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What is congenital melanocytic nevus?
The congenital melanocytic nevus (CMN) is a dark, pigmented, often hairy patch of skin. A congenital melanocytic nevus is present at birth or appears soon after birth.

It is the benign proliferation of a variant of melanocytes known as nevus cells. They are anomaly in embryogenesis and are considered as malformations or hamartomas.

The congenital melanocytic nevus lesions, are classified according their sizes. There are several classification systems proposed, but the system proposed by Kopf et al. is the most accepted. The CMN lesion present at birth that will reach a diameter of 20 cm or more in adulthood is classified as giant congenital melanocytic nevus (aka bathing trunk nevus, garment nevus or giant hairy nevus). The CMN lesions having a diameter less than 2 cm are considered as small-sized and those having a diameter more than 2 cm but less than 20 cm are considered as medium-sized.

Giant congenital melanocytic nevus (GCMN)

The giant congenital melanocytic nevus is a rare entity and its incidence is about one in every 20,000 births.

Psychosocial issues

The unsightly appearance of the hairy nevi is psychosocially devastating for the affected person and his family members. The psychological consequences of the hairy nuvi in visible areas like face are many. Nearly 25% of the patients suffer from emotional or behavioral problems. Nearly 30% of patients have to face social problems. The impaired self-image caused by the presence of the giant hairy CMN, the anxiety over the risk of complications and the unsightly appearance contribute in compounding the psychological symptoms in the patients and other family members.

Pathogenesis

The giant congenital melanocytic nevus lesion originates during 5th and 24th week of gestation.

Giant hairy congenital melanocytic nevus in a young girl with signs of neurocutaneous melanosis

Giant hairy congenital melanocytic nevus in a young girl with neurocutaneous melanosis

It is due to a morphological error occurring in the neuroectoderm during embryogenesis. The abnormal accelerated proliferation of the precursor cells of melanocytes (melanoblasts) leads to the pigmented and hairy nevus. The hepatocyte growth factor is a cytokine regulator of epithelial cells and overexpression of this factor can lead to discrepancies and disparities in differentiation, proliferation and migration of melanoblasts/melanocytes.

The size of the hairy nevus depend upon how early the accelerated proliferation of cells of melanocyte lineage has started. The melanocyte proliferation commencing after birth produces acquired melanocytic nevus. A small CMN will result if the proliferation of melanocytes in the dermal-epidermal junction begins shortly before birth. Giant and medium-sized nevi would develop when the proliferation starts, during migration of melanoblasts from the neural crest to epidermis. The giant congenital hairy nevus will be large and deep seated if the proliferation starts during the embryonic or early fetal periods.

Progression over time

The progression over time of the hairy lesions is unpredictable. Some GCMN may get lightened over time whereas some may darken. As the hairy lesion progresses the pigmentation may get more heterogeneous or homogeneous. The hairy growth may increase over time. In some patients the hairy growth may disappear. In very rare cases the giant congenital hairy lesions may spontaneously regress. In some cases it was reported that the lesions darkened through adolescence and then significantly lightened. The surface undergoes changes such as increase in roughness, thickness, hairy growth and appearance of nodules.

Health risks from giant congenital melanocytic nevus

The giant congenital melanocytic nevus in some cases develop into malignant melanoma or neurocutaneous melanosis with melanocytic tumors in the leptomeninges. The estimated lifetime risk of developing melanoma varies from 5 to 10%. There is the possibility for simultaneous occurrence of disorders like diffuse lipomatosis, atrophy and asymmetry of limbs, scoliosis, urinary tract anomalies, cafe-au-lait spots and Mongolian spots.

Melanoma associated with hairy giant congenital melanocytic nevus

The melanoma affecting patients with GCMN occurs usually in the dermis or in deeper layers. Most of other melanomas arise in the epidermis. In a study of 289 patients with hairy giant congenital melanocytic nevus, Dedavid et al. found 67 cases of melanoma. 50.7% of these melanoma appeared on the lesions. 3% of the melanomas appeared on clinically normal skin. 31.3% of them were primary central nervous system (CNS) tumors and 15% were metastatic tumors spread from unknown primary site.

