A unique case of a serous borderline tumor of the paratestis

Serous borderline tumors of the paratestis are histologically identical to their ovarian counterparts and hypothesized to arise from Mullerian metaplasia of the tunica vaginalis. They are exceedingly rare with many cases probably going clinically unnoticed. We present a case of serous borderline tumor of the paratestis, with, to the best of our knowledge, the first published sonographic and magnetic resonance (MR) images of this entity. It was successfully treated with partial orchiectomy with no disease recurrence after one-and-a-half years.