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INTRODUCTION

Nomenclature and classification schemes of lymphoproliferative disorders have undergone changes over the past 20 years. Malignant lesions are now best classified according to the current World Health Organization (WHO) schemes.1,2 In the lung and pleura, primary lymphoproliferative disorders represent a wide and overlapping spectrum of conditions from reactive polymorphous and polyclonal processes to various entities of malignant lymphomas. The natural history of these diverse conditions is variable, and further heterogeneity is recognized within distinct disease entities. Primary pleuropulmonary lymphoproliferative diseases are rare, whereas lymphomas secondarily affecting the lungs occur in up to 20% of autopsy cases. Although most diagnoses are based on light microscopy, immunohistochemical and molecular investigations have assumed a vital role. A schematic classification of lymphoid disorders involving primarily the lung and pleura is shown in Table 119-1.

TABLE 119-1Classification of Lymphoid Disorders Affecting Only or Mainly Lung and Pleura

ANATOMY AND HISTOLOGY OF THE PULMONARY LYMPHOID SYSTEM

Pulmonary lymphatics originate in superficial and deep plexuses; the interalveolar septa and the alveolar ducts and sacs have no lymph vessels.3 The superficial plexus lies deep to the visceral pleura and in the fibrocollagenous interlobular septa, and its efferents pass around the margins of the lung and its fissures, eventually reaching the bronchopulmonary (hilar) nodes. The deep lymphatics originate at the bronchiolar level and follow the divisions of the bronchial tree and pulmonary vessels up to the lung hilum, ending in the same nodes as the superficial plexus. The lymphatics communicate at lobar, lobular, and pleural boundaries and, thus, serve each other as potential collaterals. These channels ultimately flow into the intrathoracic lymphatic duct, which then typically empties into the left subclavian vein.4,5 Lymphatics are not usually obvious in histologic sections of normal lung, but they are prominent and open in some of the disorders that manifest with specific lymphatic involvement, such as cardiogenic edema and lymphangitic carcinomatosis. In the latter, lymphatic channels distended with malignant cells are apparent within the visceral pleura, interlobular septa, and adventitia of arteries, veins, and bronchioles. ...

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