[Keywords] Testis; plasmacytoma; ultrasonography The patient was a 65-year-old male. He was found to have painless enlargement of the right testicle for more than 3 months with progressive enlargement, accompanied by soreness and swelling, no fever, no urinary frequency, urinary urgency and pain. Physical examination: the right testicle was obviously enlarged, without tenderness, with medium quality. External ultrasound diagnosis: right testicle enlargement, possible orchitis. Ultrasound examination in our hospital: the right testicle was obviously enlarged, with a size of about 54×42×700px, complete envelope, uneven internal echogenicity, and several lamellar hypoechoic areas of different sizes, the largest being about 0.8×10px, but no obvious mass-like echogenicity; the left testicle was about 38×28×450px, with normal envelope and internal echogenicity; bilateral epididymis did not show any obvious abnormality; bilateral scrotum The echogenicity of both epididymis was not obvious. Color Doppler flow imaging (CDFI): the blood flow signal of the right testicle was extremely rich, with thickened and increased blood vessels, dendritic distribution, and more regular travel, almost covering the whole testicle; the blood flow signal of the left testicle and bilateral epididymal testicles did not show any obvious abnormality. Ultrasound diagnosis: right testis enlargement, seminoma? Intraoperative observation: the surface of the right testis was smooth, and a high level resection was performed. The testis was dissected and a nodule with intact envelope, about 125px in diameter and grayish and grayish yellow in color was seen on the cut surface. Pathological examination: microscopically, the tumor cells were small and dense, with round, deviated and deeply stained nuclei, clear nucleoli, visible nuclear fission phase and intranuclear inclusion bodies, and scattered varicose seminiferous tubules. Immunohistochemistry and special staining showed that CD79, MUM1, CD138, VS38C and λ were positive. Pathological diagnosis: right testicular plasmacytoma. Discussion Plasmacytoma is rare, a systemic malignancy of bone marrow origin, derived from B lymphocytes, with a differentiated nature towards plasma cells. A few cases can originate outside the bone marrow and are called extramedullary plasmacytomas, which account for less than 4% of plasma cell malignancies, mostly in men, with a male:female ratio of 3:1. Extramedullary plasmacytomas are more common in the head and neck, especially in the upper respiratory tract, while testicular plasmacytomas are rare, accounting for 0.6% of plasmacytomas and 0.03% of testicular tumors. In this case, diffuse enlargement of the testis is the main ultrasound manifestation, which is easily confused with orchitis and diffuse enlargement of the testis in spermatocytoma. The sonogram and CDFI manifestation of orchitis are similar to this case, but the onset of the disease is more rapid, and the scrotal skin on the side of the disease is usually red, hot and painful. The age of onset is similar to that of testicular plasmacytoma, and the history and clinical manifestations are similar to the present case. However, the internal echogenicity of the testis in diffuse spermatocytoma is thickened and increased, similar to the echogenicity of liver parenchyma in cirrhosis, and although the blood flow signal is increased, the vascularity is irregular. In addition, the pathology of this case suggested that the envelope of the right testis was intact, but the ultrasound failed to show the envelope, probably because the envelope was too thin and the acoustic impedance was similar to that of normal testicular parenchyma and tumor tissue, while the echogenicity of the tumor was similar to that of the testis. The above analysis shows that ultrasound has a certain differential diagnostic value for testicular plasmacytoma. For the above ultrasound manifestations of testicular abnormalities, the possibility of testicular plasmacytoma should be considered in conjunction with clinical practice to avoid misdiagnosis.