Symplastic Glomus Tumor.

Glomus tumors showing nuclear pleomorphism without any other malignant features have been defined as symplastic glomus tumors. This type of glomus tumor is rarely encountered. Another case of symplastic glomus tumor is described in this study. A 37-year-old woman referred to the hospital with the complaint of a palpable tender nodule on the fourth finger tip of her left hand. The lesion had been present for about a year and aggravation of tenderness upon cold exposure was conspicuous. It was a 0.5 cm well circumscribed lesion with round to cuboidal epithelioid cells showing high grade nuclear pleomorphism. Nests of cells more uniform in shape and showing punched out nucleus representative of typical glomus tumor could also be observed. Immunohistochemical study showed expression of smooth muscle actin, caldesmon and vimentin. Ki-67 labeling index was undetectable. Investment of tumor cells was shown by type IV collagen. In contrast to its atypical cellular morphology, symplastic glomus tumor clinically behaves benign, and it is important to differentiate it from malignant glomus tumor as well as other primary or metastatic malignant tumors.