What is a hypervascular mass in the liver made of?

Cells and vessels. A hypervascular mass in the liver is a tumor, which is made up of cells (benign or malignant) and their support structure (fibrous stroma and blood vessels). The term "hypervascular" is a radiologic term that refers to the way the tumor fills up with contrast agent on contrast enhanced imagining studies (ct or mri). All "hypervascular" masses need to be rigorously investigated to rule out cancer.