THE CONTEXT
Bruise patterns can reflect the impacting surface or clothing, while deeper bruises may become visible only after a delay.
How patterned bruises form
•
A small haemorrhage immediately beneath the epidermis may have a sharply defined pattern because the overlying layer is thin and translucent.
•
Objects with alternating ridges and grooves, such as tyre treads or ribbed shoe soles, can force skin into the grooves and distort it.
•
Intradermal red lines may correspond to the grooves because cutaneous capillaries are squeezed or burst. Ridges may remain pale because pressure forces blood out of the small vessels.
•
Forceful sole or heel compression may imprint the shoe pattern as an intradermal bruise. Combined kicking and jumping on a person is termed stomping.
•
A violent blow to a clothed area, or grabbing and twisting clothing over skin, can produce petechial haemorrhages reproducing the clothing texture.
Timing and repeat examination
•
A superficial bruise appears immediately as a dark-red swelling.
•
A deep bruise may take several hours or one or two days to appear; deeper blood extravasation may never become visible.
•
A further examination 48 hours after the first is advised to identify bruises that develop slowly.
Bruising appearing after death
•
An injury sustained before death may produce a visible bruise only after death, termed a come-out bruise.
•
The described mechanisms include further escape of blood from ruptured vessels through gravitation and mainly percolation, together with rapid haemolysis of stagnant blood and local diffusion of pigment.