Nodular Histiocytic/Mesothelial Hyperplasia: A Lesion Potentially Mistaken for a Neoplasm in Transbronchial Biopsy

Abstract

This report describes two examples of nodular histiocytic/ mesothelial hyperplasia as seen in transbronchial biopsy that initially led to serious consideration of neuroendocrine neoplasm or meningioma. The biopsies showed nodular collections of cohesive polygonal or round cells with ovoid or deeply grooved nuclei and a moderate amount of finely granular cytoplasm. Nuclear pleomorphism was mild. Immunohistochemical studies showed few cells staining for cytokeratin and the mesothelial marker HBME-1, whereas most cells were decorated by the histiocytic marker PG-M1 (CD68). This lesion appears to be identical to nodular mesothelial hyperplasia as described in hernia sacs and mesothelial/monocytic incidental cardiac excrescences, and we propose modifying the designation to "nodular histiocytic/mesothelial hyperplasia" to take into account the marked predominance of histiocytes over mesothelial cells. The clues to recognition of the true nature of the lesion are clinicopathologic correlation and identification of strips of low cuboidal (mesothelial) cells in the vicinity, and the diagnosis can be further confirmed by immunohistochemical staining. Nodular histiocytic/mesothelial hyperplasia probably results from irritation to the mesothelial lining by various causes leading to focal aggregation of histiocytes within retraction pockets or crevices of the serosal cavity.

Nodular Histiocytic/Mesothelial Hyperplasia as Consequence of Chronic Mesothelium Irritation by Subphrenic Abscess

“…The first two cases of NHMH were reported by Chan [2]. These lesions looked similar to nodular mesothelial hyperplasia described in hernia sacs and in mesothelial incidental cardiac excrescences, but "as only few cells were positive for cytokeratin and the mesothelial marker HBME-1, whereas most cells were characterized by the histiocytic marker PG-M1 (CD68)," the authors coined the term 'nodular histiocytic/mesothelial hyperplasia' to take into account the marked predominance of histiocytes over mesothelial cells.…”

“…These lesions looked similar to nodular mesothelial hyperplasia described in hernia sacs and in mesothelial incidental cardiac excrescences, but "as only few cells were positive for cytokeratin and the mesothelial marker HBME-1, whereas most cells were characterized by the histiocytic marker PG-M1 (CD68)," the authors coined the term 'nodular histiocytic/mesothelial hyperplasia' to take into account the marked predominance of histiocytes over mesothelial cells. [2] NHMH represents an undeniable potential pitfall for pathologists; immunohistochemistry is essential for highlighting the double p opulation of histiocytes and reactive mesothelial cells.…”

“…[2] Recently Rossi et al observed that NHMH frequently occurs in pleura-damaging processes, such as pneumothorax. [5] We agree with the hypotesis that NHMH is a reactive proliferation of histiocytes and mesothelium secondary to chronic pleural irritation.…”

“…Few pulmonary cases have been reported in literature [2][3][4][5][6]. Sometimes it has been reported in the pericardium [7,8] or presenting as an inguinal mass [9].…”

Lymphoproliferative Conditions of the Serosa

“…Some are associated with metastatic carcinoma; thus, careful evaluation is essential. 12,13 Immunohistochemistry confirms the histiocytic (CD68 + ) and mesothelial (AE1/3+, calretinin+) cell component. Epithelial markers, such as carcinoembryonic antigen and Ber-EP4, should yield negative results.…”