Orbital dermoid cyst

Dr Bruno Di Muzio et al.

Orbital dermoid cysts are congenital lesions representing closed sacs lined by an ectodermal epithelium and corresponding to the most common orbital tumour in children. They are typically divided according to whether or not they are deep (within the orbit) or superficial (adjacent to the orbital rim).

Epidemiology

They correspond to ~2% of orbital tumours 5. Superficial location is much more frequent.

Clinical presentation

Superficial angular dermoid are usually diagnosed relatively early. As they grow slowly, less than 25% of them are identified at birth, and they usually manifest in the first decade of life. Clinical features include painless subcutaneous mass along the zygomaticofrontal and the frontoethmoidal sutures 1,3.

It is important to note that more than 80% occur in the upper outer quadrant or the lacrimal fossa (external angular dermoid) 1.

Deep dermoids tend to be diagnosed later in life with proptosis 6.

Pathology

Dermoid cysts are thought to occur as a developmental anomaly in which embryonic ectoderm is trapped in the closing neural tube between the 5th-6th weeks of gestation1,3.

Stratified squamous epithelium lines dermoid cysts, like epidermoid cysts. Unlike epidermoid cysts, however, they also have epidermal appendages such as hair follicles, sweat and sebaceous glands. The latter is responsible for the secretion of sebum which imparts the characteristic appearance of these lesions on CT and MRI.

A common misconception is that dermoid cysts contain adipose tissue. This is not the case, as lipocytes are mesodermal in origin, and dermoid cysts (by definition) are purely ectodermal. A dermoid cyst with adipose tissue would be a teratoma.

Radiographic features

These lesions are usually extraconal, non-enhancing masses with smooth margins, cystic and/or solid components which are demonstrated on imaging by fat, fluid or soft tissue signal; occasionally calcifications may be present. Ruptured dermoids may show adjacent inflammatory changes (see case 2).

Treatment and prognosis

Treatment and prognosis depend on size, location and involvement of orbital structures. While a superficial lesion may barely need a cosmetic excision, a deeper one may require more invasive methods involving micro-dissection, orbitotomy, and rarely intracranial exploration if the lesion extends to that extent 7.

Differential diagnosis

Possible differential considerations include

orbital epidermoid cyst
orbital teratoma
- usually large lesions and associated with facial deformity
- multiloculated cystic masses
- calcification, fat, and/or ossification may be present
orbital dermolipoma
orbital haemangioma