Answer: Low grade B-cell lymphoma

Histology: This patient has a low grade B-Cell Lymphoma consistent with Mucosa-Associated Lymphoid Tissue (MALT) Lymphoma. The characteristic features are a moderate to dense interstitial lymphoplasmacytic infiltrate with a distinct tendency to grow along interlobular septa (“lymphangitic” growth pattern). In some areas the infiltrate clearly widens the interstitium. A striking feature in this case is the presence of numerous interstitial well formed and poorly formed granulomas. Special stains were negative for AFB and fungi.

Discussion: The presence of these interstitial granulomas would ordinarily raise clinical suspicion for Extrinsic Allergic Alveolitis, or atypical mycobacterial infection, but in fact, granulomas are actually quite common in lymphoid proliferations of all types in the lung. Granulomas may be seen in association with LIP or with low grade pulmonary lymphomas. There was no evidence of Bronchiolitis Obliterans Organizing Pneumonia in the biopsy and while Extrinsic Allergic Alveolitis cannot be entirely excluded, a unifying hypothesis would accept the granulomas as related to lymphoid proliferation. This patient had a Kappa-restricted B-cell lesion and the findings were confirmed by flow cytometry of the pulmonary biopsy specimen. A similar B-cell lesion had been found in the patient’s bone marrow approximately two years before the occurrence of this pulmonary lesion.