- Email: [email protected]
Imaging of the Mediastinum: Vascular Lesions as a Potential Pitfall
Imaging of the Mediastinum: Vascular Lesions as a Potential Pitfall Brett W. Carter, MD,* Patricia M. de Groot, MD,* Myrna C.B. Godoy, MD, PhD,* Edith M. Marom, MD,† and Carol C. Wu, MD*
Introduction
V
ascular lesions of the mediastinum comprise a myriad of disease processes, from abnormalities of the systemic and the pulmonary arteries and veins to benign and malignant primary vascular masses. Although the presence of these lesions may be suggested initially on chest radiography, vascular abnormalities of the mediastinum account for only 10% of all radiographically recognized mediastinal masses.1-3 Therefore, the identification and characterization of vascular lesions using advanced cross-sectional imaging techniques such as multidetector computed tomography (MDCT) and magnetic resonance imaging (MRI) are crucial to ensure appropriate patient management. The combination of clinical information such as sex, age, and symptoms at presentation and radiologic information such as location within the mediastinum and key imaging features usually establish the correct diagnosis. Therefore, it is important for the radiologist to be aware of the most common vascular abnormalities of the mediastinum that can result in abnormal findings on thoracic imaging examinations.
Classification of Vascular Lesions Vascular lesions of the mediastinum are typically classified based on the vascular tissue or organ from which they arise.3-5 Following this algorithm, vascular abnormalities may be classified as systemic arterial, systemic venous, pulmonary arterial, pulmonary venous, or lymphatic in nature. Other classification schemes characterize vascular abnormalities as posttraumatic, neoplastic, congenital, or acquired in etiology. *Department of Diagnostic Radiology, The University of Texas MD Anderson Cancer Center, Houston, TX. †Department of Diagnostic Imaging, The Chaim Sheba Medical Center, Tel Hashomer, Israel. Address reprint requests to Brett W. Carter, MD, Department of Diagnostic Radiology, The University of Texas MD Anderson Cancer Center, 1515 Holcombe Blvd, Unit 1478, Houston, TX 77030. E-mail: [email protected]
http://dx.doi.org/10.1053/j.ro.2015.01.015 0037-198X/& 2015 Elsevier Inc. All rights reserved.
For the purposes of this review, we have divided vascular lesions of the mediastinum into 2 groups: (1) abnormalities and normal variants of systemic and pulmonary arteries and veins and (2) benign and malignant vascular masses.
Imaging Techniques Although mediastinal abnormalities may initially be detected on chest radiography, contrast-enhanced MDCT and MRI are the imaging modalities of choice for the identification and characterization of these lesions as vascular in origin. The use of intravenous (IV) contrast material greatly improves the detection of vascular lesions, which may be otherwise difficult to distinguish from nonvascular soft tissue attenuation masses on noncontrast MDCT. Contrast-enhanced MDCT is best for demonstrating enhancement of vascular lesions and delineating connections with parent and branch vessels, which typically enhance to a similar degree. Abnormalities of the thoracic aorta and systemic arteries are optimally evaluated in studies timed for the evaluation of the aorta, whereas anomalies of the systemic veins are best characterized on routine contrastenhanced MDCT. Abnormalities of the pulmonary arteries are optimally evaluated on studies timed for evaluation of the pulmonary arteries, typically performed as a CT pulmonary angiogram. Use of multiple phases may be necessary to appropriately identify lesions of vascular origin (Fig. 1). MRI can be performed when contraindications to contrastenhanced MDCT are present, such as renal failure or severe allergy to iodinated contrast material. In the setting of renal insufficiency, noncontrast MR techniques can be used to characterize the abnormality and assess the adjacent vasculature. Angiography may be performed in certain situations, such as trauma, in which endovascular therapy may be necessary during the procedure.
Systemic Arteries Abnormalities or anatomical variants involving the systemic arteries represent a heterogeneous group of congenital and 241
B.W. Carter et al.
