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DISEASES & DISORDERS OF THE ORBIT

INFLAMMATORY DISORDERS

1. GRAVES' OPHTHALMOPATHY

The most common cause of unilateral or bilateral proptosis in adults or children is Graves' disease.

The terminology used to describe ocular involvement in thyroid disease is often confusing. Graves' ophthalmopathy, dysthyroid ophthalmopathy, and dysthyroid eye disease are interchangeable terms. Some degree of ophthalmopathy-usually mild-occurs in a high percentage of hyperthyroid patients. Severe infiltrative orbital myopathy with significant proptosis and restricted motility occurs in about 5% of cases of Graves' disease (Figure 13-3). This severe form, however, can also occur with hypothyroidism or with no detectable thyroid abnormality, in which case the term ophthalmic Graves' disease may be used.

Thyroid ophthalmopathy is thought to be an autoimmune disease. It is often seen in autoimmune (Hashimoto's) thyroiditis. Antithyroglobulin, antimicrosomal, and other antibodies can usually be demonstrated, but their role in pathogenesis is in question.

Clinical Findings

Proptosis associated with thyroid disease is characterized by lid retraction, which serves to distinguish it from other causes of proptosis. Lagophthalmos results from proptosis and lid retraction, and corneal exposure is a factor even in mild cases. Ocular myopathy usually begins with lymphocytic infiltration and edema of the rectus muscles. In time, the inflamed muscles may become fibrotic and permanently restricted. The eye may be tethered so as to raise the intraocular pressure when it is measured in upgaze.

Diplopia usually begins in the upper field of gaze because of infiltrative myopathy involving the inferior rectus muscle. All extraocular muscles may eventually be involved, and there may be no position of gaze free of diplopia. The extraocular muscles may become massively enlarged and-in addition to restricting eye movement-may compress the optic nerve. Compressive optic neuropathy is most common with enlargement of the posterior aspect of the muscles that occurs without severe proptosis. Early signs include an afferent pupillary defect, impairment of color vision, and slight loss of visual acuity. Blindness is liable to occur if compression is unrelieved.

Treatment

The goal of treatment of Graves' ophthalmopathy is initially to maintain corneal protection. As the disease progresses it becomes necessary to address the problems of diplopia, proptosis, and compressive optic neuropathy. Management of severe cases is difficult and multidisciplinary. An endocrinologist should manage the thyroid status, optimal control being crucial to ameliorating the orbital disease. Oral cortico-steroids (prednisone, 60-100 mg/d) may be helpful in controlling the acute phase of infiltrative myopathy. Complications and side effects limit the use of corticosteroids in long-term maintenance. Orbital radiation is effective during the active phase of the disease. Soft tissue signs of swelling and chemosis are usually relieved. Diplopia and proptosis may be improved.

Early compression neuropathy may also be relieved by radiation therapy, but neuropathy unresponsive to medical management is an indication for surgical decompression of the orbit. Several approaches have been devised to expand the orbital volume by fracture of the bony walls, usually the orbital floor into the maxillary sinus and the medial wall into the ethmoid sinus, along with removal of the lateral orbital wall in some cases. Proptosis can be reduced by surgery, but there is a risk of intractable diplopia and a lesser risk of orbital infection. For these reasons, decompression for cosmetic reasons is not routinely performed.

Eyelid retraction is often more disturbing than proptosis-both functionally, because of exposure keratitis, and cosmetically. Decompression may relieve lid retraction, but correction of the retraction camouflages proptosis to some extent. Lid retraction is corrected by surgery. The upper and lower lid retractors (aponeurosis and sympathetic muscles) can be lengthened by inserting a spacer such as eye bank sclera. Small amounts (2 mm) of lid retraction can be corrected by simply disinserting the retractors from the upper tarsal border.

Strabismus surgery should not be undertaken until the myopathy has stabilized. The adjustable suture technique is useful. Most patients can achieve at least a small area of binocular single vision in a useful position of gaze. Torsional diplopia, the result of oblique muscle involvement, complicates management.

Some patients have intractable diplopia despite all attempts at correction.

2. PSEUDOTUMOR

A frequent cause of proptosis in adults and children is inflammatory pseudotumor. The term "pseudotumor" was coined to indicate a nonneoplastic process that produces the sentinel sign of an orbital neoplasm, ie, proptosis. In some cases there is an associated systemic vasculitis, such as Wegener's granulomatosis. The site of inflammation is usually diffuse and not amenable to excision. The process can involve any orbital structure (eg, myositis, dacryoadenitis, lymphogranuloma) or cell type (eg, lymphocytes, fibro-blasts, histiocytes, plasma cells). Onset is usually rapid, and pain is often present.

Pseudotumor is usually unilateral; when both orbits are involved, it is more often a manifestation of vasculitis. The differential diagnosis includes Graves' ophthalmopathy and orbital lymphoma.

Treatment with systemic nonsteroidal anti-inflammatory drug (NSAID)s, systemic corticosteroids, or radiation is usually effective. Surgery often exacerbates the inflammatory reaction.

ORBITAL INFECTIONS

1. ORBITAL CELLULITIS (Figure 13-4)

Orbital cellulitis is the most common cause of proptosis in children. Immediate treatment is essential. Fortunately, the diagnosis usually is not difficult, because the clinical findings are characteristic. Although most cases occur in children, aged and immunocompromised individuals may also be affected.

Trauma may be responsible for introduction of contaminated material into the orbit through the skin or paranasal sinuses. In the preantibiotic era, orbital cellulitis frequently led to blindness or death resulting from septic cavernous sinus thrombosis.

