Sean Klepper M.D.
Artur Zembowicz M.D....
The following discussion refers to common nevi in general, whether junctional, dermal or compound, and includes differences between the subtypes when applicable.
- Common benign melanocytic proliferations which increase in number with age until approximately the third decade of life and subsequently tend to regress as the patient ages
- A greater number of nevi tends to occur in lighter-skinned individuals.
- Nevi on the palms and soles, nail beds and conjuntivae are more common in blacks.
- All common nevi are typically well-circumscribed round to oval lesions a few millimeters in diameter with relative symmetry.
- Common nevi sometimes have a verrucous appearance reminiscent of seborrheic keratosis and sometimes contain coarse hairs.
- General clinical appearances of the various types of common nevi are:
- Junctional: Uniform brown macules
- Compound: Variable elevation, typically lighter in color than junctional nevi
- Dermal (intradermal): Generally more elevated, lighter brown than compound nevi or skin colored, sometimes dome shaped or papillomatous
- Common nevi typically begin as junctional nevi, then evolve into compound and finally dermal nevi before ultimately involuting.
- Junctional nevus: Nests of nevus cells are confined to the epidermis, with nests mainly located at the tips of the rete ridges.
- Compound nevus (most common type): Nests of nevus cells within the epidermis as well as nevus cells within the dermis. The junctional component does not typically extend peripherally beyond the dermal component, in contrast to atypical nevi and melanomas.
- Dermal (intradermal) nevus: Nevus cells are confined to the dermis.
- Features consistent with a benign nevus of common type are:
- Cells arranged in cohesive nests with relative uniformity of the nevus cells and fairly regular spacing of the nests
- Nests located at the tips of the rete ridges (for junctional and compound nevi)
- Lack of pagetoid spread
- No extension of nevus cells deeper than the upper reticular dermis (for compound and dermal nevi)
- Maturation of nevus cells as they go deeper into the dermis (for compound and dermal nevi). See below.
- No or only rare mitoses in dermal nevus cells
- No more than minimal pleomorphism
- A key feature of benignity in nevi that contain a dermal component (compound and dermal nevi) is that of maturation: the nevus cells change their morphology as they go deeper into the dermis. Three morphologic subtypes of nevus cells are recognized, from superficial to deep:
- Type A (epithelioid): These cells are located within the epidermis and/or upper dermis. They exist in tightly cohesive nests and have an epitheliod appearance (abundant cytoplasm and polygonal shape), nuclei with uniform basophilic chromatin with a ground glass appearance and sometimes small nucleoli, and tend to produce melanin.
- Type B (lymphocytoid): These cells are found in the papillary dermis, deep to the type A cells. They form less defined nests and cords of cells. They resemble lymphocytes because of the fact that they possess much less cytoplasm than type A cells, and are much less likely to produce melanin.
- Type C: These cells are found deep to the type B cells. They are elongate to spindled, resembling fibroblasts or Schwann cells, and are separated by a delicate fibrous stroma.
- Sometimes multinucleated giant cells are encountered within a completely typical common nevus. These should not be misinterpreted as atypical cells.