Bruises/ Contusions

Bruises are caused by blunt trauma / injury to tissues, resulting in damage to blood vessels beneath the surface. Blood leaks out ('extravasation') into surrounding tissues from damaged capillaries, venules and arterioles. Bruises may be surface bruises, or deeper within tissues or organs.

Unlike abrasions, the characteristics of the object causing a bruise cannot easily be determined, because blood tends to spread out in a diffuse manner from the site of injury, particularly along fascial planes. Indeed, this phenomenon results in the apparent 'shifting' of bruises after time. For example, a scalp injury may result in a black eye. Bruses may also 'appear' after some days due again to the same phenomenon of blood tracking along tissue planes, and pathologists often re-examine a body again to look for such bruising.

Intra-dermal bruises, however, provide an exception to this general rule, as they are superficial - lying just under the epidermis. In this case, there may be good correlation between the bruise seen and the characteristics of the causative object.

Additional terms are used for bruises of a particular size,

• ecchymoses - smaller than a few milimeters
• petechiae - pinpoint bruises. (However, this type of bruise or haemorrhage are usually due to venous engorgement, for example in asphyxia, or in defects in blood coagulation such as Disseminated Intravascular Coagulation (DIC) than trauma). Light trauma may produce petechial haemorrhage, but those caused by venous congestion etc are more diffuse in nature.

A blow from an object may give rise to a combination of injuries, such as a bruise with an abrasion etc, and different parts of the body are more susceptible to bruising than others. For example, the skin over the eyelids bruises easily, whilst the tougher palmar surface or plantar surface rarely bruises.

'Tramline' bruises consist of two parallel linear bruises separated by a paler, undamaged section of skin. This type of injury occurs when the skin is struck with a rod shaped object, which sqeezes blood from the vessels at the point of inpact, thus emptying them and preventing them from leaking blood. The edges of the wound are stretched, and blood vessels are torn, causing blood to leak into the surrounding tissues. A similar phenomenon is seen when the injury is caused by a hard spherical object, such as a squash ball !

The positioning of bruising is often significant, in that a multiple row of spherical/ disc shaped bruises may be seen when an attempt is made to strangle someone with bare hands. The bruises are caused by the attacker's fingertips pressing into the skin.

Bruises change colour over time, because of the degradation of haemoglobin in the blood. However, the timescale of this degradation is not fixed, and it is therefore possible only to give a rough estimation of the age of the bruise. Colour changes are,

• dark blue/ purple (fresh)
• blue
• brown
• green
• yellow

In general, small bruises on an otherwise fit and healthy person, could pass through the spectrum of colour changes between 72 hours and 1 week. The more extensive, or deep seated the bruise, the longer it will take to dissapear. If a bruise is brown/ green or yellow it is likely that the injury is at least 18 hours old.(For a review of estimating the date of bruises, see the American Journal of Forensic Medicine and Pathology 16:203 (1995)).

An important observation is the colour of multiple bruises on the same person - markedly different coloured bruises suggest that they have been caused at different times, and may indicate signs of chronic abuse, such as of an infant etc.

A possible line of defence for a person charged with homicide could be that the bruises were not in fact made during life, but are post-mortem artifacts. However, it is very difficult to produce a bruise in a dead person, because it is very much a 'vital reaction' to injury. It may be possible to produce a bruise following very severe trauma in an area of post-mortem lividity (where blood has drained to dependant parts of the body under the influence of gravity), and if there is any doubt the pathologist should examine the 'bruise' histologically. However, in the absence of an organising haematoma, histology may only show thepresence of haemosiderin, and even then only after approximately 48 hours.For a discussion of post mortem bruises, see AJFMP 19:46 (1998).

In forensic autopsies, it is important that all possible signs of trauma are specifically looked for and excluded. This includes a thorough search for bruising, including that which is beneath the skin surface. Forensic pathologists use specialist dissection techniques to expose deeper structures, and this may entail removing all skin off whatever structure is being looked at. A discussion of these techniques can be found in the AJFMP 17:316 (1996).

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