Melanocytic lesions

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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 [2]
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 [3]
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 [4]
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) [5]
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) [6]
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 [7]
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 [8]
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 [9]

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:[10]

  • 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:

See also

References

  1. ↑ WMSP P.498.
  2. ↑ WMSP P.498.
  3. ↑ WMSP P.499.
  4. ↑ WMSP P.499.
  5. ↑ WMSP P.499.
  6. ↑ WMSP P.500.
  7. ↑ WMSP P.501.
  8. ↑ WMSP P.501.
  9. ↑ WMSP P.501.
  10. ↑ WMSP P.499.
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