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		^[1]
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		^[1]
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		^[2]
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		^[2]
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)	^[2]
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)	^[3]
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	Blue nevus (WC)	^[4]
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		^[4]
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		^[4]
Dysplastic nevus (Clark's nevus)	may be familial - precursor to melanoma	may have asymmetry in shape or pigmentation	melanocytes "bridges" btw sides of rete, "lamellar fibrosis" (collagen deep to epidermis), mod. atypia	melanocyte bridges, lamellar fibrosis		^[5]
Halo nevus	central zone of pigment		lymphocytes at perimeter of melanocytic; epidermal melanocytes not nested; may be dermal, epidermal or both	lymphocytes +++		^[5]

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:^[2]

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).
NEVER in the setting of solar elastosis.^[6]
- If there is solar elastosis -- it's melanoma.

Images:

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

References

↑ ^1.0 ^1.1 Humphrey, Peter A; Dehner, Louis P; Pfeifer, John D (2008). The Washington Manual of Surgical Pathology (1st ed.). Lippincott Williams & Wilkins. pp. 498. ISBN 978-0781765275.
↑ ^2.0 ^2.1 ^2.2 ^2.3 Humphrey, Peter A; Dehner, Louis P; Pfeifer, John D (2008). The Washington Manual of Surgical Pathology (1st ed.). Lippincott Williams & Wilkins. pp. 499. ISBN 978-0781765275.
↑ Humphrey, Peter A; Dehner, Louis P; Pfeifer, John D (2008). The Washington Manual of Surgical Pathology (1st ed.). Lippincott Williams & Wilkins. pp. 500. ISBN 978-0781765275.
↑ ^4.0 ^4.1 ^4.2 Humphrey, Peter A; Dehner, Louis P; Pfeifer, John D (2008). The Washington Manual of Surgical Pathology (1st ed.). Lippincott Williams & Wilkins. pp. 501. ISBN 978-0781765275.
↑ ^5.0 ^5.1 Humphrey, Peter A; Dehner, Louis P; Pfeifer, John D (2008). The Washington Manual of Surgical Pathology (1st ed.). Lippincott Williams & Wilkins. pp. 502. ISBN 978-0781765275.
↑ HJ. 16 July 2010.

[Ref_WMSP498-1] 1.0 ^1.1 Humphrey, Peter A; Dehner, Louis P; Pfeifer, John D (2008). The Washington Manual of Surgical Pathology (1st ed.). Lippincott Williams & Wilkins. pp. 498. ISBN 978-0781765275.

[Ref_WMSP499-2] 2.0 ^2.1 ^2.2 ^2.3 Humphrey, Peter A; Dehner, Louis P; Pfeifer, John D (2008). The Washington Manual of Surgical Pathology (1st ed.). Lippincott Williams & Wilkins. pp. 499. ISBN 978-0781765275.

[Ref_WMSP500-3] Humphrey, Peter A; Dehner, Louis P; Pfeifer, John D (2008). The Washington Manual of Surgical Pathology (1st ed.). Lippincott Williams & Wilkins. pp. 500. ISBN 978-0781765275.

[Ref_WMSP501-4] 4.0 ^4.1 ^4.2 Humphrey, Peter A; Dehner, Louis P; Pfeifer, John D (2008). The Washington Manual of Surgical Pathology (1st ed.). Lippincott Williams & Wilkins. pp. 501. ISBN 978-0781765275.

[Ref_WMSP502-5] 5.0 ^5.1 Humphrey, Peter A; Dehner, Louis P; Pfeifer, John D (2008). The Washington Manual of Surgical Pathology (1st ed.). Lippincott Williams & Wilkins. pp. 502. ISBN 978-0781765275.

[6] HJ. 16 July 2010.

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Melanocytic lesions

Contents