13
Orbit
M. Reza Vagefi, MD
Orbital disease usually arises within the bony confines of the orbit or by spread from adjacent structures, particularly the paranasal sinuses. The etiology may be inflammation, infection, neoplasia, or vascular anomaly. An orbital mass may also be a metastatic tumor and hence a harbinger of a serious and sometimes lifethreatening entity.
PHYSIOLOGY OF SYMPTOMS
An increase in orbital volume results in displacement of the globe. Since the orbit has rigid bony walls (see Chapter 1), such displacement usually manifests predominantly as forward protrusion of the globe (proptosis), which is a hallmark of orbital disease. Pathology within the muscle cone displaces the globe anteriorly (axial proptosis). Pathology outside the muscle cone also causes vertical and/or lateral displacement (nonaxial proptosis). Bilateral involvement generally indicates systemic disease, such as autoimmune hyperthyroidism (Graves’ disease). The proptosis in Graves’ ophthalmopathy is often termed exophthalmos.
Pulsating proptosis may be due to carotid-cavernous fistula, arterial orbital vascular malformation, or transmission of cerebral pulsations due to a bone defect such as in the sphenoid dysplasia of type 1 neurofibromatosis. Proptosis that increases on bending the head forward or with Valsalva maneuver can be a sign of venous orbital vascular malformation (orbital varices) or bone defect. Intermittent proptosis may be the result of a sinus mucocele. The Hertel exophthalmometer (see Chapter 2) is the standard method of quantifying the magnitude of proptosis. Serial measurements are most accurate if performed by the same individual with the same instrument. Pseudoproptosis is apparent proptosis in the absence of orbital disease. It may be due to an enlarged globe
597
from high myopia or buphthalmos, lid retraction, extraocular muscle weakness or paralysis, asymmetrical orbital size, or posterior displacement (enophthalmos) of the contralateral globe.
Proptosis does not impair vision unless there are corneal changes due to corneal exposure. However, any orbital process that arises from, involves, or compresses the optic nerve, can result in an optic neuropathy that may manifest as a relative afferent pupillary defect or reduction of color vision before there is reduction of visual acuity. In addition, visual impairment may be caused by compression of the globe resulting in distortion of the retina and possible elevation of intraocular pressure.
Limitation of ocular movements resulting in binocular diplopia (double vision) may be due to direct involvement of the extraocular muscles, interference with their mechanisms of action, or dysfunction of the third (oculomotor), fourth (trochlear), or sixth (abducens) cranial nerves. Pain may occur as a result of rapid expansion or inflammation or the orbital tissues or infiltration of sensory nerves.
Disease involving the superior orbital fissure produces a characteristic combination (superior orbital fissure syndrome) of diplopia (third, fourth, and/or sixth cranial nerves), corneal and facial anesthesia (first [ophthalmic] division of fifth [trigeminal] cranial nerve), and possible proptosis. Disease at the orbital apex also causes visual impairment because of second (optic) cranial nerve dysfunction (orbital apex syndrome). In the cavernous sinus syndrome, there is diplopia (third, fourth, and/or sixth cranial nerves) and fifth cranial nerve dysfunction, potentially involving all three divisions. There may be proptosis due to venous congestion. Vision is spared unless there is sufficient expansion to compress the intracranial optic nerve or the optic chiasm.
DIAGNOSTIC STUDIES
Computed Tomography and Magnetic Resonance Imaging
Computed tomography (CT) uses x-rays to create cross-sectional, twodimensional images of the body (Figures 13–1 and 13–2). Modern-day scanners use spiral or helical technology where the x-ray source rotates continuously in one direction within a ring of detectors as the patient is moved forward through
598
the ring. The data for the images are acquired quickly and as a continuous volume, allowing for a reduction of motion artifacts. Using complex algorithms, three-dimensional reconstructions can be rendered. The diagnostic capabilities of CT are essential to daily practice and have largely replaced the use of plain x- rays, especially for orbital trauma. Magnetic resonance imaging (MRI) generates cross-sectional images by taking advantage of the magnetic properties of atomic nuclei. Soft tissue visualization within the orbit is superior with this modality because of the near absence of signal created by bone and because resonance signals from different tissues can be manipulated to enhance contrast differentiation. Moreover, technological developments allow for suppression of the increased fat signal in the orbit and thus provide better visualization of pathology. MRI is contraindicated in the presence of a suspected or known intraorbital or intracranial foreign body. It is the preferred study of choice in children to avoid unneeded radiation exposure when trauma is not of concern.
