1504 AJR:193, December 2009 ing, typically a sign of pulmonary fibrosis, is not a feature of lymphatic disorders. The embryology of the lymphatic system is poorly understood. According to the angio- blast theory, pulmonary lymphatics develop at the hilum as buds from the pulmonary veins and then ramify out into the parenchyma un- til their connections with the veins are lost. Under this theory, developmental anomalies such as lymphangiectasis might result from uncontrolled proliferation at the initial stage. According to the local origin theory, lymphat- ics develop not from veins but from outside in as peripheral endothelium-lined spaces co- alesce into lymphatic channels. This theory explains how the abnormal lymphatic chan- nels in lymphangiomatosis and lymphangi- ectasis are isolated from the normal parts of the lymphatic system [2]. Ultimately, neither theory adequately explains all the features of pulmonary lymphatic diseases. Lymphangioma A congenital, benign lesion that results from focal, excessive proliferation of lym- phatics, lymphangioma can occur in many organs [3, 4]. It represents an isolated cluster of abnormal lymphatics that swells as lymph accumulates within it [4]. The most common location is the neck (where lymphangioma is referred to as “cystic hygroma”); in the tho- rax, it is usually mediastinal, constituting about 4.5% of all mediastinal masses [4, 5]. Rarely, lymphangioma presents as a solitary intrapulmonary lesion [3]. Other rare loca- tions are the pulmonary hila and the pericar- dium [6]. Overall, lymphangioma is more Imaging of Thoracic Lymphatic Diseases Siva P. Raman 1 Sudhakar N. J. Pipavath 1 Ganesh Raghu 2 Rodney A. Schmidt 3 J. David Godwin 1 Raman SP, Pipavath SNJ, Raghu G, Schmidt RA, Godwin JD 1 Department of Radiology, University of Washington Medical Center, Box 357115, 1959 NE Pacific St., Seattle, WA 98195. Address correspondence to S. N. J. Pipavath (snjp@u.washington.edu). 2 Department of Medicine, Division of Pulmonary and Critical Care Medicine, University of Washington Medical Center, Seattle, WA. 3 Department of Pathology, University of Washington Medical Center, Seattle, WA. Cardiopulmonary฀Imaging฀•฀Review AJR 2009; 193:1504–1513 0361–803X/09/1936–1504 © American Roentgen Ray Society D iseases of the thoracic lymphatic system have a variety of radio- graphic manifestations reflecting their pathophysiology and patho- logic anatomy. We will review the radiology of lymphangiomas, lymphangiohemangio- mas, pulmonary lymphangiomatosis, lym- phangiectasis, lymphangioleiomyomatosis, lymphatic dysplasia, and traumatic lymphat- ic injury. In addition, diseases with a lym- phatic distribution will also be discussed, including lymphangitic carcinomatosis, sar- coidosis, pulmonary lymphoma, and Kaposi sarcoma (KS). Anatomy and Embryology The thoracic lymphatic system contains two distinct lymphatic drainage portals. The first is superficial, draining the lung surface and the subpleural portion of the lung. The second drains the remainder of the lung pa- renchyma via channels along bronchi and vessels and in interlobular septa. Both of these systems converge at the pulmonary hi- lum before draining into either the thoracic duct or brachiocephalic veins [1]. The anatomy of the secondary pulmonary lobule helps in understanding manifestations of lymphatic disease. The lobule is the small- est unit of lung marginated by connective tis- sue and is usually polygonal, about 1–2 cm on a side. The margins are the interlobular sep- ta, containing pulmonary veins and lymphat- ics. Thus, lymphatic abnormalities can result in interlobular septal thickening. Lymphatics do not extend into the alveolar walls, mean- ing that fine intralobular interstitial thicken- Keywords: Kaposi sarcoma, lymphangiectasis, lymphangiohemangioma, lymphangioleiomyomatosis, lymphangioma, lymphatic dysplasia, pulmonary lymphangiomatosis DOI:10.2214/AJR.09.2532 Received February 4, 2009; accepted after revision May 31, 2009. OBJECTIVE. This review will focus on radiographic description of lymphangiomas, lymphangiohemangiomas, pulmonary lymphangiomatosis, lymphangiectasis, lymphangio- leiomyomatosis, lymphatic dysplasia, and traumatic lymphatic injury. CONCLUSION. Diseases of the thoracic lymphatic system have a wide variety of unique radiographic manifestations, all of which can be explained by the underlying pathophysiology and relationship to the normal distribution of lymphatics in the chest. Raman et al. Imaging of Thoracic Lymphatic Diseases Cardiopulmonary Imaging Review Downloaded from www.ajronline.org by 52.73.204.196 on 05/18/22 from IP address 52.73.204.196. Copyright ARRS. For personal use only; all rights reserved