242
Figure 1 (A) A contrast-enhanced axial MDCT image timed for evaluation of the thoracic aorta demonstrates a lobular hypodense mass (arrow) in the anterior mediastinum anterior to the transverse thoracic aorta. (B) The routine contrastenhanced axial MDCT image shows contrast opacification of the anterior mediastinal mass (arrow). Multiplanar reformatted images (not shown) revealed a broad-based connection to the left innominate vein in this case of a venous varix. This case illustrates the importance of administering intravenous contrast material and obtaining images in multiple phases when evaluating mediastinal masses, as the vascular nature of lesions may be overlooked.
acquired lesions, most of which involve the thoracic aorta. Other vessels such as the innominate, subclavian, and coronary arteries and coronary artery bypass grafts may also be affected.
Thoracic Aorta: Right Aortic Arch Right aortic arch (RAA) is an uncommon anomaly that occurs in 0.1% of the population.6 RAA can be classified into 3 types according to the branching pattern of the arch vessels: (1) RAA with an aberrant left subclavian artery (ALSA), (2) RAA with mirror-image branching, and (3) RAA with isolation of the LSA. The most common type is RAA with ALSA and is typically asymptomatic, although dysphagia due to the retroesophageal course of the LSA has been reported. RAA with mirror-image branching is strongly associated with congenital heart disease and is thus usually diagnosed in neonates or children. On chest radiography, RAA usually manifests as a rounded masslike opacity in the right upper mediastinum, specifically the right paratracheal region (Fig. 2). Leftward deviation of the trachea and rightward deviation of the superior vena cava (SVC) may be present.4 Unless a double aortic arch is present, a normal left aortic arch cannot be visualized. A diverticulum of Kommerell can result in focal opacity in the expected position of the left arch. An ALSA may appear as retroesophageal opacity on the lateral radiograph. On contrast-enhanced MDCT and MRI, the RAA can be seen passing to the right of the trachea and all vessels arising from the anomalous vessel can be determined. Crosssectional imaging is also beneficial for identifying other anomalies that may be associated with RAA with mirror-
image branching such as tetralogy of Fallot and truncus arteriosus.7
Thoracic Aorta: Aneurysms and Pseudoaneurysms Thoracic aortic aneurysms, defined as permanent abnormal dilatation of the thoracic aorta, are the most common abnormalities to affect the thoracic aorta in adult patients.8 These aneurysms result from atherosclerosis, trauma, inflammation or infection, and cystic medial necrosis.3 The thoracic aorta below the level of the ligamentum arteriosus is the most commonly affected segment, followed by the transverse thoracic aorta and the ascending aorta. Chronic posttraumatic pseudoaneurysms usually affect the thoracic aorta at the isthmus. On chest radiography, 80%-90% of affected patients have abnormal findings, including mediastinal widening and enlargement of the affected portion of the aorta (Fig. 3). Contrast-enhanced MDCT accurately demonstrates the size and number of aneurysms and can identify any potential complications. MRI and contrast-enhanced MR angiography can alternatively be used and lack ionizing radiation.
Thoracic Aorta: Dissection Aortic dissection is a well-described disease process characterized by separation of the aortic intima and adventitia secondary to splitting of the media by circulating blood.9,10 The most common risk factor is hypertension, followed by cystic medial necrosis and diseases that can affect the aortic
Imaging of the mediastinum
243
Figure 2 (A) A PA chest radiograph of an asymptomatic 39-year-old man demonstrates a lobular opacity (arrow) in the right paratracheal region that results in a slight leftward deviation of the trachea. The absence of a normal left aortic arch should be noted. (B) The contrast-enhanced axial MDCT image shows that the opacity in the right paratracheal region on radiography represents a right aortic arch (white arrow). The aberrant left subclavian artery arising from a diverticulum of Kommerell (black arrow) should be noted.