599
Figure 13–1. Normal computed tomography scan—axial sections (1.5 mm) demonstrating the anatomy of the orbit. A–H: Sequence of sections from inferior to superior orbit. Note the clear delineation of individual muscles, optic nerve, and major veins within the orbital fat.
600
Figure 13–2. Normal computed tomography scan—coronal sections. A–H: Sequence of sections from anterior to posterior orbit. Note the detailed demonstration of ocular and orbital structures.
Ultrasonography
CT and MRI have largely supplanted the use of ultrasonography in the diagnosis of orbital disease. Although it is a noninvasive and inexpensive form of imaging, its usefulness is limited to the anterior portion of the orbit. It is of greatest value in the hands of the clinician-ultrasonographer capable of interpreting “real-time” images. It can provide a noninvasive method of diagnosing carotid artery– cavernous sinus fistula and extraocular muscle enlargement due to Graves’ ophthalmopathy.
Fine-Needle Aspiration Biopsy
Fine-needle aspiration biopsy is an invasive procedure that has proved useful in
601
orbital diagnosis. Cytology specimens can be aspirated from a lesion, the exact location of which is determined by orbital imaging. Definitive pathological diagnosis is made more than 75% of the time.
DISEASES & DISORDERS OF THE ORBIT
INFLAMMATORY DISORDERS
1. GRAVES’ OPHTHALMOPATHY (SEE ALSO CHAPTER 15)
Graves’ ophthalmopathy (GO) (thyroid eye disease [TED], Graves’ orbitopathy, thyroid-associated ophthalmopathy or orbitopathy) is an autoimmune disorder believed to result from activation of orbital fibroblasts by antibodies initially directed at the thyrotropin receptor of thyroid follicular endothelial cells. Once activated, these fibroblasts increase the production of mucopolysaccharides that accumulate in the extraocular muscles. In addition, differentiation of the fibroblasts to adipocytes and myoblasts results in expansion of orbital fat and fibrosis, respectively. GO usually occurs in association with autoimmune hyperthyroidism (Graves’ disease), but the same disease process can occur in the euthyroid or hypothyroid states. It is associated with other autoimmune diseases, including myasthenia gravis, and can be exacerbated by cigarette smoking and radioactive iodine (RAI) therapy.
Clinical Findings
Some degree of mild eye disease, typically including upper eyelid retraction, occurs in a high percentage of hyperthyroid patients. Severe disease with marked proptosis and restricted ocular motility occurs in about 5–10% of cases of Graves’ disease (Figure 13–3).
602
Figure 13–3. Graves’ ophthalmopathy.
GO is the most common cause of unilateral or bilateral proptosis in adults. The accompanying upper eyelid retraction, manifesting as disproportionately greater exposure of sclera superiorly than inferiorly, and lid lag (von Graefe sign), manifesting as impaired descent of the upper eyelid on downward gaze, usually distinguish it from other causes of proptosis.
Ocular surface discomfort is common in all stages of the disease, in some cases due to superior limbic keratoconjunctivitis (see Chapter 5). Incomplete eyelid closure (lagophthalmos) results from proptosis and lid retraction, and corneal exposure may be present even in mild cases. Ptosis in association with GO usually is due to coexistent myasthenia gravis, which may also contribute to ocular motility disturbance.
The extraocular muscle involvement of GO begins with lymphocytic infiltration and edema of the rectus muscles, typically the inferior and medial recti (Figure 13–4). The inflamed muscles subsequently may become fibrotic. Diplopia usually begins in the upper field of gaze due to asymmetric tethering of the inferior recti that also may cause elevation of intraocular pressure on upgaze or in primary gaze in severe cases. All extraocular muscles eventually may be involved with diplopia in all directions of gaze.
603
Figure 13–4. Computed tomography scan of Graves’ ophthalmopathy. A: Axial section demonstrates markedly enlarged medial and lateral recti of the right orbit (arrows). B: Coronal section demonstrates optic nerves (arrowheads) and markedly enlarged medial and inferior recti in both orbits
(arrows).
