[Periorbital Pilomatrixoma: a Report of a Case Difficult to Diagnose].

Background: Pilomatrixoma is a benign tumor that arises from matrix cells of hair follicles. In ophthalmology, pilomatrixoma is relatively rare, yet there are reports on eyelid pilomatrixomas that were visible and/or palpable. Our case is the first report on pilomatrixoma that was found as a subconjunctival lesion and neither readily visible or palpable. Case: A 32-year-old woman presented with a chief complaint of conjunctival hyperemia of the left eye with sensation of foreign body. A previous doctor suspected allergic conjunctivitis, but the prescribed antihistamine treatment had failed. Physical exam revealed hyperemia localized to the left temporal bulbar conjunctiva, as well as a 5 mm-diameter hard mass located underneath the lateral palpebral conjunctiva. With a suspicion of inflammatory reaction to a foreign body, enucleation of the mass was performed by opening and detaching the conjunctiva using surgical scissors. Findings: The mass was hard, spherical and 5 mm×10 mm in size without adhesions. The pathology revealed hair follicles, basophilic cells, as well as shadow/ghost cells, which led to the definitive diagnosis of pilomatrixoma. Conclusion: Pilomatrixoma is a benign tumor that arises from matrix cells of hair follicles. This case shows that pilomatrixoma from lateral canthus can extend underneath the conjunctiva.