Melanocytic Naevus (Mole)

Melanocytic naevus (common name: mole) is a very common benign skin lesion that results from the rapid growth of melanocytes (pigmented cells). The exact reason why moles appear is still unknown, but the number of moles on the body depends on various factors, such as genetic predisposition, immune status, and prolonged sun exposure. A melanocytic naevus may be present from birth; in medical dermatology, this is referred to as a congenital naevus. Approximately 1% of the population is born with one or more moles. Moles may also appear during the lifespan, in which case they are referred to as an acquired naevus.

Generally, individuals with lighter skin tones are predisposed to having more moles than individuals with darker skin tones. People who have many moles often have family members who share the same trait. Additionally, individuals who undergo immunosuppressive treatment may experience an increase in mole numbers as a side effect.

In medical dermatology, moles have a distinct dermoscopic and histological appearance. Moles can be flat or protruding and may appear on any part of the body; the anatomical site influences the overall appearance of the lesion. Moles also vary in colour, ranging from pink to black. Individuals with lighter skin tend to have light-coloured moles, while individuals with darker skin tend to have dark brown or black moles. Moles vary in size as well, ranging from a few millimetres to a few centimetres in diameter. They generally have a rounded shape, though irregular shapes are observed in rare cases.

Despite their common presence and benign nature, melanocytic naevi can be mimicked by melanoma, one of the most dangerous forms of skin cancer. Initially, melanoma may resemble a regular mole, but it tends to enlarge over time and develop a more irregular shape. Individuals who have a large number of moles may also be at a higher risk of developing melanoma.

In clinical practice, moles are assessed by their appearance through dermoscopy, a skin examination tool that uses surface microscopy to evaluate the structure and patterns of the skin. Key indicators that warrant further assessment include changes in size, colour, shape, or structure of a mole. Patients who develop new moles after the age of 40 are considered to be at elevated risk for melanoma. Melanocytic naevi may also be evaluated using ABCD analysis:

• Asymmetry
• Border irregularity
• Colour variation
• Diameter greater than 6 mm

Moles that are itchy, cause bleeding, or appear crusty are also indications for a more detailed assessment. If a naevus appears suspicious for melanoma, a diagnostic biopsy is performed, involving the collection of a tissue sample for histopathological analysis. This may take the form of an excision biopsy (complete removal) or an incision or punch biopsy (removal of a small portion) of the affected skin tissue.

Melanocytic naevi are generally only removed in cases of suspected malignancy or for cosmetic purposes. Surgical removal techniques include excision biopsy for flat moles and shave biopsy for protruding moles. Removal by radiofrequency surgery is also an available option. When removal is indicated, the most appropriate technique is selected with the aim of minimising scarring.