If the extraocular muscles become markedly enlarged, there may be compression of the optic nerve at the orbital apex that is not necessarily accompanied by significant proptosis. Early signs include a relative afferent pupillary defect and impairment of color vision, followed by reduction of visual acuity. Blindness may develop if the compression is not relieved.
Treatment
In the treatment of hyperthyroidism, the risk of GO is increased by untreated hypothyroidism; is less after thyroidectomy than after RAI; and seems to be reduced by statin therapy. After RAI, about 15% of patients develop new GO or have progression of pre-existing disease. This risk is decreased by a course of
604
oral steroids after the RAI. There is negligible risk of exacerbation of inactive GO with RAI. RAI should be avoided in active smokers.
Management of GO should be multidisciplinary. An endocrinologist should manage the thyroid status, because optimal control is crucial to preventing more severe eye disease. GO activity should be graded using defined clinical activity scores. Therapy is adjusted according to disease severity.
Mild GO often manifests as ocular surface problems that usually can be controlled with topical lubricants. Oral selenium slows disease progression in mild active GO.
In moderate to severe GO, immunosuppressant therapy may be required. Pulsed intravenous glucocorticoid therapy is more efficacious with less adverse effects than oral or retrobulbar steroids. Rituximab, a biologic that targets B cells, potentially provides better therapeutic outcomes than steroids. The benefit of orbital radiotherapy is less clear. It may offer more rapid improvement of inflammation and decrease the severity of diplopia. It is contraindicated in diabetic patients with retinopathy. For immediate treatment of exposure keratitis due to severe proptosis, lateral tarsorrhaphy or chemodenervation with botulinum toxin injection of the levator palpebrae superioris muscle may be considered.
Sight-threatening, compressive optic neuropathy or proptosis with severe exposure keratitis uncontrolled by lubricants requires emergency treatment initially with high-dose systemic steroids ideally using pulsed intravenous glucocorticoids. If this is unsuccessful, surgical decompression of the orbit is usually performed.
GO is presumed to be a self-limiting disease but characterized by an active course of exacerbations and remissions, lasting months to years. Once disease activity has settled and a euthyroid state has been maintained for at least 6 months, surgical rehabilitation may be considered. Surgery is approached in a staged manner. When indicated, orbital decompression for proptosis is considered first, followed by strabismus surgery to correct ocular deviations and concluded by eyelid surgery to address malpositions.
Orbital decompression is indicated for proptosis resulting in keratitis that cannot be medically controlled or an unacceptable aesthetic appearance. Several techniques have been devised using external or transnasal endoscopic approaches. All aim to expand the orbital volume by removal of the bony walls, usually the medial wall, lateral wall, and/or floor. Because the primary goal of
605
surgery is to shift the position of the globe more posteriorly in the orbit, there is a risk of causing or exacerbating diplopia. Thus, if decompression surgery is required, it is performed before strabismus surgery.
Double vision may not be sufficiently bothersome to require treatment. While the ophthalmopathy is active, prisms or eye occlusion may be helpful. As with decompression, strabismus surgery should not be undertaken until the ophthalmopathy is inactive and the ocular motility disturbance has been stable for at least 6 months. Tight muscles, usually the inferior and medial recti, are recessed. Most patients can achieve an area of binocular vision without diplopia in primary gaze. Botulinum toxin is rarely helpful in the acute or chronic stages of the disease. Some patients have intractable diplopia despite all attempts at correction.
Eyelid retraction may result in exposure keratitis and often in an aesthetically unappealing appearance. Orbital decompression may improve lid retraction, but some patients may forego this type surgery and opt for surgical correction of lid retraction only since it offers a lower risk profile and faster recovery and can camouflage proptosis to some extent. Small amounts (2 mm) of lid retraction can be corrected by disinserting the retractors from the upper tarsal border. For larger degrees of retraction, a graded full-thickness blepharotomy can be performed, or insertion of a spacer graft, such as banked scleral tissue, to lengthen the upper and lower lid can be considered.
