The testicles of men are one big and one small, then the possible causes: first, orchitis, the inflammatory side of the testicles can increase in size, and can be accompanied by local pain or swelling, and can even pull to cause pain in the groin area or waist. In serious cases, there can be changes such as redness and swelling of the scrotal skin, increased skin temperature, and increased pain when touched, which requires further ultrasound examination of the testicles to further identify. Secondly, syringomyelia, the scrotum on the side of the syringomyelia increases in size, and the testicles are not clearly touched or are mildly swollen when touched, and the enlargement can gradually increase with further progress of the disease. In the early stage, there is no obvious pain, but in the later stage, when the volume increases, there may be a localized feeling of swelling, and ultrasound examination of the scrotum is needed to further confirm the diagnosis. Thirdly, testicular tumor, when the testicle on the affected side increases in size and is accompanied by changes such as hardening and increasing density, CT examination of the testicular area or testicular tumor index examination is needed to further confirm the diagnosis.