Jeff Nealey, age 11, of Thomasville, N.C., for his question:

WHAT IS A HEMATOMA?

Tumors are often named after the tissue from which they grow.

A lipoma, for example, is made up of lipid or fat tissue. Gliomas, or nerve‑tissue tumors, are made up of glia, the peculiar branched cells that support the nerves. A hematoma is a blood tumor, and one of the best‑known tumors. It sometimes occurs as a "black and blue„ swelling in the skin.

Any swelling or abnormal growth of tissue in the body is called a tumor. Tumors are also called neoplasmas. Some tumors are benign, which means they limit themselves to a certain region and do not spread elsewhere in the body. A malignant tumor is a cancer that can spread.