Nodular histiocytic/mesothelial hyperplasia, a benign entity posing diagnostic challenge

Nodular histiocytic/mesothelial hyperplasia (NHMH) is a benign entity that can simulate malignancies histologically. NHMH was initially described in 13 hernia sacs in 1975. Since then, several cases and case series of NHMH have been reported in the literature with variable nomenclatures. It is always an incidental finding seen in a wide range of patient populations with no predilection for gender, age or race. It is most commonly found on mesothelium-lined surfaces such as peritoneum but can also be seen at other sites. It is hypothesized that NHMH occurs due to irritation of mesothelial surfaces and interaction of adhesion molecules. The histologic mimicry by NHMH of malignant processes can pose a diagnostic challenge. This review aims to highlight clinical and pathological aspects of NHMH and to cover common differential diagnoses with special attention to those pertaining to gastrointestinal tract pathology.