If my son was born at 32 weeks, what are the chances that he has pvl?

Small. Pvl is more common in premature than term infants, and occurs more frequently with decreasing gestational age and size. Study showed the incidence of pvl is ~ 3-4% of infants who weigh < 1, 500 g (3.3 lb) have pvl, and 4-10% of those born < 33 weeks of gestation (but who survive more than three days postpartum). Another suggest <32 weeks account for~2% of all live births in usa.
Low. Pvl, or periventricular leukomalacia, is a condition where "water-shed" areas in the brain suffer ischemic injury leading to loss of brain tissue. Pvl is most often described in extremely premature (< 28 wk gestation) infants, but the exact cause is unknown. Although less premature infants may develop pvl, this is very uncommon, and is usually preceded by a profound hypoxic or inflammatory event.