A two-year-old boy with effusion in the scrotum is considered to be associated with syringomyelia, orchitis or epididymal cyst. 1. syringomyelia: syringomyelia can occur at any age, the incidence rate is 0.7%~4.7% in male infants, syringomyelia can be manifested as a cystic mass in the scrotum, which can be painless, chronic enlargement, no discomfort when the amount of fluid is small, and the scrotum can be felt to be drooping after the amount of fluid is large, and the ultrasound can diagnose the syringomyelia. syringomyelia can be absorbed by themselves, and it can be left untreated for the time being for the children aged below 2 years old. 2. Testiculitis: usually caused by viral infection, children’s pneumonia can also cause non-specific testicular inflammation, with swelling, redness and pain on the affected side of the scrotum, and the scrotum can appear turbid fluid under the effect of inflammation. 3. Epididymal cyst: it can be caused by bloodstream infection or trauma and other etiological factors, blockage of the epididymal ducts as well as retention of luminal fluid, forming epididymal cysts, forming a rounded swelling in the testicles and epididymis, and there can be a feeling of scrotal sagging. It is recommended to consult a doctor for a clear diagnosis and choose an appropriate treatment plan according to the condition.