wall, such as atherosclerosis and connective tissue diseases.11 Thoracic aortic dissection is typically classified into Stanford types A and B based on the affected portion of the thoracic aorta. Stanford type A involves the ascending aorta, with or without extension into the descending aorta, and represents 60%-70% of cases.10 Stanford type B involves the descending aorta distal to the LSA and represents 30%-40% of all cases.10 Type A dissections are treated surgically to prevent propagation into the aortic root, pericardium, or coronary arteries, whereas
type B dissections are treated medically unless complications such as end-organ ischemia are present.12 Thoracic aortic dissection can result in a variety of nonspecific findings on chest radiography that can mimic a mediastinal mass.3 For instance, widening of the mediastinum was seen in 61.1% of cases and abnormal cardiac contour was noted in 14.1% of cases in a study.11 Enlargement of the cardiac silhouette can be seen in the setting of pericardial effusion, complicating dissection. Contrast-enhanced MDCT, which may
Figure 3 (A) A PA chest radiograph of a 48-year-old man presenting with chest pain demonstrates an elongated and lobular opacity (arrows) along the inferior aspect of the left mediastinum. (B) A contrast-enhanced axial MDCT image shows that the opacity corresponds to aneurysmal dilatation of the descending thoracic aorta (arrow). The peripheral thrombus should be noted. Atherosclerosis is the most common etiology of thoracic aortic aneurysms, followed by infection and cystic medial necrosis. As this patient's aneurysm measured greater than 6.5 cm, an endovascular stent graft was placed because of the risk of rupture.
B.W. Carter et al.
244 be performed with or without Electrocardiography (ECG) gating, is the best method of identifying and characterizing aortic dissection and potential intrathoracic complications. MRI and contrast-enhanced MR angiography may be used in medically stable patients or individuals with chronic dissections.
Innominate and Subclavian Arteries Prominence or tortuosity of the innominate arteries can be seen in older patients and is associated with hypertension and atherosclerosis. In this setting, the affected artery can manifest as a superior mediastinal or apical lung mass,13 reflecting the prominent vessel or the displaced SVC.4 Aneurysmal dilatation affects approximately 8% of aberrant right subclavian arteries and can result in a masslike opacity in the upper right mediastinum (Fig. 4). On MDCT and MRI, the presence of the aberrant vessel as it arises as the last branch of the posterior margin of the arch and travels posterior to the esophagus can be seen.
Coronary Arteries Aneurysms of the coronary arteries, most of which are associated with atherosclerosis, infection, or Kawasaki disease, occur in 0.4%-0.5% of patients undergoing angiography.14 The right coronary artery is the most frequently affected coronary vessel. Although many affected patients are asymptomatic, these aneurysms can rupture and result in myocardial ischemia or infarction. Therefore, surgical resection is typically performed. On chest radiography, coronary artery aneurysms typically manifest as paracardiac masses and may be located on the right or left depending on which vessel is involved. Contrast-enhanced MDCT and ECG-gated cardiac CT angiography (CTA) optimally evaluate these aneurysms and demonstrate the vessel from which they originate.
Coronary Artery Bypass Grafts Aneurysms of coronary artery bypass grafts, usually involving the saphenous vein graft, are rare. These aneurysms, which may be true or false and can grow very large, may develop as early as 10 days following surgery.15 On chest radiography, bypass graft aneurysms manifest as paracardiac masses. Contrast-enhanced MDCT and ECG-gated cardiac CTA effectively demonstrate the size and location of these aneurysms, as well as potential complications such as rupture.
Systemic Veins Although vascular lesions of the mediastinum can potentially involve any systemic vein, the most commonly affected vessels include the superior vena cava, innominate vein, and azygos and hemiazygos veins.
