Pigmented Lesions - Ephelides, Lentigines,
Melanocytic Nevi and Melanomas
Pigmented Lesion Video
Ephelides, simple lentigines, and junctional melanocytic nevi are all small, tan to brown macules. An ephelis (freckle) is typically found on sun-exposed skin, usually on the face or dorsal forearms and hands of children or young adults with a fair-skinned phenotype. They darken in response to the sun and fade with UV abstinence. Histologically, the only differences that can be detected in lesional skin as compared to normal surrounding skin are larger-sized melanocytes (which are normal in number) with more prominent dendrites and an increased transfer of larger, darker melanosomes to surrounding keratinocytes.
ASK A QUESTION:Lentigines
Lentigines are classified into two main varieties. Solar lentigines (liver spots, age spots, senile lentigines) also occur in response to sunlight, but are more common in middle-aged or older patients, are thought to be caused by years of cumulative UV exposure, and tend to persist even in the absence of sunlight. They favor sites of maximum sun exposure such as the dorsal surface of the hands and the extensor forearms, vary in color from tan to dark brown, and can be up to 1cm in diameter. Simple lentigines, in contrast, occur at any age, have no predilection for sun-exposed areas or lighter skin types, and do not darken in response to sunlight. Lentigines have a distinct histologic pattern of elongated, club-shaped rete ridges which often anastamose (Figure 2). Solar lentigines typically have a normal number of melanocytes plus increased melanin in the basal layer of the epidermis, overlying a background of solar elastosis (abnormal elastic fibers in the dermis due to cumulative UV exposure). In contrast, simple lentigines typically have an increased number of melanocytes, singly arranged along the basal layer of the epidermis. They may be impossible to distinguish clinically from early nevi and are believed by some authors to occasionally evolve into junctional nevi.
Melanocytic nevi are benign neoplasms, histologically distinguished from lentigines or ephelides by the presence of nevus cells, which are melanocytes that group in well-demarcated nests. Acquired nevi tend to first appear in childhood as flat brown macules or minimally elevated papules (Figure 3), usually less than 6mm in diameter. They evolve during adulthood, becoming more elevated and dome-shaped and then eventually fleshy papules or nodules with loss of pigmentation (Figure 4). Further aging of a nevus can lead to a pedunculated skin tag-like lesion or even complete disappearance of the nevus. It is unusual to see melanocytic nevi in individuals older than 80 years of age. Congenital nevi, in contrast, are present at birth or become clinically apparent during early infancy. They may be small, medium or large in size; the latter is often referred to as a giant or garment nevus (Figure 5). Congenital nevi may have irregular or serrated borders and more frequently involve the hair follicles when compared to common acquired nevi.
Histologically, nevi are classified depending on the location of the melanocytic nests. In junctional nevi, the nevus cells are at the dermo-epidermal junction just above the basement membrane zone of the epidermis (Figure 6); the clinical correlate is a darkly pigmented flat or minimally elevated nevus. As nevi mature, the nests of melanocytes gradually are assimilated into the dermis; they are then classified as either compound when the nests are present at the dermo-epidermal junction and within the dermis (Figure 7) and (Figure 8) or as intradermal when the nests are exclusively within the dermis (Figure 9). As the nests descend, they become uniformly smaller and are composed of smaller-sized melanocytes which produce less pigment; the surrounding stroma becomes infiltrated by fibrofatty tissue.
Dysplastic nevi (atypical nevi, Clark's nevi, nevi with disordered architecture and cytologic atypia) are a subgroup of nevi which have an irregular outline, variable pigmentation, indistinct borders, and can be larger than 6mm in diameter. Often described as having a "fried-egg" appearance, they typically have a dome-shaped central brown papular component surrounded by a flatter zone of light brown or tan pigmentation ((Figure 10)). They show disordered histological architecture, typified by less circumscription of the nevus cell nests and extension of the junctional nests beyond the intradermal component. Dysplastic nevi also show an increased number of single melanocytes in the basal layer of the epidermis; pleomorphism of cells; and nests that vary in size, shape, and spacing. The upper dermis usually shows fibrosis and contains a host response of lymphocytes. When multiple dysplastic nevi are present in a patient with a family history of melanoma, they herald an increased risk for the development of melanoma in that patient (Figure 11). The presence of a single or few dysplastic nevi outside the context of a family history of melanoma may or may not portend an increased risk for that patient. Cutaneous melanoma may arise within a previously existing nevus or dysplastic nevus, but approximately 70% of the time, they arise de novo. Melanomas are classically divided into subtypes based on their clinical and histopathologic features. Histologically, all are typified by large, pleomorphic, and hyperchromatic melanocytes with loss of orderly architecture and maturation. Most commonly, melanomas begin as minimally elevated, asymmetrical pigmented papules or plaques with irregular, sometimes scalloped, borders and variations in color. At this stage they may be difficult to distinguish from dysplastic nevi (Figure 12). Superficial spreading melanomas typically show the ABCD's of melanoma (Asymmetry, Border irregularity, Color variegation and Diameter greater than 6mm). If neglected, the depth of tumor invasion can continue to increase; a clinical correlate would be the development of nodularity within the melanoma. Nodular melanoma classically does not have a macular or plaque phase and presents as a blue or black papule or nodule (Figure 13). The superficial spreading and nodular types of melanoma together account for approximately 80% of all melanomas. Both types occur most commonly in patients with lighter skin phenotypes, and may occur anywhere, but have a predilection for the upper back in men and women and the lower legs in women. Risk factors for developing these variants of melanoma include a family history of melanoma (with or without the presence of multiple dysplastic nevi), the presence of numerous common acquired nevi, and a history of blistering sunburns.
The other subtypes of melanoma, lentigo maligna melanoma and acral lentiginous melanoma, are not correlated with intense, intermittent sun exposure. Lentigo maligna melanoma (Figure 14) accounts for approximately 5% of all melanomas and is most commonly seen at sites of maximum sun exposure in patients with obvious photodamage, e.g., the face, hairless ("bald") scalp, extensor forearms and upper trunk. Acral lentiginous melanomas (Figure 15) comprise 3-8% of all melanomas and by definition arise on the volar skin of the palms or soles and the nailbeds. Acral lentiginous melanomas have no known correlation with sun exposure and are the most common form of melanoma in African-Americans, Asians, and Hispanics.
The most important indicator of prognosis for all subtypes of melanoma is the Breslow depth, which is the maximal thickness of tumor invasion as measured by an ocular micrometer, from the top of the granular layer of the epidermis to the base of the neoplasm. Breslow depth is recorded in millimeters with lesions less than 1.0 mm having an excellent prognosis with infrequent metastases and melanomas thicker than 4mm having a rather poor prognosis with a 5-year survival of approximately 50%. The most common sites of local and/or regional metastases are the draining lymph node basins and the skin between the primary site and these lymph nodes whereas the most common sites of systemic metastases are the lung, liver, brain, and gastrointestinal tract.
Common pigmented lesions can't return. Some birthmarks may return after a period of several months to a year. However the treatment can be repeated with similar results.
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