Dermoid and epidermoid cysts
Dermoid cysts are the most common space-occupying orbital lesions of childhood. They are benign developmental choristomas that arise from primitive dermal and epidermal elements sequestered in fetal skull suture lines. The tissue forms a cyst lined with keratinized epithelium and dermal appendages, including hair follicles, sweat glands, and sebaceous glands. Cysts containing squamous epithelium without dermal appendages are called epidermoid cysts.
Orbital dermoid cysts in childhood most commonly arise in the superotemporal and superonasal quadrants (Fig 18-20) but sometimes extend into the bony suture line. Clinically, they present as painless, smooth masses that are mobile and unattached to overlying skin. Inflammation may occur with ruptures of the cyst and extrusion of cyst contents. Most patients have no visual symptoms. Clinical examination is often sufficient for diagnosis. In some cases, imaging is indicated to identify and delineate the extent of the cyst. Imaging reveals a well-circumscribed lesion with a low-density lumen and often bony remodeling (Fig 18-21).
Figure 18-20 Eight-month-old boy with a periorbital dermoid cyst, left eye, with typical superotemporal location.
(Courtesy of Robert W. Hered, MD.)
Figure 18-21 Axial CT image showing a dermoid cyst of the superonasal anterior orbit, right eye, in a 6-year-old boy.
Management of dermoid cysts is surgical. Early excision can reduce the risk of traumatic rupture and subsequent inflammation. An infrabrow or eyelid crease incision is used, and the cyst is carefully dissected. If possible, rupture of the cyst at the time of surgery is avoided to limit lipogranulomatous inflammation and scarring. If the cyst is entered, the intraluminal material should be thoroughly removed. Sutural cysts sometimes cannot be removed intact because of their extension into or through bone. To limit the possibility of recurrence, the surgeon must attempt removal of all remaining cyst lining.
Microphthalmia with cyst
Microphthalmia with cyst (also known as colobomatous cyst) is characterized by a small, malformed globe with posterior segment coloboma and a cyst composed of tissues originating from the eye wall of the globe. Most fundus colobomas show some degree of scleral ectasia. In extreme cases, a bulging globular appendage grows to become as large as or larger than the globe itself, which is invariably microphthalmic, sometimes to a marked degree.
Microphthalmia with cyst may occur either as an isolated congenital defect or in association with a variety of intracranial or systemic anomalies. Frequently, the fellow eye shows evidence of coloboma as well. The usual location of the cyst is inferior or posterior to the globe, with which the cyst is always in contact.
Whether posteriorly located cysts cause proptosis depends on the size of the globe and the cyst. Inferiorly located cysts present as a bulging of the lower eyelid or a bluish subconjunctival mass (Fig 18-22). If fundus examination does not make the diagnosis obvious, orbital imaging may reveal a cystic lesion that is attached to the globe and has the uniform internal density of vitreous. The goal of treatment is to promote normal growth of the orbit; methods include aspiration or surgical excision of the cyst, and use of orbital expanders and conformers.
Mucoceles are cystic lesions that originate from obstructed paranasal sinus drainage. They may expand over time, potentially causing destruction of bone and eroding into the orbit or intracranial space. These lesions most commonly arise from the frontal or anterior ethmoid sinuses, resulting in inferior or medial displacement of the globe. The differential diagnosis includes encephalocele with skull base deformity. Treatment involves reestablishing normal sinus drainage and removing the cyst wall.
Figure 18-22 Microphthalmia with cyst (colobomatous cyst), left eye.
Encephalocele and meningocele
Encephaloceles and meningoceles in the orbital region may result from a congenital bony defect that allows herniation of intracranial tissue, or they may develop after trauma that disrupts the bone and dura mater of the anterior cranial fossa. An intraorbital location leads to proptosis or downward displacement of the globe. Anterior presentation takes the form of a subcutaneous mass that can be misdiagnosed as a dacryocystocele. However, encephaloceles and meningoceles are typically located above the medial canthal tendon; dacryocystoceles are typically located below it (see Chapter 19). Pulsation of the globe or the mass from the transmission of intracranial pulse pressure is characteristic. Neuroimaging confirms the diagnosis. Surgical repair is usually performed by neurosurgeons.
Excerpted from BCSC 2020-2021 series: Section 10 - Glaucoma. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.