Hamartomas and Choristomas
Hamartomas are anomalous growths of tissue consisting only of mature cells normally found at the involved site. Classic examples are infantile (capillary) hemangiomas and the characteristic lesions of neurofibromatosis. Choristomas are tissue anomalies characterized by types of cells not normally found at the involved site. Classic examples are dermoid cysts, epidermoid cysts, dermolipomas, and teratomas. This chapter discusses only some of the choristomas; further discussion of these congenital and juvenile tumors can be found in BCSC Section 6, Pediatric Ophthalmology and Strabismus.
Dermoid and epidermoid cysts are among the most common benign orbital tumors of childhood. These cysts are present congenitally and enlarge progressively. The more superficial cysts usually become symptomatic in childhood, but deeper orbital dermoids may not become clinically evident until adulthood. Dermoid cysts are lined by keratinizing epithelium and contain dermal appendages, such as hair follicles and sebaceous glands. They contain an admixture of oil and keratin. In contrast, epidermoid cysts are lined by epidermis only and are usually filled with keratin; they do not contain dermal appendages.
Orbital dermoid cysts occur most commonly in the area of the lateral brow adjacent to the frontozygomatic suture (Fig 3-6); less often they may be found in the medial upper eyelid adjacent to the frontoethmoidal suture. Dermoid cysts commonly present as palpable smooth, painless, oval masses that enlarge slowly. They may be freely mobile, or they may be fixed to periosteum at the underlying suture.
Figure 3-6 Orbital dermoid cyst. A, Young child with fullness of the right superolateral orbit. B, CT scan of the hypointense lesion in the axial plane is characteristic of a dermoid cyst (epithelial choristoma); note its location at the frontozygomatic suture line. C, Dermoid cyst removed through an upper eyelid crease incision shows dermal appendages (arrow). D, Postoperative photograph shows resolution of the eyelid fullness.
(Courtesy of Bobby S. Korn, MD, PhD.)
If the dermoid occurs in the temporal fossa, computed tomography (CT) is often indicated to rule out dumbbell expansion through the suture into the underlying orbit. A dumbbell dermoid cyst such as this can cause pulsating proptosis with mastication, a highly specific feature of this condition.
CT is also useful to evaluate medial lesions and to distinguish dermoids from congenital encephaloceles, dacryoceles, and vascular lesions that might also occur in this location. When viewed on a CT scan, an orbital dermoid cyst is typically well defined, and it has an enhancing wall and a nonenhancing lumen (see Fig 3-6B). A partially calcified margin or rim is visible in most cases. With magnetic resonance imaging, the lesion is best appreciated on fat-suppression sequences and appears as a well-defined round to ovoid structure of variable size. Most dermoids are relatively hypointense with respect to orbital fat on T1-weighted images and relatively hyperintense on T2-weighted images. Enhancement is minimal because of the lack of blood vessels in the cyst.
Dermoid cysts that do not present until adulthood often are not palpable because they are situated posteriorly in the orbit, usually in the superior and temporal portions adjacent to the bony sutures. The globe and adnexa may be displaced, causing progressive proptosis, and erosion or remodeling of bone can occur. Long-standing dermoid cysts may erode the orbital bones. In some cases, the clinical presentation of orbital dermoid cysts may be orbital inflammation, which is incited by leakage of oil and keratin from the cyst. Expansion of the dermoid cyst and inflammatory response to leakage may result in an orbitocutaneous fistula, which may also occur after incomplete surgical removal.
Dermoid cysts are usually removed surgically. Because dermoid cysts that present in childhood are often superficial, they can be excised through an incision placed in the upper eyelid crease or directly over the lesion. If possible, the cyst wall should be maintained during surgery. Rupture of the cyst can lead to an acute inflammatory process if part of the cyst wall or any of the contents remain within the eyelid or orbit. If the cyst wall is ruptured, the surgeon should remove the cyst contents. Complete surgical removal may be difficult if the cyst has leaked preoperatively and adhesions have developed.
Dermolipomas are solid tumors usually located in and beneath the conjunctiva over the globe’s lateral surface. These benign lesions may have deep extensions that can extend to the levator aponeurosis and extraocular muscles. Superficially, dermolipomas may have fine hairs that can be irritating to patients (Fig 3-7). These tumors typically require no treatment unless the lesion is large and/or cosmetically objectionable. In these cases, only the anterior, visible portion should be excised; when possible, the overlying conjunctiva should be preserved. Care must be taken to avoid damage to the lacrimal gland ducts, extraocular muscles, and the levator aponeurosis. Lesions that may simulate dermolipomas include prolapsed orbital fat, prolapsed palpebral lobe of the lacrimal gland, and lymphomas (such processes are generally found only in adults).
Figure 3-7 Dermolipoma of left lateral orbit. There are fine hairs on the surface of the tumor (arrow).
(Courtesy of Keith D. Carter, MD.)
Teratomas are rare tumors that arise from all 3 germinal layers (ectoderm, mesoderm, and endoderm) and are usually cystic. On histologic examination, a teratoma is characterized by a complex arrangement of various tissues, including clear cysts lined by either epidermis or gastrointestinal or respiratory epithelium. Islands of hyaline cartilage, cerebral tissue, epidermal cysts, and choroid plexus are frequently found. A child with an orbital teratoma characteristically presents with severe unilateral proptosis at birth. As a consequence, the globe and optic nerve may be maldeveloped. The proptosis may increase over the first few days or weeks of life, and compression of the globe can result in corneal exposure and vision loss. When the lesion is smaller, the globe is often normal. Although teratomas in other parts of the body have been known to undergo malignant transformation, teratomas confined to the orbit are generally benign; for those that are malignant, exenteration may be necessary. However, some cystic teratomas can be removed and ocular function preserved.
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.