A Rare Presentation of Benign Prostatic Hyperplasia With Pure Stromal Hyperplasia as a Large Isolated Pelvic Mass With Normal Prostate Imaging

Benign prostatic hyperplasia (BPH) is the most common benign lesion of the prostate in aging men. However, diagnosing BPH can be challenging when it presents as an exophytic pelvic mass, particularly if radiologic continuity with the prostate and prostatic glandular components are not clearly seen. Here, we report a 57-year-old male patient with a 2-year history of obstructive voiding dysfunction. Radiologic investigations, including both computed tomography and magnetic resonance imaging, revealed a large (up to 11.9 cm) solid pelvic mass located superior to the prostate with marked mass effect. No direct continuity with the prostate or multilocular/cystic structure was identified on imaging. Pathologic evaluation of the biopsy specimen showed a hypocellular lesion consisting of bland spindle cell proliferation and small blood vessels within a loose fibrous stroma. The subsequent resection specimen showed similar histologic morphology, and prostatic glands were not identified. Immunohistochemical staining demonstrated that the tumor cells were positive for CD34, desmin, androgen receptor, and progesterone receptor. Ki67 staining indicated a very low proliferative index (