Naevus - Altmeyers Encyclopedia - Department Dermatology

Synonym(s)

Birthmark; Hamartoma of the skin; Melanocyte nevus; Times

Definition
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The term "nevus" has 2 meanings:

As a pathogenetic term equivalent to " hamartoma of the skin". A nevus is a visible, sharply defined, often congenital, but also postnatally manifesting, long-term malformation of the skin or mucosa, which is characterized by excess, rarely also by underdevelopment or malformation, of one or more components of skin or mucosa, and which aetiopathogenetically represents a cutaneous mosaic (see also under malformation).
Furthermore, the term "nevus" also finds a general use for a true, benign, melanocytic tumor(melanocytic nevus - formerly also called nevus cell nevus).

Etiopathogenesis
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Hamartomas of the skin are caused by abnormal development of the epidermis with increased or decreased pigmentation and/or of the skin appendages, vessels (vascular hamartomas), nerves or connective tissue(connective tissue nevus). Various combinations of malformations are possible (organoid nevi). They are named after the predominant tissue type (e.g. sweat gland nevus).

Systematized hamartomas of the skin are those that are distributed over a body region. Systematized hamartomas of the skin usually follow the Blaschko lines in their arrangement (classification see Tab. 1).

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Differential diagnosis
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The term nevus is to be distinguished from the term malformation as a defective development from an embryonic anlage (e.g. branchial remnants in lateral neck cysts).

In clinical terminology, the term "nevus" is used synonymously with an acquired pigmentary tumor ( melanocytic nevus). However, most melanocytic nevi are not nevi in the sense of a "hamartoma of the skin" but are true acquired pigment cell tumors. For differential diagnosis see below. Melanocytic nevus.

Tables
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Classification of the nevi (n. Altmeyer 2015)

Melanocytic hamartomas	Melanocytic hamartomas	Epidermal	Café-au-lait spots
			Nevus spilus
		Dermal	Nevus bleu
			Mongolian spot
			Nevus fuscocoeruleus ophthalmomaxillaris
			Nevus fuscocoeruleus deltoideoacromialis
	Melanocytic hamartoma	Epidermal/Dermal	Congenital melanocytic nevi
			Melanosis neurocutanea
			BK-mole syndrome

Non-melanocytic hamartomas	Epithelial hamartomas (are called "epidermal nevi")		Nevus verrucosus
			ILVEN
			Keratosis areolae mammae naeviformis
			CHILD syndrome
			Nevus sebaceus
			Nevus, sweat gland nevus
			Curly hair nevus
			Hair nevus
	Connective tissue hamartomas		Lumbosacral connective tissue nevus
			coarse nodular disseminated connective tissue nevus
			Nevus elasticus
	Vascular malformations		Nevus flammeus
			Angioma serpiginosum
			Nevus araneus
			Sturge-Weber-Krabbe syndrome
			Parkes-Weber syndrome
			Teleangiectasia hereditaria haemorrhagica
			Nevus anaemicus
	Hamartomas of the adipose tissue		Nevus lipomatosus Familial lipomas

Literature
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Blum A et al (2003) The dermoscopic classification of atypical melanocytic naevi (Clark naevi) is useful to discriminate benign from malignant melanocytic lesions. Br J Dermatol 149: 1159-1164
Dawson HA et al (1996) A prospective study of congenital melanocytic nevi: progress report and evaluation after 6 years. Br J Dermatol 134: 617-623
Happle R (2004) Cutaneous mosaics: patterns and molecular mechanisms. Dt Medical Journal 101: 1575-1580