Histologic development of the sheath that forms around long-term implanted central venous catheters

Background: Chronically implanted catheters often become covered with a thin, white adherent covering of tissue that has been referred to as a fibrin sheath. This tissue often interferes with catheter function. Methods: To chronicle the development of this sheath, rats were implanted with silicone rubber central venous catheters. Five rats were euthanized at 3, 7, and 60 days postimplantation so that gross necropsy and histology could be performed on the catheterized vessels. Results: The coatthat developed around the external portion of the catheter started as a dark red thrombus containing fibrin and progressed into vascularized, fibrous connective tissue. Conclusions: The translucent to white sheath that forms around chronically implanted catheters is not composed of fibrin and is therefore not likely to be dissolved by fibrinolytic agents such as urokinase, streptokinase, or tissue plasminogen activator.