Understanding Mesothelial Cell Inclusions as a Diagnostic Pitfall

Pathologists and clinicians often face significant challenges when differentiating benign conditions from aggressive malignancies. Mesothelial cell inclusions in lymph nodes represent a particularly deceptive diagnostic pitfall. Although these inclusions are rare, they can closely mimic metastatic malignant mesothelioma or adenocarcinoma during cytologic evaluations. A recent case involving a 19-year-old man illustrates how these benign proliferations can lead to initial concerns for malignancy and the subsequent importance of precise diagnostic protocols.

The Clinical Presentation of Chylothorax

A young man presented with bilateral chylothorax, mediastinal lymphadenopathy, and extensive venous thrombosis. In clinical practice, these symptoms often signal underlying malignancies. Consequently, the medical team initially prioritized ruling out metastatic disease. Fine-needle aspiration (FNA) of an inframammary lymph node demonstrated numerous mesothelial cells. Such a finding frequently complicates the diagnostic process because mesothelial cells appearing in nodal sites usually suggest metastasis or advanced malignancy.

Distinguishing Benign Inclusions from Metastatic Disease

To confirm the nature of these cells, clinicians must consider mesothelial cell inclusions within their differential diagnosis. In this specific case, histopathologic evaluation and immunohistochemistry (IHC) played a pivotal role in the final diagnosis. Pathologists utilized markers such as calretinin, D2-40, and WT-1 to identify the mesothelial origin. Furthermore, fluorescence in situ hybridization (FISH) can detect chromosomal deletions, such as CDKN2A (p16), which are common in malignant mesothelioma. Here, ancillary studies successfully confirmed a benign reactive mesothelial proliferation rather than a lethal cancer.

Implications for Clinical Practice

Recognizing these inclusions is essential to avoid diagnostic errors and inappropriate aggressive treatments. Moreover, clinicopathologic correlation remains the gold standard for management. Practitioners should consider the patient's history of serosal inflammation or effusions, as these factors may facilitate the migration of mesothelial cells into the lymphatic system. Therefore, the judicious use of ancillary studies ensures that patients receive accurate diagnoses without unnecessary physical or psychological trauma.

FAQ

What are mesothelial cell inclusions?

They are benign mesothelial cells located within the sinuses of lymph nodes. They typically appear following episodes of serosal inflammation, surgery, or chronic effusions.

Why are they considered a diagnostic pitfall?

These cells can morphologically resemble metastatic mesothelioma or adenocarcinoma. This similarity may lead to misdiagnosis and unnecessary oncological treatments if not properly identified.

How can clinicians distinguish them from malignancy?

Clinicians use a combination of IHC markers and FISH. While IHC confirms the mesothelial lineage, the absence of cytologic atypia and the lack of specific genetic deletions (like p16) point toward a benign process.

Disclaimer: This content is for informational and educational purposes only. It does not constitute medical advice, diagnosis, or treatment. Always seek the advice of a qualified healthcare provider regarding any medical condition. Refer to the latest local and national guidelines for clinical practice.

References

1. Phom MH et al. Mesothelial Cell Inclusions in Abdominal and Thoracic Lymph Nodes in Association With Recurrent Chylothorax in a Young Man: A Diagnostic Pitfall. Int J Surg Pathol. 2026 Apr 15. doi: 10.1177/10668969261436002. PMID: 41984525.


2. Brooks JS, LiVolsi VA, Pietra GG. Mesothelial cell inclusions in mediastinal lymph nodes mimicking metastatic carcinoma. Am J Clin Pathol. 1990;93(6):741-748.


3. Kim YM, Kim KR, Ro JY. Mesothelial cell inclusions mimicking metastatic carcinoma in mediastinal lymph node: A case report. J Pathol Transl Med. 2004;38(1):46-49.