Nevus melanocytic dysplasticD48.5

Controversial term for a clinically conspicuous melanocytic nevus (see ABCD rule) with an increased probability of transformation into a malignant melanoma.

To date, there are no generally accepted histological, reflected-light microscopic or clinical features that allow an exact definition of melanoma precursors. If the corresponding range of criteria is insufficient or appears doubtful for an assessment of tumour fitness, the practical benefit of retaining the term dysplasia is that either close follow-up examinations or histological revisions are required for already excised lesions.

If a patient has a large number of such atypical melanocytic nevi, the syndrome of atypical dysplastic nevi is present (see BK-Mole syndrome).

• Junction-type dysplastic nevus
• Compound-type dysplastic nevus.

• Junction-type dysplastic nevus: The surface epithelium is mostly acanthotic. Reteleases are unevenly or broadly dilated. In the junctional zone, nests arranged at irregular intervals, but also individually distributed (epitheloid) melanocytes are visible. More rarely, nests or melanocytes are also found suprabasally. Melanocyte nests tend to confluence (bridging). Occasional signs of atypia. Occasional round cell infiltration of the upper dermis. Pigment incontinence may be present.
• Dysplastic nevus of compound type: Mostly symmetrical melanocytic tumor with epidermal and dermal parts. In some places the junctional activity exceeds the dermal part of the tumor (shoulder formation). The epidermal changes correspond to the junctional type. In the dermal parts a maturation of the melanocytes towards depth is detectable. In addition, stroma reactions such as concentric or lamellar fibroplasia occur. Bulky round cell infiltrates.

The gold standard is histology.

Incidentlight mic roscopy: Incident light microscopic features, which are otherwise only found in malignant melanomas, reach a proportion of about 14% in the group of dysplastic nevi. The vast majority of melanocytic naevi classified as dysplastic show reflected-light phenomena, as they also occur in ordinary naevi, but often in stronger expression, different frequencies and multicomponent structures. The diagnosis can be standardized by means of an evaluation protocol (see Table 1).

Reflected light microscopic vital histological evaluation protocol for dysplastic melanocytic nevi (according to Schulz)

Incident light microscopic criteria for the differentiation between junctional and dysplastic nevus (modified according to Schulz)

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