Hyperplastic mesothelial cells within abdominal lymph nodes: mimic of metastatic ovarian carcinoma and serous borderline tumor--a report of two cases associated with ovarian neoplasms.

Two cases of hyperplastic mesothelial cells within intra-abdominal lymph nodes were encountered in staging procedures in a 59-year-old woman with bilateral ovarian serous borderline tumors and in a 21-year-old woman with a Sertoli-Leydig cell tumor of intermediate differentiation. Both patients also had mesothelial hyperplasia of the pelvic and abdominal peritoneum; in one of them, the hyperplasia was striking. The intranodal mesothelial cells occupied the sinusoids of the lymph nodes and were initially suspected of being metastatic from the ovarian tumor in each case. The appearance of the cells on routine stains suggested the correct diagnosis, which was confirmed by histochemical and immunohistochemical staining. These cases represent the first reported examples of mesothelial cells within abdominal lymph nodes, although similar involvement of mediastinal lymph nodes has been described in three patients with pleural effusions. Intranodal mesothelial cells should be distinguished from metastatic tumor, an error that could result in inaccurate staging in a patient with a known tumor or prompt a futile search for an occult primary tumor. Moreover, it is important that in studies evaluating the frequency of nodal involvement by serous borderline tumors, intranodal mesothelial cells should not be misinterpreted as metastatic borderline tumor, a distinction that can be difficult with only routinely stained sections.