Spiradenoma reminiscent of thymoma: report of a case and review of the literature

Abstract

Spiradenoma (Sp) is a rare adnexal cutaneous tumor with a prominent vasculature. There are few reports in the literature suggesting that the majority of the cases contain perivascular spaces with numerous lymphocytes, a feature that is characteristic in thymus neoplasms. However, there is little information available about the nature and maturity of the lymphocytes comprising these spaces. We report a case of a Sp that presented as a palpable painless mass in a 45-year-old woman and had histological similarities with thymomas. Furthermore, we compare these two entities in detail, discussing the differences and possible similarities between them. On histological grounds, the lesion consisted of epithelial lobules with prominent ductal differentiation admixed with conspicuous perivascular spaces containing numerous lymphocytes. Immunohistochemical analysis showed that perivascular spaces contained mostly T lymphocytes (CD3 positive), which in contrast with those seen in most thymomas were mature (CD99, CD1a and Terminal deoxynucleotidyl transferase (Tdt) negative). A detailed comparison between Sps and thymomas shows that there exist several important clinicopathological and cytological differences between these two tumors. We suggest that the resemblance between Sps and thymomas is strictly architectural, and we raise some questions regarding the role of these perivascular spaces in tumor development.