DERMOID CYSTS

Background

Dermoid and epidermoid cysts are examples of choristomas, tumours that originate from aberrant primordial tissue. These tumours contain normal-appearing tissue in an abnormal location. As two suture lines of the skull close during embryonic development, dermal or epidermal elements may be pinched off and form cysts, which are adjacent to the suture line (this is shown in the image below). Approximately 50% of dermoids that involve the head are found in or adjacent to the orbit.

Pathophysiology

Orbital dermoid cysts may displace structures in the orbit, especially the globe. If the displacement is great, interference with vision by compression of the optic nerve may result or ocular motility may be disturbed, resulting in diplopia. Rupture of the dermoid may incite an inflammatory reaction. 

Clinical Presentation:

History

• Patients generally complain of a mass, which is visible in the orbital area. Growth of these lesions is generally slow. Occasionally, a history of inflammation will be present.
• Patients with deep orbital dermoids may present with marked proptosis and downward displacement of the eye
• In adults, dermoids may become symptomatic for the first time and grow considerably over a year. Based on this fact, some conclude that these lesions may be dormant for many years or have intermittent growth.

Examination of Patient:

• Children
• The most common location is in the superior temporal aspect of the orbit. The second most common location is in the superior nasal aspect of the orbit.
• Lesions located superotemporally are generally smooth, firm subcutaneous masses attached to the orbital rim in the region of the zygomaticofrontal suture.
• The mass is generally less than 1 cm in diameter, nontender, and oval in shape.
• Little displacement of the globe usually occurs.
• Orbital dermoid cysts are not attached to the skin, which helps differentiate them from sebaceous cysts. The cyst usually is tethered to the periosteum of the bone near suture lines, including the sinuses or intracranial cavity.

• Adults: The cysts are palpated less easily and have more vague borders. They are more likely to displace the globe and may erode their way into adjacent structures.

• Inflammation: If the cyst ruptures, either spontaneously or with trauma, an inflammatory response may be seen. This response may be limited to injection of the conjunctiva or may be severe and mimic orbital cellulitis. Occasionally, subconjunctival droplets of fat are seen.

• Neurologic findings
• Rarely, the cyst may press on the optic nerve and produce symptoms of optic nerve compression; reduced visual acuity, colour vision and brightness perception, and a relative afferent pupillary defect.
• More rarely, the cyst may induce diplopia by physically restricting movement of the globe or by compressing cranial nerves III, IV, or VI

Causes

• No known causes for orbital dermoid exist.
• Other diagnostic considerations
• Ruptured dermoid cysts may mimic rhabdomyosarcoma.
• Paediatric metastatic cancers
• Orbital cellulitis

Diagnostic Work up: Imaging Studies

• Radiography: Radiographs often show radiolucent defects where the cyst has eroded into bone. These defects can be large with distinct margins and may show sclerotic changes.
• CT or MRI studies have largely supplanted plain radiography for evaluating dermoid cysts.
  • A review of 160 CT studies of orbital dermoids revealed that 65% were lateral and 30% were medial to the globe, only one was entirely behind the globe, 85% had changes in adjacent bone, 73% had a visible wall, 27% had a CT attenuation similar to orbital fat, 14% had calcification, 5% had a fluid level, and 20% had abnormal soft tissue outside the cyst. The cyst lumen is generally homogeneous but can also be heterogeneous depending on the amount of lipid and keratin within it. The lumen does not enhance with contrast.
  • On MRI, features include a cystic appearance, internal fat attenuation (T1 hyperintensity), internal calcification, and fluid levels. The wall of the cyst but not the lumen may show enhancement with gadolinium. These features are uncommon in rhabdomyosarcoma.
• Ultrasound characteristics of dermoid cysts include a smooth contour and variable echogenicity.
• Colour Doppler imaging of dermoid cysts shows no intralesional blood flow, which can help differentiate them from haemangioma and rhabdomyosarcoma. 

Medical Care

• No medical care usually is required for an orbital dermoid.
• Inflammation that results from a ruptured dermoid cyst may be controlled with oral prednisone.

Surgical Care

• Dermoid cysts usually are cosmetic problems. The location of the dermoid cyst in the orbit helps determine the appropriate type of orbitotomy. A method for percutaneous drainage and ablation of orbital dermoid cysts and endoscopic-assisted removal of orbital dermoid cysts has been reported.
• Inflammation from preoperative or intraoperative rupture of the cyst can be controlled with the use of prednisone.
• Failure to remove the entire cyst may result in persistent inflammation, a draining sinus, or recurrence of the cyst. 

Further Outpatient Care

• After surgical excision of an orbital dermoid, infrequent follow-up care is necessary

Complications

• The dermoid cyst may displace the globe, depending on the location of the cyst.
• Orbital dermoid cysts may cause neurologic complications if they compress the optic nerve or cranial nerves III, IV, or IV.
• If the cyst ruptures, a marked inflammatory response follows.
• Operative complications are those common to other orbitotomy procedures.
  • Damage to the eye or adnexal structures, motility restriction, infection, inflammation, and haemorrhage may occur.
  • Partial excision of the dermoid cyst may result in persistent inflammation, a draining sinus, or recurrence.

