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The orbit and sinus cavities are highly detailed structures that share an anatomic relationship. Because of their proximal location, accurate diagnosis is highly dependent upon a detailed history, key clinical findings, and appropriate imaging studies. The objective of this article is to serve as a clinical reference for decision-making.
The article includes sections on anatomy, clinical evaluation, and imaging techniques for computed tomography (CT) and magnetic resonance imaging (MRI), followed by a section reviewing various clinical scenarios involving unilateral proptosis. This article covers the most common causes of unilateral proptosis in the adult population. Upcoming articles in this series will feature sinus-related pathologies and orbital trauma.
The orbit and sinus cavities share a close relationship from both anatomic and clinical viewpoints. The total volume of the orbit is 27 mL, 7 to 8 mL of which constitutes the globe. The remaining volume is filled with nerves, blood vessels, fat, extraocular muscles, lacrimal gland apparatus, and optic nerve. The orbit can be anatomically divided into four bony margins: temporal, nasal, superior, and inferior. The temporal margin is formed by the frontal and zygomatic bones. The nasal margin is formed by the maxillary and frontal bones. The superior margin is formed by the floor of the frontal bone, and the inferior margin is formed by the zygomatic and maxillary bones.
Clinical evaluation of the orbit and sinus cavities requires three important considerations: (1) taking a detailed history; (2) performing clinical examination of the extraocular muscles (EOMs), palpation of the sinus cavities, and exophthalmometry; and (3) performing imaging of the orbit and sinus cavities with CT and/or MRI. Acute symptoms of diplopia, vision loss, proptosis, and hyperemia are often associated with inflammation, infection, vascular anomalies, and occasionally tumors. Although symptoms and signs that are subacute and chronic are typically less urgent, they require a lower threshold for consideration of a serious orbital pathology because physical findings may be subtle.
A CT scan uses x-rays and sensors to gather data. When a CT scan is viewed, with or without contrast, the bones are visible as white, and the air-filled spaces, similar to an x-ray, appear dark. Soft tissue appears in gray tones. In evaluating the orbit and sinus cavities, a CT scan is often used to view the anatomic position of the EOMs and evaluate for bony involvement and sinus disease. Orbital trauma, acute-onset proptosis, and Graves disease are three indications for noncontrast CT of the orbit. CT can also be performed on patients with implanted medical devices of any kind. The disadvantages of CT scans for patients include the use of ionizing radiation and the possibility of iodinated contrast-induced allergy. Because of the ionizing radiation, CT imaging is not indicated in pregnant women and should be limited in children. A potential issue in the interpretation of CT scans is the presence of beam-hardening artifacts.
Magnetic Resonance Imaging
MRI can provide valuable imaging of the orbital soft tissues and sinus structures. Unlike traditional x-ray or CT, MRI analyzes biologic tissues using magnetic fields and radio waves, providing a detailed image of soft tissue. The advantages of MRI over CT include the ability to show enhanced definition between different soft tissues and the use of a safer contrast dye. MRI is contraindicated in patients with potentially loose magnetic metallic items such as cochlear implants, aneurysm clips, pacemakers, defibrillators, spinal stimulators and other electronic medical devices (some implantable devices may be “MRI conditional,” meaning that an MRI may be allowed under certain conditions, such as specific magnet strengths).1
Gadolinium contrast is often administered intravenously to increase the visibility of retro-orbital tumors, inflammation, infection and meningeal lesions. Prior to ordering an MRI with contrast, a patient should have labs performed to check for adequate kidney function, including serum creatinine and blood urea nitrogen.2
Proptosis is a clinical finding that can be a diagnostic challenge. The goal of this section is to highlight important implications for proptosis with regard to clinical diagnosis and management. Acute orbital pathologies typically manifest with pain, proptosis, EOM restriction, eyelid edema, conjunctival hyperemia, and, in some cases, decreased vision. There are numerous orbital pathologies, but the remainder of this article focuses on the most common etiologies: hemorrhage, inflammation, infection, and vascular malformation.
