Abdominal nodular histiocytic/mesothelial hyperplasia - intraoperative pitfalls, differential diagnosis, literature review: A case report

Figure 1 Imaging findings. A: Computed tomography scan documented the presence of a multifocal thickening of the peritoneum, with confluent nodules visible in the pelvic cavity; B: Positron emission tomography-computed tomography scan showing uptake of [¹⁸F]-fluorodeoxyglucose in the left pericolic region and pelvic cavity, suspicious for peritoneal carcinomatosis.

Figure 2 Pathological findings. A: Small nodules of atypical epithelioid cells on the surface of peritoneal serosa noted during frozen section examination (original magnification 200 ×); B: On definitive histopathological analysis, although atypicality of cell proliferation and areas of isolated growth patterns are observed, there is an evident histological overlap between peritoneal carcinomatosis and nodular histiocytic/mesothelial hyperplasia (original magnification 200 ×).

Figure 3 Immunohistochemical findings. A: Immunohistochemical analyses showing cytokeratin AE1/AE3 positivity in both epithelial and mesothelial cell components [immunohistochemistry (IHC); original magnification 200 ×]; B: Intestinal differentiation marker CDX2 mildly expressed in sparse nuclei of neoplastic cells, indicating a gastric origin (IHC; original magnification 200 ×); C: Immunoexpression of calretinin in mesothelial cells (IHC; original magnification 200 ×); D: Note CD68 immunopositivity highlighting the histiocytic component of nodular histiocytic/mesothelial hyperplasia, while mesothelial cells are negative (IHC; original magnification 200 ×).