Bruises are extravascular collections of blood caused by various types of blunt force [Fig 3]. They may be patterned and can reproduce the shape of the weapon or object responsible (e.g a shoe or fingertip bruises where a grip has been applied. Sometimes a characteristic tramline bruise results from forceful contact with a rounded or squared-off weapon such as a baseball bat [Fig 5].

However, the bleeding can track under the skin which leads to pattern disruption. Bruises are often larger where the skin is lax or there is underlying bone (in contrast to the palms or sole of the feet where the skin is thick bruises are seldom seen). In these areas, the bruise may enlarge and track over time. It is important to appreciate this phenomenon if your examination takes place sometime after the injury occurred. For example, a large bruise to the anterior scalp or forehead can track into the periorbital soft tissues, which could be misinterpreted as the site of the initial impact.

Assessment of the age of the bruise is not always reliable. Colour changes do not occur in a predicable or linear fashion. The most helpful colour is yellow, which does not appear in bruises less than about 18 hours old.

Figure 3. Focal early yellow change in a bruise. Note the difficulty in assessing the size without the inclusion of a scale.

Figure 4. Finger-tip type bruising.

Figure 5. Typical tram-line type bruising.