Answer: Stromal nodular hyperplasia

Histology: There is a focal area of increased stromal cellularity. Although cellular, the nuclei are bland, lack hyperchromasia, and lack mitotic figures. Throughout the nodule are medium sized vessels with thick walls cut in cross section.

Discussion: Microscopically, four patterns of STUMP have been described and include:
(1) hypercellular stroma with scattered atypical, but degenerative appearing cells admixed with benign prostatic glands;
(2) hypercellular stroma consisting of bland fusiform stromal cells with eosinophilic cytoplasm admixed with benign glands;
(3) leaf-like hypocellular fibrous stroma covered by benign appearing prostatic epithelium similar in morphology to a benign phyllodes tumor of the breast; and
(4) myxoid stroma containing bland stromal cells and often lacking admixed glands.

The current case would have to be the one consisting of myxoid stroma. The myxoid pattern of STUMP consists of extensive sheets of myxoid stroma and can only be diagnosed typically on TURP where multiple slides show a lack of nodularity identified in BPH. In addition to nodularity, which may be difficult to appreciate on needle biopsy, stromal BPH are composed of loose mesenchyme containing prominent small round vessels with thick walls cut in cross section. In a needle biopsy or transurethral resection specimen, these vessels help differentiate between a mesenchymal tumor from a stromal nodule of BPH.