Figure 18-15 Bilateral nonspecific orbital inflammation (orbital pseudotumor) in an 11-year-old boy with a 1-week history of eye pain. Ocular rotation was markedly limited in all directions. CT confirmed proptosis and showed enlargement of all extraocular muscles. Laboratory workup was negative for thyroid disease and rheumatologic disorders. Complete resolution occurred after 1 month of corticosteroid treatment.

Orbital myositis Orbital myositis describes NSOI that is confined to 1 or more extraocular muscles. The clinical presentation depends on the amount of inflammation. Diplopia, conjunctival chemosis, and orbital pain are common. Symptoms can be subacute for weeks or can progress rapidly. Vision is rarely impaired unless massive muscle enlargement is present. Imaging studies show diffusely enlarged muscles with the enlargement extending all the way to the insertion (unlike in thyroid myopathy, which mainly involves the muscle belly). Corticosteroid treatment usually produces rapid relief of symptoms; however, prolonged treatment is often necessary, and recurrence is common.

Neoplasms

Several of the most important pediatric malignancies show a predilection for orbital involvement. Benign adnexal masses are common and, in many cases, may threaten vision.

Differential Diagnosis

Diagnosis of space-occupying lesions in the orbit is particularly challenging because the clinical manifestations are both nonspecific and relatively limited:

proptosis or other displacement of the globe swelling or discoloration of the eyelids palpable subcutaneous mass

ptosis strabismus

The problem of differential diagnosis in childhood is compounded by the fact that many different

orbital processes may cause rapid onset of symptoms. These include trauma, which may occur without a reliable history. Also, mild or moderate proptosis can be difficult to detect in an uncooperative child with associated eyelid swelling.

Nevertheless, typical presentations of the more common benign orbital and periorbital masses in infants and children (eg, hemangioma and dermoid cyst; discussed later) are sufficiently distinctive to permit confident clinical diagnosis in most cases. A malignant process should be suspected when proptosis and eyelid swelling suggestive of cellulitis are not accompanied by warmth of the overlying skin or when periorbital ecchymosis or hematoma develops in the absence of an unequivocal history of trauma. Pseudoproptosis can result when the volume of the globe exceeds the capacity of the orbit. Examples include the elongation of the eyeball from primary congenital glaucoma or high myopia.

The current widespread availability of high-quality imaging permits orbital masses to be differentiated noninvasively in many cases. Because of increasing concerns about the radiation risks associated with CT scans in children, MRI is becoming the preferred approach for orbital imaging in this patient group. CT, however, is superior at detecting disturbances of bone architecture. Ultrasonography may also provide useful diagnostic information.

Definitive diagnosis still often requires biopsy. A pediatric oncologist should be consulted when appropriate, and a metastatic workup should be considered before resorting to orbital surgery, because other, more easily accessible sites can sometimes be used as tissue sources.

Primary Malignant Neoplasms

Malignant diseases of the orbit include primary and metastatic tumors. Most primary malignant tumors of the orbit in childhood are sarcomas. Tumors of epithelial origin are extremely rare.

Rhabdomyosarcoma

The most common primary orbital malignant tumor in children is rhabdomyosarcoma, which is thought to originate from undifferentiated mesenchymal cells. The incidence of this disease (which is found in approximately 5% of pediatric orbital biopsies) exceeds that of all other sarcomas combined. The orbit is the origin of 10% of rhabdomyosarcomas; 25% of these tumors arise elsewhere in the head and neck, occasionally involving the orbit secondarily. The average age of onset is 5–7 years, but it can occur at any age. Rhabdomyosarcoma in infancy is more aggressive and carries a poorer prognosis.

Although ocular rhabdomyosarcoma usually originates in the orbit, it occasionally arises in the conjunctiva, eyelid, or anterior uveal tract. Patients generally present with proptosis (80%–100%), globe displacement (80%), blepharoptosis (30%–50%), conjunctival and eyelid swelling (60%), palpable mass (25%), and pain (10%) (Fig 18-16). Onset of symptoms and signs is usually rapid. Acute, rapidly progressive proptosis with an absence of pain should raise a high suspicion of orbital rhabdomyosarcoma. Imaging shows an irregular but well-circumscribed mass of uniform density.

discussed in Chapter 28.

Ewing sarcoma

Ewing sarcoma is composed of small round cells and usually originates in the long bones of the extremities or in the axial skeleton. Among solid tumors, Ewing sarcoma is the second most frequent source of orbital metastasis. Contemporary treatment regimens involving surgery, radiation, and chemotherapy permit long-term survival in many patients with disseminated disease.

Hematopoietic, Lymphoproliferative, and Histiocytic Neoplasms

Leukemia

Leukemic infiltration of the orbit is relatively uncommon and more characteristic of acute myelogenous leukemia. Orbital involvement may be difficult to distinguish from bacterial or fungal orbital cellulitis. Orbital infiltration can cause proptosis, eyelid swelling, and ecchymosis. It may be best managed by radiation therapy. Granulocytic sarcoma, or chloroma (in reference to the greenish color of involved tissue), is a localized accumulation of myeloid leukemic cells in the orbit. This lesion may develop several months before leukemia becomes hematologically evident. Leukemia is discussed in Chapter 28.

Lymphoma

In contrast with adult disease, lymphoma in children very rarely involves the orbit. Burkitt lymphoma, endemic to East Africa and uncommon in North America, is the most likely form to involve the orbit.

Langerhans cell histiocytosis

Langerhans cell histiocytosis (LCH; formerly called histiocytosis X) is the collective term for a group of disorders, usually arising in childhood, that involve abnormal proliferation of histiocytes, often within bone. The disorders are classified as unifocal eosinophilic granuloma of the bone, multifocal eosinophilic granuloma of the bone, and diffuse soft-tissue histiocytosis.

Unifocal eosinophilic granuloma, the most localized and benign form of LCH, produces a bone lesion that involves the orbit, skull, ribs, or long bones in childhood or adolescence. Symptoms may include proptosis, ptosis, and periorbital swelling; localized pain and tenderness are relatively common. CT characteristically shows sharply demarcated osteolytic lesions without surrounding sclerosis (Fig 18-17). Treatment consists of observation of isolated asymptomatic lesions, excision or curettage, systemic or intralesional corticosteroid administration, or low-dose radiation therapy; all modalities have a high rate of success.