Pathology of Acquired Melanocytic Naevus

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Dermpath-India

Acquired Melanocytic Nevi:

A brief outline of the Pathology of Melanocytic Nevi:

Dr Sampurna Roy MD

Acquired melanocytic nevi occur at any age and may present as a macule, plaque, papule or polyps.

Some of these lesions may be lobulated or pedunculated.

The colour varies from between tan, brown to black.

These lesions are both clinically and histologically symmetrical.

Variation according to the site:

Vulvar or genital naevi : In premenopausal woman show atypical histological features characterized by enlarged junctional nests and variable shape , size and position of nests.

Pagetoid spread of melanocytes often present.

In pregnant woman nevi may display increase in basal melanocytes and increased mitotic activity.

Flexural naevi : Display nested pattern with variation in size and arrangement of nests.

Conjunctival naevi : Atypical features are noted.

Palm and soles : There may be diagnostic difficulty due to presence of skin markings (dermatoglyphics).

Acral lentiginous nevus present on plantar skin may display features similar to dysplastic naevus.

However, these lesions do not show any evidence cytological atypia or lamellar fibroplasia.

Nail Matrix Nevi: These are mostly junctional in type.

In the compound lesions the naevus cells show little maturation with depth.

The pagetoid spread of cells is confined to suprabasal layer.

Junctional Nevi -

Junctional naevi are characterized by evenly spaced theques and/or lentiginous hyperplasia together with variable keratinocytic hyperpigmentation.

In junctional naevus the theques are of similar size, gradually becoming smaller at the periphery.

Continuous runs of melanocytes are also noted (lentiginous spread).

There is evidence of circumscription characterised by presence of junctional theques at the periphery.

In malignant melanoma individual cells demarcate the periphery.

Compound Nevus -

Compound nevi are characterized by junctional melanocytic theques as well as melanocytes in the dermis.

These are symmetrical lesions and display homogeneous growth pattern.

Shrinkage and separation artifacts may be present.

There is evidence of maturation with depth.

(Type A- Round or epithelioid melanocytes in the papillary dermis;

Type B- Lymphocyte like in the mid - dermis;

Type C- Neuroid of fusiform in the deepest portion).

Intradermal Nevus -

Nevus cells are confined to the dermis.

No epidermal junctional theques are present.

The cells demonstrate maturation with depth.

The nevus cells are arranged in nests or in cords and in the deeper part may display neuroid differentiation.

Degenerative (secondary) changes in Nevi:

1. Amyloid

2. Bone

3. Neurofibroma like appearance

4. Adipose tisue (liponeuronevi)

5. Epidermal spongiosis - producing eczematous halo-Meyerson's nevus

6. Myxoid change

7. Increased elastic fibre in the dermis

Dermatopathology Quiz Case 139