Mesothelial pelvic lymph node inclusions mimicking metastatic thyroid carcinoma.

Benign lymph node inclusions are commonly encountered during surgery for gynecologic neoplasms and are potential mimics of metastatic disease. A 52-year-old woman presented with ascites, a complex adnexal mass, and a CA-125 of 1891 units/mL. A staging laparotomy was performed, diagnosing struma ovarii. Pathologic evaluation of pelvic lymph nodes demonstrated mesothelial inclusions in nodal sinuses suspicious for metastatic disease. Immunocytochemical evaluation revealed benign mesothelial inclusions rather than metastatic thyroid carcinoma. Benign mesothelial lymph node inclusions in nodal sinuses are potential mimics of metastatic carcinoma. Their presence in pelvic lymph nodes has not previously been reported. Given the potential difficulty in determining the origin of these inclusions, immunocytochemical evaluation is useful in reaching the correct diagnosis.