Extranodal marginal zone lymphoma presenting as a paraspinal mass and pleural effusion

MALT-lymphomas are a subtype of non-Hodgkin lymphomas that typically present in the gastro-intestinal tract (50% of cases), the salivary glands and lung. Pleural involvement, however, is exceedingly rare with only a few cases described in the literature to date. Here we present a case of pleural MALT-lymphoma in a 71-year-old woman presenting with progressive dyspnea since 5-6 months without cough or sputum. The CT scan showed paravertebral bilateral pleural thickening (right > left), with associated right sided pleural effusion. Positron emission tomography (PET) scan revealed FDG-uptake limited to the thickened areas of the pleura. Pleural fluid analysis was consistent with a pleural exudate with marked predominance of lymphocytes on flow cytometry (93% lymphocytes) with negative aerobic, anaerobic and mycobacterial cultures. A thoracoscopic biopsy of the right pleural mass revealed massive invasion of the pleura by a mucosa-associated lymphoid tissue lymphoma. The final diagnosis was a stage IV MALT-lymphoma for which systemic therapy with rituximab-bendamustine was administered. Follow-up FDG-PET-CT scan after 4 chemotherapy cycles confirmed complete radiological remission. The case is particularly remarkable because there was no known pre-existing pleural inflammation, which is typically a hallmark of MALT lymphoma in extranodal sites. Immunohistochemical characterization of pleural fluid lymphocyte subtypes might have provided a clue to the diagnosis. In pleural exudates with lymphocytic predominance this diagnostic step should not be overlooked.