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

• Clear or pigmented cytoplasm.
• +/-Nuclear pseudoinclusions.
• Epithelioid (superficial) or spindled (deep).

Benign lesions

Name	Key feature	Microscopic	Clinical	Gross	Image	Ref.
Lentigo simplex	no nests, epidermis only	slender rete with melanocytes; no nests of melanocytes; no dermal melanocytes	< 40 years	small flat pigmented lesion
Junctional melanocytic nevus	nests in epidermis	nests of melanocytes at tips of rete, no dermal melanocytes	usu. sun exposed skin, unusual in >50 years	small flat (uniformly) pigmented lesion
Compound melanocytic nevus	benign nests in dermis & epidermis	nests of melanocytes at tips of rete and in dermis; dermal melanocytes lack nucleoli, lack mitoses and "mature with depth" -- see Note 1.		small slightly raised (uniformily) pigmented lesion
Intradermal melanocytic nevus	nested & individual melanocytes - only in dermis	nested & individual melanocytes - only in dermis, +/- multinucleation, +/-pseudovascular spaces	Clinical DDx: fibroepithelial polyp (skin tag), basal cell carcinoma	raised, non-pigmented lesion
Spitz nevus (epithelioid and spindle-cell nevus)	long axis of nests perpendicular to surface, DE junction lesion	spindled, epithelioid or mixed melanocytes, long axis of nests perpendicular to surface, superficial mitoses common, +/-hyperkeratosis, +/-acanthosis, +/-hypergranulosis	Children & adolescents	usu. non-pigmented	Spitz nevus (drmihm.com)
Pigmented spindle cell nevus of Reed (AKA Pigmented spindle cell nevus)	nests of heavily pigmented spindle cells, DE junction lesion	heavily pigmented spindle cells in epidermis & dermis, form "basket weave" pattern, well-circumscribed	women in teens & 20s; location: shoulder, pelvic girdle region	Pigmented +++, small size	Reed nevus - low mag. (WC), Reed nevus - intermed. mag. (WC), Reed nevus - collection (histopathology-india.net)
Blue nevus	lentil-shaped (ovoid) nests btw collagen bundles, dermal lesion	lentil-shaped nests, mix of spindle or dendritic or epithelioid cell morphology, nests btw collagen	usu. head & neck or extremities; clinically confused with melanoma	blue flat or slightly raised lesion	Blue nevus (WC), Blue nevus - very low mag. (WC), Blue nevus - intermed. mag. (WC)
Cellular blue nevus	dermal lesion with pigmented spindle cells & epithelioid cells	deep dermis +/-subcutis extension; cells lack nucleoli; biphasic: (1) epithelioid cells with pale cytoplasm, (2) pigmented spindle cells +/- melanophages	congenital or acquired; usu. scalp or butt	blue flat or raised lesion
Congenital-pattern nevus	growth along dermal structures	extend along dermal structures (e.g. nerves, hair shafts, ducts); lacks atypia; +/-mitoses	congenital or acquired; large ones increased melanoma risk	small, intermediate (2-20 cm) or large
Dysplastic nevus (Clark's nevus)	melanocyte bridges, lamellar fibrosis	melanocytes "bridges" between sides of rete ridges, "lamellar fibrosis" (collagen deep to epidermis), mod. atypia	may be familial - precursor to melanoma	may have asymmetry in shape or pigmentation	Dysplastic nevus - low mag., Dysplastic nevus - high mag.
Halo nevus	lymphocytes +++	lymphocytes at perimeter of melanocytic; epidermal melanocytes not nested; may be dermal, epidermal or both	central zone of pigment

Note 1:

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

Melanocytic nevus

General

• Benign.
• Think melanoma.
• In common language: mole.

Clinical:

• ABCD = asymmetric, borders (irregular), colour (black), diameter (large).

Microscopic

Features:

• Symmetrical lesion.
• "Matures" with depth
  • Less cellular with depth
  • Less nuclear atypia with depth.
  • Smaller cells with depth.
  • Smaller nests with depth.
• Rare mitoses (superficial).
  • No deep mitoses.
• No destruction of surrounding structures.
• No nucleoli.

