Kondziolka et al developed a simple risk equation to help predict the lifetime risk of hemorrhage from an arteriovenous malformation. This can help a patient make informed decisions about management. The authors are from the University of Pittsburgh and the University of British Columbia.
Parameters:
(1) age of the patient
(2) life expectancy of the patient (from life insurance tables)
(3) annual risk of hemorrhage expected (usually 2-4%)
expected years of remaining life =
= (life expectancy for the patient) - (current age)
risk of no hemorrhage =
= 100% - (annual risk of hemorrhage)
probability of no hemorrhage during the remaining years of life =
= ((risk of no hemorrhage) ^ (expected years of remaining life))
probability of hemorrhage for the patient =
= 100% - ((risk of no hemorrhage) ^ (expected years of remaining life))
Limitations:
• The model assumes that the risk of hemorrhage every year is constant. The actual risk may be affected by changing risk factors such as a previous hemorrhage.
• The model also assumes that the risk each year is independent.
• Although the model may not be rigorous, it is simple and may be good enough for convey the degree of risk.
