Treatment of a Type II Endoleak from an Atypical Mediastinal Collateral Branch Following Total Arch Replacement with Frozen Elephant Trunk.

We present a rare case of type II endoleak (T2EL) from an atypical mediastinal artery following total arch replacement with a frozen elephant trunk (FET) for chronic aortic dissection. A 63-year-old male with a history of multiple thoracic aortic surgeries, including FET, developed enlargement of an aortic arch aneurysm on follow-up. Computed tomography and diagnostic angiography revealed a T2EL due to a newly developed mediastinal collateral artery arising from the left subclavian artery feeding the sac. Selective transcatheter embolization with N-butyl-2-cyanoacrylate successfully eliminated the endoleak. Recognizing such atypical T2EL sources is crucial for managing post-FET aneurysm expansion.