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Copyright forensic medicine resources 2007. All rights reserved.

A bruise is generally understood to mean an area of haemorrhage caused by the leakage of blood from ruptured vessels (including capillaries, but predominantly veins, venules and small arterioles) - into surrounding (perivascular) tissues, following a 'blow'.

The picture aboveis of a bruise with a mixture of colours, which is diffusing at the yellowing edges, indicating that this was probably inflicted several days before this photograph was taken.


Types of bruises

1. petechial haemorrhages

This term is used to describe very small 'pinpoint' (i.e. less than about 2mm) extravasations of blood, most often seen on the skin, conjunctivae and mucous/ serous membranes, arising at the level of the capillaries.

Their pathogenesis is poorly understood, but may relate to raised intra-capillary pressure due to an obstruction of venous return (subsequent to pressure applied to the upper chest or neck, for example), hypoxia, endothelial dysfunction (in sepsis) or a combination of these factors.

Petechiae can also be caused by blunt trauma, implying a mechanical disruption of capillaries.

The presence of petechiae has been reported in a wide variety of situations including;

Although they appear to be a non-specific manifestation of capillary damage or dysfunction, their presence demands an explanation, and in particular prompts a careful examination of the anterior neck structures in order to exclude pressure having been applied to the neck.

 

(See National Library of Medicine (USA) - image of petechial haemorrhages, and University of Toronto 'Anatomia' - anatomy of the larynx )

 

2. Intradermal bruises

Where an extravasation of blood arises within the deeper dermis, allowing extension of blood into subcutaneous tissues, the 'outline' of the briuse seen at the skin surface is usually 'blurred' or indistinct.

If the bleeding occurs more superficially, however, the result is a so-called 'intradermal bruise', where the components of the bruise are more easily deliniated (punctiform, sharply defined and 'bright red in colour'). A 'negative image' of the profile of the impacting instrument is produced i.e. a 'patterned injury'.

In these injuries, usually caused by an impact to the skin by an implement that has a surface consisting of 'grooves' or 'ridges', the outline of the implement may be 'retained'.

The finding of a 'patterned' injury is of considerable forensic interest - careful documentation and photography of such a wound may allow subsequent matching of a putative injury-causing implement with the skin surface bruise (a form of 'tool mark' analysis utilising computer-enhanced photographic 'overlay' techniques).

Examples of situations in which an intradermal bruise may be produced;

  • tyre marks in a road traffic collision
  • a punch to the face by a woolen-gloved fist
  • a 'stamp' by a shoe/ trainer etc
  • an impact by a whip

 

3. Tramline bruises

When a person is struck with a cylindrical object, such as an iron bar, baseball bat, or police asp etc, the bruise pattern formed is quite distinct.

The skin surface is indented and blood vessels at the edges are ruptured. Blood is squeezed out of any vessels along the point of contact, but the vessels remain relatively intact (particularly if the supporting tissues are lax). When the impacting object is removed, blood flows back into the undamaged vessels, but leaks from the damaged ones.

The resulting bruise is termed a ‘tramline bruise’ because it appears as a pale linear central area lined on either side by linear bruising

(See a picture of tramline bruising)

 

4. Fingertip/pad bruises

Where an assailant has forcefully gripped a person, for example around the neck (e.g. during attempted manual strangulation) or arms etc, one may see small discoid or ovoid bruises in a cluster. These may be discrete, but are often blurred or may 'merge' with one another, due to the dynamic nature of assaults and struggles with an assailant.

Sites to look for these bruises include,

 

5. Others

    • ‘Defensive’ bruises on the upper arms or forearms, where a victim has attempted to ward off their attacker’s blows to protect vital organs/ body parts
    • Bruising around the mouth or lips, which may corroborate a history of having had a hand forcibly placed over their mouth to silence the victim
    • Bruising on the shoulder prominences, which may corroborate a history of having been forcibly pushed up against a wall etc during an assault

    In addition, the following 'signs' describe subcutaneous haemorrhage resulting from blood tracking from distant sites of injury, but do not represent 'bruises' of the site at which the skin discolouration is visible

    • Battle’s sign – bruising visible behind and below the ear at the mastoid process, caused by the gravitational accumulation of blood from a basilar skull fracture,
    • ‘Racoon/ panda eyes’ – bruising of the lax soft tissues around the eyes caused by skull base fractures

    Bruises caused by injury should also be distinguished from skin discolouration seen in ‘Mongolian blue spots’ in children, ‘Campbell de Morgan spots’, striae and (senile) purpura. Further details of these innocent lesions can be obtained from standard dermatology and paediatric texts.

    (See Derm Atlas for an image of a Mongolian Blue spot)