Next Radiologic Steps for Graves Orbitopathy with Asymmetric Exophthalmos
Once CT is completed, proceed with MRI orbits with contrast to better characterize extraocular muscle involvement, assess for optic nerve compression at the orbital apex, and establish baseline disease severity. 1
Immediate Radiologic Evaluation
CT orbits has already been ordered and should be completed to confirm thyroid eye disease by demonstrating tendon-sparing enlargement of extraocular muscles (typically inferior and medial recti) and document proptosis. 2
MRI orbits without and with contrast should follow the CT to provide superior soft tissue characterization, correlate imaging findings with disease severity, and evaluate for compressive optic neuropathy. 1, 3 MRI findings correlate better with disease activity and severity than CT measurements. 3
Critical Consideration: Asymmetric Presentation Requires Broader Differential
The asymmetric left>right presentation is a red flag that mandates ruling out non-thyroid pathology, even in a patient with known Graves disease. 4, 5
Unilateral or markedly asymmetric orbitopathy occurs in only a minority of Graves cases and should prompt consideration of alternative diagnoses including orbital lymphoma, sarcoidosis, idiopathic orbital inflammatory syndrome (orbital pseudotumor), and other orbital masses. 6, 4, 5
MRI with contrast is superior to CT for identifying orbital masses, lymphoma, and inflammatory conditions that can mimic or coexist with thyroid eye disease. 6
Up to 45% of clinically unilateral cases show bilateral involvement on MRI, but progressive unilateral worsening despite treatment should raise suspicion for malignancy. 7, 5
Specific Imaging Features to Assess
The radiologist should evaluate for:
Extraocular muscle enlargement with tendon-sparing pattern (classic for thyroid eye disease) versus tendon involvement (suggests other pathology). 2
Orbital apex crowding and optic nerve compression, which indicate risk for compressive optic neuropathy requiring urgent intervention. 2, 1
Orbital fat expansion and proptosis measurements to establish baseline severity. 2, 1
Presence of discrete orbital masses or atypical enhancement patterns that would suggest lymphoma, sarcoidosis, or other infiltrative processes. 6, 4, 5
Common Pitfall to Avoid
Do not assume all orbitopathy in a Graves patient is thyroid-related, especially with asymmetric or progressive unilateral disease. 4, 5 Orbital lymphoma has been documented in patients with known Graves disease, and delayed diagnosis can occur when clinicians attribute all orbital findings to thyroid eye disease. 5
Coordination with Clinical Assessment
While imaging proceeds, ensure ophthalmology has been consulted to:
Screen for compressive optic neuropathy through visual acuity, color vision, visual fields, pupillary examination, and fundoscopy. 1
Measure exophthalmos by exophthalmometer to quantify asymmetry and establish baseline. 2
Perform forced duction testing if mechanical restriction is suspected. 2
If imaging reveals atypical features or discrete masses, biopsy should be considered to exclude lymphoma or other malignancy before initiating immunosuppressive therapy. 6, 4, 5