A dermoid cyst (orbital dermoid) is a congenital choristoma of the orbit, in which normal cells form a benign tumor in a location where such tissue is not normally present. It is composed of keratinized epithelium and adnexal structures such as hair follicles, sweat glands, and sebaceous glands. It is classified as D31.60 in ICD-10.
Choristomas appear from early childhood due to abnormalities in developmental processes. They are divided into dermoid cysts and epidermoid cysts. Choristomas are further classified into dermoid, dermolipoma, single-tissue choristoma, and complex choristoma4). Osseous choristomas account for approximately 0.1% of all conjunctival tumors and 1.7–5% of all ocular choristomas2).
Dermoid cysts account for 46% of orbital neoplasms in children and 3–9% of all orbital masses, making them the most common orbital tumor; some reports indicate they represent approximately 2% of all orbital tumors 1).
Dermoid cysts have a lining of keratinized stratified squamous epithelium and contain adnexal structures such as hair follicles, sebaceous glands, and sweat glands. In contrast, epidermoid cysts lack adnexal structures and are filled only with keratinous material (scaly content) in the lumen. When tissues derived from endoderm, mesoderm, and ectoderm are present simultaneously, the lesion is called a teratoma.
Superficial Cyst
Location: Commonly occurs in the superolateral region (near the lateral eyebrow).
Palpation findings: Elastic hard, smooth surface, no tenderness. May be mobile or fixed to bone.
Shape: In superficial areas near the skin, presents as a dome-shaped elevation. Large ones may cause mechanical ptosis.
Deep Cyst
Main findings: Proptosis, strabismus, diplopia, globe displacement, and restricted eye movement.
Inflammation: Leakage or rupture of the cyst may cause granulomatous inflammation (fat granuloma).
Shape: May be dumbbell-shaped, straddling the inside and outside of the orbital bone. Imaging is essential for lesions within the muscle cone 1).
It slowly enlarges with age. Superficial cysts may remain asymptomatic for a long time, but if left untreated, they can cause eyelid retraction and cosmetic issues. In deep cysts, enlargement leads to symptoms such as proptosis and diplopia. It is important to consult a specialist for timely surgical intervention.
Superficial cysts can be diagnosed relatively easily based on clinical findings (location along suture lines, firm texture). For deep cysts, imaging studies are essential.
| Examination | Characteristic Findings |
|---|---|
| CT | Well-defined cyst. Bone remodeling in 85%. |
| MRI | Heterogeneous T1 and T2 signal. Low signal on fat-suppressed T1. |
| Ultrasound | Mixed hypoechoic areas and irregular spike echoes. |
Small asymptomatic cysts may not require treatment. However, they may enlarge with age, so regular follow-up is necessary.
Superficial Excision
Incision site: Choose from eyebrow incision, upper eyelid crease incision, or incision directly over the lesion.
Key points: Complete excision without rupturing the cyst wall is essential. Residual tissue can cause acute inflammation, leading to recurrence, abscess formation, or orbital cutaneous fistula. Carefully review preoperative imaging; if the lesion involves bone, excision with osteotomy is necessary. Even without obvious intraosseous involvement, strong adhesion is common, requiring meticulous total excision.
Deep/Complex Excision
Orbitotomy: Choose anterior, lateral, or combined orbitotomy.
Intraconal: Transnasal endoscopic approach is also effective1). Complete excision of a 3.0 cm intraconal cyst has been reported.
Surgery for limbal dermoid: Primarily for cosmetic purposes. Tumor excision and, if necessary, superficial keratoplasty (using cryopreserved cornea, typically with a trephine diameter of about 7.0 mm) are performed.
Lipids and keratin inside the cyst may leak, causing lipid granulomatous inflammation. Copious irrigation during surgery can reduce inflammation. Incomplete removal can lead to recurrence, abscess formation, and orbital cutaneous fistula, so it is important to remove residual tissue as much as possible even after rupture.
A dermoid cyst forms when ectoderm-derived epithelium becomes entrapped along a bony suture line during development.
The histological classification of dermoid cysts is shown below.
| Classification | Histological Features |
|---|---|
| Dermoid cyst | Keratinized epithelium + hair follicles and sebaceous glands |
| Epidermoid cyst | Keratinized epithelium only (no adnexa) |
| Dermolipoma | Primarily adipose tissue4) |
| Osseous choristoma | Mature bone tissue2) |
Conal endothelial-like cysts are extremely rare, accounting for 0.5–0.6% of all cases, with only 6 cases reported on PubMed from 1986 to 2020 1). Minimally invasive surgical approaches, including the transnasal endoscopic approach, have been accumulating at the case report level.
Samal et al. (2021) reported a 3.0 cm dermoid cyst within the right eye muscle cone in a 30-year-old man 1). Complete resection was achieved via a transnasal endoscopic approach, with no recurrence at 6 months. Histologically, keratinized stratified squamous epithelium and adnexal structures were confirmed.
Research on the histological diversity of choristomas is also progressing. Mixed types with bone and cartilage, types containing tooth-like structures, and cartilaginous types with pigmented cystic changes have been reported 2). Etiological hypotheses for osseous choristomas include abnormal activation of pluripotent mesenchymal cells, atavism of the scleral bone plate, and developmental anomalies of the zygomaticofrontal suture 2).
