Keratinous Cyst of the Caruncle Developing From a Sebaceous Gland Duct: Case Report With Immunohistochemical Analysis.

An enlarging white caruncular cyst in a 24-year-old woman proved to be a keratinous cyst lined by keratinizing squamous epithelium that lacked a keratohyalin granular layer (trichilemmal keratinization). The cyst most likely originated from a sebaceous gland duct. A panel of immunohistochemical stains was employed that compared and contrasted the cyst lining with the overlying caruncular conjunctival epithelium and further eliminated the likelihood of a conjunctival cyst. The most useful confirmatory stains were the positive trichilemmal marker calretinin, the positive sebaceous ductal marker cytokeratin 17 (suprabasal epithelium), and the negative conjunctival markers cytokeratins 7 and 19. Only one previous report of a very rare similar caruncular cyst is recorded in the literature without an extensive immunohistochemical analysis.