Congenital Melanocytic Nevus

Synonyms

Pigmented birth mark.

Epidemiology

The incidence is 0.2-2.1% in newborns. The incidence in large/giant congenital nevi is 0.005%. M:F= 1:1.17 - 1:1.4.

Definition

Collection of pigmented melanocytes in epidermis and dermis, usually present at birth, often associated with increased numbers of hair follicles.

Aetiology & Pathogenesis

Embryonal acquired mutation in the tyrosine kinase NRAS (Neuroblastoma RAS) in cells of the neural crest. Rarely, lesions may appear up to 2 years after birth. They are not different from congenital nevi, but sometimes are called tardive congenital nevi.

Signs & Symptoms

Circumscribed brown to black nodules or plaques, often with hypertrichosis. At the very early beginning after birth it may be even a macular lesion which then increase in volume.

Localisation

Trunk, head, as well as extremities.

Classification

Estimated size of nevus at birth expected to reach in adulthood:

Type I. Size 1-3 cm: common and harmless, 1:100.
Type II. Size 3-20 cm: uncommon, 1:1000-1:20000, rarely malignant change.
Type III. Size >20 cm: usually on the trunk (giant or bathing trunk naevus) 1:500000, risk of melanoma 3-5%.

Laboratory & other workups

Measurement of thickness by ultrasound could be useful.

Dermatopathology

Accumulation of melanocytes at the epidermal-dermal junction and in the dermis, often extending deeply, into the lower reticular dermis, subcutaneous fat and fascia, and even deeper.

Course

Permanent, life-long. No tendency to regression.

Complications

In giant naevi, risk of leptomeningeal melanosis. Lumbosacral: spina bifida, myelomeningocele. Increased risk of neurological disorders in giant nevi in > 40 cm or those is expected to reach this size in adulthood. In patients with congenital nevi type III, the mean age at diagnosis of developing melanoma is around 15 to 16 years.

Diagnosis

Clinical features, histology.

Differential diagnosis

Haemangioma, dermatofibroma, melanoma, melanocytic nevi, plexiform neurofibromas, see also chapter 3.1.5 Melanocytic nevus.

Prevention & Therapy

Type II and Type III Congenital nevi should have an annual follow-up or whenever parents see significant changes.

Small lesions: none needed, excision if desired.

Medium-sized lesions: consider excision after puberty.

Large lesions: dermabrasion shortly after birth (does not influence leptomeningeal melanosis), close clinical follow-up and excision of suspicious areas.

The decision to remove a lesion is linked to the risk of melanoma and the cosmetically disfiguring appearance.

3.1.2 Congenital Melanocytic Nevus