Intradiploic epidermoid cyst of frontal bone with spontaneous fistulization to eyelid.

Dermoid and epidermoid cysts are choristomas that form due to the entrapment of epithelial remnants within the bony suture lines during embryologic development, around third and fifth week of gestation. Although these rare cysts, particularly the epidermoids, are most often seen in the cranial bones, they only constitute about 1% of all cranial tumors. Approximately, 25% of cranial epidermoids form in the diploic space of the membranaous bones of the skull, hence called intradiploic cysts. We describe the clinical manifestations and treatment of an intradiploic epidermoid cyst (IEC) of the orbital part of the frontal bone, which caused skin fistulization to the lateral aspect of the left upper eyelid. Clinical and surgical features are discussed and the pathogenesis of the skin fistula is analyzed.