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Bruises are common, and determining why they are there is usually relatively straightforward. But determining what the bruises of a given child mean can be a challenge. Questions that come up include "What is normal and what is abnormal?", "How many bruises are too many?", "Can bruises be aged?", and "How can accidental bruises, nonaccidental bruises, bruises associated with a coagulation disorder, or lesions that only masquerade as bruises be distinguished?"
DEFINITIONS
A bruise (or contusion or ecchymosis) is a discoloration of the skin without a laceration that is produced by blunt trauma. A bruise occurs when hemorrhage from ruptured capillaries (and small veins), primarily in the subcutaneous tissues, extravasates to produce discoloration. Bruise colors then change as hemoglobin breaks down.1
Bruises are distinguished from purpura by etiology.2 Purpuric lesions are also due to extravasation of blood into the skin but not necessarily because of trauma. Infections, diseases with vascular fragility or vasculitis, and severe abnormalities in coagulation can cause purpura without significant trauma. So, in a strict sense, bruises are purpuric lesions, but not all purpuric lesions are bruises.
Petechiae are also due to extravasation of blood (from capillaries), but are distinguished from purpura by being less than 2 mm in diameter. In contrast to hyperemic skin lesions (where blood remains within dilated vessels), petechiae and purpura will not blanch when overlying skin is stretched.2 Like bruises, petechiae can be caused by trauma, as from capillary sheering forces next to a slap or a swat.
NORMAL BRUISING
Normal bruises are due to accidental trauma and the severity of a bruise is consistent with the severity of the injury that produced it. Because of this, normal bruises are uncommon before a child begins walking and become increasingly common thereafter, at least until preadolescence.
Sugar et al. monitored the frequency of contusions using 1,001 well-child visits in 7 Seattle practices. They found that, overall, 21% of patients aged 0 to 36 months and with no known medical conditions that predisposed to bruising or suspicion of abuse had 1 or more bruises.3 But only 2 of 366 (0.6%) of the infants younger than 6 months and 8 of 473 (1.7%) of the infants younger than 9 months had any bruises. Overall, only 2.2% of the children not...