There is right sided proptosis and some periorbital preseptal stranding. Possible minimal post-septal stranding. Certainly orbital cellulitis is a diagnosis to be entertained, if the presentation was suggestive of an infection. However, there is a crucial additional finding here that the proptosis is out of proportion to any inflammation and the right superior ophthalmic vein is substantially larger than the left (@Key Finding 1). This appearance can be seen with carotid cavernous fistulization (CCF) or thrombosis and should be assessed.

The best next step when there is suspicion for CCF is a non-con TOF MRA as it nicely suppresses venous signal. CTA is an option but very often, there is venous contamination which will make assessment for abnormal arterial to venous connection difficult.

In this case, a CTA was obtained. High flow carotid cavernous fistula is confirmed (@Key Finding 2) since there is clear and robust arterial phase opacification of the right cavernous sinus (red arrow) AND no venous contamination (no contrast in the superior sagittal sinus for instance, blue arrow).

Incidentally, there are also bilateral chronic subdural hematomas (@Key Finding 3).