Can a hernia in the groin area be cause from a car accident?

My son had a physical for work in February,no sign of hernia.In July he had an auto accident,there was nothing left of the car,he hit 3 trees, he had head injury,and was in hospital for 2 weeks,and was still recovering.Im happy hes ok today.He could not return to work until around October.In December he noticed a lumb in the groin area and was scared to tell anyone,finally when he did I made a Dr. appt around December.So his Dr refered him to a surgeon.His visit with the surgeon was in January,surgury was in February.Now my auto insurance is saying it had nothing to do with accident and denied claim.Also stated that it didnt appear in cat scan.I believe so strongly that it was from auto accident. If it was before accident he has insurance through work we would of had it taken care of.His insurance through work paid there part but auto ins has denied claim.His Dr even wrote a note stating if was from auto accident.So could I please get some help on this or your imput.Thank you for your time.Pam Wickerink