Benign testicular lump. Light micrograph of tissue from a testicle in a case of Leydig's hyperplasia. The round structures are seminiferous tubules (the places where sperm cells are formed), but the one at upper centre is abnormal and flattened. This condition is a benign disorder of the testis where the hormone producing function of the Leydig cells is disrupted and various symptoms result. Some cases involve testosterone production, and others involve feminizing hormones. Leydig cells are a type of interstitial cell that are involved in stimulating sperm production. Hyperplasia is an abnormal increase in the number of cells, and is similar to, but distinct from, a tumour.