Contributor: Gordon K. Klintworth
The nevocellular nevus is a benign tumor composed of nevus cells of neural crest origin and it is common in the skin of the eyelid and other parts of the body. It is frequently, but not always pigmented. The nevocellular nevus of the skin and conjunctiva is classified according to its location. It may involve subepithelial tissue (subepithelial nevus [nevus - subepithelial]), the subepithelium and epithelium (compound nevus [nevus - compound]), or the base of the epithelium (junctional nevus [nevus - junctional]). Two features of the nevus cell distinguish it from the melanocyte. It has shorter pseudopodic cytoplasmic processes and they can not be seen by light microscopy, and nevus cells are arranged in clusters. Transmission electron microscopy has shown that the nevus cell and the melanocyte of the epidermis are similar; both cells originate from the neural crest and contain melanosomes and have pseudopodic cytoplasmic processes.  A melanoma may arise from a nevocellular nevus. It is divided into three main groups: the intradermal nevus, the junctional nevus, and the compound nevus. In practice the range of possibilities encompasses a continuous spectrum such that individual cases may, while being compound lesions have an overwhelming predominance in either the dermis or the junctional area. The clinical appearance varies greatly and it is usually possible to predict the type from the clinical appearance of the lesion. The cells tend to be spindle-shaped in the deeper dermis and plumper closer to the epidermis. When present melanin is found in nevus cells in the upper dermis and epidermis. Four variants of nevocellular nevus exist: balloon cell nevus [nevus - balloon cell], halo nevus, benign juvenile melanoma [melanoma - benign juvenile], and congenital giant pigmented nevus [nevus - congenital giant cell ]. Involvement of the eyelid with the halo nevus and giant pigmented nevus has not been documented.


Some types of nevus apparently arise from melanocytes [blue nevus ( nevus-blue)]

Nevus of Ota arises from dermal melanocytes.

Different types of nevocellular nevus are common in the conjunctiva. They are frequently pigmented, but not necessarily so.
Based on their location a nevcellular nevi of the conjunctiva are classified into subepithelial nevi (involving the subepithelial tissues only), compound nevi (involving the subepithelium and epithelium), or junctional nevi (involving the base of the epithelium). Junctional nevi are rare and are almost always found in children. Regardless of type an Increase in pigmentation or size during puberty or pregnancy often prompts excision. Conjunctival compound and subepithelial nevi typically contain cystic or solid rests of surface epithelium. The epithelial hyperplasia associated with conjunctival nevi has been confused with invasive squamous cell carcinoma. Unlike their counterpart in the skin, compound and subepithelial nevi of the conjunctiva are frequently associated with a substantial mononuclear inflammatory infiltrate in the conjunctival stroma and epithelial inclusion cysts. Occasionally, enlargement of these epithelial cysts may lead to the clinical suspicion of a conjunctival malignancy.

Different types of nevocellular nevus are common in the conjunctiva. They are frequently pigmented, but not necessarily so. Based on their location a nevcellular nevi of the conjunctiva are classified into subepithelial nevi (involving the subepithelial tissues only), compound nevi (involving the subepithelium and epithelium), or junctional nevi (involving the base of the epithelium). Junctional nevi are rare and are almost always found in children. Regardless of type an Increase in pigmentation or size during puberty or pregnancy often prompts excision. Conjunctival compound and subepithelial nevi typically contain cystic or solid rests of surface epithelium. The epithelial hyperplasia associated with conjunctival nevi has been confused with invasive squamous cell carcinoma. Unlike their counterpart in the skin, compound and subepithelial nevi of the conjunctiva are frequently associated with a substantial mononuclear inflammatory infiltrate in the conjunctival stroma and epithelial inclusion cysts. Occasionally, enlargement of these epithelial cysts may lead to the clinical suspicion of a conjunctival malignancy.