Melanocytic Nevus

INTRODUCTION Also known as nevocellular or nevomelanocytic nevi, these common benign neoplasms or hamartomas are composed of melanocytes. Nevi are nests of melanocytes that may be congenital or acquired. Congenital nevi probably represent malformations or errors in development and migration of these neural crest elements. When nevocytes are sequestered along the palpe-bral fissure of the embryo, this results in the presence of a nevus on both the upper and lower eyelid margin, so-called kissing nevi. Acquired nevi are not present at birth and the incidence increases during the first 3-4 decades of life with a peak incidence in the third to fourth decades. They are especially common in individuals with fair complexion and frequently occur on the sun-exposed areas of eyelid skin. Occasionally they arise in an eruptive fashion, usually following some generalized insult to the skin such as erythema multiforme or burns. Melanocytic nevi can take on several distinct forms. In lentigo simplex proliferating melanocytes are confined to the basal epidermal layer. In junctional nevi nested proliferations of melanocytes are located in the basal epidermis and extend into the tips of the rete ridges. Compound nevi have both a nested junctional location and an intradermal component. The intradermal nevus is confined to the dermis without any junctional component.

CLINICAL PRESENTATION The clinical appearance of melanocytic nevi is often predictive of the histologic type. The majority of nevi found in young children are junctional nevi. Clinically these are oval or round, light to dark brown macules that gradually enlarge in size. On the lid margin intradermal nevi are frequently amelanotic. When large they may cause amblyopia. After this radial expansion is completed they gradually become elevated, evolving into compound nevi found in older children and young adults. Nevi on the eyelid margin characteristically mold to the ocular surface. Occasionally they may extend deep into the eyelid tissues. The finding of coarse dark hairs is not unusual. As the raised component increase the nevus sinks into the dermis and becomes dome shaped, sessile, verrucous, or even polypoid. At this point they are referred to as intradermal nevi, which are more prevalent in adults. In this last stage of development, fine skin lines are lost and pigmentation is decreased to a light brown or flesh tone. Individuals living beyond age 70 years often see most of or all their nevi disappear.

Intradermal Nevus Eyelid
(Courtesy of Richard L. Anderson, M.D.)
Eyelid Diseases

HISTOPATHOLOGY Melanocytic nevi are composed of nevus cells, which are melanocytes that have lost their long dendritic processes. Nevus cells are oval to cuboidal, have clear to pale eosinophilic cytoplasm, and contain a variable amount of melanin. The nevus cells form nests, which often coalesce when they are in the dermis. Melanocytic nevi may have discrete nests of nevus cells at the dermoepidermal junction ("junctional melanocytic nevus"), both at the dermoepidermal junction and within the dermis ("compound melanocytic nevus"), or confined within the dermis ("intradermal melanocytic nevus," shown below). On the eyelid, compound nevi may be papillomatous with a seborrheic keratosis-like appearance to their epidermis.

Lentigo Maligna Differential Diagnosis

DIFFERENTIAL DIAGNOSIS The differential diagnosis includes lentigo maligna, malignant melanoma, neurofibroma, balloon cell nevus, papilloma, seborrheic keratosis, inverted follicular keratosis, oculodermal melanocytosis, dermatofibroma, pigmented basal cell carcinoma, and fibrous histiocytoma.

TREATMENT Malignant transformation may rarely occur, generally in the junctional or compound stages, thus suspicious lesions should be excised. Warning signs for which biopsy is indicated include irregular borders, variation in pigmentation, onset after 40 years of age, change in size or color, pain or irritation, and bleeding or ulceration. Otherwise, removal of common nevi is not required unless desired for cosmesis or relief of mechanical irritation. Shave biopsy without complete removal is acceptable for clearly benign lesions, especially those involving the eyelid margin. However, recurrence from incompletely removed lesions may occur. For non-marginal lesions, simple excision is effective.

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