A Case of Malignant Transformation of an Orbital Epidermoid Cyst to Cystic Squamous Cell Carcinoma.

Squamous cell carcinoma of the orbit is uncommon as there is no squamous epithelium in the orbit. Thus, mechanistically squamous cell carcinoma of the orbit most commonly arises from a cutaneous lesion. Although orbital epidermoid cysts are thought to have very low malignant potential, these lesions possess squamous epithelium and theoretically can undergo malignant transformation. Here, the authors present the case of a 63-year-old woman who presented with a 3-month history of diplopia and forehead tenderness with an orbital extraconal lesion on MRI consistent with a ruptured epidermoid cyst. Six months following resection, she suddenly experienced new-onset left upper eyelid ptosis, recurrent diplopia, and left orbital pain. MRI revealed a recurrence of the left orbital mass. Left anterior orbitotomy and biopsy revealed cystic squamous cell carcinoma. This case appears to demonstrate a very rare malignant transformation of an epidermoid cyst to cystic squamous cell carcinoma.