To introduce a case of a cyst containing a parasite misdiagnosed as a dermoid cyst, which is to the best of our knowledge, the first report in Korea of a parasite in a cyst located at the medial side of the orbit.

A 31-year-old male visited the hospital with a 2-year history of a slowly growing mass at the medial side of the right orbit. The patient had a history of mass excision in the same location 18 years previously, however, biopsy was not performed at that time. Orbital computed tomography and magnetic resonance imaging revealed a 5.0 × 1.4 × 1.8 cm³ well-defined T1 high signal intensity unilocular cyst, thus our first impression was a dermoid cyst. The cyst was surgically removed with anterior orbitotomy. The cyst ruptured during the operation, and thus complete aspiration of the cystic fluid and in situ irrigation with antibiotics were performed. Histopathological examination revealed a fragmented adult parasite worm with chronic granulomatous change.

A differential diagnosis for orbital cyst based on clinical and radiological results is difficult. Thus, histopathological confirmation is required. A cyst containing a parasite located in the orbit has rarely been reported. A full examination of all infected patients must be conducted for parasite infection.