First published online April 26, 2006
British Journal of Radiology (2006) 79, 999-1000
© 2006 British Institute of Radiology
doi: 10.1259/bjr/82484604
CT of thoracic lymph nodes. Part II: diseases and pitfalls
T Suwatanapongched, MD1 and
D S Gierada, MD2
1 Department of Radiology, Ramathibodi Hospital, Faculty of Medicine, Mahidol University, 270 Rama VI Road, Rajathevi, Bangkok 10400, Thailand, 2 Mallinckrodt Institute of Radiology, Washington University School of Medicine, 510 South Kingshighway Blvd., Campus Box 8131, Saint Louis, Missouri 63110, USA
Correspondence: D S Gierada, 510 S. Kingshighway Blvd., St. Louis, MO 63105, USA. E-mail: gieradad{at}wustl.edu
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Abstract
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CT is the primary non-invasive technique for the diagnostic evaluation of thoracic lymph nodes. The CT patterns and anatomic location of thoracic lymph node involvement can provide important clues in the diagnosis of many diseases. Part I of the pictorial review illustrates the anatomic location and drainage of thoracic lymph nodes in the chest wall, mediastinum, and lungs through examples of pathologic involvement. Part II of the pictorial review focuses on CT patterns of lymph node involvement in various pulmonary and extrapulmonary diseases, differential diagnoses based on CT findings, and pitfalls.
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Introduction
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Part II of this pictorial review focuses on diseases involving thoracic lymph nodes, differential diagnoses based on CT findings and findings that can mimic thoracic lymphadenopathy.
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Lung cancer
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For staging and reporting, lymph node stations are classified as defined by the American Joint Committee on Cancer and the Union Internationale Contre le Cancer (see Figure 1
in Part I) [1]. With size greater than 10 mm, the conventional criterion, the sensitivity (49–66%) and specificity (77–86%) of CT for lymph node metastases is limited [2]. Diagnostic accuracy may be improved using positron emission tomography (PET), or integrated PET-CT scanning [2]. Due to poor survival, surgery for lung cancer is generally contraindicated when mediastinal lymph nodes are involved. Some surgeons perform pre-operative sampling of mediastinal nodes in all patients, while others limit pre-operative sampling to those with enlarged nodes on CT or positive PET scans.
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Figure 1. Enhanced CT scan in a 37-year-old woman with lymphoma demonstrating enlarged pre-vascular (arrowheads) and left upper paratracheal (arrow) nodes, encasing the patent left carotid (C) and left subclavian (S) arteries. Lack of vessel invasion or constriction is a feature that may be helpful for distinguishing lymphoma from metastatic carcinoma. (From Glazer HS, Semenkovich JW, Gutierrez FR. Mediastinum. In: Lee JKT, Sagel SS, Stanley RJ, Heiken JP, editors. Computed body tomography with MRI correlation, 3rd edn. Philadelphia, PA: Lippincott-Raven Publishers, 1998:261–349 [13]. Reprinted with permission).
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Lymphoma
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Mediastinal lymph node involvement is more frequent than hilar, which is usually asymmetric and accompanied by mediastinal involvement [3]. Lymphoma tends to expand along or around rather than invade existing structures (Figure 1
). In Hodgkin's disease, upwards of 85% of patients have intrathoracic involvement on CT, compared with approximately 50% with non-Hodgkin's lymphoma [3, 4]. Hodgkin's disease tends to spread contiguously between lymph node groups, while non-Hodgkin's lymphoma more frequently involves atypical lymph node sites, such as posterior mediastinal and anterior diaphragmatic nodes (Figures 5 and 6 in Part I) [3, 4].
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Figure 5. Enhanced CT scan in a 43-year-old man with AIDS and Mycobacterium Avium-Complex infection revealing slightly low attenuation subcarinal (black arrowheads) and right hilar (white arrow) lymphadenopathy. There was no visible lung disease.
