Pathology of Blue Nevus - Dr Sampurna Roy MD

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Dermpath-India

Pathology of Blue Nevus

"A benign pigmented tumour with bluish gray appearance"

Dr Sampurna Roy MD 2023

Dermatopathology Quiz Case: 261

Answer - Cellular Blue Naevus

Dermatopathology Quiz Case: 203

Answer - Blue Naevus

Syn: Tieche's nevus ; Blue nevus of Jadassohn-Tieche

Blue naevus was first described by Tiesche in 1906.

These lesions may cause diagnostic difficulty in case of large size, involvement of subcutaneous tissue, asymmetrical pigmentation and presence of lymphnode metastasis.

Unlike benign melanocytic nevi, blue nevi show the following features:

(1) There is no evidence of diminution in cellularity and cell size towards the base of the lesion.

(2) No associated loss of pigmentation.

(3) No loss of proliferative activity.

The macroscopic bluish appearance is due to the presence of deep intradermal melanin pigment viewed through intact skin (Tyndall effect).

Site: Although it usually occurs in skin, it has been reported in other locations, such as oral mucosa, sclera, uterine cervix, vagina, prostate, spermatic cord, pulmonary hilus, orbit, conjunctiva, maxillary sinus, breast, and lymph nodes.

The two main variants:

1) Common Blue Nevus:

2) Cellular Blue Nevus:

1) Common Blue Nevus:

This is a common subtype and presents as slate grey, blue or black papules usually less than 1 cm in diameter.

These are usually located on the head, hands and feet.

Microscopic features:

Histologically, these are ill-defined proliferation of elongated, sometimes finely branched dendritic, finely pigmented melanocytes within the dermis.

Variable numbers of melanin laden macrophages (melanophages) containing large aggregates of melanin are present.

A Grenz zone usually separates the lesion from the epidermis.

There may be increased cellularity and pigmentation close to the adnexae or along nerves and blood vessels.

Occasionally, the lesion is hypomelanotic (Differential diagnosis: Dermatofibroma).

Usual differential diagnosis include nevi of Ito, Ota and the Mongolian spot.

2) Cellular Blue Nevus:

Arthur Allan in 1949 for the first time recognised that this larger, cellular and often mitotically active melanocytic lesions were actually benign.

These acquired lesions are usually located in the sacrococcygeal/gluteal region and less common sites include face, scalp and extremities.

These lesions clinically presents as nodule, tumour or plaques, usually 1 - 2 cm in diameter (sometimes much larger).

Microscopic features:

Microscopically, this is a symmetrical lesion composed of two distinct cell types, dendritic melanocytes as in the common type, together with islands of plump, oval melanocytes with abundant cytoplasm.

The plump cells have a round or oblong nucleus and central nucleolus.

Often intranuclear cytoplasmic pseudoinclusions are present.

Often mitotic figures are noted (less than 2/sq mm).

No atypical mitotic forms are present.

The deeper portions are often well circumscribed and can extend into the subcutis.

The growth pattern may be diffuse or nested.

The terms used to describe the nested pattern include zellballen, fascicular and alveolar.

The differential diagnosis include malignant melanoma, fibrous histiocytoma, pigmented dermatofibrosarcoma protuberans and schwannoma.

Other variants of Blue Nevus:

Epithelioid Blue Nevus:

Microscopically, the lesion consists of two cell types:

(i) globular to fusiform and heavily pigmented

(ii) polygonal or spindle shaped and light pigmented or non pigmented.

Atypical Cellular Blue Nevus:

Proposed by Mihm et al, the lesion demonstrates clinico-pathological features intermediate between cellular blue nevus and malignant blue nevus.

There is evidence of architectural and cytological atypia together with necrosis.

No atypical mitoses were present and there was no evidence of metastasis.

Malignant Blue Nevus:

This lesion is noted in middle aged individuals, and is usually located on the scalp and rarely trunk and extremities.

The patient usually complains of sudden increase in size of a longstanding lesion or there may be history of repeated unsuccessful local excision.

The lesion includes clear cut areas of malignant and benign blue nevus, or the histological appearances may resemble cellular blue nevus together with pleomorphism prominent atypical mitoses and areas of coagulative necrosis.

Follow up of the cases reveal significant morbidity and death by metastatic disease.

Carney's Syndrome:

Syndrome is characterised by multiple pigmented lentigines of skin and mucous membrane (Example: Epithelioid type blue nevi or usual type of blue naevi) , cardiac myxoma, endocrine overactivity syndromes and neurinomas including psammomatous melanotic schwannoma.

Blue Nevus with Lymphnode metastasis:

Blue naevus with lymphnode metastasis is characterised by cellular blue naevus in the skin associated with the finding of melanocytes within a regional lymphnode.

In contrast to melanoma cells, blue nevus cells within lymphnodes are confined to capsule and do not show atypical features or mitosis.

It has been suggested that the presence of cells of a blue nevus within a lymphnode is due to error during migration of melanocytes from the neural crest to the skin.