Melanocytic lesions

Melanocytic lesions are commonly encountered in dermatopathology and an area which causes some difficulty, i.e. it is hard to decide in some cases whether a lesion is benign (e.g. Spitz nevus) or malignant (malignant melanoma).

Overview

Identifying melanocytes

• Pigmented.
• Clear cytoplasm.

Benign lesions

Name	Clinical	Gross	Microscopic	Key feature	Image
Lentigo simplex	< 40 years	small flat pigmented lesion	sender rete with melanocytes; no nests of melanocytes; no dermal melanocytes	no nests, epidermis only
Junctional melanocytic nevus	usu. sun exposed skin, unusual in >50 years	small flat (uniformly) pigmented lesion	nests of melanocytes at tips of rete, no dermal melanocytes	nests in epidermis
Compound melanocytic nevus		small slightly raised (uniformily) pigmented lesion	nests of melanocytes at tips of rete and in dermis; dermal melanocytes lack nucleoli, lack mitoses and "mature with depth" -- see Note 1.	benign nests in dermis & epidermis
Intradermal melanocytic nevus	Clinical DDx: fibroepithelial polyp (skin tag), basal cell carcinoma	raised, non-pigmented lesion	nested & individual melanocytes - only in dermis, +/- multinucleation, +/-pseudovascular spaces	nested & individual melanocytes - only in dermis
Spitz nevus (epithelioid and spindle-cell nevus)	Children & adolescents	usu. non-pigmented	spindled, epithelioid or mixed melanocytes, long axis of nests perpendicular to surface, superficial mitoses common	long axis of nests perpendicular to surface	Spitz nevus (drmihm.com)
Pigmented spindle cell nevus of Reed (AKA Pigmented spindle cell nevus)	women in teens & 20s; location: shoulder, pelvic girdle region	Pigmented +++, small size	heavily pigmented spindle cells in epidermis & dermis, form "basketweave" pattern, nests (???)	nests of heavily pigmented spindle cells	Reed nevus - collection of images (histopathology-india.net)
Blue nevus	usu. head & neck or extremities	blue flat or slightly raised lesion	dermal lentil-shaped nests, mix of spindle or dendritic or epithelioid cell morphology, nests btw collagen	lentil-shaped (ovoid) nests btw collagen bundles
Cellular blue nevus	congenital or acquired; usu. scalp or butt	blue flat or raised lesion	deep dermis; cells lack nucleoli; biphasic: (1) epithelioid cells with pale cytoplasm, (2) pigmented spindle cells +/- melanophages	dermal lesion with pigmented spindle cells & epithelioid cells
Congenital-pattern nevi	congenital or acquired	small, intermediate (2-20 cm) or large	extend along dermal structures (e.g. nerves, hair shafts, ducts); lacks atypia; +/-mitoses	growth along dermal structures

Note 1:

• "Maturation" in the context of melanocytic lesions means (1) the cells get smaller with depth, (2) cells are less mitotic with depth.

Spitz nevus

• AKA epithelioid and spindle-cell nevus.

Epidemiology

• Children & adolescents.

Microscopic

Features:

• Architecture:
  • Nests of cells (spindle, epithelioid or spindle/epithelioid) - in both dermis and epidermis.
    • Nests are vertically arranged, i.e. the long axis of the nests are perpendicular to the skin surface.
      • Nest arrangement/orientation described as "cluster of bananas".
• +/-Hyperkeratosis (more keratin, i.e. thick stratum corneum).
• +/-Hypergranulosis (thick stratum granulosum).
• +/-Acanthosis (thick stratum spinosum).

Images:

• Spitz nevus - collection of images (drmihm.com).

See also

• Dermatopathology.
• Cytopathology.
• Non-malignant skin disease.