Superior Vena Cava Persistent left SVC occurs in 0.5% of normal patients and 5% of patients with congenital heart diseases4,16 such as cor triatriatum.17 Persistent left SVC results from persistence of the left anterior and common cardinal veins and left sinus horn.16,18 The anomalous vessel typically empties into the coronary sinus; drainage into the left atrium is much less common. Chest radiographs typically show widening of the aorta or a left paramediastinal opacity that can mimic abnormalities such as mediastinal lymphadenopathy.19 However, the vascular nature of these lesions is readily identifiable on contrast-enhanced MDCT and MRI. Enlargement or dilatation of the SVC is typically due to an increase in central venous pressure resulting from tricuspid valvular heart disease, heart failure, or pericardial disease.5 Dilatation of the proximal SVC due to partial or complete distal
Figure 4 (A) A PA chest radiograph of a 63-year-old man with chest pain demonstrates a lobular opacity (black arrow) in the upper right mediastinum. Extensive atherosclerosis of the thoracic aorta (white arrow) should be noted. (B) A contrastenhanced axial MDCT image shows marked aneurysmal dilatation of an aberrant right subclavian artery (arrows), which accounts for the opacity seen on chest radiography. As on the radiograph, atherosclerosis of the thoracic aorta should be noted. Rupture of these aneurysms has been associated with atherosclerotic disease.
Imaging of the mediastinum obstruction by mediastinal fibrosis, neoplasm, or lymphadenopathy can also occur.5 Idiopathic aneurysmal dilatation of the SVC has been reported but is rare. SVC aneurysms have been associated with cystic hygromas.20 SVC enlargement manifests as widening of the right aspect of the mediastinum on chest radiography. However, these abnormalities can be readily identified as vascular lesions on contrast-enhanced MDCT and MRI.
Abnormalities of the Pulmonary Arteries and Veins The most common congenital anomalies that produce mediastinal abnormalities include congenital pulmonic stenosis, pulmonary sling, and idiopathic dilatation of the pulmonary artery (PA) and the acquired anomalies include pulmonary hypertension and PA aneurysms and pseudoaneurysms.
Pulmonic Stenosis Pulmonic stenosis is characterized by the fusion of the valve leaflets at the commissures, resulting in restricted opening of the leaflets during systole.21 Overall, 95% of cases are congenital in etiology, and pulmonic stenosis accounts for 10% of patients with congenital heart disease.22 Patients with minimal or mild stenosis are typically asymptomatic, whereas those with moderate or severe stenosis may demonstrate signs and symptoms related to systemic venous congestion. On chest radiography, the most characteristic feature is enlargement of the pulmonary trunk and the left PA because of poststenotic dilatation. The hila may appear asymmetric because of the normal right PA. MDCT demonstrates poststenotic dilatation of the pulmonary trunk and the left PA. Thickening and immobility of the pulmonic valve leaflets may be present on MDCT or cardiac-gated CTA. MRI is beneficial for evaluating pulmonic valve morphology and characterizing the abnormal flow jet associated with pulmonic stenosis.
Pulmonary Hypertension Pulmonary hypertension (PH) is characterized by the mean PA pressure greater than 25 mm Hg at rest or greater than 30 mm Hg during exercise.23 Pulmonary arterial hypertension represents elevation in pulmonary arterial pressure and vascular resistance with normal PA wedge (or left heart) pressure. pulmonary arterial hypertension may be idiopathic or related to human immunodeficiency virus infection, connective tissue diseases, pulmonary veno-occlusive disease, or pulmonary capillary hemangiomatosis. PH can be associated with left heart diseases such as mitral stenosis or left heart failure; congenital left-to-right shunts, including atrial septal defects and ventricular septal defects and patent ductus arteriosus; pulmonary disease, such as interstitial lung disease or chronic obstructive pulmonary disease; chronic pulmonary thromboemboli; and drugs and toxins.24 On chest radiography, the most common finding of PH is a convex opacity in the left aspect of the mediastinum that
245 represents enlargement of the pulmonary trunk. Dilatation of the left or right pulmonary arteries may result in hilar prominence. Enlargement of the pulmonary trunk greater than 29 mm on MDCT is suggestive of PH, with a sensitivity and a specificity of 87% and 89%, respectively.23
