Airway granulation response to lung-implantable medical devices: a concise overview

Abstract

Increasing numbers of endoscopically implantable devices are implanted in the airways, such as airway stents, one-way valves and coils, to treat both malignant and benign diseases. They significantly improve patient outcomes, but their long-term effectiveness and sustainability is hampered by the reaction of the formation of granulation tissue. Factors including procedural-related tissue injury; micro-organism presence; device-related factors, such as the material, design and sizing in relation to the airway; and patient-related factors, including genetic susceptibility, comorbidities and medication use, might all effect the severity of the tissue response and the subsequent degree of granulation tissue formation. However, research into the underlying mechanism and risk factors is scarce and therefore our knowledge is limited. Joint efforts from the scientific community, both pre-clinical and clinical, are needed to gain a deeper understanding and eventually improve the long-term treatment effectiveness of lung-implantable devices.

FIGURE 1

Granulation tissue in the airway formed after implantation of a covered self-expanding nitinol bronchial airway stent. a) Bronchoscopic image of granulation tissue with stent in place. b) Haematoxylin and eosin stain image of airway granulation tissue (10× magnification). ECM: extracellular matrix. Scale bar=100 µm.

FIGURE 2

Foreign body reaction upon device implantation.

FIGURE 3

Scanning electron microscope image of uncovered airway stent (Ultraflex™ Tracheobronchial stent, Boston Scientific, Galway, Ireland). Macroscopically, the stent surface appears even. Magnification shows the roughness of the surface that could accommodate cell adhesion which drives the foreign body response upon implantation, leading to a more severe repetitive injury during the respiratory cycle than a device with a smoother surface. a) 50× magnification. b) 250× magnification. c) 2500× magnification. d) 15 000× magnification.

FIGURE 4

Hypothetical model of factors that might influence the airway tissue response upon device implantation. DAMP: damage-associated molecular pattern.