Blue nevus D22.-

Benign, early childhood acquired (less commonly congenital), atavistic, dermal, melanocytic neoplasm composed of mature, pigmented, dendritic, spindle cell and/or epithelioid melanocytes.

Acquired blue nevi may also occur in late adulthood and are often clinically mistaken for malignant melanoma because of their color.

• Simple blue nevus (most common type)
• Combined blue nevus ( combined nevus)
• Cellular (cell-rich) blue nevus
• Blue neuronaevus (Masson)
• Blue nevus, malignant
• Familial blue nevus (also as part of a Carney syndrome/complex- mutations in the

  PRKAR1A gene/75% of cases and CNC2 gene)

The prevalence of blue nevus is about 1%.

Usually acquired in early childhood or early adulthood.

More common in patients with a dark skin type.

Women are preferentially affected.

• Ubiquitous distribution possible.
• Extremities: Back of hands and feet (50% of all blue nevi are localized here)
• Face, Capillitium
• rarely mucous membranes.

Blue nevi have also been described in lymph nodes (capsule and trabecula) in the sense of pseudometastases and in the vagina, cervix and prostate.

The blue neuronaevus (Masson) is usually located on the buttocks.

Usually solitary, rarely > 1.0 cm in size, sharply defined, usually surprisingly coarse, indolent, blue-black nodule with smooth, shiny, like polished surface. Often, single hairs of the termial hairs penetrate the tumour. In other places, gaping follicle openings are visible on the surface.

As rare special forms are cocard-like nevi (target blue nevi), plaque-like blue nevi, grouped blue nevi ("agminate type"), eruptive multiple blue nevi (see also LAMB syndrome) and the combination with a melanocytic nevus (" combined nevus").

Simple (vulgar) type (most common type): Proliferation of dendritic or bipolar spindle-shaped, pigment-rich melanocytes, which are partly grouped in single formations, partly also in wavy fascicles parallel to the surface, located in the dermis and partly also in the subcutaneous fatty tissue. Typical is a pronounced fibrosis with sclerotic collagen fibers (clinical correlate is the very firm consistency). Usually also numerous melanophages. The papillary dermis is usually spared.

Combined type: Combination of a melanocytic nevus of the dermal or compound type with a blue nevus. S.a.u. Combined nevus.

Cellular (cell-rich) type: Numerous, spindle-shaped or dendritic cells; also cytoplasm-rich, pigment-poor or pigmentless, large oval cells with small spindle-shaped chromatin-dense nuclei. Frequently melanophages.

Blue neuronaevus (Masson): Is a variant of the cell-rich blue nevus. Histologically, nodular tumor proliferates in the dermis and subcutis are impressive, consisting of large-volume melanocytes with oval nuclei and dendritic cells in the surrounding area.

The blue colour of the "blue nevus" is caused by the deep dermal black pigment and the Tyndall effect (milk glass effect) of the overlying uncoloured dermis and epidermis.

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