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), Spitz nevus - high mag. (WC), Spitz nevus - intermed. mag. (WC)
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.

Lentiginous melanocytic lesions

Lentigo simplex

• AKA simple lentigo.

General

• Benign.
• Usually <40 years old.

Fits into the larger category of lentiginous melanocytic proliferations - these include:

• Solar lentigo.
• Lentigo simplex.
• Lentiginous nevus.
• Lentiginous melanoma in situ.

Associated syndromes:

• Peutz-Jeghers syndrome.
• LEOPARD syndrome.
• LAMB syndrome.

Gross

• Small flat pigmented lesion.

DDx - clinical:

• Melanocytic nevus.

Microscopic

Features:

• Melanocytes in epidermis only.
  • Melanocytes basally located (normal location) with hyperpigmentation.
• No melanocytic nests.
• +/-Mild/moderate elongation of the rete ridges.

DDx:

• Solar lentigo - in sun exposed areas.
• Ephelis (freckle) - change with UV light exposure.
• Melanotic macule.
• Lentiginous nevus.

Images:

• Lentigo simplex - several images (dermamin.com).
• Lentigo simplex (humpath.com).

Sign out

SKIN LESION, LEFT ABDOMEN, BIOPSY:
- SIMPLE LENTIGO, COMPLETELY EXCISED IN THE PLANE OF SECTION.

SKIN LESION, LEFT ABDOMEN, BIOPSY:
- BENIGN SIMPLE LENTIGO.

Solar lentigo

• Plural solar lentigines.

General

• Benign.

Fits into the larger category of lentiginous melanocytic proliferations - these include:

• Solar lentigo.
• Lentigo simplex.
• Lentiginous nevus.
• Lentiginous melanoma in situ.

Gross

Features:

• Small (< 4 mm), irregular brown macule.
• Usu. sun-exposed area.

DDx (clinical):

• Lentigo maligna - melanoma in situ on sun damaged skin.
• Seborrheic keratosis, flat.

Microscopic

Features:

• Hyperpigmented melanocytes - may be present in increased quantities - key feature.
  • Classically at the tips of the rete ridges.
• No (melanocyte) nuclear atypia.
• Solar damage (solar elastosis).

Notes:

• Should not be present:
  • Nests of melanocytes.
  • Pagetoid spread of melanocytes.

DDx:

• Pigmented actinic keratosis.
• Lichen planus-like keratosis.
• Pigmented seborrheic keratosis.

Images:

• Solar lentigo (WC).
• Solar lentigo (dermammin.com).

Sign out

FOREARM LESION, RIGHT, PUNCH BIOPSY:
- SOLAR LENTIGO.

Micro

The sections show hair-bearing skin with basilar pigmentation at the tips of the rete ridges and solar elastosis. No melanocytic nests are identified. The epidermal cells mature to the surface. No significant inflammation is present.

Lentiginous melanocytic nevus

• AKA lentiginous nevus.

General

• Benign.

Fits into the larger category of lentiginous melanocytic proliferations - these include:

• Solar lentigo.
• Lentigo simplex.
• Lentiginous nevus.
• Lentiginous melanoma in situ.

Gross

• Small flat pigmented lesion.

Microscopic

Features:

• Melanocytes without atypia in the epidermis only - key feature.
• Melanocytic nests.
• +/-Rete ridge elongation.

DDx:

• Atypical lentiginous nevus.
• Dysplastic nevus.
• Melanoma in situ - especially if solar elastosis is present.

Images

www:

• Lentiginous nevus (derm101.com).

• 

  Lentiginous nevus. (WC)

Sign out

SKIN LESION, BACK, SHAVE EXCISION:
- JUNCTIONAL LENTIGINOUS NEVUS.
-- COMPLETELY EXCISED (LATERAL CLEARANCE 1 MM).

Micro

The sections show skin with non-nested melanocytes in the epidermis. The melanocytes have no significant cytologic atypia. There is no upward scatter of melanocytes. The lesion is completely excised the in plane of section.

Nested melanocytic lesions

Common melanocytic nevus

• AKA common nevus.
• In common language: mole.

General

• Benign.
• Common.
• Think melanoma.

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

• Abbreviated CMN and CN.

• In the dermis and epidermis - key feature.

Junctional melanocytic nevus

• Abbreviated JN.

• In the epidermis - key feature.

