Pleural MALT lymphoma diagnosed on thoracoscopic resection under local anesthesia using an insulation-tipped diathermic knife

A 79-year-old man presented with back pain. Chest CT scan showed elevated nodular lesions in the right parietal pleurae with pleural effusion. There were no intrapulmonary or mediastinal abnormalities. Under local anesthesia, right thoracoscopy and subsequent thoracoscopic pleural resection were performed using an insulation-tipped diathermic knife (IT-knife). The resected pleura, 2.2 cm in diameter, had a rough granular surface. Lymphoid cells histologically infiltrated diffusely into the pleura. They were composed of centrocyte-like and monocytoid cells. On immunohistochemistry they were found to be positive for Bcl2, CD20, CD45RB and CD79a, but negative for CD3, CD5, CD10 and cyclin D1. EBV-encoded small RNA-1 (EBER-1) in situ hybridization was negative. A diagnosis of extranodal marginal zone B-cell lymphoma of mucosa-associated lymphoid tissue (MALT lymphoma) arising in the pleura was therefore made. To the authors' knowledge this is the first case in which IT-knife was used for diagnosis of a pleural lesion. This large, single-piece, only slightly crushed pleural specimen, enabled study of histopathological findings (listed here) that could not have been obtained on conventional biopsy: (i) lack of apparent evidence of plasmacytic differentiation; (ii) no recognition of lymphoid follicles; (iii) mesothelial cells not infiltrated by lymphoma cell clusters; (iv) thin layer of hyperplastic mesothelial cells continuously covering the surface; and (v) no proliferation of fibroblast-like submesothelial cells.