Perineural involvement by benign prostatic glands on needle biopsy.

Uncommonly, benign prostatic glands can be seen in the perineural space, known as "benign perineural involvement." This phenomenon has not been specifically studied on needle biopsies; 27 needle biopsy cases with perineural involvement were evaluated; 22 (81.4%) were received in consultation, while 5 (18.5%) were in-house cases. In 15 of 22 (68.2%) consult cases, a question was raised by the submitting pathologist regarding the focus. The following patterns of perineural involvement were observed: indentation 14 (51.8%) cases, by up to 3 glands; tracking 8 (29.6%) cases, by up to 6 glands; wrapping 7 (25.9%) from one half to three fourths around the nerve, by up to 3 glands, 1 case showed 95% wrapping; intraneural 4 (14.8%) cases by up to 3 glands; adjacent 2 (7.4%) cases by up to 2 glands. Partial atrophy in the involved glands was seen in 10 (38.4%) cases and complete atrophy in 6 (23%). Of 8 cases with the lesion still present on slides for immunohistochemistry, high molecular weight cytokeratin (HMWCK) and p63 were positive in 6 (75%) and negative in the 2 (25%) cases with partial atrophy. A total of 6 (27%) cases had more than one pattern of perineural involvement. On hematoxylin and eosin sections, basal cells were not identified in 12 (46%) cases, including 2 negative and 1 positive cases stained for HMWCK. Patterns most closely mimicking cancer included intraneural and incomplete perineural encirclement. Perineural invasion by benign atrophic glands cause diagnostic difficulty, especially with negative HMWCK. Careful attention to hematoxylin and eosin morphology and comparison of perineural involvement to adjacent and distant benign glands are necessary.