Perineal Nodular Induration of the Cyclist: A Dermatopathologic Study of Eight Cases with Practical Diagnostic Clues.

Perineal nodular induration (PNI), also known as cyclist's nodule, is an uncommon reactive pseudotumoral lesion related to repetitive mechanical trauma in saddle sports. Although clinically recognized, its histopathologic spectrum remains incompletely characterized. We performed a retrospective dermatopathologic study of 8 cases of PNI independently reviewed by 2 experienced dermatopathologists using conventional microscopy and digital slide imaging. The study included 7 men and 1 woman, with a median age of 48.5 years (range, 34-76 years). All cases showed a poorly circumscribed fibrohyaline proliferation centered within the deep dermis and subcutaneous tissue. Consistent findings included marked stromal hyalinization, rounded hyalinized collagen nodules, septal remodeling, adipose tissue entrapment, low cellularity, bland spindle cells, and vasculolymphatic dilatation. Significant cytologic atypia, mitotic activity, pseudocyst formation, and neural hyperplasia were absent in all cases. Rounded hyalinized collagen nodules were identified in all cases, and although previous reports describe stromal hyalinization and dense collagen deposition, this nodular collagenous pattern has not been specifically emphasized. Immunohistochemical studies, performed in 2 cases, were nonspecific and overlapped with previously reported profiles. Orcein staining, performed in 2 cases, demonstrated marked reduction or near-complete absence of elastic fibers in both specimens. Our findings suggest that PNI exhibits a reproducible fibrohyaline pattern that may facilitate recognition on routine hematoxylin-eosin sections in the appropriate clinicopathologic setting and may reduce the need for ancillary immunohistochemical studies in selected cases.