Radiography
Findings
Conventional radiographs are not useful in the diagnosis of thyroid ophthalmopathy, because bony abnormalities usually are not associated with the disease.
Degree of Confidence
The degree of confidence is poor. Radiographs cannot determine the amount of extraocular muscle enlargement, degree of optic nerve compression, or presence of other orbital processes that may mimic thyroid ophthalmopathy. Perform orbital ultrasonography, CT scanning, or MRI instead.
Computed Tomography
Computed tomography axial section of the orbit. Note the enlargement of the muscle bellies that spare the tendinous insertion on the globe.
Computed tomography axial section demonstrates enlarged inferior rectus muscles.
Computed tomography coronal section of the same patient as in Image 7. The extraocular muscle bellies, especially the inferior rectus muscle on the right, are enlarged.
Computed tomography coronal section deeper in the orbit near the apex demonstrates crowding of the optic nerve by the enlarged extraocular muscles.
Findings
CT scanning provides excellent visualization of the extraocular muscles and intraconal fat, as well as the orbital apex. Enlargement of the muscles occurs almost uniformly within the muscle belly (see Images 3-4), and thickening is usually greater than 4 mm. The tendinous insertion (which is easily visualized in axial sections) usually is not enlarged. Prominent intraconal fat can also result in proptosis (see Image 5).
Computed tomography axial image demonstrates the enlarged bellies of the extraocular muscle without involvement of the tendinous insertion to the globe.
Computed tomography coronal section through the orbit demonstrates enlargement of multiple muscles within the orbit.
Prominent intraconal fat can also result in proptosis and straightening of the optic nerve. In addition, this patient has mild enlargement of the extraocular muscles.
Pay particular attention to the orbital apex to assess for evidence of optic nerve compression, which is identified more readily in coronal sectioning of the orbit. The degree of globe proptosis relative to the lateral orbital rim can be measured with CT scan studies. In addition, scans of the bony architecture of the orbit and adjacent sinuses are available when an orbital decompression is required.
Degree of Confidence
The degree of confidence is high. An additional test rarely is required for the diagnosis of thyroid ophthalmopathy. Orbital ultrasonography also can provide the diagnosis with a high degree of confidence, but cost and convenience considerations make ultrasonography more useful when serial imaging is required.
False Positives/Negatives
Orbital myositis often can mimic the clinical appearance of thyroid ophthalmopathy. This condition most often is unilateral, and the tendinous insertions of the extraocular muscles also are enlarged. Metastatic tumors to the extraocular muscles also may mimic thyroid eye disease, although they are usually associated with other orbital and bony metastases. However, other etiologies should be considered in the presence of isolated lateral rectus muscle enlargement, because this is almost never seen in thyroid orbitopathy.
Magnetic Resonance Imaging
Findings
Similar to CT scan studies, MRI also provides excellent imaging of the extraocular muscles, their insertions, and the anatomy of the orbital apex (see Image 6).
In addition, the amount of fat within the orbit and imaging of the optic nerve can be assessed and localized on MRI better than on CT scans. Typically, however, MRI is not the ideal imaging modality because of the associated increased cost.4,5,6
Because of the significant amount of fat present within the orbit, fat-suppression techniques are utilized in its evaluation, particularly if MRI contrast agents are administered. Fat normally appears bright on both T1-weighted and fast T2-weighted pulse sequences; however, fat suppression significantly reduces the signal from fat, thereby rendering it dark on MRIs. This greatly improves lesion detection by increasing the contrast between the orbital fat and pathologic processes. With MRI contrast administration, enhancing lesions become much more conspicuous with fat suppression during T1-weighted imaging. Likewise, in evaluating tumor or inflammatory processes with higher water content, these abnormalities become easily visible with fat suppression during fast T2-weighted sequences.
The MRI signal intensity of the enlarged extraocular muscles is usually isointense on T1-weighted images and isointense to minimally hyperintense on T2-weighted images. High intensity in the extraocular muscle on T1-weighted images is occasionally seen, which is consistent with fatty infiltration. This finding can aid in differentiating thyroid orbitopathy from pseudotumor.
Increased T2 signal in the extraocular muscles is likely caused by increased water content. Patients with elevated T2 relaxation times have increased response to anti-inflammatory treatment (this is similar to octreotide accumulation [see Nuclear Medicine section]).
Degree of Confidence
The degree of confidence is high. Similar to CT scanning, MRI usually can provide the diagnosis of thyroid ophthalmopathy with or without optic nerve compression. Additional testing usually is not required if an MRI study already has been obtained.
False Positives/Negatives
MRI may be better than CT scanning in identifying other causes of proptosis, such as orbital tumors.
Ultrasonography
B-scan ultrasonography reveals enlargement of the extraocular muscle belly. The tendinous insertion of the extraocular muscle at the globe is not thickened, which is characteristic of thyroid-related orbitopathy.
A-scan ultrasonography reveals medium to high internal reflectivity of the extraocular muscle belly.
