A hematoma develops when:

A hematoma develops when large blood vessels beneath the skin are damaged. This occurs because when a significant blood vessel is injured, blood leaks out and accumulates in the surrounding tissue rather than just under the skin surface. The collection of blood forms a localized pool that creates the characteristic swelling and discoloration associated with a hematoma.

In contrast, options related to small amounts of blood leaking into the epidermis or damage to small vessels typically involve minor bleeding or bruising rather than a full hematoma formation. When swelling compromises arterial circulation, it involves a different mechanism, often related to pressure and not the actual vessel rupture or blood accumulation that defines a hematoma. Thus, the term specifically implies a larger and more significant accumulation of blood due to the rupture of larger blood vessels rather than minor injuries or conditions.