Acute Painful Proptosis and Hemorrhage
A patient with severe subconjunctival hemorrhage and chemosis can be a diagnostic challenge. Although most cases present in the setting of trauma, postoperative status and prolonged anticoagulation therapy are risk factors. The most important condition to consider in this setting is retrobulbar hemorrhage. If there is a history of trauma, the patient should be evaluated for an open globe injury. Evidence of rupture warrants transportation to the closest emergency department for surgical repair. If the globe is intact, a thorough inspection of the posterior sclera should be performed, looking for scleral clearance. In suspicious cases, double lid eversion can be performed with a Desmarres lid retractor. Additionally, the patient should undergo pupil testing, intraocular pressure measurement, motility testing, and posterior segment evaluation to determine the extent of retro-orbital involvement and risk of optic nerve compression.
Because a retrobulbar hemorrhage constitutes an ocular emergency, it is prudent to have a low index of suspicion. After identifying the presence of, or risk for, retro-orbital involvement, the patient should be referred for immediate noncontrast orbital CT to determine the extent of orbital involvement. If there is concurrent vision loss or the threat of vision loss, a lateral canthotomy can be performed in order to relieve pressure within the orbit. If such pressure is left untreated, chronic buildup of fluid can cause distention within the orbit, leading to acute orbital compartment syndrome and resulting in tissue necrosis and/or explosive choroidal hemorrhage.
Acute or Subacute Painful Proptosis, Chemosis, and Diplopia
Inflammatory causes of painful proptosis, conjunctival hyperemia, and diplopia are typically heralded by a relentless ache, described by the patient as “behind the eye,” and are most commonly attributed to orbital inflammatory syndrome (OIS). OIS is a disorder of the orbit characterized by a polymorphous lymphoid infiltrate with varying degrees of fibrosis.3 In a review by Swamy et al, the most common orbital component affected was intraconal fat, followed by lacrimal gland enlargement and EOM restriction.4 To determine the level of soft tissue involvement, evaluation of OIS is best assessed with contrast-enhanced orbital MRI.4 Kapur et al employed the use of MRI diffusion-weighted imaging sequence intensities to describe the differences among OIS, orbital cellulitis, and orbital lymphoma.5 (Clinical pearl: because lymphoid tumors show morphologic, immune-phenotypic, and molecular genetic characteristics that are similar to OIS, orbital lymphoma represents a masquerade syndrome.6)
OIS is associated with autoimmune diseases such as Crohn disease, systemic lupus erythematosus, rheumatoid arthritis, granulomatosis with polyangiitis (formerly known as Wegener granulomatosis), and sarcoidosis.7
The first line therapy for OIS is systemic corticosteroids; with this treatment, 75% of cases show improvement within 24 to 48 hours.7 An initial dose of 60 to 80 mg of prednisone should be started after MRI is used to discount alternative etiologies such as orbital cellulitis and lymphoma.
Infectious causes of unilateral painful proptosis are much less common; they include orbital cellulitis and mucormycosis. The clinical characteristics of orbital cellulitis include fever and antecedent sinusitis, periorbital swelling with proptosis, conjunctival hyperemia with chemosis, and EOM restriction.
Management involves emergent referral to the emergency department for immediate intravenous broad-spectrum antibiotics including a third-generation cephalosporin and flucloxacillin, which are effective against Staphylococcus aureus, Staphylococcus epidermidis, Streptococci and Haemophilus species.8 Next, a noncontrast CT of the brain and orbits should be ordered to demonstrate an infective source in order to obtain cultures, evaluate for intracranial extension, and assess the need for surgical drainage within the orbit and/or paranasal sinus cavities. Surgical treatment is indicated for significant sinus disease, including orbital or subperiosteal abscess. Emergency surgical drainage is indicated when visual function is compromised.9 Most cases of orbital cellulitis are bacterial in nature; however, fungal organisms should be suspected in cases of chronic cellulitis and in immunocompromised patients.
