๐ ็ธฝ็ฎ้ ๏ฝ ๐ ่ฑๆๅๆ๏ผๆฌ็ฏ๏ผ ๏ฝ ๐ ๅฎๆด็ฟป่ญฏ ๏ฝ โญ ็ฒพ่ฏ็ญ่จ
INTRODUCTION
Melanocytic nevi are benign melanocytic neoplasms that most commonly develop within the epidermis or dermis. Histologically, there is a proliferation of melanocytes, both in nests and as solitary cells, with the nests defined as aggregates of three or more melanocytes in direct contact. Melanocytic nevi are usually caused by genomic aberrations (oncogenic mutations or translocations) that activate oncogenes and result in a clonal proliferation of affected melanocytes.
The non-nevus melanotic lesions discussed in this chapter can also be tan to dark brown or black in color, but in contrast to melanocytic nevi, they have minimal, if any, increase in melanocyte density. In addition, there is no nesting of melanocytes. Their hyperpigmentation is due to an increase in melanin synthesis and its subsequent transfer to keratinocytes. Other benign and malignant tumors (e.g. seborrheic keratoses, keratinocyte carcinomas) that can also be hyperpigmented are discussed in Chapters 108โ111 and 115.