Causes for Zero sperm count after having 2 previous successful pregnancies

After my OB requested a SA from my Dh he admitted to having hardly any ejaculate for almost 2 years. This is following a hemorrhagicstroke(05/07) and diagnosis with high blood pressure. Apon original check up the dr. replied that unless he had the proof in front of him he would never know a stroke had occured. His 1st urologist felt this might be retrograde ejaculation, but did nothing but a physical examination. We recently saw another urologist that deals with infertility. He did a SA and urinalysis after and found zero sperm in either sample. We are presently awaiting BW. We have had 2 children, but DS passed away leaving dd without a sibling. Obviously DH hasn't always had this problem. So is it definitely an issue with the pituitary/hormones? It seems like they should have also checked for a blockage.(prostate was fine)I know we are very lucky for the outcome DH has had and I am sorry for my impatients. It takes so long to see anyone that I would like to be armed with more information. Thank-you for your time. I appreciate any information.