Mesothelial cell inclusions in pelvic and para-aortic lymph nodes: a clinicopathologic analysis.

Benign lymph node inclusions are commonly encountered during surgery for gynecologic neoplasms and are potential mimics of metastatic tumor. The presence of mesothelial cell inclusions in pelvic lymph nodes is extremely rare. We report the clinicopathologic features of 10 patients with ovarian tumors and mesothelial cell inclusions detected in the sinuses of pelvic and paraaortic lymph nodes. All patients had concurrent massive ascites and mesothelial cell hyperplasia at the time of lymph node dissection. Histologically, nodal mesothelial cells were identified predominantly within the subcapsular, trabecular and medullary sinuses. Moreover, intra- and extranodal lymphatics also contained mesothelial cells, confirming their mode of lymphatic transport to nodal sinuses. This finding, together with mesothelial cell hyperplasia and massive ascites suggest that mesothelial cells derive from reactive serosal mesothelium and are dislodged into draining lymphatics. This study indicated the pathogenic significance of the lymphatic transport mechanism. Nodal mesothelial cell inclusions should be distinguished from metastatic tumor to avoid inaccurate staging in a patient with a known tumor or the false negative diagnosis of an occult primary tumor. Recognition of this entity by immunohistochemical evaluation in addition to routinely stained sections is important to prevent a diagnosis of metastatic carcinoma or malignant mesothelioma.