Mucormycosis is an aggressive opportunistic fungal infection that enters through the paranasal sinus mucosa and travels to the orbital apex, where it can breach the intracranial space. (Clinical pearl: consider mucormycosis in patients with poorly-controlled diabetes or compromised immune systems, including those on immunosuppressant therapies.) Because the ethmoid sinus is separated from the orbit by a thin bone, localized sepsis can induce necrosis and increase the risk of orbital invasion. Early symptoms may be nonspecific and may include sinus pressure and pain, postnasal drip, dark blood-tinged or purulent rhinorrhea, headache, fever, and malaise.10 A patient with acute symptoms should have emergent noncontrast CT of the head, orbit, and sinuses. Signs and symptoms that indicate chronic disease can be managed on an outpatient basis with contrast-enhanced MRI of the sinus and orbit. Early MRI findings include lack of enhancement within the sinus mucosa and cavernous sinus, a finding consistent with devitalized tissue. Biopsies of involved tissues and sinus mucosal secretions are then taken. First-line medical therapy includes intravenous amphotericin B and counteracting the potential sequelae of acidemia and hyperglycemia. However, because the efficacy of systemic therapy may be limited due to tissue necrosis, early aggressive surgical debridement is advisable until clinical improvement is seen.10
Intermittent Pain and Proptosis
The clinical presentation of a young adult with complaints of intermittent positional pain and proptosis exaggerated during Valsalva-type maneuvers should be initially evaluated with noncontrast CT, looking for an enlarged superior ophthalmic vein consistent with orbital varices.11 These lesions are venous malformations that consist of low-pressure and low-flow plexi that intermingle within the orbital circulation. If the clinical history is suspicious for varices and CT imaging is normal, magnetic resonance venography should be performed to evaluate the orbital and intracranial venule system. Orbital complications include acute retrobulbar hemorrhage, venous sinus thrombosis, and optic nerve compression. Surgery is reserved for varices that cause significant pain, proptosis, and optic nerve compression. Small lesions with minimal signs and symptoms can be observed.12
Painless Progressive Proptosis
Cavernous hemangioma is the most common orbital tumor in adults which typically presents with painless, progressive, unilateral proptosis causing premature presbyopia and choroidal folds.13 The differential diagnosis includes orbital metastasis, orbital lymphoma and hemangiopericytoma. Most orbital processes are best evaluated with MRI, but progressive signs of proptosis, optic neuropathy, and choroidal folds often signal a retro-orbital mass, easily identifiable with contrast-enhanced orbital CT.14
Most cavernous hemangiomas are located laterally within the intraconal space of the orbit. Cavernous hemangiomas that are found incidentally and are causing no ocular sequelae can be monitored every 6 months with a clinical ophthalmologic exam, visual field, and repeated imaging until stability is seen. Thereafter, yearly imaging is prudent. Lesions causing significant proptosis, optic neuropathy, and/or visually significant choroidal folds should be surgically removed.
Painful Proptosis, Chemosis, and Diplopia
Arteriovenous malformations (AVMs) are described as either high-flow or low-flow communications between arteries and veins with no interposed capillary bed, the most common of which are carotid-cavernous fistulas (CCF).15 Specifically, a CCF is an abnormal communication between the carotid artery and the cavernous sinus or between meningeal branches of the external or internal carotid artery and the cavernous sinus. These AVMs can be classified as traumatic versus spontaneous, high-flow versus low-flow, and direct versus dural.
The clinical scenario of acute unilateral proptosis with severe chemosis, pain, orbital bruit, restricted ocular motilities, elevated intraocular pressure, and dilated episcleral veins suggests a high-flow fistula from trauma or an aneurysmal rupture of the internal carotid artery within the cavernous sinus necessitating emergent imaging of the brain and orbits.16 Key imaging findings of high-pressure CCF include unilateral proptosis, mild enlargement of all EOMs, a diffuse opacification within the orbital fat, and engorged and tortuous orbital vessels. CT findings may be sufficient for diagnosing most cases, but contrast-enhanced magnetic resonance angiography and CT angiography are superior for evaluating venous distention, the lumen of aneurysms, and increased flow to the cavernous sinus.17 Surgical treatment with embolization is warranted when there is optic nerve compression or when congestion from the superior ophthalmic vein or from within the cavernous sinus places the cerebral venous circulation at risk for thrombosis.
Painless Proptosis and Chronic Red Eye
The other form of CCF is classified as low-flow. Astute clinical evaluation is essential because the signs and symptoms are relatively mild and often overlooked in favor of more benign entities such as ocular surface disease, conjunctivitis, or episcleritis. It is prudent to consider low-flow AVM in a chronic, unilateral red eye with chorioretinal dysfunction including ischemic optic neuropathy and central retinal vein occlusion. Contrast-enhanced MRI or magnetic resonance angiography of the head and orbit is the preferred imaging modality. Most lesions undergo spontaneous occlusion without visual sequelae.
