<2% of children under the age of 6 months will have any bruising at all.
Accidental bruising is common in children >9 months of age but not in children <9 months of age. Accidental bruises are not clustered, not patterned, and are usually found over bony prominences. Common locations include the anterior lower leg and forehead. Bruises involving the buttocks, back, ear, neck, and torso are more likely to be non-accidental.
Beware of any history that does not explain the bruising seen on exam.
Hematologic disorders can cause bruising as well.
vWB disease is the most common bleeding disorder (1% prevalence in general population).
Ask for family history of easy bruising, bleeding after dental procedures, heavy menstrual periods,
excessive bleeding with circumcision, etc.
If you have a low suspicion for non-accidental trauma, but bruising is present on exam,
consider a workup for hematologic disorders – CBC, PT, PTT.
If you have concern for non-accidental trauma as well, pursue both diagnoses.
Consider skeletal survey, CT head if appropriate, and a thorough exam including genital, anal,
intra-oral, and a close look at the ears, behind the ears, and inside skin folds.