[Seminal vesicle cyst with ipsilateral renal agenesis]

A formerly healthy 41-year-old male with monosymptomatic swelling of his left testicle was diagnosed with testicular cancer (seminoma). During staging of the cancer a computed tomography showed left renal agenesis and an 8 x 6 cm retrovesical space-occupying lesion in the left side of the pelvis. The lesion was interpreted as a group of enlarged lymph nodes, but PET/CT and MRI later demonstrated that it was a left seminal vesicle cyst. An association between congenital seminal vesicle cysts and ipsilateral renal agenesis is rare and can be explained by their common embryologic origin.