Prognosis

• Dermoid cysts generally have a benign prognosis.
  • If they are excised completely, usually only a minimal scar occurs.
  • If they are observed rather than excised, slow growth can be expected.

FAQ – Dermoid Cyst

What is a dermoid?

A dermoid is an overgrowth of normal, non-cancerous tissue in an abnormal location. Dermoids occur all over the body. The ones in and around the eye are usually comprised of skin structures and fat [See figure 1].

Where are dermoids found around the eyes?

There are two main dermoid types that occur on or around the eyes. An orbital dermoid is typically found in association with the bones of the eye socket. An epibulbar dermoid is found on the surface of the eye, either at the junction of the cornea and sclera (limbal epibulbar dermoid) or more posteriorly on the eye where the conjunctiva that covers the eye meets the conjunctiva that covers the lid (posterior epibulbar dermoid or lipodermoid).

What does an orbital dermoid look like?

An orbital dermoid present as an egg-shaped mass under the skin adjacent to the bones of the eye socket. The mass is soft. The skin overlying the mass is normal in appearance. Dermoids can remodel the bone adjacent to them so that they often 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. Dermoids are cysts and are typically filled with a greasy material that is yellow in color

Where are orbital dermoids usually found?

Orbital dermoids usually form anteriorly in the eye socket where two of the facial bones that form the eye socket touch each other. The most common place for dermoids to occur is in the upper and outer part of the eye socket near the end of the eyebrow. They can also occur adjacent to the nose but are rarely found in association with the bones in the lower part of the eye socket. Rarely orbital dermoids are found more posteriorly in the eye socket.

Do orbital dermoids need to be removed?

Sometimes dermoids can cause vision loss in the affected eye.  There is also a small risk that orbital dermoids can rupture and cause an inflammatory reaction.  For these reasons your pediatric ophthalmologist may recommended that the dermoid be removed.

How are orbital dermoids removed?

The skin overlying the dermoid is opened and the surrounding tissues are dissected until the dermoid is revealed. The dermoid is then carefully dissected free from the surrounding tissue. The excised mass is typically sent to a pathologist who can confirm the identity of the tissue.

Do orbital dermoids cause vision loss?

Not usually.

Are orbital dermoids found in association with other diseases?

No.

What does a posterior epibulbar dermoid or lipodermoid look like?

A posterior epibulbar dermoid is typically yellow in colour and soft in consistency, moulding to the curve of the eye. The conjunctiva overlying it may be thickened. Occasionally there is one or more hairs sticking out from the mass.

Where are posterior epibulbar dermoids usually found?

Posterior epibulbar dermoids are usually found under the outer upper eyelid in the recess where the eyeball meets the eyelid [See figure 1]. Depending on their size, they may be visible only when the upper lid is lifted or if larger, they may be seen with the eyelids in the usual position.

Do posterior epibulbar dermoids need to be removed?

Not always. If they are small and not bothersome to the patient or patient’s family, posterior epibulbar dermoids can be left alone.

How are epibulbar dermoids removed?

Posterior epibulbar dermoids are usually not attached to the eyeball itself. They are attached to the conjunctiva that covers the eye. They often extend posteriorly into the eye socket and usually cannot be entirely removed. Excision involves stripping the dermoid free of the overlying conjuctiva, clamping the mass at the most posterior extent of the dissection and removing the anterior part of the mass. The excised mass is typically sent to a pathologist who can confirm the identity of the tissue.

Do posterior epibulbar dermoids cause vision loss?

Not usually.

Are posterior epibulbar dermoids associated with other diseases?

Yes, sometimes. They can be found in persons with Goldenhar syndrome, linear nevus sebaceous syndrome, and encephalocraniocutaneous lipomatosis.

Are posterior epibulbar dermoids associated with other diseases?

Yes, sometimes. They can be found in persons with Goldenhar syndrome, linear nevus sebaceous syndrome, and encephalocraniocutaneous lipomatosi

Where are limbal dermoids usually found?

They are found on the surface of the eye one the cornea or at the junction of the cornea and sclera.

Do limbal epibulbar dermoids need to be removed?

Because they can cause eye irritation and because the appearance is abnormal, epibulbar dermoids are usually removed.

How are limbal epibulbar dermoids removed?

The dermoids are cut flush with the surface of the eye. Sometimes the dermoid extends into the sclera and/or the cornea and care must be taken to avoid entering the eye when excising them. After excision, the site where the dermoid lay can be covered by a piece of transplanted cornea.

Do limbal dermoids cause vision loss?

Occasionally the dermoid is so large that it blocks visual input from entering the eye. More often however, the vision loss occurs because the presence of the dermoid causes the cornea of the affected eye to have an irregular shape. This warping of the cornea can cause a large amount of astigmatism and a blurred image. The blurred image encourages the developing brain to ignore the input from the affected eye, thus causing vision loss through amblyopia. Fortunately, amblyopia if detected during childhood can often be successfully treated (amblyopia).

Does the risk of vision loss go away after the dermoid is removed?

Usually not, even though the dermoid is gone, the warpage it causes in the cornea remains and the risk of amblyopia developing remains.

Are limbal dermoids associated with other diseases?

Yes, sometimes. They can be found in persons with Goldenhar syndrome, linear nevus sebaceous syndrome, and encephalocraniocutaneous lipomatosis.