potential for malignant transformation. Port-wine stains are discussed in Chapter 17.
Tumors of bony origin
During the early years of life, a variety of uncommon benign orbital tumors of bony origin can present with gradually increasing proptosis. Fibrous dysplasia and juvenile ossifying fibroma are similar disorders in which normal bone is replaced by fibro-osseous tissue. In both conditions, orbital CT shows varying degrees of lucency and sclerosis.
Fibrous dysplasia has a slow progression that ceases when skeletal maturation is complete. The most serious complication is vision loss caused by optic nerve compression, which may occur acutely. Periodic assessment of vision, pupil function, and optic disc appearance is indicated. Surgical treatment is indicated for functional deterioration or disfigurement.
Juvenile ossifying fibroma is distinguished histologically by the presence of osteoblasts. It tends to be more locally invasive than fibrous dysplasia; some authorities recommend early excision.
Brown tumor of bone is an osteoclastic giant cell reaction resulting from hyperparathyroidism. Aneurysmal bone cyst is a degenerative process in which normal bone is replaced by cystic cavities containing fibrous tissue, inflammatory cells, and blood, producing a characteristic radiographic appearance.
Tumors of connective tissue origin
Benign orbital tumors originating from connective tissue are rare in childhood. Juvenile fibromatosis may present as a mass in the inferoanterior portion of the orbit. These tumors, sometimes called myofibromas or desmoid tumors, are composed of relatively mature fibroblasts. They tend to recur locally after excision and can be difficult to control, but they do not metastasize.
Tumors of neural origin
Optic pathway glioma is the most important orbital tumor of neural origin in childhood. Optic pathway gliomas are usually low-grade astrocytomas, but the rate of growth with or without therapeutic intervention is unpredictable. Management of these tumors is thus controversial and depends largely on their location. Approximately 30% of optic pathway gliomas are associated with neurofibromatosis type 1. Plexiform neurofibroma nearly always occurs in the context of neurofibromatosis and frequently involves the eyelid and orbit. These tumors are discussed in Chapter 28. Orbital meningioma and schwannoma (neurilemoma, neurinoma) are rare before adulthood.
Ectopic Tissue Masses
The term choristoma is applied to growths consisting of normal cells and tissues appearing at an abnormal location. The growths may result from abnormal sequestration of germ layer tissue during embryonic development or from faulty differentiation of pluripotential cells. Masses composed of such ectopic tissue growing in the orbit can also be a consequence of herniation of tissue from adjacent structures.
Cystic Lesions
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 suture lines at the time of closure. 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 18-21) but sometimes extend into the bony suture line. Clinically, they present as painless, smooth masses that are mobile and unattached to overlying skin. Episodes of inflammation may occur with small ruptures of the cyst wall and consequent 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 wellcircumscribed lesion with a low-density lumen and often bony remodeling (Fig 18-22).
Figure 18-21 Eight-month-old boy with periorbital dermoid cyst, left eye, with typical superotemporal location. (Courtesy of
Robert W. Hered, MD.)
Management of dermoid cysts is surgical. Early excision can eliminate 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 often 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.
Figure 18-22 Axial CT image showing a dermoid cyst of the superonasal anterior orbit, right eye, in a 6-year-old boy.
Microphthalmia with cyst
Also known as colobomatous cyst, microphthalmia with cyst is composed of tissues that originate from the eye wall of a malformed globe with posterior segment coloboma. 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. The cyst communicates with the vitreous cavity, sometimes through a channel so small it is undetectable even with high-resolution imaging.
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 18-23). 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. A variety of methods are used, including aspiration of the cyst, surgical excision of the cyst, and use of orbital expanders and conformers.
Figure 18-23 Microphthalmia with cyst (colobomatous cyst), left eye.
Mucocele
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.
Encephalocele and meningocele
Encephaloceles and meningoceles in the orbital region may result from a congenital bony defect that