Pigmented Nevus

A pigmented nevus is a benign neoplasm composed of nevus cells, also known as nevus cell nevus, cellular nevus, and melanocytic nevus. This condition is common and almost everyone has it. It can occur from infancy to old age, with the number of nevi increasing with age and often significantly during puberty. Women tend to have more nevi than men, and whites have more than blacks. Pigmented nevi are occasionally seen on the surface of mucous membranes. There are various clinical manifestations, with the color mostly being dark brown or ink black, and a small number being colorless.

Cause and Pathogenesis

Pigmented nevus is a developmental malformation. During the migration of melanocytes from nerves to the epidermis, melanocytes are locally aggregated due to accidental abnormalities.

Clinical Manifestations

The basic lesions are generally macules, papules, nodules, or papillary lesions with a diameter of less than 6mm, mostly round, often symmetrically distributed, with clear boundaries, regular edges, and uniform color. The number of nevi varies, ranging from single to several or even dozens. Some lesions may have one to several short and thick black hairs. Due to the different pigment content of nevus cells, they may appear brown, brown, blue-black, black, or normal skin color, light yellow, or dark red. Sun exposure can increase the number of pigmented nevi in exposed areas. According to the distribution of nevus cells, they are divided into junctional nevus, mixed nevus, and intradermal nevus.

(i) Junctional Nevus

Junctional nevus is present at birth or occurs shortly after birth. It is usually small, with a diameter of 1 to 6 mm, smooth, hairless, flat, or slightly above the skin surface, and light brown to dark brown macules. It can occur anywhere on the body.

(ii) Mixed Nevus

Mixed nevus looks similar to junctional nevus but may be higher, sometimes with hair protruding, and is more common in children and teenagers.

(iii) Intradermal Nevus

Intradermal nevus is common in adults. It is a hemispherical raised papule or nodule with a diameter of several millimeters to several centimeters. The surface is smooth or nipple-shaped, or has a pedicle and may contain hair. Intradermal nevus generally does not increase in size. It is more common on the head and neck. Pigmented nevi are unstable and often undergo a growth and evolution process from maturity to aging. Most moles start out as small and flat junctional moles, then develop into mixed moles, and eventually become intradermal moles. When junctional moles become malignant, there is often mild pain, burning, and tingling in the local area, and satellite dots appear at the edge. If they suddenly increase in size, darken in color, have inflammatory reactions, rupture, or bleed, it's important to be vigilant.

Pathological Characteristics

Nevus cells are arranged in nests, with clear boundaries and often contain melanin. During the maturation process, nevus cells change from large to small from top to bottom, and the cell nucleus also gradually becomes smaller, tends to mature, and finally degenerates. There are roughly four types of cells: transparent nevus cells, epithelial cell-like nevus cells, lymphocytic nevus cells, and fibrous nevus cells (the most mature nevus cells).

(I) Junctional Nevus

Junctional nevus is the early development stage of pigmented nevus. Nevus cells are completely located in the deep epidermis, or the cell nest is in the "dripping" stage, that is, the lower part of the nevus falls into the dermis, but the upper part is still connected to the epidermis, and can simultaneously involve the outer hair root sheath, sebaceous glands, or sweat glands. The nevus cells are mainly transparent nevus cells, and sometimes epithelial nevus cells are seen. Most of them are gathered into nests. The size and shape of the nests and nevus cells are consistent, with neat edges, equidistant and evenly distributed, and rarely fused. Nuclear division images are extremely rare, and there is generally no inflammatory cell infiltration in the dermis.

(ii) Intradermal Nevus

The nevus cells of intradermal nevus are relatively mature, no longer proliferate, and are located in the dermis. Most of the upper part is epithelial cell-like, arranged in nests or cords, separated by collagen fibers. The cells in the middle and lower parts are mostly lymphocyte-like and fibrous cells.

(iii) Mixed Nevus

Mixed nevus has the dual characteristics of junctional nevus and intradermal nevus.

Diagnosis and Differential Diagnosis

The diagnosis of this condition is mainly based on clinical manifestations, such as the appearance of varying numbers of macules, papules, or nodules on the skin or mucous membranes, with different colors and clear boundaries. Childhood junctional nevus should be differentiated from lentigo and freckles. Mixed nevus and intradermal nevus should be differentiated from seborrheic keratosis, pigmented basal cell carcinoma, dermatofibroma, neurofibroma, etc. Differentiating from malignant melanoma is important as the latter often presents with asymmetry, unclear boundaries, rough edges, uneven colors, and rapid tumor growth, and can form irregular scars. The tumor cells are often atypical.

Treatment

(1) Reduce friction and external factors that damage the nevus. Treatment is generally not required except for cosmetic needs.

(2) Pigmented nevus occurring on areas prone to friction should be closely observed, especially those with irregular edges, uneven colors, and diameters >1.5cm. Surgical excision should be carried out in a timely manner if rapid expansion or other concerning signs are observed.

(3) Ultra-pulsed CO2 laser treatment can be considered for pigmented nevus with a diameter of less than 0.5cm for patients who require nevus removal for cosmetic reasons.

Ultra-pulsed CO2 Laser Therapy Device

(I) Introduction

The wavelength is 10600 mm, similar to continuous CO2 laser. It uses the principle that CO2 laser energy can be completely absorbed by water molecules in skin tissue to carbonize or vaporize skin lesions. Its pulse width is very short, causing less thermal damage to surrounding normal tissues and fewer scars than traditional CO2 laser.

(II) Operation

Preoperative precautions include considerations for contraindications and suspected malignant transformation. During surgery, a suitable dose should be chosen, and the wound should be treated carefully to prevent unnecessary thermal damage. Postoperative care involves applying antibiotic ointment, avoiding sun exposure, and monitoring for complications such as scarring or pigmentation changes. If the treatment is not thorough, a second CO2 laser treatment or surgical removal may be necessary to prevent recurrence.

(III) Possibility of Mutagenesis

There is no clear conclusion on whether CO2 laser treatment of pigmented

Source: Pigmented Nevus