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Figure 6. (a, b) Enhanced CT scans in a 64-year-old woman with hyaline-vascular type of Castleman's disease demonstrating (a) enhancing para-aortic (arrows), (b) subaortic (arrowhead), (a,b) right paratracheal (curved arrow), and (b) left hilar (open arrow) nodes, separated from subaortic nodes by the first branch of the left pulmonary artery (wavy arrow). The hyaline-vascular type is most common, and usually presents as an asymptomatic, solitary lymph node mass in the middle or posterior mediastinum or hilum. The less common plasma-cell type is usually associated with systemic symptoms and disseminated disease.
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Metastases
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In addition to lung cancer, malignancies that may metastasise to thoracic lymph nodes include breast (Figure 4 in Part I), melanoma, head and neck, genitourinary (Figures 7 and 9 in Part I), and gastrointestinal carcinomas including oesophageal carcinoma (Figure 8 in Part I) and melanoma [5]. Lymph node involvement is usually asymmetric [5].
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Figure 4. Enhanced CT scan with lung-window setting in a 48-year-old woman with haemoptysis showing calcified left hilar node (arrow) eroded into the left main bronchus, consistent with broncholithiasis. Multiple calcified subcarinal and left hilar nodes (arrowheads) are seen, characteristic of prior granulomatous infection.
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Figure 7. A 64-year-old man with idiopathic pulmonary fibrosis (a) Enhanced CT scan shows mild para-aortic (arrow), subaortic (arrowheads) and right hilar (open arrow) lymphadenopathy. (b) Lung-window setting at the corresponding level shows peripheral, subpleural reticular opacities, characteristic of idiopathic pulmonary fibrosis. (From Sagel SS, Slone RM. Lung. In Lee JKT, Sagel SS, Stanley RJ, Heiken JP, editors. Computed body tomography with MRI correlation, 3rd edn. Philadelphia, PA: Lippincott-Raven Publishers, 1998:351–454 [15]. Reprinted with permission).
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Figure 9. Non-enhanced CT scan in a 41-year-old man with amyloidosis demonstrating calcified bilateral hilar, subcarinal, subaortic, and para-aortic nodes. Although an unusual cause of mediastinal lymphadenopathy, 75% of patients with thoracic amyloidosis have mediastinal lymph node enlargement, which may contain punctate calcification (as in this case), often associated with pulmonary parenchymal disease or pleural effusion. A = ascending aorta, D = descending aorta, S = superior vena cava (From Glazer HS, Molina PL, Siegel MJ, Sagel SS. High-attenuation mediastinal masses on unenhanced CT. AJR Am J Roentgenol 1991;156:45–50 [16]. Reprinted with permission).
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Figure 8. Enhanced CT scan in a 38-year-old man with silicosis showing enlarged right and left lower paratracheal (arrows), subaortic (open arrows), and para-aortic (thin arrow) nodes with eggshell calcification. Note calcified bilateral intrapulmonary nodes (arrowheads). A = ascending aorta, D = descending aorta, V = superior vena cava.
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Sarcoidosis
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In sarcoidosis (Figure 2), CT commonly reveals involvement of the lower paratracheal, aortopulmonary window, subcarinal, and bilateral hilar and interlobar nodal stations, slightly more frequently on the right [6]. Unilateral hilar disease, mediastinal lymphadenopathy without hilar disease and posterior mediastinal adenopathy are rarely seen with sarcoidosis, and are more suggestive of lymphoma, metastatic cancer, or granulomatous infection. Lymph node calcification (occasionally eggshell pattern) can be seen in up to 25% of cases, usually in long-standing disease [6].
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Figure 2. A 37-year-old woman with sarcoidosis. (a) Enhanced CT scan at level of aortic arch reveals enlarged para-aortic nodes (straight arrows) lying anterior and lateral to the aortic arch at the levels below the superior margin of the aortic arch (A); enlarged right lower paratracheal nodes (open arrows); and enlarged retrotracheal node (wavy arrow). Note mild contrast enhancement of these enlarged lymph nodes. V = left brachiocephalic vein, Oe = oesophagus. (b) Enhanced CT scan at the subcarinal level reveals enlarged bilateral interlobar nodes (open arrows) and subcarinal nodes (closed arrow). As with lymphoma, obstruction of mediastinal or hilar vessels or bronchi is rare, even with marked lymph node enlargement. A = ascending aorta, D = descending aorta.
