Mucicarminophilic histiocytosis (benign signet-ring cells) and hyperplastic mesothelial cells: Two mimics of metastatic carcinoma within a single lymph node

Archives of Pathology & Laboratory Medicine, Mar 1998 by Groisman, Gabriel M, Amar, Mary, Weiner, Paltiel, Zamir, Doron

* We describe a unique case of simultaneous signet-ring histiocytes containing polyvinylpyrrolidone (mucicarminophilic histiocytosis) and hyperplastic mesothelial cells within a single supraclavicular lymph node. Both types of cells expanded the nodal sinuses and were initially suspected of being metastatic carcinoma. Histologic features suggested the correct diagnoses, which were confirmed by histochemical and immunohistochemical staining. It is important for pathologists to be aware of these phenomena, so as to avoid a misdiagnosis of metastatic carcinoma.

(Arch Pathol Lab Med.1998;122:282-284)

Benign inclusions mimicking metastatic carcinoma within lymph nodes have been generally classified as epithelial, decidual, and melanocytic.1 Recently, benign mesothelial inclusions mimicking metastatic carcinoma have been added to this list. Benign mesothelial inclusions have been reported in mediastinal lymph nodes from three patients with pleural effusions1,2 and in abdominal lymph nodes from two patients with ovarian malignancy.3 In addition, metastatic signet-ring cell carcinoma may be closely mimicked when vacuolated histiocytes containing the mucicarmine-positive material polyvinylpyrrolidone (PVP) infiltrate the nodal sinuses.4

Herein, we present the unique case of a supraclavicular lymph node simultaneously harboring two rare mimickers of metastatic carcinoma, namely, hyperplastic mesothelial cells and mucicarminophilic histiocytes. To our knowledge, this is the first case in which hyperplastic mesothelial cells have been observed within a superficially located and frequently biopsied lymph node.

REPORT OF A CASE

A 41-year-old man, having emigrated 2 months earlier from Uzbekistan, was hospitalized because of fever, weakness, weight loss, and exertional dyspnea of 4 months' duration. A prior medical evaluation, performed in Uzbekistan, disclosed bilateral pleural effusions. As hypoalbuminemia was suspected to be the cause of the effusions, he was treated with plasma expanders. Later, a positive tuberculine test led to treatment with isoniazid, in spite of negative cultures for Mycobaterium tuberculosis. On physical examination the patient was tachypneic, and no breath sounds were heard up to the fifth intercostal space in both lungs. Laboratory tests, including blood cell count, electrolytes, plasma proteins, and liver and kidney function tests, were within normal limits. A tuberculin test was positive. Chest roentgenograms and computerized tomography revealed bilateral pleural effusions and mild pleural thickening. The pleural fluid was tapped and found to be exudative in nature, containing predominantly lymphocytes. Repeated cultures and cytologic examinations of the fluid and the sputum were negative. Nevertheless, the patient was considered to have tuberculosis and treated with isoniazid, rifampin, and ethambutol. The therapy improved the general physical condition of the patient, but did not eliminate the bilateral pleural effusions.

Two months after his admission. an enlarged left suvraclavicular lymph node was found and excised. An initial histologic diagnosis of suspected metastatic malignancy led to an extensive search for a primary tumor. However, upper and lower gastrointestinal endoscopies and computerized tomography of the neck, chest, and abdomen were negative. One month later, the patient was in generally good condition, although the pleural effusions still persisted. He underwent open bilateral thoracoscopies, which included pleural biopsies. Grossly, both pleural surfaces were mildly thickened and smooth. No tumors were seen. Histologically, there was mild mesothelial hyperplasia with underlying fibrosis. No granulomatous disease, signs of malignancy or histiocytic infiltration were present. One year after his first admission, the patient was alive and asymptomatic. The pleural effusions had not fully resolved.

PATHOLOGIC FINDINGS

Examination of the excised supraclavicular lymph node revealed the presence of three different processes. The first was represented by a granulomatous inflammation, the second by aggregates of signet-ring cells, and the third by groups of epithelial-like cells (Fig 1).

The granulomas were of nonnecrotizing type and were composed of epithelioid cells and scattered Langhans type giant cells. They caused marked distortion of the lymph node architecture. No pathogens were identified with special stains, including Ziehl-Neelsen, methenamine silver, Gram's, and periodic acid-Schiff.

The collections of signet-ring cells and round to cuboidal epithelial-like cells filled and distended the subcapsular sinus (Fig 2). The interstitial sinuses were less prominently involved. The signet-ring cells were initially suspected of representing metastatic carcinoma; however, their histologic and histochemical characteristics were consistent with the morphologic and tinctorial attributes of histiocytes storing PVP Histologically, these cells were characterized by a markedly distended and vacuolated cytoplasm displaying a glassy-blue or pink-gray appearance, and by an eccentrically located small nucleus lacking atypia. The cells were strongly positive for mucicarmine, Congo red, and methenamine silver, but negative for periodic acid-Schiff and Alcian blue. No birefringence was observed when the Congo red-stained slides were viewed under cross-polarized light. Immunohistochemistry demonstrated lack of reactivity for cytokeratin (AE1/AE3), epithelial membrane antigen, and carcinoembryonic antigen. Vimentin and CD68 (KP-1) showed weak focal positivity. All of these antibodies were products of Zymed Laboratories, South San Francisco, Calif.