2. NONSPECIFIC ORBITAL INFLAMMATION
Nonspecific orbital inflammation (NSOI) (idiopathic orbital inflammation or orbital inflammatory syndrome) is typically a unilateral process of rapid onset that presents with pain, periocular and conjunctival edema, proptosis, and diplopia. (The previous term orbital pseudotumor to indicate an orbital mass simulating a neoplasm with inflammatory histology is a confusing anachronism.) In the pediatric population, it more often presents as bilateral disease with accompanying uveitis, disk edema, and eosinophilia.
NSOI is characterized by a pleomorphic inflammatory response involving several cell types (eg, lymphocytes, fibroblasts, histiocytes, and/or plasma cells). The inflammatory process can be diffuse or localized, specifically involving any orbital structure (eg, myositis, dacryoadenitis, superior orbital fissure syndrome,
606
or optic perineuritis). There may be extension to involve the cavernous sinuses and intracranial meninges. MRI helps to identify the involved tissues. The differential diagnosis includes GO, orbital lymphoma, and other specific types of orbital inflammation including sarcoidosis, granulomatosis with polyangiitis (Wegener’s granulomatosis) and IgG4-related disease. Laboratory testing may sometimes indicate a more specific cause for inflammation.
Systemic treatment with glucocorticosteroids is typically the first line. Recurrence or lack of treatment response is common, and alternative nonspecific (eg, cyclophosphamide) or biologic (eg, infliximab) immunosuppressants should be considered. It is unclear if radiotherapy is beneficial as the studies involve small cohorts and different protocols with a significant number of patients having partial or no response. Surgery is reserved for biopsy to establish the diagnosis or rarely for surgical debulking or exenteration in cases of refractory disease once vision has been irreparably lost.
ORBITAL INFECTIONS
1.ORBITAL CELLULITIS AND PRESEPTAL CELLULITIS
Orbital cellulitis is a bacterial infection located posterior to the orbital septum (postseptal). It is the most common cause of proptosis in children. Immediate treatment is essential because delay can lead to blindness due to optic nerve compression or infarction, or rarely death from septic cavernous sinus thrombosis or intracranial sepsis. Although most cases occur in children, elderly and immunocompromised individuals may also be affected.
The majority of cases of childhood orbital cellulitis arise from extension of acute sinusitis through the thin ethmoid bone via emissary veins. The organisms usually responsible are Staphylococcus aureus with an increasing number of cases caused by methicillin-resistant S aureus (MRSA), Streptococcus anginosus, Streptococcus pneumonia, and Streptococcus pyogenes. Haemophilus influenzae type B (Hib) infection is infrequently seen because of Hib immunization. In adolescents and adults, when there is often chronic sinus
607
infection, anaerobic organisms may also be involved, and there is a higher risk of intracranial infection. If there is a history of penetrating trauma, S aureus, including MRSA, and S pyogenes are commonly responsible.
In comparison, preseptal cellulitis is a bacterial infection superficial to the orbital septum. It is usually caused by infection arising within the eyelid from a hordeolum (see Chapter 4), recent lid surgery, traumatic wound, or an insect or animal bite. Predominate pathogens include S aureus and Streptococcus species.
Clinical Findings
Orbital cellulitis is characterized by fever, pain, eyelid edema and erythema, proptosis, chemosis, limitation of extraocular movements, and leukocytosis (Figure 13–5A). Nonaxial proptosis suggests subperiosteal or intraorbital abscess. Extension to the cavernous sinus can produce contralateral orbital involvement, trigeminal dysfunction, and more marked systemic illness. Intracranial extension can result in subdural empyema and meningitis. Few orbital processes, other than fungal disease, progress as rapidly as bacterial infections.
Figure 13–5. A: Orbital cellulitis secondary to frontal sinusitis. B: Coronal
608
computed tomography scan shows right orbital abscess (arrow).
Preseptal cellulitis may also mimic the initial stages of orbital cellulitis; however, there is lack of proptosis, chemosis, or limitation of extraocular movements. Other entities to be considered are rhabdomyosarcoma in children, GO, and NSOI.
A CT scan or MRI provides essential information regarding the source and extent of infection (Figure 13–5B). MRI is preferred over CT to detect cavernous sinus thrombosis and organic foreign bodies. Plain x-rays are rarely performed.