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Infectious granulomatous disease
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Primary tuberculosis and histoplasmosis (Figure 3) may produce low attenuation lymphadenopathy, sometimes with rim enhancement, which suggests active disease [7]. Lymph node calcification resulting from these infections may be seen on chest CT studies performed for other indications. CT is useful in diagnosing complications from granulomatous infections, such as broncholithiasis (Figure 4), middle lobe syndrome and fibrosing mediastinitis. Rare infections associated with hilar or mediastinal lymphadenopathy include tularaemia, plague and anthrax, the latter of which has been found to have high attenuation adenopathy, possibly due to haemorrhage [8].
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Figure 3. Enhanced CT scan in a 58-year-old man with histoplasmosis revealing enlarged subaortic (arrow) and left lower paratracheal (arrowhead) nodes, secondary to left upper lobe histoplasmosis pneumonia (open arrows).
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Thoracic lymphadenopathy in AIDS
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Mediastinal lymph node enlargement (short axis > 10 mm) is seen in approximately 35–40% of HIV-infected patients and raises concern for infection or malignancy [9]. Tuberculous and non-tuberculous mycobacterial disease and bacterial pneumonia are the primary infectious causes, while lymphoma and Kaposi's sarcoma are the major neoplastic causes [9]. Lymphadenopathy without parenchymal lung disease may occur with tuberculosis, Mycobacterium Avium-Complex (Figure 5) and cryptococcal infection [10]. Lymphadenopathy is not a typical feature of Pneumocystis carinii infection, but widespread lymph node calcification with a characteristic cloud-like or foamy appearance has been described [11].
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Castleman's disease
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Castleman's disease (Figure 6) is a type of lymph node hyperplasia of unknown aetiology with female preponderance. Because the lesions are highly vascular, contrast enhancement is almost invariable. Calcification may be seen [12].
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Chronic infiltrative lung disease
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Presumably related to chronic inflammation, mild mediastinal and hilar lymphadenopathy (short axis 
1.0 cm, usually < 1.5 cm) may be seen in idiopathic pulmonary fibrosis (Figure 7), collagen vascular diseases such as rheumatoid arthritis and scleroderma, extrinsic allergic alveolitis, cryptogenic organizing pneumonia, and some inhalational lung diseases such as silicosis and asbestosis [13, 14]. Lymph nodes in patients with silicosis are frequently calcified, often in an eggshell pattern (Figure 8).
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Differential diagnosis of CT findings
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Calcified lymph nodes
In addition to old granulomatous disease (Figure 4), sarcoidosis, silicosis (Figure 8), and Pneumocystis carinii infection, lymph node calcification may be seen with certain metastases, such as ovarian (Figures 7 and 9 in Part I) or colonic adenocarcinoma, osteosarcoma, papillary thyroid carcinoma and bronchogenic carcinoma [13]. Amyloidosis (Figure 9) and healed lymphoma after radiation therapy are other causes. Uptake of lymphangiographic contrast in lymph nodes can mimic calcification.
Enhancing lymph nodes
In addition to Castleman's disease (Figure 6), marked lymph node enhancement may occur in hypervascular metastases from melanoma, renal cell carcinoma, carcinoid (Figure 11 in Part I), papillary thyroid cancer and Kaposi's sarcoma. Mild enhancement may be seen in tuberculosis, fungal disease, lymphoma, metastatic lung cancer and sarcoidosis (Figure 2) [13].
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Figure 11. Arterial phase CT scan(a) in a 50-year-old man with liver cirrhosis demonstrating soft tissue density (arrows, a and b) surrounding the oesophagus (Oe), seen to represent enhancing tubular structures during the portal venous phase (b), characteristic of oesophageal varices. A = descending aorta, V = inferior vena cava, L = liver, S = stomach.
