Dermoid cysts are congenital choristomas that result from entrapped ectodermal elements at fetal suture lines during embryogenesis, occurring most commonly near the frontozygomatic or frontonasal sutures. Histologically, dermoid cysts consist of both epidermal components and adnexal structures, distinguishing them from epidermoid cysts (which have only epidermal components) and lipodermoids (which have a prominent lipid component).
Dermoid cysts represent 4%-16% of childhood orbital lesions and are classified clinically on the basis of location. A superficial dermoid cyst presents as a firm, painless, subcutaneous mass located in the anterolateral periorbital region. Patients typically present to a clinician after incidental discovery by a caretaker during the first several years of life. The lesion may become more apparent as the child grows and loses periorbital facial fat. Due to its anterior location, the lesion usually does not cause displacement of ocular structures, but the patient may develop visually significant ptosis.
Deep dermoid cysts are more insidious and often present in later childhood or young adulthood. Because of their less conspicuous location, these lesions may remain clinically occult until they manifest by mass effect on surrounding structures. Patients may present with progressive globe displacement, motility defects, visual loss, or diplopia. Intracranial extension is possible with sphenoid or frontal bone involvement.
A dermoid cyst may also present as a dumbbell-shaped lesion straddling the orbital bone, with a deeper orbital component and a superficial extraorbital component. Less commonly, these lesions may masquerade as an acute inflammatory lesion following traumatic or spontaneous cyst rupture. In rare cases, a secondary fistula between the cyst and skin may form, with intermittent drainage of cyst contents.
Lesions with a characteristic location and classic presentation can be diagnosed clinically. However, those with atypical features and a deep or medial location may require imaging to assess for intracranial involvement or encephalocele, and to assist with surgical planning.
On CT, a dermoid cyst is typically well-defined, with a hyperdense wall and a hypodense lumen that does not enhance with contrast. Irregular heterogeneous areas can be seen within the cyst, which presumably correspond to epithelial debris and keratin. Adjacent bony changes are common and can appear as a smooth, bony fossa near the affected suture. In cases of a dumbbell cyst, a full-thickness bony channel can be seen with a cystic component on either side of the bone.
MRI has the advantage of not exposing the patient to radiation, which is an important consideration in the pediatric population. Dermoid cysts are typically hypointense on T1-weighted imaging with respect to orbital fat and are best appreciated with fat-suppression techniques.
Treatment of orbital dermoids is surgical excision. Accidental traumatic rupture may result in a subcutaneous spread of cyst contents, causing inflammation and making complete extraction difficult. Additionally, growth over the years may result in bone and soft tissue deformation.
The primary goal of excision is to achieve complete cyst removal without rupture, because leakage of cyst contents can result in significant inflammation and promote recurrence. The surgical approach is customized based on the location of the lesion. Superficial dermoids of the periorbital area are typically accessed via an anterior orbitotomy through an eyelid crease or sub-brow incision, although endoscopic approaches have been described, particularly for lesions in the nasoglabellar region. Deeper, posterior dermoids are approached on the basis of their location and relationship to adjacent orbital structures. In cases with intracranial involvement, a multidisciplinary approach may be necessary.
Medscape Ophthalmology © 2011
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