Unilateral proptosis often presents a diagnostic dilemma for the clinician. However, taking a detailed history, performing a comprehensive clinical exam, and utilizing appropriate neuroimaging techniques will help rule out emergent causes and increase the chance of early diagnosis.
To review the main points of the article: A patient with acute, painful, unilateral proptosis should undergo a detailed history and examination to discount visual and life-threatening conditions such as orbital cellulitus, mucormycosis, and high-flow CCF. When in doubt, emergent noncontrast CT of the orbit and sinuses should be ordered because this imaging modality is easily accessible, accurate, and inexpensive. In the absence of retrobulbar hemorrhage, acute infection, or vascular malformation, inflammatory and mass lesions should be considered. Albeit challenging, accurate diagnosis and proper management of orbital pathologies can offer great rewards for both the clinician and the patient. n
1. Johnson M, Policeni B, Lee A, Smoker W. Neuroimaging in Ophthalmology. New York, NY: Oxford University Press; 2011.
2. American College of Radiology (ACR) Committee on Drugs and Contrast Media. ACR Manual on contrast Media. 2015. www.acr.org/~/media/37D84428BF1D4E1B9A3A2918DA9E27A3.pdf. Accessed June 14, 2016.
3. Orbits, Eyelids, and Lacrimal System. Basic Clinical Science Course, Section 7. San Francisco: American Academy of Ophthalmology; 2011-2012: 59.
4. Swamy BN, McCluskey P, Nemet A, et al. Idiopathic orbital inflammatory syndrome: Clinical features and treatment outcomes. Br J Ophthalmol. 2007;91:1667-1670.
5. Kapur R, Sepahdari AR, Mafee MF, et al. MR imaging of orbital inflammatory syndrome, orbital cellulitis, and orbital lymphoid lesions: the role of diffusion-weighted imaging. Am J Neuroradiol. 2009;30:64-70.
6. Yan J, Wu Z, Li Y. A clinical analysis of idiopathic orbital inflammatory pseudotumor. Yan Ke Xue Bao. 2000;16:208-213.
7. Mombaerts I, Goldschmeding R, Schlingemann RO, Koornneef L. What is orbital pseudotumor? Surv Ophthalmol. 1996;41:66-78.
8. Chaudhry IA, Shamsi FA, Elzaridi E, et al. Outcome of treated orbital cellulitis in a tertiary eye care center in the middle East. Ophthalmology. 2007;114:345-354.
9. Harris GJ. Subperiosteal abscess of the orbit: age as a factor in the bacteriology and response to treatment. Ophthalmology. 1994;101:585-595.
10. Kauh CY, Nelson CC. Diagnosis and management of orbital mucormycosis. EyeNet Magazine. June 2014.
11. Shields JA, Dolinskas C, Augsburger JJ, et al. Demonstration of orbital varix with computed tomography and valsalva maneuver. Am J Ophthalmol. 1984;97:108-110.
12. Islam N, Mireskandari K, Rose GE. Orbital varices and orbital wall defects. Br J Ophthalmol. 2004;88:1092-1093.
13. Cohen AJ. Hemangioma, cavernous. MedScape. September 2015. http://emedicine.medscape.com/article/1218120-overview. Accessed June 14, 2016.
14. Thorn-Kany M, Arrue P, Delisle MB, et al. Cavernous hemangiomas of the orbit: MR imaging. J Neuroradiol. 1999;26(2):79-86.
15. Flanagan JC. Vascular problems of the orbit. Ophthalmology. 1979;86:896-913.
16. Levy JV, Zemek L. Ophthalmic arteriovenous malformations. Am J Ophthalmol. 1966;62:971-974.
17. Gean AD. Imaging of Head Trauma. New York, NY: Raven Press; 1994: 349-354, 474.
Michael DelGiodice OD, FAAO
• Past Vice President, New Jersey Academy of Optometry
• Private practice at Associated Eye Physicians, Clifton, New Jersey
• (973) 472-6405; firstname.lastname@example.org