The orbit is surrounded by the paranasal sinuses, and part of their venous drainage is through the orbit. Most cases of orbital cellulitis arise from extension of sinusitis through the thin ethmoid bones. The organisms usually responsible are those most frequently found in sinuses: Haemophilus influenzae, Streptococcus pneumoniae, other streptococci, and staphylococci.

Clinical Findings

Preseptal cellulitis is the most common presentation. CT scan or MRI is helpful in distinguishing between pre- and postseptal involvement as well as identifying and localizing an orbital abscess or foreign body. Plain x-rays alone can only identify the presence of sinusitis.

It is important to distinguish between preseptal and orbital infections. Both present with edema, erythema, hyperemia, pain, and leukocytosis. Chemosis, proptosis, limitation of eye movement, and reduction of vision indicate deep orbital involvement. Extension to the cavernous sinus may cause bilateral involvement of cranial nerves II-VI, with severe edema and septic fever. Erosion of the orbital bones may cause brain abscess and meningitis.

In children, few orbital diseases develop as rapidly as cellulitis. Confusion may exist with rhabdomyosarcoma, pseudotumor, and Graves' ophthalmopathy.

Treatment

Treatment should be initiated before the causative organism is identified. As soon as nasal, conjunctival, and blood cultures are obtained, intravenous antibiotics should be administered. Initial antibiotic therapy should cover staphylococci, H influenzae, and anaerobes. Posttraumatic cellulitis-especially following animal bites-must be covered for gram-negative and gram-positive bacilli. Hot compresses help localize the inflammatory reaction. Nasal decongestants and vasoconstrictors help drain the paranasal sinuses. Early surgical drainage is indicated in suppurative preseptal cellulitis. MRI is useful in deciding when and where to drain an orbital abscess. Most cases respond promptly to antibiotics. Those that do not may require drainage of the paranasal sinuses. Early consultation with an otolaryngologist may be helpful.

2. MUCORMYCOSIS

Diabetics and immunocompromised patients have a propensity to develop severe and often fatal fungal infections of the orbit. The organisms are of the Zygomycetes group, which have a tendency to invade vessels and create ischemic necrosis. Infection usually begins in the sinuses and erodes into the orbital cavity. A necrotizing reaction destroys muscle, bone, and soft tissue, frequently without causing signs of orbital cellulitis.

The patient is usually quite ill and presents with pain and proptosis. Examination of the nose and palate often reveals a necrotic area of mucosa, a smear of which shows broad branching hyphae.

Without treatment, the infection gradually erodes into the cranial cavity, resulting in meningitis, brain abscess, and death usually within days to weeks. Treatment is difficult and often inadequate. It consists of correction of the underlying disease combined with surgical debridement and administration of amphotericin B intravenously. Recurrences are common.

CYSTIC LESIONS INVOLVING THE ORBIT

1. DERMOID

Dermoids are not true neoplasms but benign choristomas arising from embryonic tissue not usually found in the orbit. Orbital dermoids arise from surface ectoderm and often contain epithelial structures such as keratin, hair, and even teeth. Most are cystic and filled with an oily fluid that can incite a severe inflammatory reaction if liberated into the orbit. Most dermoids occur in the superior temporal quadrant of the orbit, but they can occur at any bony suture line.

X-rays show a sharp, round bony defect from the pressure of a slowly growing mass affixed to the periosteum.

Epidermoid cyst is a superficial keratin-filled mass, usually near the superior orbital rim. It may be congenital or posttraumatic. Excision is usually not difficult.

A dermolipoma is a solid mass of fatty material that occurs below the conjunctival surface. Hair growth on the overlying conjunctiva is not uncommon. Dermolipomas are often much larger than they appear to be, and excision may cause considerable damage to vital structures. If treatment is necessary, limited excision is usually advised.

2. SINUS MUCOCELE

The proximity of the orbit to the paranasal sinuses may lead to invasion of the bony walls and extension of an obstructed sinus into the orbit. Plain x-ray will usually make the diagnosis, but CT or MRI may be required to differentiate sinus mucocele from dermoid cyst and to define the extent of the lesion (Figure 13-5). Otolaryngologic and neurosurgical assistance may be necessary for surgical removal.

3. MENINGOCELE

Erosion of the meninges into the orbital cavity through a congenital dehiscence in the bony sutures creates a cystic mass filled with cerebrospinal fluid known as a meningocele. Both brain and meninges are frequently included in a meningoencephalocele. The resultant fluctuant mass in the superior medial orbit typically enlarges with Valsalva's maneuver. Most cases are present at birth, but those arising from the sphenoid bone may not become apparent until adolescence.

VASCULAR ABNORMALITIES INVOLVING THE ORBIT

1. ARTERIOVENOUS MALFORMATION

Arteriovenous malformations are an uncommon cause of proptosis. Varices produce intermittent prop-tosis, sometimes associated with pain and transient reduction of vision. Some degree of proptosis can be induced with Valsalva's maneuver or by placing the head in a dependent position. MRI scan is usually diagnostic, and venography is seldom indicated.

Surgery is the only method of treatment available and is fraught with hazard. Morbidity following eradication of the varix may jeopardize visual function. Most varices are best left untreated unless vision is at risk.

2. CAROTID ARTERY-CAVERNOUS SINUS FISTULA

Carotid artery-cavernous sinus fistulas with high-flow shunts are easily diagnosed. Although sometimes occurring spontaneously, they usually follow trauma. Physical signs include severe congestion and chemosis, with pulsating proptosis and a loud bruit.

Low-flow shunts (dural carotid cavernous sinus fistula) are usually spontaneous and often misdiagnosed. Mild congestion, venous engorgement and arterialization, elevated intraocular pressure, mild proptosis, and a faint bruit are the usual features. Diagnosis is by contrast MRI or subtraction angiography, and treatment is by selective intra-arterial or transvenous embolization.

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