Reactive fibroblastic and myofibroblastic proliferation of the vulva (Cyclist's Nodule): A hitherto poorly described vulval lesion occurring in cyclists.

Perineal nodules occurring in male cyclists are reported in the literature, although the histologic features are not extensively documented. There has been little description of similar lesions in the female population. We describe 4 cases in which a vulval nodule or swelling developed in competitive female cyclists aged 15 to 45 years. The lesions were unilateral and occurred on the right or left labium majus (2 cases each). The histologic features were similar in all cases and consisted of a haphazard admixture of adipose tissue, variably cellular hyalinized tissue containing bland spindle-shaped fibroblasts, blood vessels, and nerve fibers. In some areas, thick cords of fibrous tissue imparted a keloid-like appearance. Other histologic features included plump mesenchymal cells with round or ovoid nuclei and abundant eosinophilic cytoplasm resulting in an epithelioid, plasmacytoid, or ganglion-like appearance (2 cases), a lymphocytic infiltrate around blood vessels (3 cases), foci of fat necrosis (1 case), and collections of elastic fibers (2 cases). One case recurred, the histologic features of the recurrent lesion being identical to the original. The overall morphologic appearances, especially in the cases with plump mesenchymal cells, bore some resemblance to proliferative fasciitis. Immunohistochemically, the cells were estrogen receptor positive and the plump mesenchymal cells were smooth muscle actin positive, in keeping with myofibroblasts. Desmin, S100, CD34, and HMGA2 were negative. Pathologists should be aware of this pseudoneoplastic lesion occurring on the vulva, which arises in a specific clinical setting and has the potential to be misdiagnosed as a variety of other mesenchymal lesions. We term this lesion as reactive fibroblastic and myofibroblastic proliferation of the vulva or "cyclist's nodule."