- Congenital, choristoma
- Ectodermal rests pinched off from neural tube adjacent to suture lines of orbital or other cranial bones
- Classic epidermal dermoid cyst is lined by keratinizing stratified squamous epithelium with dermal tissue containing skin appendages including hair follicles and sebaceous and sweat glands (Figure 1).
- Rare reports of squamous cell carcinoma of cyst lining (Ahuja, Semin Ophthalmol, 2006)
- Less common conjunctival dermoid cyst is lined by nonkeratinizing squamous epithelium, with goblet cells in addition to dermal appendages
Figure 1. High power photomicrograph of dermoid cyst wall showing sebaceous glands.
- Greater than 80% of dermoids are found in the head, and majority of those are periocular (Shields, Surv Ophthalmol, 2004)
- Might represent between 2% and 14% of all orbital tumors (Bonavolontà, Ophthal Plast Reconstr Surg, 2013; also, Shields, Ophthalmology, 2004)
- If rim site is counted, likely most common pediatric orbital tumor (Shields, Surv Ophthalmol, 2004)
- Most common cystic orbital lesion (Shields, Surv Ophthalmol, 2004)
- Typically presents as a slowly progressive mass in superotemporal or superomedial orbital quadrant (Figure 2)
- Visible at or near birth
- Slowly enlarges as the child grows
Figure 2. External photograph showing clinical appearance of dermoid cyst present along frontozygomatic suture in a child.
- Divided into superficial and deep
- Superficial is usually recognized in childhood, often in the first few months of life. Small, subcutaneous, nontender, well-circumscribed, firm mass; sometimes mobile, sometimes adherent to periosteum
- Most commonly seen at the superolateral orbital rim (frontozygomatic suture)
- Second most common location is superomedial orbital rim.
- Must be careful to differentiate from meningoencephalocele, thus these are typically imaged preoperatively.
- Occasionally present with rupture and acute inflammation or as sinus tract with drainage
- Deep is rarer, presenting later in life (teenage years or older) with globe displacement or as in incidental radiographic finding.
- Usual presentation is globe displacement due to a large mass.
- Long duration can gradually erode bone.
- Soft tissue locations including lateral rectus muscle, lacrimal gland have been reported.
- Quantitative analysis of an incidentally noted deep dermoid in a young child did show significant growth, though not clinically overt (Hou, J AAPOS, 2012).
- Rarely, the lesion might involve both the superficial and orbital sides of the bone, resulting in what is described as a dumbbell configuration.
Indications for imaging
- Atypical lesion
- Atypical location, deep adherence require imaging
- Confirm diagnosis
- Rule out intracranial or intraorbital dumbbell component
- Discuss typical lesions with parents to make a joint decision. Not scanning will avoid sedation.
- Less sedation for shorter CT duration compared to MRI, but radiation exposure with CT
- Consider ultrasound.
- Round, smooth borders, well-circumscribed mass
- Enhancing wall, nonenhancing center
- Bony erosion confirms long-standing nature of lesion
- Adjacent bone changes may be seen in 85% of cases (Chawda, Clin Radiol, 1999)
- Useful for identifying dumbbell extension on other side of bone
- Rarely, bone erosion may progress through lateral orbital wall, so dermoid takes on hourglass shape
- Bone erosion does not usually require treatment in these cases
- More rarely, bone erosion may progress intracranially
- Lucent center due to fat content. Layering of contents can occur
- Internal calcification may be seen in 14% of cases (Chawda, Clin Radiol, 1999)
- Useful for demonstrating bony details
MRI also useful
- Fat-suppressed view
- Fat density of cyst content helpful in making diagnosis
- Intra-cyst signal intensity variable
- Unlike CT, does not show bone detail
- Might be preferred to CT to avoid radiation exposure to children
- Image acquisition time is longer than CT, however, so requires longer sedation time in small children
- Differentiate simple versus complex cyst structure
- Differentiate varying tissue densities
- No radiation, no sedation
- Congenital developmental abnormality with no known risk factors