the pathological differential diagnosis.