Ocular Pathology

Anatomy and pathology of the human eye. Use it to review eye pathology for Ophthalmology Board Review or OKAP.

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Sunday, September 10, 2006

What is a nevus of the eyelid?

Eyelid Nevi
Definition: Nevocellular nevi are benign proliferations of melanocytic cells divided into 3 categories depending on their architecture: junctional, compound and intradermal. The congenital nevus of the eyelid is a special category with implications for malignant transformation.
Incidence/Prevalence: The intradermal nevus is by far the most common nevus seen on the eyelid.
Etiology: There is some controversy whether nevocytes arise from melanocytic precursors in the nerve sheaths or in the epidermis.
Clinical Findings: On the eyelid the nevus often arises at the eyelid margin and may be flat, elevated, dome-shaped, and even pedunculated. The flat lesions are often junctional nevi. The domeshaped lesions are often intradermal or compound nevi and the pedunculated lesions are usually intradermal nevi. The image shows a dome-shaped pedicle at the eyelid margin which was diagnosed clinically as a “squamous papilloma”. Close examination reveals subtle brown areas on the surface and a tan color. Histology showed an intradermal nevus. Generally nevi will be tan in color and often will feature deep brown pigmentation. The nevus is generally well circumscribed and not associated with ulceration.

The congenital nevus of the eyelids may present as a "kissing nevus" in which the melanocytes are present symmetrically on the upper and lower eyelids. Presumably this nevus was present prior to eyelid separation (9 -20 weeks of gestation).
Gross Findings: As shown in the macroscopic image of a bisected eyelid lesion, the surface of the lesion may be domeshaped or irregular (arrows 1) and in this nevus, nests of cells near the surface are more darkly pigmented (arrow 2). The lesion is elevated as nest of cells begin to fill the dermis (arrow 3).
Histopathology: Nests of nevocytes may be present at the epidermal-dermal junction (hence junctional nevus), confined to the dermis (intradermal) or both (compound). The nevus shown in the
image is an intradermal nevus. Nests are composed of uniform cells with bland nuclei and variable amount of cytoplasmic pigmentation (number 1). Cells deeper in the lesion tend to have smaller nuclei, be less pigmented and the cells appear more organoid in architecture and more spread out. The nuclei may show invaginated cytoplasm that give the appearance of a vacoule or an inclusion within the nucleus (arrows 3). The invaginated cytoplasm may contain brown pigment. Some cells may contain clumps of pigment (number 2). There are usually very few if any mitotic figures. Nevi are believed to progress over time from junctional nests, or theques, to nests that migrate into the superficial dermis. Eventually the nevus becomes a dome-shaped as it expands and fills the dermis locally and finally as a pedunculated lesion.
The kissing nevus or congenital nevus of the eyelid will have similar features to the compound nevus but may show extensive pilosebaceous apparatus involvement.
Treatment: Suspicious pigmented lesions of the eyelid, that have a history of growth, alteration in pigment pattern, vascularity, associated inflammation should be removed as the early diagnosis of melanoma is critical and may be confused with a nevus. Some nevi in which the diagnosis is obvious may be cosmetically unacceptable to the patient or may cause irritation, particularly if they are pedunculated. These are easily removed at the slit lamp.

Prognosis: Most nevi of the skin are not considered to be at increased risk of malignancy. However, the large congenital melanocytic nevus appears to have an increased risk of malignant
transformation of 4.6% during a 30 year period in a Danish study (see Wu-Chen et al.). The risk of transformation of the kissing nevus of the eyelid has never been firmly established; a single case was published in 1950 by Fuchs, but this was anecdotal and no pathology was provided.

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