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

Background: 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.

Methods: 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.

Results: 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.

Conclusions: 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.