Treatment
Treatment of orbital cellulitis should be initiated before the causative organism is identified. As soon as nasal, conjunctival, and blood cultures are obtained, antibiotics should be administered. Intravenous therapy is preferred with a thirdgeneration cephalosporin (eg, cefotaxime or ceftriaxone) or a β-lactamase– resistant drug, such as nafcillin, imipenem, or piperacillin/tazobactam. Vancomycin is also typically administered to cover for MRSA. Possible anaerobic infection requires addition of metronidazole or clindamycin. For patients with penicillin hypersensitivity, vancomycin, levofloxacin, and metronidazole are recommended. Success with oral ciprofloxacin and clindamycin has been reported in uncomplicated cases.
Early consultation with an otolaryngologist is important for sinus infections. Nasal decongestants and vasoconstrictors help drain the paranasal sinuses. Observation for antibiotic response may be considered in children aged less than 9 years with a medial, subperiosteal abscess of modest size and without compromised vision. Otherwise surgical drainage of the abscess should be performed in conjunction with functional endoscopic sinus surgery to address the source of infection.
Preseptal cellulitis can usually be treated with oral antibiotics, such as amoxicillin/clavulanate, but the patient should be monitored closely for development of postseptal involvement. Therapy should be adjusted if there is high likelihood of MRSA infection, for a dirty wound, or if the patient is immunocompromised, in which case gram-negative organisms should be covered.
609
2.ACUTE FULMINANT INVASIVE FUNGAL SINUSITIS
Acute fulminant invasive fungal sinusitis (AFIFS) (zygomycosis, mucormycosis) occurs predominately in patients with severe immunosuppression. AFIFS is usually due to Aspergillus species or fungi from the class Zygomycetes, including Rhizopus, Rhizomucor, Absidia, and Mucor. In 80% of diabetic patients, a species of Zygomycetes is responsible, and in 80% of neutropenic patients, Aspergillus is responsible. The fungi invade blood vessels, leading to ischemic necrosis. Infection usually begins in the sinuses and spreads into the orbit, resulting in periorbital edema, ptosis, ophthalmoplegia, visual loss, and proptosis. Central nervous system involvement may manifest as decreased mentation. Examination of the nose and palate characteristically reveals black, necrotic mucosa, a smear of which demonstrates branching hyphae.
Without treatment, the infection quickly invades the intracranial space, resulting in meningitis, brain abscess, and death usually within days to weeks. Treatment is fraught with difficulties and often inadequate. It consists of reversing the underlying immunosuppression if possible, administration of intravenous antifungal agents (including amphotericin B, caspofungin, and/or posaconazole) and surgical debridement. Local injections of amphotericin B in the orbit may also be considered.
CYSTIC LESIONS INVOLVING THE ORBIT
1. DERMOID AND EPIDERMOID CYSTS
Dermoid and epidermoid cysts are not true neoplasms but benign choristomas arising from embryonic tissue not usually found in the orbit. They originate from surface ectoderm and are lined by a keratinizing epithelium. A dermoid cyst contains epithelial structures such as keratin, hair, and even sometimes teeth, while an epidermoid cyst is filled with keratin but lacks dermal appendages. The
610
contents of either type of cyst can incite a severe inflammatory reaction if liberated into the orbit. Preseptal dermoid and epidermoid cysts most commonly occur at the lateral brow at the frontozygomatic suture, but may develop at any suture line (Figure 13–6). Cysts that are within the orbit typically occur in the superior temporal quadrant and do not present until adulthood. CT scan demonstrates a sharp, round bony defect from the pressure of a slowly growing mass affixed to the periosteum. En-bloc surgical removal with preservation of the cyst wall during surgery is the treatment of choice.
Figure 13–6. Dermoid cyst of the left frontozygomatic suture.
2. SINUS MUCOCELE
Obstruction of drainage from a paranasal sinus may lead to a benign, expansile, mucus-filled cyst called a sinus mucocele. Frontal or ethmoid sinus mucoceles typically present with progressive nonaxial proptosis, whereas sphenoid sinus mucoceles present with optic neuropathy (Figure 13–7). Presentation may be rapid if there is associated infection. CT scan is usually diagnostic. MRI may be required to differentiate from a dermoid cyst and to define the extent of the lesion. Preferred treatment is endoscopic sinus surgery performed by otolaryngology to marsupilize the cyst and reestablish sinus drainage.
611
