Orbital Disorders
Peter A. D. Rubin
The orbits are bony cavities located on each side of the nose. Each orbit contains a complex structure of soft tissues including the globe, optic nerve, extraocular muscles, fat, fascia, and vessels. Orbital disorders are associated with a wide variety of local and systemic diseases, and their treatment requires a thorough knowledge of regional anatomy, radiology, neurology, and endocrinology.
I. Orbital Anatomy
Each bony orbit is pear-shaped, tapering posteriorly toward the apex and the optic canal. The medial orbital walls are nearly parallel and approximately 25 mm apart in the average adult, whereas the lateral orbital walls are perpendicular.
Orbital walls. The surfaces of each orbit (roof, lateral wall, medial wall, and floor) are composed of seven bones: Ethmoid, frontal, lacrimal, maxillary, palatine, sphenoid, and zygomatic. The thinnest of these surfaces are the lamina papyracea over the ethmoid sinuses (along the medial wall) and the maxillary bone over the infraorbital canal (along the orbital floor).
Orbital apertures
The ethmoidal foramen is located in the medial orbital wall, at the junction of the ethmoid and frontal bones, through which pass the anterior and posterior ethmoidal arteries.
The superior orbital fissure is located between the greater and lesser wings of the sphenoid, through which pass most of the orbital veins; some sympathetic fibers; the third, fourth, and sixth cranial nerves; and the ophthalmic division of the fifth cranial nerve.
The inferior orbital fissure is located at the lower portion of the orbital apex, through which pass some orbital veins, the zygomatic nerve, and the maxillary division of the fifth cranial nerve.
The zygomaticofacial and zygomaticotemporal canals are located in the lateral orbital wall, through which pass vessels and branches of the maxillary nerve.
The nasolacrimal canal is formed by the maxilla and lacrimal bone, through which passes the nasolacrimal duct between the lacrimal sac and the inferior nasal meatus.
The optic canal is located in the lesser wing of the sphenoid, through which pass the optic nerve, the ophthalmic artery, and sympathetic nerves. This canal is 5 mm to 10 mm long and is separated from the superior orbital fissure by the bony optic strut. The orbital end of the canal is the optic foramen, which normally measures 6.5 mm or smaller in diameter.
II. Orbital Evaluation
(see Chapter 1). The evaluation and diagnosis of an orbital abnormality is guided by considering the most common disorders that occur among children and adults (see Section III). A clinical history should include questions about the presence of malignant tumors or thyroid disease that might involve the orbit. Evaluation of the orbits should be preceded by a careful ophthalmic examination.
X-rays provide a simple method of studying the orbital bones, but their use is limited because of poor soft tissue definition.
Ultrasonography is a sensitive technique for evaluating intraocular details and visualizing many orbital lesions. However, the sound waves cannot penetrate bone, and some orbital masses may not be detected unless the waves strike a perpendicular surface. This is occasionally a helpful adjunctive imaging modality. Color Doppler, a specialized type of ultrasound, permits detection of blood flow, which is useful in the assessment of vascular orbital lesions.
Computed tomography (CT) uses thin x-ray beams to obtain tissue density values, from which detailed cross-sectional images of the body are produced by a computer. Newer, rapid spiral CT permits acquisition of an orbital CT in less than 30 seconds. These continuously acquired scans (spiral CT) can be reformatted with minimal artifact, thus obviating the need for both direct and axial scans. CT simultaneously visualizes orbital and intracranial structures, including soft tissues, bones, and many foreign bodies. Vessels may be seen most clearly after intravenous (i.v.) injection of contrast material. CT is the most useful single imaging technique for orbital evaluation and should be the imaging modality of choice unless proven otherwise.
Magnetic resonance imaging (MRI) is a method of visualizing thin anatomic sections by exposing patients to a magnetic field and then recording the radiofrequency emissions from protons (which are the nuclei of hydrogen atoms). The advantages of MRI include the lack of ionizing radiation (as used in x-rays and CT) and the ability to distinguish among certain vascular and neurologic abnormalities. A disadvantage is that bone does not give magnetic resonance signals; therefore most orbital lesions may be better evaluated by CT scans. MRI is the imaging modality of choice if one needs to assess intracranial disease or is assessing pathology and the cranio-orbital junction (e.g., optic nerve tumors). Magnetic resonance angiography provides a noninvasive view of vascular anomalies.
Arteriography is performed by injection of radiopaque dye into the carotids to visualize the orbital and intracranial arteries. It has a low but significant risk of serious neurologic and vascular complications. Maximum information can be obtained from arteriography through the use of selective internal and external carotid injections, magnification, and radiographic subtraction. Given the recent advances in resolution with CT and magnetic resonance angiography, direct arteriography has a diminishing role, except when transarterial intervention is contemplated (e.g., embolization).
III. Incidence of Orbital Abnormalities
It is useful to group orbital disorders into those that most commonly occur during childhood through the second decade of life and those that are found predominantly among adults.
Common orbital abnormalities among children
Orbital cellulitis.
Idiopathic inflammation (“pseudotumor”).
Dermoid and epidermoid cysts.
Capillary hemangioma.
Lymphangioma.
Rhabdomyosarcoma.
Optic nerve glioma.
Neurofibroma.
Leukemia.
Metastatic neuroblastoma.
Common orbital abnormalities among adults
Thyroid eye disease.
Idiopathic inflammation (“pseudotumor”).
Metastatic neoplasms.
Secondary neoplasms.
Cavernous hemangioma.
Lymphangioma.
