Orbit Infection and Inflammation

Periorbital and Orbital Cellulitis

Etiologies, Pathophysiology, and Clinical Presentation.

Infections of the orbit account for more than half of primary orbital disease processes. An orbital infection is described by its location with respect to the orbital septum, specifically as either preseptal (periorbital) or postseptal (orbital). The orbital septum—the anterior reflection of the periosteum of the orbital wall onto the tarsal plate of the eyelid—divides the orbit into preseptal and postseptal compartments. Periorbital cellulitis refers to infection anterior to the orbital septum involving the eyelid and ocular adnexa. Orbital cellulitis refers to infection posterior to the orbital septum. This distinction is important because orbital cellulitis carries the risks of abscess, blindness, venous thrombosis, intracranial extension, and death. Defects in the orbital septum, direct extension from sinus infection, and valveless veins provide infection access to the postseptal orbit. Sinusitis is the most common cause (60%–85%), with stye, dacryoadenitis/cystitis, dental abscess, skin breaks, and hematogenous seeding being less common. Staphylococcus aureus , S. epidermidis , and S. pyogenes account for ~75% of infections; rates of Hemophilus influenzae and streptococcal pneumonia are declining as a result of immunization. Patients present with erythema, swelling, warmth, and tenderness of the eyelid. Although ophthalmoplegia and proptosis predict postseptal involvement and abscess, approximately 50% of patients with an abscess do not have these symptoms. As a result, the guidelines for imaging are unclear and vary: edema preventing a complete examination, signs of central nervous system involvement, deteriorating vision, proptosis, ophthalmoplegia, and/or deterioration after 24 to 48 hours of treatment.

Imaging.

Periorbital cellulitis presents with eyelid swelling and thickening of the preseptal soft tissues on computed tomography (CT) ( Fig. 6.1A ) and with T2 hyperintensity on magnetic resonance imaging (MRI). In orbital cellulitis, similar inflammatory changes of the extraconal and/or intraconal orbital fat are present. The most common complication of orbital cellulitis is subperiosteal abscess, frequently involving the lamina papyracea, and directly extending from ethmoid sinus disease ( Fig. 6.1B ).

Treatment.

Treatment consists of oral antibiotics covering staphylococcus and streptococcus for periorbital cellulitis and admission to the hospital with administration of intravenous (IV) antibiotics for orbital cellulitis. Surgical intervention for drainage of an abscess is required in only 12% of admitted patients, and an orbital abscess can be treated with IV antibiotics if it is small or appears in a young child.

Superior Ophthalmic Vein Thrombosis

Superior ophthalmic vein (SOV) thrombosis is a complication of orbital cellulitis that results from inflammatory thrombophlebitis or direct venous invasion by infection; 33% to 75% of isolated SOV thrombosis leads to cavernous sinus thrombosis, which carries a mortality rate of 20%. Imaging with CT or MRI demonstrates an enlarged S-shaped SOV below the superior rectus muscle with a filling defect and peripherally enhancing vasa vasorum on postcontrast images, with thrombus sometimes also seen in the ipsilateral cavernous sinus ( Fig. 6.2 ). Restricted diffusion of the SOV also has been reported, facilitating identification. Treatment consists of aggressive use of antibiotics with or without corticosteroids and anticoagulation, which are not proven therapies.

Dacryocystitis

Dacryocystitis is inflammation and dilatation of the lacrimal sac, a structure located along the inner canthus. In neonates, dacryocystitis can complicate 33% to 65% of cases of congenital dacryocystocele caused by incomplete canalization of the distal nasolacrimal duct. In older children, dacryocystitis can result from other causes of nasolacrimal duct obstruction, including rhinitis/sinusitis, tumor, or trauma/fracture. CT or MRI demonstrates a cystic medial canthus mass with adjacent inflammatory changes ( e-Fig. 6.3 ). Treatment typically consists of antibiotics and dacryocystorhinostomy.

Ocular Toxocariasis

Ocular toxocariasis refers to infection of the globe by the nematodes Toxocara canis or Toxocara cati and is most common in the southeastern United States in children 6 to 12 years of age as a result of ingestion of food or soil contaminated by the feces of dogs or cats. It presents with painless unilateral vision loss, strabismus, and leukocoria.

CT and MRI demonstrate an intravitreal enhancing mass with or without adjacent uveoscleral thickening and retinal detachment. A normal-sized globe containing a mass without calcification differentiates toxocariasis from other common causes of leukocoria (e.g., retinoblastoma, persistent hyperplastic primary vitreous, Coats disease, and retinopathy of prematurity).

Orbital Pseudotumor (Idiopathic Orbital Inflammation)

Etiologies, Pathophysiology, and Clinical Presentation.

Idiopathic orbital inflammatory syndrome, also known as orbital pseudotumor (OP), is an inflammatory, nongranulomatous process with unknown underlying cause. Essentially, this is a diagnosis of exclusion for patients presenting with exophthalmos. Pediatric OP is rare, accounting for only 7% to 16% of cases of OP. Children present similarly to adults with pain, proptosis, a mass, swelling, and motility restriction; however, children more frequently demonstrate ptosis and bilateral or intraocular involvement.

Imaging.

Both CT and MRI are useful in evaluating OP. Lacrimal gland involvement is most common, with enlargement and adjacent inflammatory change. Myositis also occurs frequently, typically with unilateral tubular thickening of extraocular muscles and tendons (compared with Graves orbitopathy, which tends to be bilateral with tendon sparing). OP may involve the uvea and sclera with thickening and enhancement ( Fig. 6.4 ). Perineuritis, which involves the optic nerve sheath, demonstrates “tramline” inflammatory changes and enhancement surrounding the optic nerve (see Fig. 6.4 ). Inflammation can extend through the orbital fissures and optic canal into the cavernous sinus and middle cranial fossa. The differential diagnosis includes infection, lymphoma, Wegener granulomatosis, sarcoidosis, and Graves orbitopathy. Diffusion-weighted imaging may be helpful in the diagnosis with the intensity of lymphoid lesions > OP > cellulitis on b-value = 1,000 images.

Treatment.

Administration of oral corticosteroids often results in a rapid response (within 1–2 days); radiation is used in refractory cases. Recurrence after withdrawal of steroids occurs frequently in adults (~50%) but has been reported in only one child. Biopsy is reserved for atypical symptoms or poor response. Recently, cases of OP have been identified as part of IgG4-related disease, a systemic inflammatory disease demonstrating excellent response to rituximab and corticosteroids.

Graves Orbitopathy (Thyroid Orbitopathy)