Etiologies, Pathophysiology, and Clinical Presentation: 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 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 with access to the postseptal orbit. Sinusitis is the most common cause (60% to 85%), with stye, dacryoadenitis/cystitis, dental abscess, skin breaks, and hematogenous seeding being less common.1,2 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.¹ 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.^3–5

Imaging: Periorbital cellulitis presents with eyelid swelling and thickening of the preseptal soft tissues on computed tomography (CT), with T2 hyperintensity on magnetic resonance imaging (MRI) (Fig. 6-1, A).^2,6,7 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. A subperiosteal abscess presents as a broad-based, peripherally enhancing fluid collection along the medial wall of the orbit that displaces the medial rectus muscle laterally (Fig. 6-2, A). Less commonly, an abscess can form in the extraconal or intraconal orbit separate from the bone, which also is seen as a peripherally enhancing fluid collection. MRI can be helpful in identifying an abscess by demonstrating restricted diffusion.⁸

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,³ and an orbital abscess can be treated with IV antibiotics if it is small or appears in a young child.^9,10

Etiologies, Pathophysiology, and Clinical Presentation: Orbital pseudotumor (OP) is a noninfectious inflammatory condition of the orbit of unclear etiology. In adults it is the most common painful orbital mass, accounting for ~10% of orbital masses, and is the third most common orbital disease. Pediatric OP is rare, with only 68 cases reported in the medical literature as of 2008, accounting for only 7% to 16% of cases of OP.24,25 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.26–28 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. 6-3, A). Perineuritis, which involves the optic nerve sheath, demonstrates “tramline” inflammatory changes and enhancement surrounding the optic nerve (Fig. 6-3, B-D). 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 = 1000 images.²⁹

Treatment: Administration of oral corticosteroids often results in a rapid response (within 1 to 2 days); radiation is used in refractory cases.25,30 Recurrence after withdrawal of steroids occurs frequently in adults (~50%) but has been reported in only one child.^24,31 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.^32,33

Etiologies, Pathophysiology, and Clinical Presentation: Graves orbitopathy is an orbital inflammatory process seen in persons with Graves disease, which is an autoimmune thyroid disease from thyroid-stimulating hormone receptor autoantibodies. Pediatric Graves disease is uncommon, yet children who have the disease experience Graves orbitopathy at similar rates as do adults, in one third to two thirds of cases.34–36 Graves orbitopathy is milder in children than in adults, with mild proptosis and mild eyelid retraction or lag. In children, no cases of compressive optic neuropathy have been reported, and strabismus is rare.

Imaging: Imaging demonstrates fusiform enlargement of extraocular muscles (involving muscle bellies and sparing tendons), which is bilateral in 90% of cases and frequently involves the inferior and medial recti. Increased volume of orbital fat and lacrimal gland enlargement also can be seen.³⁷ Active disease can be differentiated from fibrotic disease by evaluating the T2 signal intensity and dynamic contrast enhancement of the muscles (T2 hyperintensity, shorter time to peak, and greater enhancement and washout ratios are found in persons with active disease). This distinction is important, because medical therapy is not effective in persons with fibrotic disease.^38–40

Treatment: Most pediatric cases can be controlled with antithyroid medication alone; steroids, radiation therapy, or surgery are not required, as is often the case with adults.34–36

Etiologies, Pathophysiology, and Clinical Presentation: Optic neuritis (ON) is an inflammatory disease of the optic nerve with acute onset of vision loss and periocular pain (in >90% of adults). ON may be idiopathic or related to multiple sclerosis (MS), neuromyelitis optica, or acute disseminated encephalomyelitis. ON behaves differently in children than in adults, likely reflecting different etiologies, with parainfectious ON being common in children (in one third to two thirds of cases).54–58 Compared with adults, ON in children is more often bilateral (in 37% to 66% of cases), less often painful (in 37% of cases), and more often demonstrates disk swelling (in 46% to 85% of cases) and profound vision loss. In children it tends to have better visual recovery and is less often associated with MS.

Imaging: MRI demonstrates contrast enhancement (>90%), T2-weighted hyperintensity, and mild enlargement of the optic nerves acutely, with mild volume loss developing chronically (Fig. 6-5).^59,60 If frank enlargement of the optic nerve is seen, an optic pathway glioma should be considered. Intraorbital involvement is most common. Intracanalicular and long segment involvement and persistent signal change over time correlate to worse visual outcomes. Retinal nerve fiber layer thinning on optical coherence tomography also correlates to vision loss.^61,62 Diffusion tensor imaging of optic nerves is difficult perform clinically, yet demonstrates decreased axial diffusivity acutely and increasing radial diffusivity and apparent diffusion coefficient values during recovery, correlating to changes in visual acuity and retinal nerve fiber layer thinning.^63–65 Decreased fractional anisotrophy values also can be seen in the optic tracts and radiations, possibly as a result of Wallerian and transsynaptic degeneration.^66–68 Magnetization transfer ratios (MTRs), which are thought to decrease with demyelination, are more sensitive than T2 spin echo imaging. They progressively decrease in the optic nerve, with a nadir at 240 days, and then mildly increase (possibly from remyelination), also correlating to changes in visual acuity.^69,70

Figure 6-5 Optic neuritis.
T2- (A) and T1-weighted fat-saturated postcontrast (B) magnetic resonance (MR) images of the orbits demonstrating abnormal T2 hyperintensity and enhancement of the left optic nerve (arrows). C, A sagittal T2-weighted MR image of the cervical spine demonstrates a characteristic central long segment cord lesion in a patient with neuromyelitis optica (NMO) (arrow). D,

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