Intradermal melanocytic nevus

• AKA dermal nevus.
• AKA intradermal melanocytic nevus.
• AKA intradermal nevus, abbreviated IDN.

• Only in the dermis - key feature.
• +/-Adipocytes - uncommon.

Note:

• In the oral cavity these are known as intramucosal nevi.

Sign out

Junctional melanocytic nevus

SKIN LESION, RIGHT LATERAL UPPER ARM, BIOPSY:
- BENIGN JUNCTIONAL NEVUS.

Micro

The sections show melanocytes in nest confined to the epidermis. The lesion is symmetrical in its architecture and pigment distribution. There is no pagetoid spread of melanocytes in the epidermis. No significant nuclear atypia is identified. No mitotic activity is appreciated.

The lesion is completely excised in the plane of section.

Compound melanocytic nevus

SKIN LESION, RIGHT NECK, SHAVE BIOPSY:
- BENIGN COMPOUND NEVUS.

Micro

The sections show melanocytes in the dermis and epidermis. The lesion is symmetrical in its architecture and pigment distribution. There is no pagetoid spread of melanocytes in the epidermis. Superficially, melanocytes are in nests. Melanocytes show no apparent cytologic atypia and mature with depth. No mitotic activity is appreciated.

The lesion is completely excised in the plane of section.

Barely compound

The sections show melanocytes predominantly in the dermis. Rare melanocytic nests are seen at the dermal-epidermal junction. There is no pagetoid spread of melanocytes in the epidermis. The lesion is symmetrical in its architecture. Superficially, melanocytes are in nests and pigment is present. The melanocytes mature with depth. No mitotic activity is appreciated.

The lesion is present at the margin.

Intradermal melanocytic nevus

SKIN LESION, BACK, PUNCH BIOPSY: 
- BENIGN INTRADERMAL NEVUS.

Adipocytes present

SKIN LESION, BACK, PUNCH BIOPSY: 
- BENIGN INTRADERMAL NEVUS WITH MATURE ADIPOCYTES.

Clinically suspicious

SKIN LESION, LEFT UPPER ARM, PUNCH BIOPSY:
- BENIGN INTRADERMAL NEVUS, INCOMPLETELY EXCISED.

COMMENT:
HMB-45 marks very rare superficial cells. Ki-67 staining does not show apparent melanocyte
staining. MITF marks the melanocytes and demonstrates maturation of the melanocytes with depth.

Micro

The sections show melanocytes in the dermis separated from the epidermis by a Grenz zone. The lesion is symmetrical in its architecture and pigment distribution. Superficially, melanocytes are in nests. Melanocytes mature with depth. No mitotic activity is appreciated.

The lesion is completely excised in the plane of section.

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.
  • "Deep" melanocytes.
• Lacks nuclear atypia.
• +/-Mitoses.
• +/-Less nesting.

DDx:

• Intradermal melanocytic nevus.
• Malignant melanoma.

Images:

• Congenital nevus - 4 (dermpedia.org).
• Congenital nevus - 5 (dermpedia.org).

Sign out

SKIN LESION, LEFT UPPER BACK, BIOPSY:
- COMPOUND MELANOCYTIC NEVUS WITH CONGENITAL FEATURES.

Recurrent melanocytic nevus

• AKA persistent melanocytic nevus.
• AKA pseudomelanoma.

General

• Classically, arises at the site of a partially excised nevus.

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.

May have:

• Pagetoid spread of melanocytes.
• Confluent nests at the DE junction.
• Nuclear atypia - uncommon.

DDx:

• Melanoma in situ - classically spread beyond the scar, unlike pseudomelanoma - growth confined to epidermis.
• Sclerosing nevus.

IHC

• HMB-45 deep component -ve.
• Ki-67 - non-proliferative.

Sclerosing melanocytic nevus

• AKA sclerosing nevus.

General

• Similar to recurrent nevus.
• Clinically may be confused with melanoma.
• No history of trauma or prior excision.

Microscopic

Features:

• Trizonal - may be described as a sandwich:
  1. Junctional or compound nevus.
     • May have pagetoid spread of melanocytes, i.e. non-basal melanocytes in the epidermis.
     • Cannot have cytologic atypia - presence of cytologic atypia in this layer makes it melanoma.
  2. Fibrotic tissue with irregular melanocytic nests.
  3. Nevus below scar - may be common, congenital-type, dysplastic, Spitz.

