Introduction:
Nevi, commonly known as moles, are benign proliferations of melanocytes that can present in various histologic patterns. Understanding the differences between intradermal, junctional, and compound nevi is crucial for accurate diagnosis and patient management. In this blog post, we will delve into the histologic features of these nevi types, accompanied by a tabulated comparison and insights into immunohistochemistry findings.
Histologic Features:
Intradermal Nevus:
- Predominantly located within the dermis.
- Features mature melanocytes without junctional activity.
- Epidermal component is typically absent.
Junctional Nevus:
- Primarily located at the junction between the epidermis and dermis.
- Characterized by the presence of melanocytes along the basal layer of the epidermis.
- Absence of dermal involvement.
Compound Nevus:
- Combines features of both junctional and intradermal nevi.
- Melanocytes are present in both the epidermis and dermis.
- Often characterized by nests of melanocytes at the epidermal-dermal junction and within the dermis.
| Feature | Intradermal Nevus | Junctional Nevus | Compound Nevus |
|---|---|---|---|
| Location | Mainly in the dermis | Epidermal-dermal junction | Epidermis and dermis |
| Melanocyte Presence | Mature melanocytes | Melanocytes at basal layer | Melanocytes in both layers |
| Epidermal Component | Typically absent | Present | Present |
| Dermal Involvement | Significant absence | Absent | Present |
Types of nevus cells in Intradermal nevus
1️⃣Type A morphology:
In superficial dermis
Pigmented epithelioid cells with well defined cell boundaries
Abundant eosinophilic to amphophilic cytoplasm containing coarse melanin granules
Uniform round / oval nuclei slightly smaller than that of adjacent keratinocytes
Finely dispersed chromatin
Delicate nuclear membrane
No / small distinct eosinophilic nucleoli
2️⃣Type B morphology:
In intermediate dermis
Cells more lymphoid than epithelioid
Decreased cytoplasm with no melanin
Smaller and slightly hyperchromatic nuclei with dispersed chromatin and no nucleoli
3️⃣Type C morphology:
In deep dermis
Spindled, fibroblast-like or schwannian cells with oval nuclei and bland chromatin
Single cell infiltration of superficial reticular collagen
Maturation:
Deeper portion of lesion has smaller cells with less pigment and less atypia
Deep cells grow in smaller sized nests or single cells
May resemble neural tissue
Terminal differentiation recapitulates some aspects of Schwann cell development
Video explanation:
Immunohistochemistry Findings:
- S100 Protein:
- Positive in all nevus types, highlighting melanocytes.
- Melan-A (MART-1):
- Positive staining in melanocytes, aiding in their identification.
- Ki-67 (MIB-1):
- Low proliferative index in nevi, distinguishing them from malignant melanomas.
MCQs on the topic
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References:
- https://pdfs.semanticscholar.org/9e18/ae3360b0079a8d9aafbc48372338d3530c48.pdf
- https://www.researchgate.net/publication/327483392_Benign_melanocytic_lesions_with_emphasis_on_melanocytic_nevi_-_A_histomorphological_analysis
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