What is a Nevus?
A
nevus (plural: nevi) is a common benign growth or lesion on the skin, often referred to as a mole. It typically arises due to an accumulation of
melanocytes, the cells responsible for producing the pigment melanin. Nevi can be congenital (present at birth) or acquired over the course of one's life.
Histological Features
Nevi are composed of
nevus cells, which are a type of melanocyte. These cells can be found in clusters or nests within the epidermis, dermis, or at the junction of these two layers. The histological examination often reveals:
- Junctional Nevi: Nevus cells located at the junction of the epidermis and dermis.
- Compound Nevi: Nevus cells found in both the epidermis and dermis.
- Intradermal Nevi: Nevus cells situated entirely within the dermis.
Types of Nevi
1. Junctional Nevus:
- Usually appears as a flat, darkly pigmented lesion.
- Nevus cells are confined to the base of the epidermis.
2. Compound Nevus:
- Often raised and can be lighter in color.
- Nevus cells are found in both the dermis and the epidermis.
3. Intradermal Nevus:
- Typically raised and may be flesh-colored.
- Nevus cells are located entirely within the dermis.
Clinical Significance
While most nevi are benign, they can sometimes evolve into malignant
melanoma. Features that raise concern include asymmetry, border irregularity, color variegation, diameter greater than 6 mm, and evolving characteristics. Histological examination is crucial for distinguishing benign nevi from malignant melanomas.
Histological Stains
To study nevi under the microscope, various histological stains are used. The most common one is
Hematoxylin and Eosin (H&E), which helps in identifying the basic structure and cell types. For more detailed study, immunohistochemical stains like
S-100,
HMB-45, and
Melan-A are used, which specifically highlight melanocytic cells.
Diagnosis and Treatment
The diagnosis of nevi is primarily clinical, supported by dermoscopic and histological examination. Biopsies are performed to rule out malignancy. Treatment is generally not necessary for benign nevi unless they are cosmetically concerning or symptomatic. In cases where malignancy is suspected, surgical excision is the treatment of choice.Conclusion
Understanding the histological characteristics of nevi is essential for accurate diagnosis and management. Regular monitoring and histological examination can help detect any early signs of malignancy, ensuring timely and effective treatment.
