Small Acini in the Prostate

Junqi Qian, M.D.

Specimen Type:



A 72-year-old male presented with benign prostatic hyperplasia and underwent transurethral resection of the prostate. The specimen consists of numerous chips of pink-tan prostatic tissue in aggregate weighing 11 gm and measuring 3.0 x 3.0 x 2.0 cm. Representative sections were submitted.

Pathologic Features:

Histologically, the vast majority of specimen consisted of proliferation of fibrotic muscular tissue and prostatic glands. One focus showed a proliferation of closely spaced acini arranged in lobules or infiltrating between muscle bundles and prostatic acini without a stromal desmoplastic response (Fig.1). Acini varied in size but were usually small; larger acini often contained eosinophilic colloid-like luminal material, a distinctive finding that was apparent at low power magnification (Fig .1-4). Acini were lined by a single layer of small to medium size cuboidal cells with scant amounts of eosinophilic or amphophilic cytoplasm (Fig 3, 4). Nuclei were regular with finely dispersed chromatin and occasional small round punctuate nucleoli (5). No mitotic figures were identified.

Immunohistochemically, these cells were not reactive with antibodies to prostate specific antigen (PSA) or prostatic acid phosphatase (PAP); high-molecular weight cytokeratin 34BE12 was positive in the basal cells (Fig. 6).

Differential Diagnosis:

  • Atypical adenomatous hyperplasia (AAH)
  • Atrophy, postatrophic hyperplasia
  • Basal cell hyperplasia
  • Sclerosing adenosis
  • Verumontanum mucosal gland hyperplasia
  • Atypical small acinar proliferation suspicious for but not diagnostic of malignancy (ASAP)
  • Prostate cancer


Mesonephric Remnants in Prostate

Mesonephric remnants in the prostate are an unusual mimic of adenocarcinoma. It is considered benign, similar to its counterpart in the female genital tract. Histologically, mesonephric remnants consist of a proliferation of benign acini arranged in lobules or showing infiltrative growth between smooth muscle bundles without stromal desmoplasia. The acini are typically round or oval, varied in size and spacing, and are lined by a single layer of low cuboidal cells with scant to moderate cytoplasm and inconspicuous small nucleoli. The cells of mesonephric remnants are negative for PSA and PAP; but high-molecular weight cytokeratin is positive in the basal cells. Mesonephric remnants are a rare histologically and immunohistochemically distinct finding in the prostate that should be distinguished from adenocarcinoma and other small acinar proliferations of the prostate.


  1. Bostwick DG et al. Mesonephric remnants of the prostate: incidence and histologic spectrum. Mod Pathol. 2003 Jul;16(7):630-5