A sperm granuloma is a lump of extravasated sperm that appears along the vasa deferentia or epididymides in vasectomized men. Sperm granulomas are rounded or irregular in shape, one millimeter to one centimeter or more, with a central mass of degenerating sperm surrounded by tissue containing blood vessels and immune system cells. Sperm granulomas can be either asymptomatic or symptomatic, i.e. either not painful or painful, respectively. (see post-vasectomy pain syndrome). The vast majority of sperm granulomas in vasectomized men are present as a result of the pressure-induced changes of vasectomy.