Melanocytic naevi (moles) are common neoplasms that result from the proliferation of cutaneous melanocytes that grow in clusters on clumps. Melanocytic naevi (Moles) are benign proliferations of a type of melanocyte known as a “naevus cell.” However they can sometimes become malignant and require close monitoring.
There are 2 types of melanocytes. The naevus cell vs ordinary melanocyte. The two major differences between ordinary melanocytes that reside in the basal layer of the epidermis and naevus cells are:
- Naevus cells cluster as nests within the lower epidermis and/or dermis, whereas epidermal melanocytes are evenly dispersed as single units.
- Naevus cells do not have dendritic processes, except for those naevus cell found within blue naevi.
Both melanocytes and naevus cells can produce the pigment melanin. Melanocytic naevi may be congenital or acquired. Acquired naevi can be classified as common (banal) or atypical, and several additional mole variants including variants like halo naevi, Spitz naevi and blue naevi.
Naevus can be acquired or congenital:
- Congenital melanocytic naevi (CMN) are defined as melanocytic naevi that are present at birth or develop within the first few months of life. They are often associated with hair, usually represent harmatoma and typically have a higher chance of turning into melanoma compared to acquired mole. Like acquired Navei, BRAF mutation has been identified in a high number of CMN.
- Junctional Naevi:
They typically have a flat macular or minimally elevated appearance with preserved skin markings. Their color range from brown to black in color, sometimes with darker pigmentation in the center than at the edge: They usually have very similar appearance with simple lentigo. Junctional naevi begin as nest of melanocytes at the dermal-epidermal junction hence called (junctional naevus). Junctional naevi are the most common mole in children
- Compound Naevi:
Junctional Naevi that grows by extension into the dermis. A mixture of junctional and intradermal naevus: pigmented papules (elevated lesion), but in some lesions the degree of elevation is subtle. Their surface can be smooth and dome-shaped or papillomatous, and they vary in color from tan to dark brown.
- Intradermal Naevi:
They are naevi where the junctional naevi component eventually lost, resulting in an Intradermal naevus, which is the most common mole in adults. (Naevus cells residing in the dermis often lose their capacity to produce melanin. As a result, intradermal naevi are usually skin-colored to tan papules that are dome-shaped, papillomatous, or pedunculated with a soft, rubbery texture)
Cause and Risk factors
- The exact cause of mole not clearly elucidated but may be an defect in embryologic development especially the first 12 weeks of pregnancy.
- The melanocyte proliferate in clusters instead of spreading out, causing the abnormal growth or dense pigmentation seen.
- Sunlight has been implicated in acquired mole but more research are needed.
Symptoms and Clinical Presentations
- Acquired Naevi frequently present as pigmented macules, papules, or plaques, but may also be flesh-colored or pink.
- Characterized by a flat macule or raised papule with symmetry, sharp borders, evenly distributed color and small diameter (< 6 mm).
- Dysplasia may arise (dysplastic naevus) from moles and are considered a precursor to melanoma
The diagnosis of a naevus is based upon the clinical appearance. Melanocytic naevi with atypical features must be differentiated from melanoma. Clinical characteristics suggestive of melanoma include ABCDE signs:
- Borders that are irregular
- Color that are not uniform or changing
- Diameter >6 mm
- Evidence of enlargement or change.
Treatment and Management
Most acquired naevi remain benign for life and require no treatment except longitudinal observation for signs of atypical or dysplastic appearance. However, having a large number of acquired naevi increases the risk of melanoma, and patients with multiple acquired naevi should be followed with periodic total body skin examinations and counseled regarding sun protection.
However a large number of naevi can increase your risk of melanoma. Since more than 50% of cutaneous melanoma arise de novo instead of arising from naevi, there has no proven benefit to prophylactically removal naevi expect for cosmetic reason. Regardless of the reason for resection, all specimen are sent for histological evaluation.