Benign mesothelial cells may be found in mediastinal or intra-abdominal lymph nodes. It is important not to misdiagnose them as metastatic carcinoma. The presence of nonneoplastic mesothelial cells within a lymph node sinus is referred to as a mesothelial lymph node inclusion.

Risk factors:

(1) mesothelial proliferation secondary to inflammation

(2) mesothelial proliferation associated with tumor growth


Location: within expanded nodal sinuses, as single cells or a small cluster of cells


Cytologic features: bland nuclei, low nuclear to cytoplasmic ratio and well-defined cell borders


Diagnostic workup:

(1) demonstration of mesothelial markers on immunohistochemical stains

(2) absence of immunohistochemical markers for the malignant tumor (if present)

(3) microvilli on electron microscopy

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