Presumed Nontraumatic Myositis Ossificans of the Extraocular Muscle

A 68-year-old woman had progressive left exotropia with restrictive adduction and mild pain for 10 years. She denied previous trauma or surgery. Computed tomography scan showed a 0.5 mm–length high-density lesion (A, arrow) at the attachment of the thickening lateral rectus muscle (A and B, ellipse), leading to a focal eminence of the retina (C, arrow). Surgical removal of the high-density lesion combined with the correction of exotropia was performed. Pathological examination demonstrated a mature bone nodule (D, × 200 magnification). Muscle biopsy revealed inflammatory cells, consistent with extraocular muscle myositis ossificans (Magnified version of Figure A-D is available online at www.aaojournal.org).