Cases

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Dermoid cyst in the external angle of the left orbit: The MRI in A shows proptosis and a mass in the external angle of the left orbit. It is a short-tau inversion recovery (STIR) sequence and suppresses the fat signal intensity in the mass. The T1-weighted image in B reveals hypointense and hyperintense areas indicative of fat or hemorrhage. The T2-weighted image in C shows the mass to be uniformly bright.

The most common cause of this appearance is a dermoid cyst, which most often occurs in the external angle of the orbit. Other sites include the root of the nose, the area around the ear, and the submental region. Dermoid cysts are more common in females than in males.

Pathologically, the mass is globular and cystic. Dermoids have thick capsules lined by stratified squamous epithelium. The cysts contain hair follicles, hair, keratin, sweat and sebaceous glands, and liquefied cholesterol (tissues derived from the ectoderm and mesoderm).

Dermoid cysts can extend in a dumbbell fashion into the orbit, or they cause erosion of the orbital plate of the frontal bone and attach to the dura. Surgical excision is the treatment of choice.

For more information on dermoid cysts, see the eMedicine article Dermoid Cyst (within the Dermatology specialty) and the eMedicine Consumer Health article Dermoid Cyst Removal.

Reference:

Davenport M. ABC of general surgery in children: lumps and swellings of the head and neck. BMJ 1996;312:368-371.