COW-2019-22

1. c

Paraganglion tissue

The biopsy reveals nests of cells with abundant clear-to-amphophilic slightly granular cytoplasm and small round-to-oval bland nuclei embedded within a prominent capillary network, consistent with paraganglionic tissue. The neuroendocrine component is surrounded by flattened supporting (sustentacular) cells that are usually inconspicuous on H&E. The nests are identified in close proximity to a peripheral nerve as is characteristic for paraganglia. Additional immunohistochemistry in the current case demonstrates positive staining for S100 and negative staining for pan-cytokeratin AE1/AE3, NKX3.1 and PSMA.
Detected in up to 8% of radical prostatectomy, paraganglionic tissue is a rare finding in transurethral resections or needle biopsies as in this case. It is typically located in the posterolateral loose connective and adipose tissue, more commonly closer to the base of the prostate than the apex, although cases with paraganglionic cells detected within prostatic pseudocapsule have been described. The importance of diagnosis lies in distinguishing this benign mimicker from high grade prostatic adenocarcinoma, notably poorly formed and fused glands of Gleason pattern 4 or solid growth of Gleason pattern 5, and avoiding misinterpretation of extraprostatic extension. Absence of surrounding benign glands, association with neurovascular bundles and degenerative-type nuclear atypia are clues to the diagnosis. While the paraganglionic cells can have occasional nucleoli, prominent eosinophilic nucleoli characteristic of prostatic adenocarcinoma are absent. In terms of immunohistochemistry, neuroendocrine markers can be used to highlight the neuroendocrine cells while the sustentacular cells stain positive for S100 and SOX10. Conversely, the paraganglionic cells are negative for prostatic markers and cytokeratins. As such, interpretation of immunonegativity for basal cell markers (especially CK 34BE12) in isolation in what is erroneously thought to be a suspicious carcinoma focus constitutes a potential diagnostic pitfall.

Howarth SM, Griffiths DF, Varma M. Paraganglion of the prostate gland: an uncommon mimic of prostate cancer in needle biopsies.
Histopathology. 2005 Jul;47(1):114-5.

Ostrowski ML, Wheeler TM. Paraganglion of the prostate gland: an uncommon mimic of prostate cancer in needle biopsies.
Am J Surg Pathol. 1994 Apr;18(4):412-20.

Gertruda Evaristo & Fadi Brimo
McGill University
gertruda.evaristo@mail.mcgill.ca

Prostate

Paraganglion, benign mimics, adenocarcinoma