PA Aneurysms and Pseudoaneurysms PA aneurysms represent focal dilatation involving all the 3 layers of the affected vessel. The most common causes include congenital heart diseases, particularly those resulting in left-to-right shunts, pulmonary hypertension, pulmonic stenosis, and vasculitides, such as Behçet disease and Hughes-Stovin syndrome. Pseudoaneurysms do not involve all the 3 layers of the affected vessel and are associated with an increased risk of rupture. The most frequent etiologies include pulmonary infections, thoracic malignancies, and iatrogenic causes such as malpositioned Swan-Ganz catheters, thoracic surgery, and biopsy.25 PA aneurysms and pseudoaneurysms may manifest as mediastinal masses when the central vessels are affected and patchy, poorly circumscribed pulmonary opacities due to adjacent hemorrhage when more peripheral vessels are affected. Contrast-enhanced MDCT is the noninvasive imaging modality of choice, as the number, size, and location may be determined.26
Pulmonary Veins Pulmonary Venous Varix A pulmonary venous varix (also referred to as pulmonary varix) represents congenital or acquired dilatation of one or more pulmonary veins, most commonly at the confluence with the left atrium. Patients with congenital varices are usually asymptomatic. However, those with acquired varices typically report clinical symptoms related to the associated disease process, of which mitral valve disease is the most common.27 Pulmonary venous varices manifest as masses in the perihilar or infrahilar regions or middle mediastinum28 on radiographs (Fig. 5). Contrast-enhanced MDCT and MRI can characterize the varix as the cause of the radiographic abnormality.
Vascular Masses of the Mediastinum Numerous lesions of vascular origin can present as mediastinal masses separate from the systemic and pulmonary vasculature. There are also mediastinal masses that, although not of vascular origin, are vascular in nature and may result in strong enhancement similar to vessels. These abnormalities can be neoplastic or developmental, as well as benign or malignant. For the purposes of this review, we consider several of the most common primary vascular masses of the mediastinum.
B.W. Carter et al.
246
Figure 5 (A) A lateral chest radiograph of an asymptomatic 39-year-old man demonstrates a lobular opacity (arrow) in the right hilar or infrahilar region. (B) A contrast-enhanced axial MDCT image shows focal dilatation at the confluence of the right inferior pulmonary vein and the left atrium. These findings are characteristic of a pulmonary venous varix.
Lymphangioma Lymphangiomas, also known as cystic hygromas, are benign lesions that arise as abnormal collections of lymphatic channels and are most commonly encountered in the neck. However, they may also be identified in the mediastinum, where they affect the anterior and mediastinal compartments and rarely the heart.29,30 Primary mediastinal lymphangiomas have been described in a wide age range, from 5 months to 74 years.31 Most patients with lymphangiomas are usually asymptomatic. When symptoms are present at presentation, they are usually secondary to mass effect exerted on mediastinal structures.
On chest radiography, lymphangiomas typically manifest as smooth or lobular mediastinal masses. MDCT and MRI optimally demonstrate these lesions. Although these lesions usually grow around normal tissues, they can infiltrate adjacent organs and prevent complete surgical excision when large.32 On MDCT, lymphangiomas manifest as uniform cystic mass. Regions of internal high attenuation may be due to proteinaceous components. Following the administration of IV contrast material, most lymphangiomas do not enhance. However, hemangiomatous elements or associated aneurysms may enhance33 (Fig. 6). On MRI, lymphangiomas are hyperintense to muscle on T1-weighted images and demonstrate high signal intensity on T2-weighted images.
Figure 6 (A) A PA chest radiograph of a child presenting with dyspnea demonstrates marked widening of the mediastinum and loss of the normal mediastinal contours. (B) A contrast-enhanced axial MDCT image shows a large low attenuation mass encasing the mediastinal vessels without evidence of obstruction or invasion. Biopsy revealed lymphangioma. Multiple regions of enhancement (arrows) represent hemangiomatous elements.
