A hard, sometimes painful lump about the size of a pea may form as a result of sperm vas deferens, may cause discomfort for two to 12 weeks after vasectomy . vasectomy, each vas deferens (the two tubes that move sperm) are sealed off. This blocks sperm from reaching the semen that is ejaculated from the penis. After. Up to two semen tests are done after the operation, to ensure that all During a no-scalpel vasectomy, the doctor will feel the vas deferens . In rare cases, sperm can collect in the surrounding tissue, forming hard lumps that.