Early Appearance of Epicardial Adipose Tissue through Human Development

Figure 1. Embryonic period. a: Coronary artery. b: Cardiac bulbus. CS: Carnegie stage. GD: Gestational day. M: Myocardium. LA: Left atrium. LV: Left ventricle. RA: Right atrium. RV: Right ventricle. v: Coronary vein. A: Stage 1. Axial oblique sections of a 33–35 GD embryo. (A1): General view. The back is on the top of the image, and the developing heart is at the lower part. The square of solid lines delimits the right auricle-bulbus groove. The square of dotted lines marks the left auricle-bulbus groove. Successive higher-power magnification of rectangles showing loose undifferentiated mesenchyme tissue (arrowheads) composed of an amorphous ground substance of fibers and cells with a spindle-like morphology, corresponding to stage 1 of adipose tissue (AT) development, in the right (A2) and left (A3) auricle-bulbus grooves. B: Stage 2. Axial section of a 42–45 GD embryo. (B1): General view of the heart, which is analogous to the adult. Atrioventricular (squares) and interventricular (arrow) grooves are clearly identifiable. The interventricular groove shows vessels, but no mesenchymal tissue. (B2): Higher-power magnification of the square of solid lines in (B1), which marks the right…

Figure 2. Fetal period. Coexistence of stages 1, 2 and 3. a: Coronary artery. Ao: Aorta artery. GW: Gestational week. LA: Left atrium. LV: Left ventricle. RA: Right atrium. RV: Right ventricle. v: Coronary vein. A: Stage 2. Axial oblique sections of a 12 GW fetus, the end of the first trimester. (A1): General view of the heart. The condensation of mesenchyme continues, with vascular proliferation in the atrioventricular grooves. A new accumulation of mesenchymal cells is visible on the posterior wall of the left auricle, next to the interatrial groove. (A2): Higher-power magnification of the square of solid lines in (A1), which marks the right atrioventricular groove with mesenchymal cells surrounding the right coronary vessels. (A3): Higher-power magnification of the square of dotted lines in (A1), showing the posterior wall of the left auricle, where vessels are developing. (A4): Axial oblique section from a different fetus of 12 GW. General view of the heart. (A5): Higher-power magnification of the square of solid lines in (A4), showing the onset of mesenchyme accumulation in the interventricular groove (arrow). (A6): Higher-power magnification of the square of dotted lines in (A4),…

Figure 3. Final fetus period. Heart has grown considerably. Axial oblique sections of a 32–33 GW fetus, third trimester. Coexistence of stages 1, 2, 3, 4 and 5. a: Coronary artery. Ao: Aorta artery. GW: Gestational week. LV: Left ventricle. RA: Right atrium. v: Coronary vein. A: Stage 4. (A1): Left atrioventricular groove. Primitive fat lobes around the aorta artery are clearly visible. (A2): Higher-power magnification of the square in (A1), which marks the primitive fat lobes with fat vacuoles in cells (arrowheads) and connective tissue partitions or septa next to the left coronary vessels (black arrows), intermingled with the minor differentiated and condensed mesenchyme (asterisk). It cannot be excluded that some of the developing perivascular adipose tissue may correspond to brown fat. Coexistence of stages 1, 2 and 3. B: Stage 5. (B1): Left coronary artery on the left atrioventricular groove, next to its origin in the aorta. (B2): Higher-power magnification of the square in (B1), showing definitive fat lobes of fat cells. C: Stage 5. (C1): Epicardium on the right atrioventricular groove and posterior wall of the right atrium. (C2): Higher-power magnification of the square in (C1),…

Figure 4. Summary of EAT appearance in human development. AV: Atrioventricular grooves; IV: interventricular groove; IA: interarticular groove. a: Coronary artery. v: Coronary vein. Presence (+); absence (-).