Intratarsal Keratinous Cyst Misdiagnosed as a Chalazion Complicated by an Intralesional Triamcinolone Injection: A Case Report.

An intralesional triamcinolone acetonide injection is one of the treatment options for chalazia. However, lesions clinically resembling chalazia may occasionally represent other pathological entities, potentially leading to unexpected complications after treatment. We report the case of a 54-year-old man with a left upper eyelid mass initially diagnosed as a chalazion and treated with an intralesional triamcinolone acetonide injection. The following day, the lesion showed marked worsening, with swelling, redness, and pain. Imaging revealed a cystic lesion, and bacterial infection could not be excluded. Intravenous antibiotics were initiated; however, the lesion continued to worsen, and drainage yielded sterile purulent material. Surgical excision revealed a cystic lesion containing keratinous material. Histopathological examination demonstrated marked inflammatory cell infiltration without granulomatous inflammation or lipid-laden macrophages characteristic of chalazion. Based on the surgical findings, histopathological findings, and clinical course, the lesion was diagnosed as an intratarsal keratinous cyst complicated by rupture and foreign body inflammatory reaction following intralesional steroid injection. This case highlights the importance of careful differential diagnosis in eyelid lesions mimicking chalazia. An intralesional steroid injection may cause severe inflammatory complications when administered to inappropriate lesions.