DDx:

• Malignant melanoma.
• Recurrent melanocytic nevus - also trizonal; however, has a fibrotic layer that does not have melanocytes in it.

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.
• Malignant melanoma.

Images

• 

  PSCN - low mag. (WC)

• 

  PSCN - intermed. mag. (WC)

• 

  PSCN - high mag. (WC)

www:

• Reed nevus - collection (histopathology-india.net).

Sign out

SKIN LESION, RIGHT POSTERIOR NECK, EXCISION:
- PIGMENTED SPINDLE CELL NEVUS OF REED.
-- COMPLETELY EXCISED (CLEARANCE ~ 1 MM).

Micro

The sections show spindled pigmented melanocytes in nests confined to the epidermis. The lesion is symmetrical in its architecture and pigment distribution. There is no pagetoid spread of melanocytes in the epidermis. No significant nuclear atypia is identified. No mitotic activity is appreciated. Melanophages are present in the superficial dermis. The lesion is completely excised in the plane of section.

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

• 

  Spitz nevus - low mag. (WC)

• 

  Spitz nevus - intermed. mag. (WC)

• 

  Spitz nevus - high mag. (WC)

www:

• Spitz nevus - collection of images (drmihm.com).
• Spitz nevus with arrow to camino body (unibas.ch).

Acral nevus

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

General

• Palms or soles.

Note:

• Volar refers to the palmar aspect or plantar aspect.

Gross

• Pigmented lesion.

Note:

• Should be bisected perpendicular to the dermatoglyphs (ridges).
  • Lesions sectioned parallel to the ridges (on microscopy) may appear to have confluent junctional nests (leading to the diagnosis of melanoma).

Microscopic

Features:

• Acral skin:
  • Thick stratum corneum (hyperkeratotic).
  • Thick stratum spinosum (acanthotic).
• Nevus with intraepidermal ascent of cells.
  • May be referred to as Pagetoid scatter.
  • Should not be present at the edge of the lesion - key feature.

Notes:

• Intraepidermal ascent of cells is usually suggestive of melanoma.
  • In acral sites (esp. at the centre of a lesion) the criteria are relaxed, i.e. this is considered benign for this site.
• Nests in the ridges raise the suspicion of melanoma.
  • Memory device "ridges are risky, furrows are fine".

DDx:

• Acral lentiginous melanoma.

Dysplastic melanocytic nevus

• AKA dysplastic nevus.
• AKA Clark nevus.
• AKA nevus with architectural disorder.
  • This term is recommended by the American NIH; however, it is not widely adopted.

General

• Benign.
• Dysplastic 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:

• Dysplastic nevi with severe nuclear atypia are treated like melanoma - excision with a 5 mm margin.
• Dysplastic nevi with moderate nuclear atypia with margin involvement are re-excised.

Gross

Features:

• "Ugly duckling sign" - lesion looks different than the rest.
• ABCDE criteria of in melanoma.
• Tend to be greater than 5 mm - important.†

Note:

• † Size matters - things smaller than 4 mm are usually not a dysplastic nevus.

Microscopic

Features:

• Melanocytes "bridges" between sides of rete ridges.
  • Joining of three or more adjacent rete ridges = suspicious for melanoma.
• 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:

• Melanoma in situ - especially on sun damaged skin (lentigo maligna).
• Malignant melanoma - especially on sun damaged skin (lentigo maligna melanoma).
• Compound melanocytic nevus.
• Atypical lentiginous nevus.

Images

• 

  Dysplastic nevus - low mag. (WC/Nephron)

• 

  Dysplastic nevus - intermed. mag. (WC/Nephron)

• 

  Dysplastic nevus - high mag. - shows bridging and lamellar fibrosis. (WC/Nephron)

• 

  Dysplastic nevus - very high mag. - shows bridging and lamellar fibrosis. (WC/Nephron)

Grading

These lesions are often 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".

Notes:

• § There is no consensus on this and practise (embarrassingly) is all over the map.
  • A two-tier grading system also exists (low-grade (leave it alone) / high-grade (cut it out)).
  • Some pathologists do not grade dysplastic nevi.

