Thyroid carcinoma metastatic to the medial rectus muscle

Isolated extraocular muscle metastasis is rare and is unreported for thyroid carcinoma. The authors describe a 72-year old man who presented with pain, redness, and proptosis of the right eye. Orbital computed tomography showed a large fusiform soft tissue mass along the medial aspect of the right orbit, involving the medial rectus. Orbital exploration disclosed a mass within the medial rectus muscle sheath involving the muscle belly. Histopathologic examination including electron microscopy, revealed metastatic thyroid carcinoma. Systemic treatment with radioactive iodine was recommended and refused by the patient. One year later, he died of complications from his metastatic disease.