The skin’s color originates from cells called melanocytes, which are responsible for producing the pigment melanin. These specialized cells normally live scattered individually along the basal layer of the epidermis. The term “nests of melanocytes” describes a specific pattern where these pigment-producing cells have grouped together in a tight, concentrated cluster.
Defining the Cellular Clusters
A melanocyte nest is a microscopic aggregation of nevus cells, which are melanocytes that have undergone a benign proliferation. Normally, individual melanocytes maintain a specific distance from each other, a phenomenon known as contact inhibition. In a nest, this inhibition is lost, causing the cells to multiply and form distinct spherical or oval clumps. The presence of these cell aggregates is the defining feature of a melanocytic nevus, the medical term for a common mole.
Location within Skin Layers
The classification of a melanocyte nest depends on its specific location relative to the two main layers of the skin: the epidermis and the dermis. Nests found exclusively at the junction where these two layers meet are called junctional nests. If the clusters have migrated deeper and are found entirely within the dermis, they are classified as dermal nests. A third common type is the compound nest, which contains melanocyte clusters spanning both locations.
Nests and Benign Moles
The formation of a common mole, or nevus, is a direct result of the benign proliferation of these nested melanocytes. A mole is the clinical manifestation of these organized cellular clusters. The location of the nest determines the mole’s physical appearance, which is typically small, symmetrical, and uniform in color.
Types of Nevi
Junctional nevi, with nests confined to the epidermal-dermal border, are usually flat and present as a macule with a tan to dark brown pigmentation. Dermal nevi, which contain only dermal nests, often appear elevated, dome-shaped, and may be flesh-colored or lightly pigmented. Compound nevi, having nests in both layers, are frequently raised papules or nodules.
When Nests Become Atypical or Malignant
While most melanocyte nests are well-organized and benign, disorganized proliferation can result in an atypical nevus or melanoma. Benign nests are uniform in size and shape, with the cells becoming smaller and less active as they descend deeper into the dermis. Atypical nests, also known as dysplastic nevi, lose this orderly structure, showing variation in cell size, irregular distribution, and the absence of cellular maturation. Malignant transformation is characterized by nests that exhibit uncontrolled, invasive growth. These nests show marked cellular abnormality and disorganized architecture, such as the spread of melanocytes upward into the upper layers of the epidermis, a feature called pagetoid spread.
Monitoring Moles (The ABCDE Rule)
To help monitor for these concerning changes, the public can use the ABCDE rule to evaluate their moles. The appearance of any of these features warrants an evaluation by a dermatologist:
- Asymmetry in shape.
- Irregular Borders.
- Multiple Colors.
- Diameter larger than 6 millimeters.
- Evolution, which is any change in the lesion over time.