The nature and origin of nevi is a controversial subject. A nevus has been defined1 in the restricted sense as "a neoplasm containing nevus cells" and in the broader sense as "malformations consisting of (1) hypertrophy or hyperplasia of normal skin elements in their normal locations; (2) the appearance of skin structures or elements in areas where they are not normally found." The latter definition would embrace a great variety of conditions.
The origin of nevus cells has been stated at various times to be endothelial, epithelial and mesoblastic and recently by Masson2 to be neuroectodermal. The literature on the subject tends to overlap that on neurofibromatosis, described by Ewing3 as a "disturbance in the growth and differentiation of the fetal neuro-ectoderm, and a maladjustment with the mesoblastic tissue which it innervates." One's confusion as to the nature of a nevus is not lessened by Rea,4
SHERMAN AR. TERATOID TUMOR OF CONJUNCTIVA AND OTHER DEVELOPMENTAL ANOMALIES WITH NAEVUS VERRUCOSUS OF SCALP: REPORT OF A CASE. Arch Ophthalmol. 1943;29(3):441–445. doi:10.1001/archopht.1943.00880150115005
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