Subtypes

Compound melanocytic nevus

• In the dermis and epidermis - key feature.

Junctional melanocytic nevus

• In the epidermis - key feature.

Intradermal melanocytic nevus

• AKA dermal nevus, AKA intradermal melanocytic nevus.
• Only in the dermis - key feature.

Sign out

SKIN, PUNCH BIOPSY: 
	- INTRADERMAL MELANOCYTIC NEVUS.

Congenital-pattern nevus

• AKA congenital nevus.

General

• Congenital or acquired - thus "congenital-pattern".
• Large ones increase melanoma risk.
  • Small (<2 cm), intermediate (2-20 cm), large (>20 cm).

Microscopic

Features:

• Growth along dermal structures - key feature.
  • Nerves, hair shafts, ducts.
• Lacks nuclear atypia.
• +/-Mitoses.

Recurrent nevus

General

• Partially excised nevi. (???)

Microscopic

Features - three layers (often described as a "sandwich"):

1. Features of a compound nevus or junctional nevus.
2. Scar.
   • Thick collagen bundles arranged parallel to the skin surface.
3. Features of an intradermal nevus.

Pigmented spindle cell nevus

• AKA pigmented spindle cell nevus of Reed.

General

• Uncommon.
• Women in teens & 20s.
• Location: shoulder, pelvic girdle region.

Microscopic

Features:

• Nests of heavily pigmented spindle cells at dermal-epidermal junction - key feature.
  • Nevoid cells in epidermis & dermis - form "basket weave" pattern
• Well-circumscribed lesion.

Notes:

• No epithelioid nevus cells.

DDx:

• Spitz nevus.
• Melanoma.

Images:

• PSCN - low mag. (WC). *PSCN - intermed. mag. (WC). *Reed nevus - collection (histopathology-india.net).

Spitz nevus

• AKA epithelioid and spindle-cell nevus.

General

• May be very difficult to differentiate from melanoma.

Epidemiology:

• Children & adolescents.

Treatment:

• Complete excision.

Gross

• Usually face or extremity.

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).
• Kamino bodies (also written Camino bodies) - dense eosinophilic bodies.
  • Apoptotic cells.
  • Kamino bodies are rare in melanoma.

Notes:

• Never in the setting of solar elastosis.
  • If there is solar elastosis -- it's melanoma.

DDx:

• Malignant melanoma.
• Pigmented spindle cell nevus of Reed.

Images:

• www:
  • Spitz nevus - collection of images (drmihm.com).
  • Spitz nevus with arrow to camino body (unibas.ch).
• WC:
  • Spitz nevus - intermed. mag. (WC).

Blue nevus

Common blue nevus redirects here.

• Abbreviated BN.

General

• Usually head & neck, extremities (e.g. dorsum of wrist or foot) or buttock.
• Clinically confused with malignant melanoma.

Clinical:

• Blue flat or slightly raised lesion.

Microscopic

Features:

• Lentil-shaped (ovoid) nests between collagen bundles.
• Mix of spindle or dendritic or epithelioid cell morphology.

Notes:

• No epidermal component.
• May be assoc. with a hair follicle.

DDx:

• Dermatofibroma - esp. amelanotic BN.
• Malignant melanoma.
• Clear cell sarcoma.

Images:

• Blue nevus (WC).
• Blue nevus - very low mag. (WC).
• Blue nevus - intermed. mag. (WC).

Variants of blue nevus

Several histologic variants:

• Common blue nevus - the blue nevus not otherwise specified.
• Cellular blue nevus.
• Amelanotic blue nevus - may be confused with a dermatofibroma.
• Sclerosing blue nevus - has stromal fibrosis.
• Epithelioid blue nevus.

Memory device:

• C CASE = Common, Cellular, Amelanotic, Sclerosing, Epithelioid.

Sign out

SKIN LESION, RIGHT WRIST DORSUM, PUNCH BIOPSY: 
	- COMMON BLUE NEVUS.