Imaging of the mediastinum
Hemangioma Hemangiomas are uncommon benign lesions that account for less than 0.5% of all mediastinal masses and may represent true neoplasms or developmental vascular abnormalities.34,35 Young patients are typically affected, with 75% of lesions identified before 35 years of age, and men and women are affected equally.34,36 Most patients are asymptomatic at the time of clinical presentation. When symptoms are present, they are typically due to local mass effect and include cough, stridor, hoarseness, chest pain, or dysphagia.36 Hemangiomas may be classified as capillary, cavernous, or venous types based on the size of the vascular spaces.37 Most hemangiomas occur in the anterior mediastinum.38 On chest radiography, hemangiomas typically manifest as well-circumscribed mediastinal masses. Small foci of calcification representing phleboliths may be seen on 10% of radiographs; however, calcification is better visualized on MDCT.39 The appearance of hemangiomas on cross-sectional imaging depends on the stromal content and thrombosed vascular channels. On noncontrast MDCT, hemangiomas are typically heterogeneous. Following the administration of IV contrast material, hemangiomas typically demonstrate heterogeneous enhancement,39 with increasing and persistent enhancement present on dynamic contrast-enhanced studies.40 Prominent vessels may be identified, particularly on the delayed images41 (Fig. 7).
Carcinoid Carcinoid tumors are rare primary neuroendocrine neoplasms of the mediastinum which may arise from the thymus gland, paraganglionic structures, or neoplastic transformation of
247 misplaced embryonal rests.42 Thymic carcinoid is the most common type to affect the mediastinum and is usually encountered in the anterior compartment. Thymic carcinoids tend to behave more aggressively than carcinoids of the lung and the gastrointestinal tract do. On chest radiography, these tumors can result in nonspecific mediastinal widening, loss of normal contours, or focal mass. The most common appearance on contrast-enhanced MDCT is a well-circumscribed anterior mediastinal mass. Regions of internal heterogeneity are due to internal vascularity and intratumoral thrombus. Following the administration of IV contrast material, most lesions demonstrate heterogeneous enhancement. On MRI, carcinoid tumors demonstrate low to intermediate signal intensity on T1-weighted images and high signal intensity on T2-weighted images. As on MDCT, lesion enhancement is typically heterogeneous (Fig. 8). Internal cystic regions show low signal intensity on T1-weighted images and high signal intensity on T2-weighted images.
Paraganglioma Most (90%) of the tumors of chromaffin cell origin arise from the adrenal glands and are designated as pheochromocytomas. The remainder (10%) may originate as primary tumors called paragangliomas from the neck, chest, elsewhere in the abdomen, and pelvis. When paragangliomas arise from the chest, most involve the mediastinum and can originate from paraaortic and paravertebral sympathetic chain ganglia in the middle and the posterior mediastinum, respectively.43,44 Unlike pheochromocytomas, they are rarely functional, and clinical presentation is often delayed until compression of nearby structures causes pain or shortness of breath.
Figure 7 (A) A PA chest radiograph of a 57-year-old man presenting with chest pain demonstrates a masslike opacity (arrow) projecting over the left lower lung zone and silhouetting the left heart border. Because of the history of previous median sternotomy and coronary artery bypass grafting, this opacity was concerning for a left ventricular pseudoaneurysm. (B) A contrast-enhanced axial MDCT image shows a large heterogeneous mass in the left mediastinum adjacent to the left ventricle. Extensive internal vascularity, some of which demonstrates enhancement (white arrow) and some of which does not (black arrow), should be noted. Although most hemangiomas demonstrate enhancement, the pattern may be highly variable.
B.W. Carter et al.
248
Figure 8 (A) A PA chest radiograph of a 45-year-old man presenting with chest pain and shortness of breath demonstrates a large right mediastinal mass. Presence of the “hilum overlay sign,” indicating that the mass is located within the anterior or posterior mediastinum, should be noted. (B) A contrast-enhanced T1-weighted MR image demonstrates a large heterogeneous mass in the anterior mediastinum with regions of internal enhancement (arrows). Biopsy revealed neuroendocrine tumor, specifically carcinoid of thymic origin.
