• Major complications associated with a microscopic vasectomy reversal are uncommon.
• In many ways the complications that do occur are similar to that associated with a vasectomy.
• As the picture above illustrates, there is a large and intricate complex of blood vessels associated with vas deferens.
• One can see that is removing the inch or so segment of the post-vasectomy vas deferens involves severing numerous vessels including the vasal artery.
• Surgeons fear veins more than arteries because a vein has a thin outer covering and it is not pulsatile.
• The bleeding from a vein is more sneaky than an artery; the vein slowly oozes  but an artery by having a pulse is easy to detect when it is bleeding.

So the most common complication of a vasectomy and a vasectomy reversal is a hematoma or a collection of blood, which will accumulate until the space around it has enough pressure to make it stop. It is important for the surgeon to thoroughly inspect the reversal site before finishing the reversal to detect even the slightest amount of bleeding. Using the microscope for this purpose allows for detection of bleeding that might not be noted with the naked eye. 

If a hematoma occurs the usual treatment is conservative i.e. allow for it to resolve and be absorbed by the  body on its own. Hematoma occurrence can be minimized by the patient following the post-operative instructions of limited activity and the use of  compression underwear. It is important to stop any aspirin or ibuprofen well in advance of the procedure.