SKIN LESION, LEFT SHIN, PUNCH BIOPSY: 
	- SCLEROSING BLUE NEVUS.

Cellular blue nevus

General

• Congenital or acquired.
• Usually scalp or butt.
• Variant of the common blue nevus.

Microscopic

Features:

• Dermal lesion with pigmented spindle cells & epithelioid cells - key feature.
• Cells lack nucleoli.
• Biphasic:
  1. Epithelioid cells with pale cytoplasm.
  2. Pigmented spindle cells +/- melanophages.

Images:

• Cellular blue nevus (dermpedia.org).

Acral nevus

• AKA melanocytic nevus with intraepidermal ascent of cells (MANIAC).

General

• Palms or soles.

Microscopic

Features:

• Nevus with intraepidermal ascent of cells.

Notes:

• Intraepidermal ascent of cells is usually suggestive of melanoma.
  • In acral sites the criteria are relaxed, i.e. this is considered benign for this site.

Clark nevus

• AKA dysplastic nevus.
• AKA dysplastic melanocytic nevus.

General

• Benign.
• Clark nevi are considered a risk factor for melanoma and may be a precursor of melanoma, as the name dysplastic nevus suggests.
  • Most melanoma cases do not have evidence of a pre-existing (dysplastic) nevus.
• Large numbers of these nevi (10-100) are seen in dysplastic nevus syndrome.
  • Individuals with this syndrome have an increased risk of melanoma and approximately one third of their melanomas arise from a Clark nevus. The other two thirds arise de novo.

Clinical:

• Associated with sun exposure.

Treatment:

• Clark nevi with severe nuclear atypia are treated like melanoma.

Gross

Features:

• "Ugly duckling sign" - lesion looks different than the rest.
• ABCDE criteria of in melanoma.

Microscopic

Features:

• Melanocytes "bridges" between sides of rete ridges.
• Drapping fibrous tissue - "lamellar fibrosis" - collagen deep to epidermis.
• Usually moderate nuclear atypia (small nucleoli present) - see grading section.
• Junctional component (cells in the epidermis at the DE junction) larger than the intradermal component - shoulder phenomenon.

DDx:

• Malignant melanoma.
• Compound melanocytic nevus.

Images:

• Dysplastic nevus - low mag. (WC).
• Dysplastic nevus - intermed. mag. (WC).
• Dysplastic nevus - high mag. (WC) - shows bridging and lamellar fibrosis.
• Dysplastic nevus - very high mag. (WC) - shows bridging and lamellar fibrosis.

Grading

These lesions are usually graded:

Grade	Size of nucleus	Other features
Mild	1x keratinocyte nucleus	no nucleoli/very small nucleoli †, slight hyperchromasia
Moderate	1-2x keratinocyte nucleus	small nucleoli †, irregular nuclear contours
Severe	>2x keratinocyte nucleus	prominent nucleoli †‡

† The sizes "very small", "small" and "prominent" are not defined; it is suggested that "very small" is visible with the 40x objective, "small" with the 20x objective and "prominent" with the 10x objective. Focal, rare small nucleoli are not significant; they can be seen in benign melanocytic nevi.
‡ Prominent nucleoli (alone) is considered enough to call "severe".

Sign out

SKIN, EXCISION:
- DYSPLASTIC NEVUS WITH MILD NUCLEAR ATYPIA.
- MARGINS NEGATIVE FOR NEVUS CELLS.

Micro

The sections show hair-bearing skin with a compound melanocytic lesion. The epidermal component extends at least three rete ridges further than the dermal component (shoulder phenomenon). There is bridging between the sides of the rete ridges and lamellar fibrosis. The melanocyte nuclei are approximately the size of the keratinocyte nuclei, and do not have a prominent nucleolus (mild nuclear atypia).

There is no upward scatter of melanocytes and melanocytes in the dermis are mature. No mitotic activity is appreciated.

Neurocristic hamartoma

Main article: Neurocristic hamartoma

See also

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