Nodular histiocytic/mesothelial hyperplasia: a potential pitfall

Benign Mesothelial Cells in transbronchial biopsy specimens: A potential diagnostic pitfall for lung cancer

Bronchoscopy is a common diagnostic procedure used to identify lung cancer. Specimens acquired through transbronchial biopsy are pivotal in the diagnosis and molecular characterization of this disease. The occurrence of benign mesothelial cells during a transbronchial biopsy (TBB) is relatively rare. Furthermore, these lesions can sometimes be erroneously identified as malignant, potentially resulting in unwarranted or inappropriate treatment for patients with and without lung cancer. In this retrospective analysis, we examined 619 TBB cases at our institute from 2019 to 2021. Benign mesothelial cells were identified via immunohistochemical studies in eight (1.3%) of 619 cases. These cells were classified into three patterns based on their cellular morphology: monolayer, lace, and cobblestone. Recognizing this phenomenon during the procedure is crucial to accurately distinguish benign mesothelial cells from their cancerous counterparts.

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.

Reactive histiocytic proliferation in the pleural fluid mimicking metastatic signet ring adenocarcinoma

Reactive nodular and diffuse histiocytic proliferations of mesothelial and non-mesothelial lined sites have been sporadically reported in the literature. However, there is no cytologic literature describing this process. We report a case of reactive histiocytic proliferation mimicking a metastatic signet ring adenocarcinoma in pleural fluid from a 33-year-old white male. Ancillary studies such as immunohistochemistry should be used to elucidate the cell of origin and avoid diagnostic errors.

Nodular histiocytic/mesothelial hyperplasia as consequence of chronic mesothelium irritation by subphrenic abscess

PURPOSE

Pleural nodular histiocytic/mesothelial hyperplasia is a nodular histiocytic/mesothelial proliferation, often delimiting cystic cavities, due to irritation by a pulmonary noxa. Case report results: The patient had right pleural parietal and diaphragmatic thickness, with pleural effusion, without lung alterations. He previously underwent left hemicolectomy and liver resection, due to a diverticulitis and a liver histiocytes-rich abscess. Video-assisted thoracoscopy biopsy showed a double population of reactive mesothelial cells and histiocytes.

CONCLUSION

Nodular histiocytic/mesothelial hyperplasia represents a potential pitfall for pathologists. Immunohistochemistry is crucial for the differential diagnosis with some malignancies. We suggest that in our patient, a chronic mesothelium inflammation happened by transdiaphragmatic involvement as a consequence of the liver abscess. Some pathogenetic mechanisms are hypothesized.

A unique case of diffuse histiocytic proliferations mimicking metastatic clear cell carcinoma in the hydrocele sac

Reactive histiocytic proliferations are extremely rare in paratesticular structures. Nodular histiocytic proliferations have been described in mesothelial-lined locations and only at few nonmesothelial sites. Diffuse histiocytic proliferations are described only in the pelvic peritoneum. We report the first case of diffuse histiocytic proliferation in the hydrocele sac of a 45-year-old man. Predominant histiocytes showed clear cytoplasm and signet ring-like change. Mucicarmin stain did not demonstrate mucin in the cytoplasm. Immunohistochemistry (IHC) staining showed nonspecific staining of these cells with carcinoembryonic antigen and negative staining with epithelial membrane antigen, pan-Cytokeratin, calretinin, cytokeratin 7, 20 and prostate-specific antigen. Strong diffuse cytoplasmic positivity for CD68 defined the mononuclear phagocyte nature of these cells. Diffuse histiocytic proliferations can occur in the hydrocele sac. Histochemical and IHC stainings are critical for accurate diagnosis and to avoid unnecessary surgery.

Nodular histiocytic aggregates in the endometrium: a report of 7 cases

Nodular aggregates of nonfoamy histiocytes in the endometrium are uncommon. We describe herein the clinical and pathologic characteristics of 7 additional cases in endometrial biopsies or curettages. The patients ranged in age from 48 to 72 years, and the most common presenting symptom was abnormal uterine bleeding. Five of seven patients had undergone prior endometrial sampling (including 1 who had undergone 3 endometrial biopsies over the preceding 5 yr for follow-up of abnormal uterine bleeding). In 2 cases, an endometrial polyp was present in the same sample, and an additional 2 were found to have endometrial polyps on subsequent biopsies that were performed within 4 months of original samplings. The lesions, which ranged in size from 1 to 8 mm, were composed of monomorphic cells with abundant pink eosinophilic cytoplasm with a vaguely nodular arrangement. Two cases showed focally high mitotic activity with up to 4 mitoses per high-power field. Patient outcomes were unremarkable, which affirms the benign nature of the proliferation. Several features of this lesion, including mitotic activity, focal necrosis, and tight aggregation of cells, may raise the possibility of a neoplastic proliferation. This differential diagnosis can be readily resolved by awareness of the lesion and immunohistochemical analyses. Possible pathogenetic considerations are discussed, but these nodules represent, in our opinion, reaction to necrotic tissue in the endometrial cavity, possibly related to prior procedure.

Lymphoproliferative conditions of the serosa

CONTEXT

A diverse and complex variety of lymphoproliferative diseases may involve the serosa, with widely differing clinical outcomes encompassing a spectrum of benign and malignant conditions.

OBJECTIVE

To review lymphoproliferative disease involving the serosa and to provide a practical approach to the evaluation of lymphoid and plasma cell infiltrates in the serosa, together with a review of various tumors and tumorlike conditions that may mimic lymphoproliferative disease.

DATA SOURCES

Analysis of published literature.

CONCLUSIONS

All forms of hematologic malignancy may involve the various serosal sites, although this is usually observed as secondary involvement in persons with known lymph nodal, marrow-based, or extranodal disease. Primary pericardial, pleural, and peritoneal lymphomas are rare; many nonneoplastic conditions may mimic lymphoma and a variety of nonhematolymphoid tumors may simulate hematologic malignancies. An understanding of the role of ancillary tests, together with an appreciation of their limitations, will prevent misdiagnosis.

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.

A case of mesothelial/monocytic incidental cardiac excrescence and literature review

Mesothelial/monocytic incidental cardiac excrescence (MICE) is a rare entity which is an amalgam of mesothelial cells, histiocytes, and fibrin, often found occasionally during cardiac valve replacement. We report a case in a 25-year-old Chinese female with serous mitral stenosis and patent foramen ovale. Routine and immunohistochemical stains and ultrastructure examination revealed the vegetation was predominantly composed of histocytes with scattered mesothelial cells. In fact nodular histiocytic/mesothelial hyperplasia (NHMH) is a similar lesion to MICE. MICE and NHMH could be unified, and NHMH may be a better choice.