The photo seen below is of a patient presenting with proptosis, pain and increased intraocular pressure on the left. A corresponding MRI is below. What is the most likely diagnosis?

Correct Answer: Carotid-cavernous fistula

C-C fistulas are characterized by proptosis, episcleral venous congestion, increase episcleral venous pressure leading to increased intraocular pressure, and a pulsatile bruit in 1/3 of patients. The photo shows the typical episcleral venous dilation seen in this condition. The corresponding MRI shows a largely dilated superior ophthalmic vein on the right, indicative of a C-C fistula. Cavernous hemangiomas are benign tumors that can be found in the orbit. Imaging studies would reveal a well circumscribed lesion usually intraconally. A retrobulbar hematoma would also present on imaging study as a collection of fluid behind the globe. Thyroid eye disease would show fusiform enlargement of the extraocular muscles.