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57-Year-Old Female with Proptosis
This case features a 57-year-old female presenting with proptosis, ultimately diagnosed with extraocular muscle metastases.
Imaging overview:
Coronal T2 fat-saturated MRI demonstrates T2 hyperintense masses within the left superior rectus and left medial rectus muscles. Coronal T1 fat-saturated post-contrast MRI shows homogeneous enhancement of both lesions. Axial ADC mapping reveals hypointensity within the extraocular muscle masses, reflecting dense cellularity consistent with metastatic disease.
Clinical insight:
Metastatic disease to the orbit accounts for 1 to 13% of all orbital masses, and extraocular muscle metastases represent only 5 to 9% of orbital metastases, making this an uncommon but important diagnosis. Unilateral involvement, rapid progression, and a non-classic distribution of extraocular muscle enlargement should raise concern for metastasis or lymphoma. In contrast, thyroid eye disease and IgG4-related disease, the most common causes of extraocular muscle enlargement, are bilateral with specific muscle predilections: the inferior and medial rectus muscles in thyroid eye disease, and the lateral and inferior rectus muscles in IgG4 disease. ADC hypointensity reflecting restricted diffusion is a useful feature in distinguishing high-cellularity malignant lesions. The differential diagnosis also includes carcinoid tumor metastases and idiopathic orbital inflammation.
Case courtesy of Jonathan Amodio, MD, MPH, and Momin Muzaffar, MD, The University of Chicago Medical Center.