摘要：

Most primary pulmonary non-Hodgkin's lymphomas are now thought to arise from mucosa-associated lymphoid tissue (MALT), with most cases previously termed 'pseudolymphoma' also regarded as neoplastic. In the past, open lung biopsies and resections have been the commonest diagnostic procedures, but immunohistochemistry and PCR are enabling diagnosis on smaller samples. Microscopically, low grade tumours characteristically spread along bronchovascular bundles, with subsequent expansion and destruction of alveoli, leading to formation of single or multiple nodules that tend to spare the airways. High grade tumours are more diffuse and destructive, often with necrosis. Surgery has resulted in prolonged remission in low grade MALT lymphomas, but chemotherapy has also been shown to be effective. Most patients with high grade lymphoma require combination chemotherapy. Five-year survival is 84–94% for low grade tumours and 0–60% for high grade. The most common differential diagnoses are lymphoid interstitial pneumonia and follicular bronchiolitis, disorders which show both clinical and histopathological overlap to form a spectrum of reactive pulmonary lymphoid hyperplasia. The dominant histological feature in lymphoid interstitial pneumonia is an interstitial infiltrate of small lymphocytes, plasma cells and histiocytes, with germinal centres often identified. In follicular bronchiolitis, there is abundant peri-bronchiolar germinal centre formation, but most cases also show extension of a mixed lymphoid infiltrate into the interstitium. Reactive pulmonary lymphoid hyperplasia may be histologically indistinguishable from low grade lymphoma but can usually be differentiated via immunohistochemistry and PCR. Lymphoid interstitial pneumonia may also be histologically indistinguishable from extrinsic allergic alveolitis and non-specific interstitial pmeumonia, requiring close clinical/radiological association for diagnosis. Lymphomatoid granulomatosis remains a distinct angiocentric lymphoproliferative disorder containing an atypical lymphoid population, which is now thought to represent an Epstein-Barr virus (EBV) related T-cell rich B-cell lymphoproliferative disorder. Intravascular lymphomatosis and Castleman's disease and secondary lymphomatous disease may also present in the lung, and primary pleural lymphomas have also been described.

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