Some hematomas are visible under the surface of the skin (commonly called bruises) or possibly felt as masses or lumps.

Lumps may be caused by the limitation of the blood to a sac, subcutaneous or intramuscular tissue space isolated by fascial planes.

The slow process of reabsorption of hematomas can allow the broken down blood cells and hemoglobin pigment to move in the connective tissue.

A misdiagnosis of a hematoma in the vertebra can sometimes occur; this is correctly called a hemangioma (buildup of cells) or a benign tumor.

The word derives from the Greek αἷμα haima "blood" and -ωμα -oma, a suffix forming nouns indicating a mass or tumor.