A twisting of the testicle on its blood supply, which blocks blood flow. Torsion usually affects only one testicle, and it typically causes sudden, severe pain accompanied by nausea and vomiting. The testicle quickly swells, the skin of the scrotum (the pouch between the legs containing the testicles) turns red, and the pain radiates into the abdomen. The condition is most common in adolescents and young men between 12 and 20 years of age. Immediate medical treatment is needed to prevent the death of the tissues in the testicles. In most cases, surgery is required to untwist the testicle and to attach it with surgical stitches to the wall of the scrotum; this prevents the condition from occurring again.