Congenital Melanocytic Nevi

 < 1.5 cm = small


image > 1.5 cm to < 20 cm = medium

image > 20 cm = large


• Risks, particularly for large congenital melanocytic nevus
image ~ 5% risk of developing cutaneous melanoma

image Neurocutaneous melanosis




Microscopic




• Melanocytes usually extend into lower reticular dermis and sometimes subcutaneous tissue
• Infiltration of

image Arrector pili muscle

image Adnexal structures

image Nerves

• Clustering around blood vessels

• Cells become smaller and more dispersed with depth

• Nodular proliferations (more common in large nevi)
image Based in dermis, no epidermal involvement or necrosis


Top Differential Diagnoses




• Acquired melanocytic nevi: Not present at birth
image Usually limited to upper 1/2 of reticular dermis)

• Atypical (dysplastic/Clark) melanocytic nevi: Not present at birth
image Junctional component shows cytologic atypia, bridging, and lateral extension beyond intradermal cells, which are often limited to upper 1/2 of reticular dermis

• Malignant melanoma arising in congenital nevus
image In differential diagnosis of dermal nodular proliferation, very rare if age is < 1 yr

image Well-demarcated, highly cellular nodules of atypical epithelioid to spindled cells with cytologic atypia; nuclear pleomorphism and necrosis often present

image
Congenital Melanocytic Nevus
This light tan, medium-sized congenital melanocytic nevus, which measured 10 x 8 cm, has coarse terminal hairs within it. The patient also has keratosis pilaris image and an acquired melanocytic nevus image.


image
Compound, Predominantly Intradermal Congenital Nevus
This congenital compound nevus has nests of larger, more heavily pigmented superficial cells image progressing to smaller, less pigmented cells deeper in the dermis image, consistent with maturation with dermal descent.

image
Congenital Intradermal Nevus
This congenital intradermal melanocytic nevus extends deeply throughout the dermis, with clustering of melanocytes image around vessels and adnexa.

image
Congenital Junctional Nevus
Some congenital nevi, especially if small, may be purely junctional, with scattered nests image and single melanocytes image at the tips and sides of rete, mimicking an acquired junctional melanocytic nevus.


TERMINOLOGY


Synonyms




• Giant/bathing suit/garment-type melanocytic nevus

Apr 24, 2017 | Posted by in PATHOLOGY & LABORATORY MEDICINE | Comments Off on Congenital Melanocytic Nevi
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