In its classic definition, by FranÃ§ois-Louis Ganshof (1944), feudalism describes a set of reciprocal legal and military obligations among the warrior nobility revolving around the three key concepts of lords, vassals and fiefs.
The exact cause of intracardiac echogenic foci remains unclear; however, they appear to be caused by small deposits of calcium in the papillary muscle of the fetal heart.
The most characteristic ultrasonographic feature of an angiomyolipoma is its echogenicity; however, angiomyolipomas may also cause acoustic shadowing. The echogenic appearance of the tumor is thought to be related to its fat content and the presence of multiple tissue interfaces within it.