Findings
Orbital ultrasonography is excellent for the diagnosis of thyroid ophthalmopathy, and medium to high internal reflectivity of the extraocular muscles, as well as enlargement of the muscle belly, is characteristic. The tendinous insertion of the extraocular muscle also can be visualized easily. Patients with thyroid ophthalmopathy show lower peak-systolic and end-diastolic velocities that may be appreciated with Doppler imaging. Visualization of the orbital apex is difficult with orbital ultrasonography, and CT scanning or MRI may be preferred when compression of the optic nerve is suspected.7
Degree of Confidence
The degree of confidence is high. Additional examinations to diagnose thyroid ophthalmopathy are not needed if the characteristic high reflectivity and enlargement of the extraocular muscles with sparing of the tendinous insertion are present on sonograms. However, to better visualize the apex of the orbit for evidence of optic nerve compression, CT scanning or MRI may be required if warranted by the clinical presentation.
False Positives/Negatives
Orbital myositis is characterized by high reflectivity and enlarged extraocular muscle bellies when examined with ultrasonography. However, in orbital myositis, the tendinous insertion is enlarged, which differentiates this condition from thyroid ophthalmopathy.
Nuclear Imaging
Findings
Although not clinically useful in the diagnosis of thyroid ophthalmopathy, functional studies such as positron emission tomography (PET) scans or somatostatin-receptor scintigraphy (SRS) may assess disease activity. Orbital infiltration with mononuclear cells in thyroid ophthalmopathy can be identified by receptor imaging with octreotide, a radiolabeled somatostatin analogue.
Patients with active thyroid ophthalmopathy show higher octreotide uptake and may respond better to treatments such as corticosteroids or radiation therapy. Patients with inactive disease, however, do not respond to these treatments. In the future, nuclear medicine testing may determine whether stability of the orbital disease has been achieved before proceeding to surgical decompression.8,9
Degree of Confidence
Patients with thyroid ophthalmopathy often present when their disease is no longer active. PET scans or somatostatin-receptor scintigraphy (SRS) in these patients is not informative, and alternative imaging methods (ultrasonography or CT scanning) are required.
False Positives/Negatives
Other orbital inflammatory processes also may result in increased uptake during functional imaging.
Angiography
Findings
Angiography typically is not used in the diagnosis or management of thyroid ophthalmopathy. Enlarged orbital vessels with increased blood-flow velocities may be present.
More on Ophthalmopathy, Thyroid |
| Overview: Ophthalmopathy, Thyroid |
 Imaging: Ophthalmopathy, Thyroid |
| Follow-up: Ophthalmopathy, Thyroid |
| Multimedia: Ophthalmopathy, Thyroid |
| References |
| Further Reading |
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References
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Mayer EJ, Fox DL, Herdman G, et al. Signal intensity, clinical activity and cross-sectional areas on MRI scans in thyroid eye disease. Eur J Radiol. Oct 2005;56(1):20-4.
Taoka T, Sakamoto M, Nakagawa H, et al. Evaluation of extraocular muscles using dynamic contrast enhanced MRI in patients with chronic thyroid orbitopathy. J Comput Assist Tomogr. Jan-Feb 2005;29(1):115-20.
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Kuo PH, Monchamp T, Deol P. Imaging of inflammation in Graves'' ophthalmopathy by positron emission tomography/computed tomography. Thyroid. Apr 2006;16(4):419-20.
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Gerding MN, van der Zant FM, van Royen EA, et al. Octreotide-scintigraphy is a disease-activity parameter in Graves'' ophthalmopathy. Clin Endocrinol (Oxf). Mar 1999;50(3):373-9. [Medline].
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Kahaly GJ. Imaging in thyroid-associated orbitopathy. Eur J Endocrinol. (Aug) 2001;145(2):107-18.
Nunery WR. Ophthalmic Grave's disease: a dual theory of pathogenesis. Ophthalmol Clin North Am. 1991;4:73-87.
Ozgen A, Alp MN, Ariyurek M, et al. Quantitative CT of the orbit in Graves'' disease. Br J Radiol. Aug 1999;72(860):757-62. [Medline].
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Further Reading
Related eMedicine topics
Thyroid Ophthalmopathy (from Ophthalmology)
Thyroid Disease
Hyperthyroidism (from Endocrinology)
Hyperthyroidism (from Pediatrics: General Medicine)
Hyperthyroidism, Thyroid Storm, and Graves Disease
Clinical guidelines
ACR Appropriateness Criteria Orbits, Vision, and Visual Loss
Screening for Thyroid Disease: Recommendation Statement
Clinical trials
Thyroid-Associated Ophthalmopathy Subtypes and Orbital Antibodies
Rituximab in the Treatment of Graves' Disease
Keywords
thyroid ophthalmopathy, thyroid eye disease, Graves disease, Graves' disease, Graves ophthalmopathy, thyrotoxic ophthalmopathy, thyrotoxic exophthalmos, thyroid-associated ophthalmopathy, endocrine exophthalmos
