Nodular Histiocytic/Mesothelial Hyperplasia Mimicking Mesenteric Metastasis

Abstract

Nodular histiocytic/mesothelial hyperplasia (NHMH) is a rare histologic entity, characterized by localized benign reactive proliferation of histiocytes and mesothelial cells. The presence of this rare entity poses a challenge in differential diagnosis, both in radiological findings and pathological interpretations under certain circumstances, and consequently has been misdiagnosed as malignancy. Here, we report a case of mesenteric NHMH in a patient with colonic mucinous adenocarcinoma. Histology shows numerous large calretinin (+) mesothelial cells mixed with CD68 (+) histiocytes by immunohistochemistry. In contrast to almost all previously reported cases with typical features of histiocytic predominance, the current case of NHMH mainly consists of mesothelial cells with intermixed histiocytes. The findings expand the histologic spectrum of NHMH and contribute to awareness of this entity in the differential diagnosis.

Cytology of Benign Peritoneal Fluids and Pelvic Washing Specimens: Diagnostic Cytomorphologic Features and Pitfalls

“…Inflammatory changes may lead to a profound proliferation of epithelioid cells in pelvic washing specimens, which may create concern based on their arrangement and cytologic atypia. One particular entity, nodular histiocytic/mesothelial hyperplasia, refers to a cellular proliferation composed predominantly of histiocytes with admixed (perhaps entrapped) mesothelial cells [10,11]. Though relatively rare, this finding is seen most commonly on peritoneal surfaces and is believed to represent a reactive process following mechanical irritation, trauma, or nonspecific inflammation.…”