An orbital dermoid cyst (orbital dermoid cyst) is a congenital choristoma caused by an abnormality in development, in which normal cells form a benign mass in a place where that tissue does not normally exist. In ICD-10, it is classified as D31.60.
There are two types of choristoma: dermoid cyst and epidermoid cyst. A dermoid cyst contains skin appendages in the cyst cavity, such as hair follicles, hair, and sebaceous glands, as well as fat and smooth muscle. An epidermoid cyst does not have appendage structures and the cavity is filled only with keratinized material from the epidermis (so-called debris). When tissues derived from the endoderm, mesoderm, and ectoderm are all present together, it is called a teratoma.
Orbital dermoid cysts account for 46% of orbital neoplasms in children and 3% to 9% of all orbital masses, making them the most common orbital tumor; some reports say they account for about 2% of all orbital tumors1). Osseous choristoma is a relatively rare subtype, accounting for about 0.1% of all conjunctival tumors and 1.7% to 5% of all ocular choristomas2).
Choristomas are further subclassified into dermoid, dermolipoma, single-tissue choristoma, and complex choristoma4).
A dermoid cyst has a keratinizing stratified squamous epithelium lining the cyst wall and contains appendage structures such as hair follicles, sebaceous glands, and sweat glands. By contrast, an epidermoid cyst does not have appendage structures and the cavity is filled only with keratinized material (debris-like contents). When tissues derived from the endoderm, mesoderm, and ectoderm are all present together, it is called a teratoma.
Orbital dermoid cysts are broadly divided into three types according to the site of origin: superficial, deep, and dumbbell.
| Type | Common site | Main symptoms |
|---|---|---|
| Superficial type (anterior type) | Lateral eyebrow and orbital rim | Painless subcutaneous mass |
| Deep type (deep intraorbital type) | Deep orbit, intraconal | Proptosis, displacement, and restricted eye movement |
| Dumbbell-shaped | Extending across the inside and outside of the orbital bone | With bone destruction |
Common sites are the sutures of the zygomatic and frontal bones, and the frontozygomatic suture is the most common, accounting for about 60% of cases. The frontolacrimal suture accounts for about 25%.
Superficial cyst
Location: Most often found at the outer eyebrow (frontozygomatic suture) and felt as a dome-shaped mass.
Palpation findings: Elastic and firm, smooth surface, and no tenderness. If fused with the orbital bone, it is not mobile.
Shape: Large lesions may cause mechanical ptosis.
Deep cyst
Main findings: Proptosis, ocular deviation, and limited eye movement.
Inflammation: Lipogranulomatous inflammation may occur when the cyst leaks or ruptures.
Shape: A dumbbell-shaped lesion that extends across the orbital bone on both sides is accompanied by bone destruction. If it arises within the muscle cone, imaging is essential1).
The cause of orbital dermoid cysts is the trapping of embryonic ectoderm during fetal development.
Among benign orbital tumors, dermoid cysts and epidermoid cysts are common and are among the representative diseases of pediatric orbital tumors.
Superficial cysts can be diagnosed relatively easily from clinical findings such as their position along a suture line and their firm texture. Imaging is essential for deep cysts.
| Examination | Characteristic findings |
|---|---|
| CT | Well-defined cystic mass. Bone remodeling is seen in 85%. |
| MRI | Heterogeneous T1 and T2 signals (reflecting mixed fat and fluid). Low signal on fat-suppressed T1 |
| Ultrasound | Mixture of low-reflective areas and irregular spike reflections |
On CT, it appears as a well-defined cystic mass, and bone remodeling is seen in 85% of cases. On MRI, it shows heterogeneous signal intensity on both T1 and T2, reflecting a mix of fat and fluid. It shows low signal on fat-suppressed T1, which is useful for identifying the fatty component.
Small, asymptomatic cysts may be managed with observation. However, they tend to enlarge with age, so regular follow-up and consideration of the right timing for surgery are necessary.
The principle is complete removal without rupturing the cyst wall. If any tissue remains, it can trigger sudden inflammation and cause recurrence, abscess formation, and an orbital cutaneous fistula.
Superficial excision
Incision site: choose from an eyebrow incision, an upper eyelid crease incision, or an incision directly over the lesion.
Key points of surgery: Complete excision without rupturing the cyst wall is essential. If the lesion is within the bone, removal with osteotomy is necessary. Because it is often strongly fused to the orbital bone, careful dissection is required.
Postoperative course: If complete excision is achieved, the prognosis is good and recurrence is rare.
Deep and complex excision
Orbital incision: choose a lateral approach or a combined anterior-lateral orbitotomy.
Intraconal: a transnasal endoscopic approach is also effective, and there is a report of complete removal of a 3.0 cm intraconal cyst1).
Dumbbell type: when it extends across the inside and outside of the orbital bone, coordination with neurosurgery is required. Perioperative planning that includes the intracranial component is important.
Limbal dermoid surgery: the main goal is cosmetic, and tumor excision and, if needed, superficial corneal transplantation (frozen-preserved cornea can be used; a trephine diameter of about 7.0 mm is often used) are performed.
Lipids and keratin inside the cyst can leak out and cause lipogranulomatous inflammation. Copious irrigation during surgery can reduce the inflammation. Because incomplete removal can lead to recurrence, abscess formation, and an orbital cutaneous fistula, it is important to remove as much remaining tissue as possible even after rupture. Steroids are given after surgery to control inflammation.
It is a congenital lesion that slowly enlarges with age. Superficial lesions may remain asymptomatic for a long time, but if left untreated, the risk of eyelid compression, bone destruction, and cyst rupture increases. Deep lesions may cause symptoms such as proptosis and diplopia as they enlarge. It is important to discuss the timing of surgery with a specialist.
Orbital dermoid cysts are choristomas that arise when ectoderm is trapped at embryonic fusion lines. Skin-derived structures such as hair follicles, sebaceous glands, sweat glands, and keratinous material form ectopically within the orbit, where they do not normally belong.
The histological classification of choristomas is shown below.
| Classification | Histological features |
|---|---|
| Dermoid cyst | Keratinized epithelium + adnexal structures such as hair follicles and sebaceous glands |
| Epidermoid cyst | Only keratinized epithelium (no adnexal structures) |
| dermolipoma (lipoma type) | Mainly adipose tissue4) |
| osseous choristoma | Mature bone tissue2) |
The intraconal epithelial cyst is an extremely rare subtype, accounting for only 0.5–0.6% of all orbital dermoid cysts, and only six cases were reported on PubMed from 1986 to 20201).
Samal et al. (2021) reported a 3.0 cm right intraconal dermoid cyst in a 30-year-old man1). Complete removal was achieved with a transnasal endoscopic approach, and there was no recurrence at 6 months. Pathology confirmed keratinizing stratified squamous epithelium and adnexal structures.
Minimally invasive surgical techniques, including the transnasal endoscopic approach, have been accumulating at the case-report level, and standardization is expected in the future.
Research on the histological diversity of choristomas is also advancing. Reported patterns include mixed bone-and-cartilage types, types containing tooth-like structures, and cartilaginous types with pigmented cystic change2). For osseous choristoma, proposed etiologic hypotheses include abnormal activation of pluripotent mesenchymal cells, reversion to a scleral bone plate, and developmental anomalies of the zygomaticofrontal suture2). For lacrimal gland choristoma, rare cases have been reported that include ectopic tissues such as cartilage, muscle, and nerve tissue within the lacrimal gland3), and the diverse tissue origins of choristomas are becoming clearer.
