Fibrin sheath formation is a well-described sequela of an indwelling central venous catheter. Fibrin sheaths may also develop around other foreign bodies within the venous system. We describe a case of fibrin sheath formation within the left brachiocephalic vein secondary to automatic implantable cardioverter-defibrillator (AICD) leads with subsequent embolization of sheath material presenting as calcifications within the pulmonary vasculature on computed tomography (CT). Most of the relevant literature focuses on catheter-related sheath formation and associated complications while reports on fibrin sheaths from other foreign bodies are sparse. We advise that radiologists who encounter intraluminal calcifications within the pulmonary arteries on CT should consider the possibility of a fibrin sheath as the source and search for its remnants in the central venous system for confirmation.