Sign out

Compound

SKIN LESION, BACK, EXCISION:
- DYSPLASTIC COMPOUND NEVUS WITH MILD CYTOLOGIC ATYPIA AND MILD ARCHITECTURAL ATYPIA,
  COMPLETELY EXCISED IN THE PLANE OF SECTION (2 MM CLEARANCE).

SKIN LESION, CENTRAL BACK, EXCISION:
- DYSPLASTIC COMPOUND NEVUS WITH MILD CYTOLOGIC ATYPIA.
- NEAREST MARGIN (LATERAL MARGIN) 6 MM.

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 cytologic atypia).

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

Junctional

SKIN LESION, LOWER BACK, EXCISION:
- DYSPLASTIC JUNCTIONAL MELANOCYTIC NEVUS WITH MILD NUCLEAR ATYPIA.
- NEAREST MARGIN (LATERAL MARGIN) 1 MM.

Micro

The sections show hair-bearing skin with a junctional melanocytic lesion. 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. No mitotic activity is appreciated.

Desmoplastic melanocytic nevus

• AKA sclerosing melanocytic nevus.

General

• Benign.

Gross

• Usu. "small" and symmetric.

Clinical DDx:

• Dermatofibroma.
• Dermal scar.

Microscopic

Features:

• Compound nevus or intradermal nevus with prominent dermal fibrosis.
  • Fibrosis: extra pink - versus surrounding.

DDx:

• Desmoplastic neurotropic malignant melanoma.
• Dermatofibroma.

IHC

Features:

• Melan A (MART-1) +ve (not usu. +ve in desmoplastic melanoma).
• S-100 +ve.
• Ki-67 -- only rare cells.

Miscellaneous

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.
• Second most common melanocytic lesion of the oral cavity.
  • Most common melanocytic lesion intramucosal melanocytic nevus.

Gross

• 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:

• Classically no epidermal component.
  • The entity compound blue nevus has been described; it is rare.
• May be assoc. with a hair follicle.

DDx:

• Malignant melanoma - mitotic figures, necrosis, cytologic atypia, asymmetry (architecure, pigment).
• Atypical blue nevus - have some of the features of melanoma.
• Clear cell sarcoma.
• Dermatofibroma - esp. amelanotic BN.
• Combined melanocytic nevus - blue nevus found together with another nevus (classically common melanocytic nevus), superficial.
• Pigmented epithelioid melanocytoma - superificial dermis, has nuclear atypia.
• Vascular lesions (venous lake, hemangioma).

Images

• 

  Blue nevus (WC)

• 

  Blue nevus - very low mag. (WC)

• 

  Blue nevus - intermed. mag. (WC)

www:

• Several types of blue nevi (dermatopathonline.com).

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.

IHC

• HMB-45 diffusely +ve.^{[citation needed]}
  • Melanoma patchy +ve.
• MART-1 diffusely +ve.
• Ki-67 low.

Sign out

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

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

Micro

The sections show pigmented spindle cells in the dermis between collagen bundles. The spindle cells show no nuclear atypia and no mitotic activity is appreciated.

The lesion does not extend into the epidermis. There are no melanocyte nests. There is no significant inflammation. The lesion is completely excised.

The pigmented cells are negative on the Prussian blue stain.

Sclerosing blue nevus

The sections show pigmented spindle cells in the dermis between densely packed collagen fibres. The spindle cells show no significant nuclear atypia, and no mitotic activity is appreciated. The lesion extends up to the epidermis; however, it does not appear to involve the epidermis. The overlying epidermis has hyperkeratosis; otherwise, it is unremarkable. There are no nests of melanocytes. There is no significant inflammation. The lesion is completely excised in the plane of section.

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).

Combined melanocytic nevus

• AKA combined nevus.

General

• Uncommon.
• Morphologic features of two types of melanocytic nevi.
  • Most common: blue nevus and common nevus.

Microscopic

Features:

• Morphologic features of two types of melanocytic nevi.

DDx:

• Malignant melanoma.
• Pigmented epithelioid melanocytoma - superificial dermis, has nuclear atypia.

Sign out

A. SKIN LESION, LEFT UPPER ARM, PUNCH BIOPSY:
- BENIGN COMBINED MELANOCYTIC NEVUS (INTRADERMAL MELANOCYTIC NEVUS AND BLUE NEVUS).

Neurocristic hamartoma

Main article: Neurocristic hamartoma

See also

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

External links

• Dear 16 year-old me (youtube.com) - with Dr. G.