Clinical diagnosis
Case 168
【Progress】
He was scheduled to undergo pulmonary biopsy.
【Discussion】
There are two lymphatic pathways in the lung: superficial and deep (1). Superficial lymphatic pathways play a role of collecting lymph flow in peripheral pulmonary area and direct to hilum with assistance of fissure and pleura. Deep lymphatic pathways collect lymph in the central pulmonary area and direct to hilum via bronchus-vascular bundle. It is often encountered in daily radiological interpretation of chest CT that small nodules associated with emphysema are found in pulmonary area on chest CT in patients with heavily smoking. These nodules are usually not enlarged in the follow-up CT. The configuration of these nodules is oval, triangle, round, rectangular and dumbbell. These nodules exist adjacent to pleura or fissure. It is known that these small nodules whose sizes are less than 10 mm are intrapulmonary lymph-nodes (2-5).
In a normal human, pulmonary lymph-nodes exists at the fourth order branch or more proximal of bronchial tree and rarely at the more peripheral order branch (2-5). The histology structure of the normal lymph-node include germinal center (B cells and/or dendrites), paracortical area (T cell), medullary cords (macrophage and plasma cell). It is known that there is a mere aggregation of lymphocytes without the lymph-node structure at the level of terminal bronchioles or respiratory bronchioles called minute lymph-node (1). The minute lymph-nodes stay at the fissure or pleura. It can enlarge or increase in response to irritants of smoking, silicon or tar. Immune response makes lymphocytes and macrophage accumulate, inducing the formation of intra-pulmonary lymph-node.
Radiologic characteristic is the linear density connecting the nodule. The linear density is reported to be the dilated lymphatic channels (6). A normal lymph-node has one efferent vessel and several afferent vessels. It is considered that inorganic irritants cause the occlusion of lymphatic channels leading to enlargement of non-occlusive channels and/or fibrosis due to persistent exposure. In our case, there are the minute linear density connecting to the nodule, looking like an intra-pulmonary lymph-node.
Bronchus associated lymphoid tissue (BALT) has no afferent vessels but efferent vessels different from normal lymph nodes. BALT is formed by organic infection and composes of M cell, dendrites, T cell, B cell, plasma cell and germ center which produces Ig G, Ig A and Ig M (1). Arising from BALT, various malignant and benign lymphoid diseases appear. Follicular bronchiolitis, lymphoid interstitial pneumonia, nodular lymphoid hyperplasia (pseudo-lymphoma), primary pulmonary lymphoma (MALT lymphoma) are listed (1, 7). Follicular bronchiolitis indicates the hyperplasia of BALT which occurs surrounding bronchus-vascular bundle. Chest CT shows centrilobular nodules or small ground-glass opacities sometimes with a tree-in-bud sign which appears in rheumatic arthritis or other auto-immune disease. Lymphoid interstitial pneumonia (LIP) indicates not only BALT hyperplasia but also lymphocytes infiltration to the alveolar septum. Further, infiltration to bronchioles causes occlusive lumen, inducing check-valve mechanism to form a bronchus-vascular cyst. LIP is also associated with autoimmune diseases. Nodular lymphoid hyperplasia appears a mass-like lesion with air bronchogram, often at subpleural in location (can be at peri-bronchial) without involvement to the adjacent pulmonary parenchyma. Primary pulmonary lymphoma can be MALT lymphoma (mucosa-associated lymphoid tissue, low grade marginal zone B-cell lymphoma) or Hodgkin lymphoma and other non-Hodgkin lymphoma. Of the pulmonary lymphoma, MALT lymphoma occurs in approximately 90% (1, 7). Chest CT shows solitary and multiple mass-like lesion with dilated air bronchogram associated with swollen hilar and mediastinal nodes.
【Summary】
We present a sixty four year-old male suffering from mild fever, appetite loss, disorder of taste sensation and sputum. Laboratory test revealed high values of LDH and Interleukin II, and chest CT showed 19mm sized mass in the left lower lobe with several fine linear density associated mediastinal swollen lymph nodes, indicative of the suspicious pulmonary malignant lymphoma. It is borne in mind that as lymphoid tissue lesions, intrapulmonary lymph node, follicular bronchiolitis, lymphoid interstitial pneumonitis, nodular lymphoid hyperplasia and malignant lymphoma are present. The last four diseases arise from BALT. The configuration of intrapulmonary lymph node is oval, triangle, round, rectangular and dumbbell. The large intrapulmonary lymph node owns linear density corresponded to dilated lymphatic channel due to occlusive mechanism by non-organic irritants. The configuration of follicular bronchiolitis is centrilobular nodules or small ground-glass opacities sometimes with a tree-in-bud sign. Lymphoid interstitial pneumonia (LIP) indicates not only BALT hyperplasia but also lymphocytes infiltration to the alveolar septum. Further, infiltration to bronchioles causes occlusive lumen, inducing check-valve mechanism to form a bronchus-vascular cyst. Nodular lymphoid hyperplasia and primary pulmonary lymphoma appear a mass-like lesion with air bronchogram.
【References】
1.Sirajuddin A、et al. Primary Pulmonary Lymphoid Lesions: Radiologic and Pathologic Findings. Radiographics. 2016 ;36:53-70.
2.MacMahon et al. Guidelines for Management of Incidental Pulmonary Nodules Detected on CT Images: From the Fleischner Society 2017. Radiology (2017) DOI10.1148/radiol.2017161659.
3.Shaham D, Vazquez M, Bogot NR et-al. CT features of intrapulmonary lymph nodes confirmed by cytology. Clin Imaging. 2010;34 (3): 185-90. doi:10.1016/j.clinimag.2009.05.005 - Pubmed citation
4.Ahn MI, et al. Perifissural nodules seen at CT screening for lung cancer. Radiology. 2010;254 (3): 949-56.
5.Miyake H, et al. Intrapulmonary lymph nodes: CT and pathological features. Clin Radiol. 1999 Oct;54(10):640-3.
6.Hyodo T, et al. Intrapulmonary lymph nodes: thin-section CT findings, pathological findings, and CT differential diagnosis from pulmonary metastatic nodules. Acta Med Okayama. 2004 Oct;58(5):235-40.
7.Hare SS, et al. The radiological spectrum of pulmonary lymphoproliferative disease. Br J Radiol. 2012 Jul; 85(1015): 848–864.
2019.11.6