Red blood cell (RBC) rouleaux formation is a reversible phenomenon that occurs during low blood flow and small shearing forces in circulation. Certain pathological conditions can alter the molecular constituents of blood and properties of the RBCs leading to enhanced rouleaux formation, which results in impaired perfusion and tissue oxygenation (Fayruz Kibria et. al.)
Normally Blood flow is anechoic due to the size of the RBC’s inability to reflect the sound waves. However when they aggregate or stack they become mobile reflectors. The flow is typically slow and sluggish. Compression of the vessel is still feasible and will clear the rouleaux momentarily.
This phenomenon can be seen in a “normal” patient, however it is associated with many conditions including, malignancies, connective tissue disorders, inflammation, diabetes and pregnancy to name a few.