Pigmented lesions in childhood can pose diagnostic and therapeutic challenges for pediatric surgeons.
This chapter examines the common pigmented lesions encountered in childhood.
The skin is the largest organ in the body and is composed of 3 layers: the epidermis, dermis, and subcutaneous fat. It serves many functions including thermoregulation, sensory perception, and protection microbial invasion.
The epidermis originates from ectodermal cells and consists of several layers: stratum basalis (inner layer), stratum spinosum, stratum granulosum, stratum lucidum, and stratum corneum (outer layer) (Figure 59.1).
Cell types found in the epidermis includes keratinocytes, melanocytes, and Langerhans (dendritic) cells.
Keratinocytes are the stem cells that will repopulate the other layers over an individual’s lifetime.
They progress from the stratum basale to the stratum corneum.
Melanocytes are derived from neural crests cells and are found in the stratum basale.
Their primary function is to produce the pigment melanin for defense against UV injury.
Melanin accumulates in melanosomes, which are then phagocytosed by neighboring keratinocytes for melanin storage.1
Skin color results from the variable production and degradation of melanosomes and not on numbers of melanocytes.
Langerhans (dendritic) cells are bone marrow-derived, antigen-presenting cells that detect and present foreign antigen to T cells.
The dermis is of mesodermal origin and consists of consist of connective tissue, nerve endings, blood and lymphatic vessels, and adnexal structures (eg, hair shafts, sweat glands, and sebaceous glands).
It is divided into a superficial papillary layer and a deeper reticular layer.
Common terminologies to be familiar with are shown in Table 59.1.
Nevus skin lesions are collections of well-differentiated cells within the tissue of origin.
Classified based on the cell of origin (melanocytic and nonmelanocytic).
Melanocytic nevi are derived from melanocytes or their precursors.
Vary in their location within the dermis and epidermis and in their content of melanin.
Nonmelanocytic nevi are derived from keratinocytes and are also referred to as epidermal nevi.
Can be primarily keratinocytic or organoid, which originate from adnexal structures.
TABLE 59.1 Common Dermatologic Terminology
Melanocytic nevi are divided into acquired nevi (those that appear after birth) and congenital nevi (those that are present at birth) (Figure 59.2).
They are then further subclassified as junctional, compound, or dermal according to the location of the nevus cells in the skin.
Junctional nevi are at the junction of the epidermis/dermis.
Compound nevi involve both the epidermis and dermis.
Dermal nevi are confined to the dermis.
In childhood, >90% of nevi are junctional.2
Most nevi then become compound or dermal nevi as they migrate into the papillary dermis.
In general, the deeper the nests of nevus cells, the more raised and less pigmented the lesion (ie, dark flat lesions vs raised tan lesions).
The common variants of melanocytic nevi are shown in Table 59.2
TABLE 59.2 Common Melanocytic Nevi