Obstruction of the vas deferens is usually the result of an earlier elective vasectomy procedure. Over time this obstruction may lead to significant "backpressure" experienced by the fragile epididymal tubules, thus causing a secondary epididymal obstruction, often referred to as a "blowout." Vasal obstruction, and even secondary epididymal obstruction, usually can be corrected using special microsurgical techniques to bypass the obstruction.

These microscopic procedures are among the most technically demanding ones performed by urologists, and they are best accomplished by individuals with special training in the area.