Orbital dermoid is an egg-shaped mass formed under the skin adjacent to the bones of the eye socket. The mass is smooth, yet firm and non tender. Dermoids can remodel the bone adjacent to them so they can comfortably sit in a depression in the bone. Sometimes dermoids are dumbbell-shaped, with one half of the mass on the outer part of the rim of the eye socket and the other part in the inside of the rim of the eye socket.
Orbital dermoids are one of the most common orbital tumours in children that are thought to develop between 3 and 5 weeks gestation.
They are often evident soon after birth, majorly because parents are concerned about a periocular lump, or an asymmetry of the eyelids or brows of their babies. In rare cases, the cyst may be asymptomatic until the time it presents with apparent enlargement or with inflammatory symptoms like pain, redness and eyelid swelling.
In the periorbital area, dermoid cysts are typically located near the zygomatico-frontal and fronto-ethmoidal sutures, sites of particularly complex embryology. Even if the patient does not have any signs of inflammation, most periocular dermoid cysts show evidence of inflammation due to leakage of the lipid and keratin contents from the cyst, the incidence being similar at all ages. This may spread them to surrounding structures.
According to one survey of 307 orbital tumors, 35% were found to be dermoid cysts, while another one found that of 645 orbital biopsies of all age groups, 24% were dermoid cysts.
However, among the 250 children under 18 years, 46% were dermoid cysts. The survey found that more than 70% of orbital dermoid cysts were diagnosed before the age of 5 years.
Basically there are two types of cysts – superficial ones that are formed adjacent to the orbital rim and the deep ones that are formed within the orbit.
Superficial angular dermoids are usually diagnosed early in childhood. As they grow slowly, less than 25% of them are identified at birth, and they usually manifest in the first decade of life.
Deep dermoids tend to be diagnosed later in youth or during adulthood.
Stratified squamous epithelium lines dermoid cysts, like epidermoid cysts. However, unlike epidermoid cysts, they also have hair follicles, sweat and sebaceous glands. These glands are responsible for the secretion of sebum.
A common misconception is that dermoid cysts contain adipose tissue. This is not the case, as lipocytes are mesodermal in origin, and dermoid cysts are purely ectodermal. A dermoid cyst with adipose tissue would be a teratoma.
These lesions are usually extraconal, non-enhancing mass with smooth margins, cystic or solid components which are characterised by fat, fluid or soft tissue signal. Occasional calcifications may be present. Ruptured dermoids may show adjacent inflammatory changes.
Imaging studies such as ultrasonography, computed tomography and magnetic resonance may help define the extent, depth and relationship of deep dermoid with surrounding tissues and eye.
The lipid and keratin content of dermoid cysts typically induces a marked inflammation in the cyst wall and secondary fibrosis may complicate surgical excision. There can be difficulty in defining the plane of excision. It can cause damage to healthy neighbouring structures. Although rarely a severe, but sterile, orbital cellulitis will be caused due to an underlying leaking dermoid cyst, evidence of inflammation is usually present in most lesions, even in childhood.
Treatment depends on the 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.
Most of the treatments for orbital dermoid cysts are done due to cosmetic reasons, recurrent inflammation or risks of amblyopia. While there is minimal risk of amblyopia, majority of the dermoid cyst are removed because of family’s concern for growing lesions. Also, episodes of recurrent inflammation after direct trauma make it necessary to remove these cysts.
Types of incisions could be direct over the dermoid cyst through the sub brow or over the eyelid crease. Dissection is carried around the lesion without rupturing the cyst. However, when the cyst is large, deep in orbit and filled with fluid, your doctor may decompress the lesion first.
This approach can help to keep the external incision small and also aid in gentle dissection around the lesion deep into the orbital cavity. The dermoid cyst should be completely removed from its attachments to the bony sutural lines. The area should be thoroughly irrigated with corticosteroids solution especially if there is any leakage of cystic contents. The incision is usually closed in 2 layers; deep layer should be closed with 6.0 chromic and superficial layer with 6.0 plain-gut especially in children, as suture removal is difficult in this age.