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Low-attenuation lymph nodes
Low attenuation lymphadenopathy, which may be a result of necrosis or cystic degeneration, can be seen in metastatic carcinoma from the lung, testis, ovary and lymphoma (Figure 5 in Part I), in infectious disease such as tuberculous or fungal infections and in Whipple's disease [13].
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Pitfalls
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Anomalous or aberrant mediastinal vessels, such as an aberrant right subclavian artery (Figure 10), anomalous left brachiocephalic vein, persistent left superior vena cava and azygos continuation of the inferior vena cava, and nodular diaphragmatic crura occasionally imitate mediastinal lymph node masses. Confusion is avoided by tracing such structures on contiguous scans, along with an awareness of such variations, when intravenous contrast is not administered. Para-oesophageal varices (Figure 11) and extramedullary haematopoiesis (Figure 12) can mimic posterior mediastinal adenopathy.
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Figure 10. Aberrant right subclavian artery in a 75 year-old woman with gastric cancer. (a) Non-enhanced CT scan at the level of the left brachiocephalic vein (V) shows a well-defined, soft tissue nodule (arrow) lying to the right of the oesophagus (*), mimicking an enlarged lymph node. Note relatively smaller brachiocephalic artery (a) than usual. T = trachea. (b) Non-enhanced CT scan at the lower level shows that the nodule is seen to represent an aberrant right subclavian artery (arrows) arising from the aortic arch (AA). It crosses the mediastinum from left to right behind the oesophagus (*) and trachea (T). S = superior vena cava.
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Figure 12. Enhanced CT scan in a 54-year-old woman with sickle cell disease showing bilateral paravertebral soft tissue masses (arrows), consistent with extramedullary haematopoiesis. (From Slone RM, Gierada DS. Pleura, chest wall, and diaphragm. In Lee JKT, Sagel SS, Stanley RJ, Heiken JP, editors. Computed body tomography with MRI correlation (3rd edn). Philadelphia, USA: Lippincott-Raven Publishers, 1998:351–454 [17]. Reprinted with permission).
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Characteristic low attenuation and lack of intravenous contrast enhancement help to distinguish fluid in the pericardial recesses (Figure 13) and mediastinal bronchogenic cysts from mediastinal lymph nodes. The cisterna chyli (Figure 14) may mimic low attenuation posterior diaphragmatic or retrocrural lymphadenopathy.
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Figure 13. (a, b) Non-enhanced and enhanced CT scans in a 52-year-old woman showing normal superior pericardial recesses seen as small, non-enhanced near-water density structures (arrows) posterior to the ascending aorta (AA) and in the groove between the ascending aorta and pulmonary artery (P). The typical location and CT appearance allow pericardial recesses to be distinguished from mediastinal lymphadenopathy. Note a normal right lower paratracheal node containing a fat hilum (arrowhead). DA = descending aorta.
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Figure 14. Enhanced CT scan in a 71-year-old man with aortic dissection showing slightly lobulated retrocrural structure of water attenuation (arrows), consistent with cisterna chyli.
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Lesions that may mimic high attenuation, enhancing lymphadenopathy include mediastinal paraganglioma, intrathoracic thyroid (Figure 15), ectopic parathyroid adenoma (Figure 16) or parathyroid hyperplasia, and haemangioma [13].
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Figure 15. (a–c) Enhanced CT scans in a 70-year-old man with intrathoracic goitre showing a large, inhomogeneously enhancing left paratracheal mass (arrowheads), displacing the trachea (T) to the right side. The mass is contiguous with the left lobe of the thyroid gland (th, c) on cephalad scan. Contiguity with the thyroid gland helps to distinguish intrathoracic goiter from lymphadenopathy.
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Figure 16. Enhanced CT scan in a 54-year-old woman with ectopic parathyroid adenoma demonstrating an intensely enhancing soft tissue mass (arrow) in the aortopulmonary window region. A = ascending aorta, D = descending aorta, P = pulmonary artery.
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Received for publication April 11, 2005.
Revision received June 23, 2005.
Accepted for publication July 11, 2005.
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Abstract
Introduction
