Testicular torsion – sounds painful, right? Testicular torsion occurs when a testicle twists on the spermatic cord that allows blood to flow to the testicle. The lack of blood flow to the testicle causes a great deal of severe pain and swelling which often appears rather suddenly. Testicular torsion is a serious medical emergency that requires immediate treatment. If testicular torsion is left untreated, the testicles can become permanently damaged.