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. 2021 Nov 23;8:749523. doi: 10.3389/fcvm.2021.749523

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Copyright © 2021 Porcari, Bussani, Merlo, Varrà, Pagura, Rozze and Sinagra.

This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

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Gross evaluation of unfixed heart and histological characterization with dedicated staining. Left Top: massive cardiac hypertrophy of the left ventricle involving the subvalvular aortic region extending to the right ventricle, the papillary muscles and the inter-atrial septum. The heart exhibits a heterogeneous color with pale areas and faint yellowish tone. Bottom: increased atrial wall thickness with diffuse granulations on the endocardial surface and nodular deposits of amyloid. Right: left column (optical field 10×) and right column (optical field 20×): H&E, severe amyloid infiltration in the interstitium and vessels with degeneration of myocytes; Congo Red and polarized light microscope, Congo Red binding to amyloid fibrils showing the typical apple-green birefringence and revealing predominant interstitial infiltration; amyloid infiltration involves the interstitial space and vessel walls, including the sinoatrial nodal artery; IHC for TTR and FLCs, positivity of transthyretin (left, 40×) and immunoglobulin light chain Kappa (right, 20×) in advanced cases of cardiac amyloidosis. H&E, Hematoxylin and Eosin; FLCs, Free Light Chains; IHC, Immunohistochemistry; TTR, Transthyretin.