Acquired melanocytic mass
This is the most common type of nevus and is often referred to as a “nevus”. These nevi are small in diameter, have sharp borders, and appear as pigmented patches, papules, or nodules containing melanocytes. Depending on the level of the skin where the melanocytes are located, they can be classified as junctional nevi (located at the dermal-epidermal junction), compound nevi (present in both the epidermis and the dermis), and intradermal nevi (located in the dermis).
These nevi usually change over time and have a tendency to “fall” from the epidermis into the dermis. They first appear in early childhood and progress from junctional nevi to complex nevi and then to intradermal nevi. Eventually, intradermal nevi become fibrotic and may disappear after the age of 60. The deeper the location of the melanocyte, the weaker its ability to produce pigment, so the stage of the nevus can be initially determined by observation. Crossed nevi have a flat surface and dark color; compound nevi have a raised surface and dark color; and intradermal nevi have a raised surface and light color.
Congenital melanocytic nevus
Congenital melanocytic nevus is a benign tumor of melanocytes. Most of them are present at birth, while a few of them may appear gradually within a few weeks after birth, and their size may be small or large. Congenital melanocytic nevi often result in localized skin changes, often seen as rough skin covered with a layer of hair. For this reason, congenital melanocytic nevi are often referred to as “black hair nevi”.
From both an aesthetic and medical point of view, patients with melanocytic nevi should have them surgically removed because they have a higher chance of malignant transformation than ordinary nevi. Also, congenital melanocytic nevi of large size tend to have a poor prognosis once they become malignant because they are not easily detected.
Halo nevus
A so-called halo nevus is a ring of depigmented skin around a mole that resembles a halo. This phenomenon is the result of the body activating its immune mechanism. Halo nevi often occur in patients with vitiligo and can appear earlier than other symptoms of vitiligo.
Blue nevus
Blue nevi are dark blue or gray-black textured nodules on the skin that result from ectopic aggregation of melanocytes in the dermis. Cellular blue nevi are those that are relatively large in size. Blue nevi most commonly occur on the back of the hands and feet, but can also occur on the face. Cellular blue nevi can occur on the buttocks, lower back, scalp, and face.
Macular nevus
Pemphigoid nevi are also relatively common and are characterized by small dark brown macules (2-3 mm) scattered over a larger patch of light brown (up to 375 px or more). The chance of malignancy in speckled nevi is relatively small.
Spitz nevus
Spitz nevus is a benign lesion with the typical appearance of small, dome shaped, hairless nodules (<25px in diameter), mostly pink or brown in color. Patients with Spitz nevus often have a history of rapid nevus growth over a short period of time.
Nevus of Ota
Nevus of Ota is a pigmented abnormality that is very common in Asia. Its typical appearance is a dull patch of skin mixed with blue and brown, most often on the face. Similar to blue nevi, nevus of Ota is caused by ectopic melanocytes in the dermis, and in some patients the blue areas can even involve the sclera of the eye. Nevus of Ota may be congenital but is not hereditary and is very effective when treated with laser.
Mongolian Spots
The name is very oriental. Yes, Mongolian spots occur most often in Asian populations and often present as grayish-blue patches on the lower back of newborns. Similar to nevus of Ota, this lesion is also caused by ectopic melanocytes in the dermis. However, unlike nevus of Ota, Mongolian spots often fade on their own as the child grows.
Baker’s nevus
Baker’s nevus is actually a type of dysplasia. This developmental abnormality includes changes in pigmentation, hair and skin surface. Baker’s nevus is seen almost exclusively in males and most often occurs on the back of the shoulder. It typically has the appearance of a light brown map-like area with well-defined borders. Hair growth may be present on the surface of the lesion. The hyperpigmentation in Baker’s nevus is not caused by melanocytes, but rather by the high amount of melanin contained in the basal cells.
Epidermal nevus
Similar to Baker’s nevus, epidermal nevus is also not associated with melanocytes. The essence of an epidermal nevus is an overgrowth of epidermal structures. Because of its cauliflower-like appearance, epidermal nevi are often also referred to as verrucous nevi. All epidermal nevi that occur on the head and neck are congenitally present. Epidermal nevi often appear as a linear arrangement on the body, especially on the lower legs.