Paragangliomas can result in focal mediastinal abnormalities on chest radiography depending on their size and location. On contrast-enhanced MDCT, these tumors manifest as mass lesions near the bifurcation of the great vessels and demonstrate intense and homogeneous enhancement44 (Fig. 9). Heterogeneous enhancement can be seen in the setting of necrosis. On MRI, paragangliomas demonstrate intermediate signal intensity on T1-weighted images and high signal intensity on T2weighted images.44
Castleman Disease Castleman disease (CD) is an uncommon benign lymphoproliferative disorder.45,46 It is classified based on histopathology and distribution. Hyaline vascular type represents 90% of all CD and is the most common type; plasma cell and mixed forms are less common. CD may also be localized or multicentric in distribution. The middle and posterior mediastinal compartments are involved more commonly than the anterior mediastinal compartment is.
Figure 9 (A) A PA chest radiograph of a 32-year-old man presenting with chest pain shows widening of and masslike opacity in the mediastinum (arrows). (B) A contrast-enhanced axial MDCT image demonstrates a large mass involving the anterior and middle mediastinum, most of which exhibits intense enhancement. The vessels (arrows) within the mass should be noted. Biopsy revealed paraganglioma.
Imaging of the mediastinum
249
Figure 10 (A) A PA chest radiograph of a 22-year-old man presenting with chest pain shows a lobular masslike opacity (arrow) in the right hilum. (B) A contrast-enhanced axial MDCT image demonstrates a lobular, enhancing mass (asterisk) in the right hilum that corresponds to the opacity seen on radiography. Histopathologic findings at the time of surgical resection were consistent with unicentric Castleman disease.
On chest radiography, unicentric CD affecting the mediastinum usually manifests as a mediastinal or hilar mass with smooth margins or lobular contours, whereas multicentric CD may result in bilateral hilar and mediastinum enlargement.46 On contrast-enhanced MDCT, unicentric CD can manifest as a solitary, noninvasive mass; a dominant mass with involvement of contiguous structures; or matted lymphadenopathy, limited to a single mediastinal compartment45-47 (Fig. 10). As CD is hypervascular in nature, intense contrast enhancement is characteristic. In multicentric CD, bilateral hilar and mediastinal lymphadenopathy is the most common manifestation of mediastinal involvement.46
Conclusions Vascular lesions of the mediastinum include a wide variety of abnormalities of systemic and pulmonary vessels and primary mediastinal masses of vascular origin. The correct identification and characterization of these lesions using advanced crosssectional imaging techniques such as MDCT or MRI are crucial to ensure appropriate patient management. Failure to recognize the vascular nature of these lesions can lead to potentially life-threatening complications such as excessive bleeding during biopsies. Therefore, it is important for the radiologist to be aware of the most common vascular abnormalities of the mediastinum that can result in abnormal findings on thoracic imaging examinations.
