Congenital melanocytic naevus

Congenital melanocytic nevus
Other names	Congenital nevus, CMN
File:Congenital melanocytic nevus.jpg
A large congenital melanocytic nevus on the back
Specialty	Dermatology
Symptoms	Dark, pigmented skin lesion present at birth
Complications	Melanoma, psychological impact
Usual onset	Present at birth
Duration	Lifelong
Causes	Genetic mutations
Risk factors	Larger size, multiple nevi
Diagnostic method	Clinical examination, biopsy
Treatment	Monitoring, surgical removal, laser therapy
Frequency	1 in 100 births (small nevi)

Congenital melanocytic nevus (CMN) is a type of nevus (or mole) that is present at birth. These nevi are characterized by an overgrowth of melanocytes, the cells responsible for producing melanin, the pigment that gives skin its color. CMN can vary greatly in size, shape, and color, and they may appear anywhere on the body.

Classification

Congenital melanocytic nevi are classified based on their size:

• Small CMN: Less than 1.5 cm in diameter.
• Medium CMN: 1.5 to 20 cm in diameter.
• Large or Giant CMN: Greater than 20 cm in diameter. These are sometimes referred to as "bathing trunk nevi" when they cover large areas of the body.

Causes

The exact cause of congenital melanocytic nevi is not fully understood, but they are believed to result from genetic mutations that occur during fetal development. These mutations lead to the proliferation of melanocytes in a localized area of the skin.

Symptoms

CMN are typically dark brown or black in color and may have a smooth, rough, or nodular surface. They are usually present at birth or become apparent shortly thereafter. Over time, these nevi may change in size, color, or texture.

Complications

One of the primary concerns with congenital melanocytic nevi is the potential for malignant transformation into melanoma, a serious form of skin cancer. The risk of melanoma is higher in larger nevi. Additionally, large or visible nevi can have a significant psychological impact on affected individuals, particularly during adolescence.

Diagnosis

Diagnosis of CMN is primarily clinical, based on the appearance of the lesion. In some cases, a biopsy may be performed to rule out malignancy or to confirm the diagnosis.

Treatment

Treatment options for CMN depend on the size and location of the nevus, as well as the risk of complications. Options include:

• Monitoring: Regular skin examinations to monitor for changes.
• Surgical removal: Excision of the nevus, which may be recommended for large or suspicious lesions.
• Laser therapy: Used to lighten the color of the nevus or to remove smaller lesions.

Prognosis

The prognosis for individuals with CMN varies. Small and medium-sized nevi generally have a good prognosis with minimal risk of complications. Large or giant nevi require careful monitoring due to the increased risk of melanoma.

Also see

• Melanoma
• Nevus
• Skin cancer
• Dermatology