A previously healthy 52-year-old man presented with a 1-year history of painless left scrotum enlargement and mild discomfort, but no lower urinary tract symptoms. He was admitted 1 month after his symptoms worsened, with subjective fever, but still without lower urinary tract symptoms. Before admission to hospital, he had been treated at a local community hospital and had received oral empiric antibiotic levofloxacin for 2 weeks, with no significant improvement in his symptoms. The patient had no history of cryptorchidism, scrotal trauma, scrotal inflammation, or urinary tuberculosis, and no history of neoplastic disease or family history of genetic diseases.
Physical examination of his testes revealed an enlarged, hard, and non-tender left testis, a clinically normal right testis, and no palpable inguinal lymphadenopathy. Ultrasound examination of the scrotum revealed a mainly cystic, heterogeneous echogenic mass occupying most of the left testicle. The tumor had a clear boundary, regular morphology, and disordered internal echo ( Figure 1A ). Viscous fluid was seen in the cystic part, and large calcified spots were detected in some areas ( Figures 1B, C ). A few irregular solid protrusions were visible on the cyst wall with a small blood supply ( Figure 1D ). There were no obvious enlarged lymph nodes in the groin area on either side. The ultrasound findings suggested a testicular tumor or abscess. However, the testicular tumor marker serum alpha-fetoprotein (AFP) was 2.2 ng/mL (normal reference value 0-20 ng/mL), beta-human chorionic gonadotropin (beta-HCG) was 0.6 mIU/mL (normal reference value 0.5-2.67 mIU/mL), and lactate dehydrogenase (LDH) was 136.3 IU/L (normal reference value 120-250 IU/L). Renal function, inflammatory markers, and routine urine and blood tests were all normal. We therefore decided to perform exploratory surgery of the left testicular mass.
Surgery revealed a multilocular cystic mass in the left testis. There was no abnormality in the left epididymis or spermatic cord. Intraoperative frozen pathology indicated a testicular mucinous tumor, and radical resection of the left testis was performed. Postoperative gross pathology showed a multilocular cystic mass in the left testis measuring about 4.5x3.5x2.5 cm and occupying almost the entire testicular parenchyma, with irregular thickening of the cyst wall and filled with gray-yellow jelly ( Figure 2A ). Microscopy showed that the inner wall of the capsule was lined with a single layer of pseudo-stratified mucus columnar epithelial cells, some showing mild nuclear atypia, but with no interstitial infiltration. There was also fibrous tissue proliferation of the cyst wall and mucus overflow into the cyst wall in some areas ( Figures 2B, C ). The cyst cavity was filled with mucus, with focal calcification in some areas, but no teratoma component. Based on the pathological characteristics, the diagnosis was primary or secondary testicular mucinous tumor.
On the basis of this unexpected pathological finding, a further diagnostic work-up was carried out, including abdominal and pelvic computed tomography (CT) and upper and lower gastrointestinal tract endoscopy, but no other suspicious primary tumors or metastases were found. The tumor was thus finally diagnosed as a primary borderline mucinous tumor of the testis, according to the 2016 edition of the WHO Classification of Tumors of the Urinary System and Male Reproductive Organs.
The patient underwent postoperative follow-up examinations once a year for 4 years after surgery. His serum tumor markers remained at normal levels, and scrotal ultrasound, abdominal and pelvic CT scans, and colonoscopy and gastroscopy revealed no evidence of metastases or any other primary adenocarcinoma. His postoperative recovery was uneventful.
Patient perspective: "I was previously healthy with no known diseases. Before coming to the hospital, I had had a 1-year history of painless left scrotum enlargement and mild discomfort, and had felt the symptoms worsening for more than a month. After coming to the hospital and undergoing left orchiectomy surgery, my left scrotum discomfort disappeared. My postoperative recovery was uneventful, and there were no abnormal findings during annual postoperative follow-up examinations."