Divided Nevus

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Bruce Becker, MD, Jainam Shah

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Bruce Becker, MD

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Overview

A divided nevus (also known as a "kissing nevus," "split ocular nevus" and "panda nevus") is a rare congenital dermatological abnormality and type of congenital melanocytic nevus (CMN) that spans both the upper and lower eyelid margins as two mirror-image halves that align when the eye closes. It is a subtype of periorbital CMN, which encompasses any melanocytic nevus present at birth or within the first few months of life in the eyelid and periorbital region. The divided nevus is distinguished from other periorbital CMN by its bilobed, trans-lid configuration, which reflects the specific embryological window during which the lesion forms.

The figure below shows a divided nevus in a 15-year-old boy extending from the eyebrow to the eyelash-bearing region with cheek involvement. The figure was reproduced from  https://journals.lww.com/prsgo/fulltext/2016/12000/a_novel_reconstructive_procedure_for_the_divided.27.aspx under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License (CC BY-NC-ND 4.0) (https://creativecommons.org/licenses/by-nc-nd/4.0/).

Divided Nevus

Divided nevus in a 15-year-old boy extending from the eyebrow to the eyelash-bearing region with cheek involvement.

ICD-10

D22.1

ICD-9

216.1

Etiology

Embryological Basis

The divided nevus arises as a direct consequence of the embryological fusion and subsequent separation of the eyelids. The upper and lower eyelid folds begin forming from the surface ectoderm during the 6th week of gestation. By the 7th week, distinct upper and lower folds are well defined. At this stage, the upper eyelid begins to assume a dominant role compared with the lower eyelid. By approximately the 8th to 10th weeks of gestation, the eyelids fuse along their margins, forming a continuous epithelial surface. They remain fused until the 26th to 28th weeks of gestation, when they separate via programmed desquamation.

A single melanocytic proliferation is believed to arise within the shared, fused eyelid tissue during this period. When the lids subsequently separate, the nevus is physically divided between the upper and lower lid margins, yielding mirror-image halves. This mechanism accounts for the characteristic kissing appearance: when the eye is closed, the two halves of the nevus precisely re-appose along the line of embryological fusion.

Periorbital Congenital Melanocytic Nevi

Periorbital CMN are a clinically heterogeneous group, classified by size using criteria adapted from those developed for CMN elsewhere on the body. Below are the criteria:

• Small CMN: less than 1.5 cm in greatest diameter
• Medium CMN: 1.5 to 19.9 cm
• Large CMN: 20 cm or greater
• Giant CMN: generally defined as greater than 40 cm, or covering a proportionally large body surface area in an infant

Periorbital CMN encompass lesions of the eyelid skin, eyelid margin, conjunctiva, orbit, and adjacent facial skin. Divided nevi are typically small to medium in size, though larger variants exist. Giant periorbital CMN, though rare, carry a substantially higher risk of associated complications including neurocutaneous melanosis and malignant transformation.

Epidemiology

Divided nevus is uncommon, and no sex or racial association has been established. The vast majority of cases are congenital, noted at birth or during the first weeks of life, though occasional cases may first draw clinical attention during childhood as lesions darken or become more prominent with age. The medial lid margin is the most frequently reported location, though any segment of the upper and lower lid margin may be involved. Bilateral cases (involving both eyes) are exceedingly rare.

Periorbital CMN as a broader group have an estimated birth prevalence of approximately 1% for all sizes combined, with large and giant lesions being substantially rarer (approximately 1 in 20,000 to 1 in 500,000 live births).

References

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