The term "nevus" implies a localized, permanent skin malformation. If it is a localized "new growth" (neoplasm), then it is a skin "nevoid tumor". The dividing line is hazy and controversial and has lead to confusing nomenclature. Some of them would be referred to as "birth marks".

• congenital melanocytic nevus: (carries a risk of melanoma)...a "mole" composed of melanocytes:
  • clues: Have linear rows of dermal cells tracking vessels and adnexal structures & within arrector muscle. Even a single nest of small melanocytes in a sebaceous lobule is a clue³.
  • common small nevi
  • Mongolian spot (located over sacrum): dermal melanocytes
  • nevus of Ota (located over face and eye): dermal melanocytes and spotty epidermal freckle-type hyperpigmentation (nevus fuscoceruleus ophthalmomaxillaris)
  • nevus of Ito (located on shoulder): dermal melanocytes and spotty epidermal freckle-type hyperpigmentation
  • bathing trunk nevus (animal pelt nevus): combination excessive hair and dermal nevus cells.
• birth mark (flat & can't feel it):
  • pigment type:
    • increased pigment:
      1. nevus spilus (when large = cafe-au-lait spot); macular epidermal hyperpigmentation
    • decreased pigment:
      1. nevus depigmentosus
  • vascular type
    • nevus flammeus (port wine stain)
    • strawberry mark
• organoid nevus (composed of two or more skin elements): (1) carries risk of later development of carcinoma in lesion...BCC most common; (2) large lesions may herald internal abnormalities (as in "linear epidermal nevus syndrome").
  • (spontaneous & skin only) nevus sebaceous: presents as an area of alopecia & biopsy shows increases of epidermis, sebaceous glands (inconspicuous until after puberty), papillary dermis, immature hair follicles; apocrine & sebaceous moreso after puberty and may get verrucoid.[S-05-5410; S-05-9164]
  • nevus sebaceous of Jadassohn (a neurocutaneous phakomatosis): as with above.
  • verrucous epidermal nevus (increases of epidermis and papillary dermis [a nevus sebaceous can be inevident prior to adolescence because hormones needed to bloom the glandular component]) [S07-10677].
  • nevus of Becker: a shoulder lesion of slight papillomatosis, epidermal hyperpigmentation, and hypertrichosis.
• vascular nevi: hemangioma; telangiectasia
• neurofibroma: 
  • common...sporadic
  • type of neurocutaneous phakomatosis (skin & brain lesions)
• mast cell nevus: mastocytoma
• histiocytic nevus: juvenile xanthogranuloma
• nevus of abnormal skin thickness:
  • cutis aplasia, focal
  • focal dermal hypoplasia of Goltz syndrome
  • connective tissue nevus
• nevus of abnormal hair (hair nevus...nevus pilosus) or lack of hair:
  • congenital triangular alopecia
  • patch of unusually strong/coarse hair for the location: "hair nevus"
  • patch of divergent hair color: focal pilar dichromism
  • patch of divergent texture:
    • wooly-hair nevus of Wise (kinky patch in straight hair scalp)
    • straight hair nevus (straight patch in kinky hair scalp)
• nevus of abnormal adnexal element:
  • too many or too few sebaceous glands (sebaceous nevus or asebaceous nevus)
  • too many or too few sweat glands
  • too many or too few hair follicles
  • too enlarged, plugged hair follicles (nevus comedonicus)
• other oddities:
  • skin-tag-like configurational abnormality: whereas a skin tag consists only of epidermal and & papillary dermal components, this "lesion" is exophytic and has all skin components (the ear is the most frequent site of congenital configuration abnormalities). [LMC-04-1229]
  • branchial-associated skin tags from ear to sternum

References:

1. A Guide to Dermatohistopathology, Pinkus & Mehregan, 2nd Ed., 1976.
2. Cutaneous Adnexal Tumors..., Wick MR & Swanson PE, 1991, 238 pages (BWD's office).
3. Ackerman AB, A Philosophy of Practice of Surgical Pathology: Dermatopathology as a Model, Ardor Scribendi, Ltd., 1999, 470 pages.

(posted 25 January 2004; latest addition 9 September 2007)