Late enhancement in cardiac amyloidosis: correlation of MRI enhancement pattern with histopathological findings

Late enhancement (LE) in cardiac magnetic resonance imaging (MRI) is a characteristic finding in patients with cardiac amyloidosis (CA) but the histomorphological explanation has not been clarified yet. Five patients with CA were evaluated by MRI prior to heart transplantation. This consisted of morphological, volumetric, and functional data, including LE analysis. For LE analysis, left ventricular (LV) short-axis sections from basal, midventricular, and apical positions were divided into 12 segments resulting in a 36-segment model. Each segment was differentiated by subendocardial, midmural, and subepicardial localization. Histological amyloid and collagenous fiber deposition was correlated with LE in corresponding MRI slides. LE was visualized in 103/180 (57.2%) predominantly subendocardial segments. Histological analysis of amyloid deposition was (peri-)vascular (n = 5), diffuse interstitial (n = 3) and/or nodular (n = 4). Extent of fibrosis was moderate to severe. Cytoplasmatic vacuolization and decline of myofibrils was seen in all patients. Fibrosis was significantly associated with LE in subendocardial and midmural localizations (p < 0.05), whereas the extent of amyloid deposition was not associated with LE findings in any region. LE seems to be associated with fibrosis due to ischemia of cardiomyocytes by small vessel amyloid deposition rather than with amyloid deposition in CA, suggesting that amyloid deposition might be present prior to LE detection.