Lacrimal gland tumors.
Lymphoma.
Meningioma.
Dermoid and epidermoid cysts.
IV. Exophthalmos
is one of the most common clinical manifestations of an orbital abnormality. Exophthalmos is defined as an abnormal prominence of one or both
eyes, usually resulting from a mass, a vascular abnormality, or an inflammatory process. Among adults, the usual distance from the lateral orbital rim to the corneal apex is approximately 16 mm; it is uncommon for a cornea to protrude more than 22 mm beyond the orbital rim. An asymmetry of more than 2 mm between the eyes, with one eye having normal measurements, is suggestive of unilateral exophthalmos.
eyes, usually resulting from a mass, a vascular abnormality, or an inflammatory process. Among adults, the usual distance from the lateral orbital rim to the corneal apex is approximately 16 mm; it is uncommon for a cornea to protrude more than 22 mm beyond the orbital rim. An asymmetry of more than 2 mm between the eyes, with one eye having normal measurements, is suggestive of unilateral exophthalmos.
Unilateral exophthalmos among children is most commonly caused by orbital cellulitis as a complication of either ethmoid sinus disease or a respiratory infection. Among adults, prominence of one eye is most commonly due to thyroid eye disease.
Bilateral exophthalmos among children may be caused by leukemia or by metastatic neuroblastoma. Among adults, bilateral exophthalmos is most often caused by thyroid eye disease.
Pseudoexophthalmos is either the simulation of an abnormal prominence of the eye or a true asymmetry that is not caused by a mass, a vascular abnormality, or an inflammatory process. Causes of pseudoexophthalmos are as follows:
Enlarged globe.
Myopia.
Trauma.
Glaucoma.
Asymmetric orbital size.
Congenital.
Postradiation.
Postsurgical.
Asymmetric palpebral fissure.
Contralateral ptosis.
Lid retraction.
Facial nerve paralysis.
Lid scar, ectropion, entropion.
Extraocular muscle abnormalities.
Postsurgical muscle recession.
Paralysis or paresis.
Contralateral enophthalmos.
Contralateral orbital fracture.
Contralateral small globe.
Contralateral cicatricial tumor.*
V. Orbital Inflammations
Inflammations of the orbit are responsible for more cases of exophthalmos than are neoplasms. Among adults, thyroid eye disease causes more unilateral and bilateral exophthalmos than any other disorder. Among children, orbital cellulitis probably produces exophthalmos more often than any neoplasm. Pseudotumors are idiopathic inflammations that resemble neoplasms and are often associated with exophthalmos and pain. The orbit is a common site of occurrence for a wide variety of other inflammatory disorders related to infections, trauma, and systemic disease.
Thyroid eye disease or ophthalmic Graves disease has been defined as multisystem disease of unknown etiology characterized by one or more of three pathognomonic clinical entities: Hyperthyroidism with diffuse thyroid hyperplasia, infiltrative dermopathy, and infiltrative ophthalmology. Histopathologic changes seen within the orbital tissues, which are not diagnostic, include a polytypic infiltrate, increased fibroblastic activity, glycosaminoglycan deposition, edema, and fibrosis.
Ophthalmic Graves’ disease includes any of the orbital manifestations of this disorder. Thyroid eye disease appears in 30% to 70% of patients with Graves thyroid disease. Females are affected approximately four times more commonly than males. Orbitopathy may appear before, during, or after thyroid disease and is directly correlated with the level of endocrine dysfunction. Up to 25% of patients present initially to an ophthalmologist prior to detection of systemic disease. The most common finding among patients with thyroid eye disease is widening of the palpebral fissure, termed lid retraction. Lid “lag,” or upper eyelid trailing behind the globe on downgaze, is another subtle finding of thyroid eye
disease. The orbitopathy seems to be most severe in patients who are smokers, thus patients with signs of orbitopathy are given yet another compelling reason to eliminate smoking. The defining features on the clinical examination include proptosis, eyelid retraction, restrictive myopathy with diplopia, and compressive optic neuropathy.
The orbitopathy exhibits great heterogeneity and has been subclassified:
Type I orbitopathy
Symmetric proptosis
Symmetric eyelid retraction
Minimal orbital inflammation
Minimal extraocular muscle (EOM) inflammation/restriction
Occurs more often in women
EOM moderately or diffusely enlarged
Type II orbitopathy
EOM myositis
Restrictive myopathy
Hypotropia, esotropia
Compressive neuropathy
Incidence in males similar to that in females
Thyroid tests are usually abnormal among 90% of patients with ophthalmic Graves’ disease. Some patients, however, will be euthyroid by all tests, so that the diagnosis of Graves’ disease is established by clinical features alone.
Initial screening tests. Thyroid stimulating hormone is the single best screening test to evaluate for Graves’ disease. Affected patients will typically have abnormally low levels.
Anatomic tests allow the clinician to visualize characteristics but not pathognomonic changes in orbital anatomy with Graves’ disease.
CT shows enlarged EOM, typically sparing the tendons. The inferior rectus muscle is most commonly involved, followed by the medial rectus and superior rectus. It is rare to see lateral rectus enlargement alone in the setting of thyroid eye disease.
Treatment. Most patients can be effectively managed with local measures, including lid taping, lubrication, and sunglasses. Medical anti-inflammatory treatment (oral steroids) is reserved for more severe cases of inflammation or optic neuropathy and should be viewed as a temporary modality (<6 weeks). For patients who initially respond to steroids but cannot be successfully tapered, low-dose radiotherapy should be contemplated. Surgery
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