The right common carotid artery is occluded. Collateral circulation from the inferior thyroid artery supplies the superior thyroid artery which fills the external carotid retrograde. 

The external carotid artery is also receiving retrograde flow from a vertebral to occipital artery collateral. The ascending pharyngeal artery is filling from the vertebral system, likely through the neuromeningeal trunk.

The cavernous internal carotid is reconstituted via the ascending pharyngeal artery. Vertebral to occipital artery flow, with filling of the external carotid artery, is again seen.