Abstract 17661: Optical Coherence Tomography Identifies Artifactual Thin-cap Fibroatheromas: A Histologic Study

Abstract

Introduction: Current methods to identify thin-cap fibroatheroma (TCFA) with optical coherence tomography (OCT) are qualitative. While two mechanisms for the appearance of false TCFA have been identified and include macrophages that cause superficial shadowing and tangential light dropout, we report three new mechanisms for the appearance of false TCFAs in OCT images. Methods: 13 coronary arteries from 8 human cadaver hearts (6 male, 2 female, aged 63 ± 12 years) were imaged with OCT. OCT TCFAs were identified independently by three expert OCT readers and defined by a bright homogenous fibrous cap overlying a diffusely shadowed signal-poor region. Analysis was performed to confirm the identification of TCFA or to identify the histologic origin of the OCT TCFA appearance. Arc length of the signal-poor region of each OCT TCFA was also measured. Results: 38 OCT TCFA were identified, of which only 5 were verified with histology. Measurements of arc length and thickness of the cap are summarized in the table. Of the 33 false TCFA, three morphologic plaque types were identified: thick-cap fibroatheroma (TkFA; N=18), pathologic intimal thickening (PIT; N=10), and fibrocalcific (FC; N=5). New mechanisms for the signal-poor regions that appeared as lipid cores included loose connective tissue (N=7), neovasculature (N=3), and proteoglycans (N=4). Superficial shadowing of macrophages caused the appearance of TCFA in 5 cases. In the 18 TkFA cases, OCT underestimated the thickness of the fibrous cap (45.2 ± 4.0 μm by OCT compared to 197.5 ± 18.8 μm by histology). Conclusion: Using an arc length of greater than 90 degrees will aid in differentiating true from false TCFA. Additionally, due to incomplete light penetration, TkFA can be mistaken for TCFA. These results demonstrate that caution should be used when diagnosing vulnerable plaque with OCT.