Colombo P, Dani G, Saracini B, Castoro C, Spaggiari P. Abdominal nodular histiocytic/mesothelial hyperplasia - intraoperative pitfalls, differential diagnosis, literature review: A case report. World J Gastroenterol 2026; 32(25): 116783 [DOI: 10.3748/wjg.116783]
Corresponding Author of This Article
Piergiuseppe Colombo, Associate Professor, Department of Biomedical Science, Humanitas University, Via Rita Levi Montalcini, 4, Pieve Emanuele, Milan, Italy. piergiuseppe.colombo@hunimed.eu
Research Domain of This Article
Pathology
Article-Type of This Article
case-report
Open-Access Policy of This Article
This article is an open-access article which was selected by an in-house editor and fully peer-reviewed by external reviewers. It is distributed in accordance with the Creative Commons Attribution Non Commercial (CC BY-NC 4.0) license, which permits others to distribute, remix, adapt, build upon this work non-commercially, and license their derivative works on different terms, provided the original work is properly cited and the use is non-commercial. See: http://creativecommons.org/licenses/by-nc/4.0/
Carlo Castoro, Department of Upper Gastrointestinal Surgery, IRCCS Humanitas Research Hospital, Rozzano, Milan, Italy
Author contributions: Colombo P was involved in the conceptualization, revising histological specimen, interpretation of immunohistochemical results, writing and revision of the final manuscript; Dani G and Saracini B were involved in literature retrieval, writing the manuscript, and immunohistochemical results interpretation; Castoro C was involved in management of patient, providing clinical data and follow up; Spaggiari P selected histological slides for immunohistochemistry, and critically revised the final manuscript; and all authors have read and approved the final manuscript.
Informed consent statement: Informed written consent was obtained from the patient for publication of this report and any accompanying images.
Conflict-of-interest statement: All the authors report no relevant conflicts of interest for this article.
CARE Checklist (2016) statement: The authors have read the CARE Checklist (2016), and the manuscript was prepared and revised according to the CARE Checklist (2016).
Corresponding author: Piergiuseppe Colombo, Associate Professor, Department of Biomedical Science, Humanitas University, Via Rita Levi Montalcini, 4, Pieve Emanuele, Milan, Italy. piergiuseppe.colombo@hunimed.eu
Received: November 21, 2025 Revised: January 9, 2026 Accepted: March 26, 2026 Published online: July 7, 2026 Processing time: 222 Days and 2.5 Hours
Abstract
BACKGROUND
Nodular histiocytic/mesothelial hyperplasia (NHMH) is a rare, benign lesion characterized by a proliferation of histiocytes and mesothelial cells displaying a biphasic architectural pattern. First described by Rosai in the 70s, it may closely mimic malignant processes, particularly within the abdominal cavity. NHMH may be indistinguishable from carcinomatosis intraoperatively, potentially altering surgical management. Because nodules typically measure only a few millimeters, their macroscopic appearance and epithelioid features of cell proliferations histologically can closely resemble metastatic implants, particularly during intraoperative frozen section examination. Recognition of this entity is therefore essential to prevent diagnostic errors and unnecessary interventions.
CASE SUMMARY
We report the case of a 57-year-old woman in whom NHMH was incidentally identified during exploratory laparoscopy performed for staging metastatic gastric adenocarcinoma. Multiple small peritoneal nodules (2-5 mm) mimicked carcinomatosis intraoperatively. Frozen section examination interpretation was challenging due to the presence of epithelioid cell clusters with stromal desmoplasia that, together with surface irregularity, suggested metastatic implants, creating a high risk of overcalling carcinoma. Final histopathology demonstrated the coexistence of metastatic gastric adenocarcinoma and NHMH. Immunohistochemistry revealed CD68 positivity in histiocytes, calretinin and WT-1 expression in mesothelial cells, thus confirming the diagnosis.
CONCLUSION
NHMH must be considered in the differential diagnosis of peritoneal nodules identified during staging surgery. Frozen section analysis alone is insufficient and correlation with permanent sections and immunohistochemistry is essential to avoid misdiagnosis and overtreatment during intraoperative decision-making.
Core Tip: Nodular histiocytic/mesothelial hyperplasia is a rare benign lesion that may mimic peritoneal dissemination of malignancy, especially during frozen-section examination. This case emphasizes the diagnostic pitfalls arising from its histologic resemblance to metastatic carcinoma and highlights how coexistence with true metastatic implants increases the risk of misinterpretation. Few reports describe concurrent metastatic carcinoma and nodular histiocytic/mesothelial hyperplasia, making intraoperative differentiation particularly challenging. Knowledge of its characteristic morphology and immunoprofile is crucial for surgeons and pathologists.
