Nodular histiocytic/mesothelial hyperplasia: a process mediated by adhesion molecules?

Cytomorphology of nodular histiocytic/mesothelial hyperplasia

Nodular histiocytic/mesothelial hyperplasia (NHMH) is a pathologic entity that has not been well characterized in the cytopathology literature. This is unfortunate because if unrecognized, NHMH may be misdiagnosed when encountered in cytology specimens. The aim of this communication is to accordingly alert cytologists about NHMH by means of an illustrative case report.

Lesion of aggregated monocytes and mesothelial cells: mesothelial/monocytic incidental cardiac lesion

A 58-year-old woman with a history of childhood acute rheumatic fever and resultant mitral valve stenosis was admitted to our cardiovascular surgery clinic complaining of tachycardia, dyspnea, and chest pain. After clinical and radiological findings were evaluated, mitral valve replacement, tricuspid De Vega annuloplasty and plication, and resection of giant left atrium were performed. Atrial thrombus was removed from the top of the left atrial wall. Operation material considered as thrombus was sent to a pathology laboratory for histopathological examination. It was diagnosed with mesothelial/monocytic incidental cardiac lesion (cardiac MICE). Microscopic sections revealed that morphological features of the lesion were different from thrombus. The lesion was composed of a cluster of histiocytoid cells with abundant cytoplasm and oval shaped nuclei and epithelial-like cells resembling mesothelial cells within a fibrin network. Epithelial-like cells formed a papillary configuration in the focal areas. Mitotic figures were absent. Here we present a case which was incidentally found in a patient who underwent mitral valve replacement surgery, as a thrombotic lesion on the left atrium wall.

Nodular histiocytic aggregates in the greater omentum of patients with ovarian cancer

Nodular histiocytic aggregate (NHA) of the omentum is a rare benign proliferative process composed predominantly of histiocytes with scattered mesothelial cells. NHA is a differential diagnosis for neoplasms or metastatic tumors in cancer patients. To further clarify this clinical pitfall issue, the authors investigated surgical samples of the greater omentum from 96 patients with gastrointestinal malignancies and 53 patients with gynecologic neoplasms. Visible NHA of greater omentum was identified in 3 patients with ovarian neoplasms (borderline mucinous cystadenoma, low-grade papillary serous cystadenocarcinoma, and juvenile granulosa-cell tumor) but in none of the patients with gastrointestinal malignancies. Similar lesion was also identified on the cell blocks from peritoneal washings in 1 of the 3 patients. Grossly, the lesions formed small yellow-red nodules on the greater omentum, and the NHA lesion was also found diffusely on the surface of the appendix and fallopian tubes in 2 of the 3 patients. Histological study showed that typical NHA changes over an inflammatory background, which may indicate that NHA is a consequence of a chronic inflammatory process of omentum. The predominant infiltration of T lymphocytes in the NHA lesions indicates that the aggregation of histiocytes may be related to the activation of T-cell immunity. This report has first demonstrated visible NHA in the greater omentum of patients with ovarian malignancies, and awareness of this entity should be brought to clinicians to avoid misdiagnosis.

Nodular histiocytic/mesothelial hyperplasia: a potential pitfall

We present five cases of nodular histiocytic/mesothelial hyperplasia (two peritoneal, two pulmonary, and one pericardial) with identical microscopic features. All the lesions were biphasic and composed of cohesive monotonous epithelioid clusters of polygonal or oval cells with round or deeply grooved nuclei in association with darker cuboidal cells. Because of the increased cellularity and monotonous histologic pattern with some degree of cytologic atypia, neoplastic processes were seriously considered in the differential diagnoses. The majority of the cells marked as histiocytes by immunostain. A few scattered individual cells or small epithelial cell clusters were confirmed by calretinin stain to be mesothelial cells. The histologic patterns of the current lesions, irrespective of the location, were identical to nodular histiocytic/mesothelial hyperplasia. Histiocytic proliferations can be erroneously confused with primary mesothelial lesions or neoplasms such as granulosa cell tumor, eosinophilic granuloma, chronic myelogenous leukemia, and carcinoma. The purpose of this article is to describe the clinicopathologic features of nodular histiocytic/mesothelial hyperplasia and help familiarize pathologists with this lesion to prevent an erroneous diagnosis, particularly when it occurs in locations where mesothelial cells are not normally present.