The patient in the present case was a 2-day-old boy with a cystic lesion in his left testis, which was detected during the prenatal period by a maternal ultrasound examination at 34 weeks of gestation. At 37 weeks of gestational age, the 2,890 g boy was delivered by caesarean section. A cystic lesion of 10 mm size was recognized in a postnatal imaging examination, but no apparent solid or fat component was noted. A simple cyst or an epidermoid cyst was suspected. Considering the possibility of

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... esticular atrophy due to a cystic lesion, we performed an operation at 1 month of age, which revealed a monoclastic cyst with a clear edge, which only nucleated the cyst. Histopathological analysis revealed squamous epithelial cells on the cyst wall surface, fibromuscular tissue, and intestinal tissue. Mature cystic teratoma was the diagnosis based on the examination findings of extirpated tissue. As shown in this case, the prenatal diagnosis of testicular tumors in the scrotum is very rare. In this case, a simple testicular cyst was initially considered to be the most likely diagnosis because no solid component was recognized on imaging after birth. In neonatal patients with testicular tumors, even lesions that only contain a cyst require a careful diagnosis and treatment with the possibility of germ cell tumors kept in mind.