Patients having multiple satellite nevi and hairy giant congenital melanocytic nevus on locations such as the back, neck or head have the increased risk of developing melanoma. The probability of a GCMN patient developing melanoma is more in the early childhood. Dedavid et al. found that 50% of the melanomas were diagnosed before five year age. Benign tumors may also develop on the hairy melanocytic nevus.

Neurocutaneous melanosis (NCM)

Neurocutaneous melanosis is a congenital disorder associated with the presence of giant congenital nevus on the skin and melanocytic tumors in the leptomeninges. These lesions occur in brain and spinal cord. Nearly 50% of the patients with NCM develop malignancy. It occurs in the form of leptomeningeal melanoma. The cause is believed to be related to abnormal development of melanoblasts and mutations of the NRAS gene. Some of the symptoms of NCM are, increase in intracranial pressure, seizures, vomiting, headache and papilledema. There is no effective treatment for the disorder.

Treatment

Several treatment options are available for treating hairy congenital melanocytic nevus. The age of the patient, size and location of the lesion and risk of melanoma are to be considered while selecting a treatment option. Surgery, dermabrasion, skin curettage, chemical peels and laser treatment are the options available.

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Types of melanocytic nevi

Depending upon the location, the nevi are variously classified as junctional, intramucosal, compound, Ota, simplex, intradermal, Spitz or blue nuvi. The atypical (dysplastic) mole appear different from other moles and most of the melanoma arise from them. Further the mole may be present at birth (congenital) or acquired later in life.

melanocytic nevus on the nose

Junctional melanocytic nevus

The junctional mole is located along the junction of epidermal and dermal skin layers. These moles usually appear flat or slightly raised. They are usually acquired lesions. As they age they may become compound moles and become increasingly papular. Depending upon the depth and density and number of cells involved they may range in color from brown to black. There is slight risk of these moles turning into melanoma. Junctional intramucosal lesions are found usually in the mouth or genital area.

Intradermal melanocytic nevus

The intradermal moles are extremely common type of moles and are located in the dermis. They are flesh colored. Though there is proliferations of melanocytes, because of their depth from skin surface, the skin does not appear colored. These intradermal lesions appear usually as small, raised, round, dome-shaped or wart-like growths on the skin. If they are of recent origin or appear to grow fast, differential diagnosis is required to rule out basal cell carcinoma.

Compound melanocytic nevus

The compound mole represents the melanocyte proliferation of junctional as well as intradermal origins. These compound nevi are slightly raised and appear light brown to dark brown. They may be present at birth or appear later in life. If there is enlargement or symptomatic changes in compound lesion medical examination is required.

Congenital melanocytic nevus

Congenital moles are present at birth or appear soon after birth.

Acquired melanocytic nevus

Acquired moles appear later in life and are considered as benign neoplasms. Acquired moles may of junctional, compound or intradermal types. They are believed to be caused by sun exposure. In fair persons the sunburn areas can develop into these lesions.

Dysplastic (atypical) melanocytic nevus

Dysplastic moles are atypical and tend to have irregular borders and irregular coloration. These atypical moles may be flat or raised. When a number of atypical lesions are present, medical help must be sought to rule out melanoma, a virulent form of skin cancer. Atypical mole syndrome is an hereditary condition.

Causes
The cause of congenital moles is considered to be a defect in embryological development or hereditary condition. Sun damage, overexposure to sunlight and the resultant premature aging of skin are believed to be the causes of acquired moles.

Management
The melanocytic nevi may be left alone. If there is cosmetic or other concern they may be removed either by surgery or by medical lasers. A raised mole may also interfere with daily life chores like shaving or dressing. If there are any remnants of the lesion after the removal, it may regrow. If the mole is growing fast, if it is crusting and oozing, if there is any familial incidence of skin cancer or a number of atypical melanocytic nevi are present, immediate medical help is to be sought to rule out melanoma.