References 1. Gozdziuk K, Czekajska-Chehab E, Wrona A, et al: Saccular aneurysm of the superior vena cava detected by computed tomography and successfully treated with surgery. Ann Thorac Surg 78(6):e94-e95, 2004 2. Lyons HA, Calvy GL, Sammons BP: The diagnosis and classification of mediastinal masses. 1. A study of 782 cases. Ann Intern Med 51:897-932, 1959
3. Boateng P, Anjum W, Wechsler AS: Vascular lesions of the mediastinum. Thorac Surg Clin 19(1):91-105, 2009 4. Kelley MJ, Mannes EJ, Ravin CE: Mediastinal masses of vascular origin. A review. J Thorac Cardiovasc Surg 76(4):559-572, 1978 5. Shields TW, LoCicero III J, Ponn RB, et al: Vascular masses of the mediastinum. In: Shields TW, Ponn JB, Rusch VW (eds) ed 6: General Thoracic Surgery, Vol 2. Philadelphia: Lippincott Williams & Wilkins, 2523-2544, 2005 6. McElhinney DB, Hoydu AK, Gaynor JW, et al: Patterns of right aortic arch and mirror-image branching of the brachiocephalic vessels without associated anomalies. Pediatr Cardiol 22:285-291, 2001 7. Hastreiter AR, D'Cruz IA, Cantez T, et al: Right-sided aorta. Part I. Occurrence of right aortic arch in various types of congenital heart disease. II. Right aortic arch, right descending aorta, and associated anomalies. Br Heart J 28:722-725, 1966 8. Green CE, Klein JF: Multidetector row CT angiography of the thoracic aorta. In: Boiselle PM, White CS (eds): New Techniques in Cardiothoracic Imaging. New York, NY: Informa Healthcare, 105-126, 2007 9. Dähnert W: Cardiovascular disorders: Aortic dissection, Radiology Review Manual, ed 5. Philadelphia, PA: Lippincott Williams & Wilkins, 607-609, 2003 10. McMahon MA, Squirrell CA: Multidetector CT of aortic dissection: A pictorial review. Radiographics 30(2):445-460, 2010 11. Hagan PG, Nienaber CA, Isselbacher EM, et al: The International Registry of Acute Aortic Dissection (IRAD): New insights into an old disease. J Am Med Assoc 283(7):897-903, 2000 12. Castañer E, Andreu M, Gallardo X, et al: CT in nontraumatic acute thoracic aortic disease: Typical and atypical features and complications. Radiographics 23:S93–S110 (suppl), 2003 13. Smyth PT, Edwards JE: Pseudocoarctation, kinking, or buckling of the aorta. Circulation 46(5):1027-1032, 1972 14. Syed M, Lesch M: Coronary artery aneurysm: A review. Prog Cardiovasc Dis 40(1):77-84, 1997 15. Trop I, Samson L, Cordeau MP, et al: Anterior mediastinal mass in a patient with prior saphenous vein coronary artery bypass grafting. Chest 115(2):572-576, 1999 16. Gandhi SK, Siewers R: Anomalies of systemic venous drainage. In: Kaiser LR, Kron IL, Spray TL (eds): Mastery of Cardiothoracic Surgery. Philadelphia: Lippincott Williams & Wilkins, 708-715, 2007
250 17. Kouchoukos NT, Blackstone EH, Doty DB, et al: Cor triatriatum, Kirklin/ Barratt-Boyes Cardiac Surgery, ed 3. Philadelphia: Churchill Livingstone, 781-789, 2003 18. Pahwa R, Kumar A: Persistent left superior vena cava: An intensivist's experience and review of the literature. South Med J 96(5):528-529, 2003 19. Wong PS, Goldstraw P: Left superior vena cava: A pitfall in computed tomographic diagnosis with surgical implications. Ann Thorac Surg 50 (4):656-657, 1990 20. Joseph AE, Donaldson JS, Reynolds M: Neck and thorax venous aneurysm: Association with cystic hygroma. Radiology 170(1 Pt 1):109-112, 1989 21. Ryan R, Abbara S, Colen RR, et al: Cardiac valve disease: Spectrum of findings on cardiac 64-MDCT. Am J Roentgenol 190(5):W294-W303, 2008 22. Waller BF, Howard J, Fess S: Pathology of pulmonic valve stenosis and pure regurgitation. Clin Cardiol 18(1):45-50, 1995 23. Frazier AA, Galvin JR, Franks TJ, et al: From the archives of the AFIP: Pulmonary vasculature—hypertension and infarction. Radiographics 20:491-524, 2000 24. Peña E, Dennie C, Veinot J, et al: Pulmonary hypertension: How the radiologist can help. Radiographics 32(1):9-32, 2012 25. Bartter T, Irwin RS, Nash G: Aneurysms of the pulmonary arteries. Chest 94:1065-1075, 1988 26. Nguyen ET, Silva CI, Seely JM, et al: Pulmonary artery aneurysms and pseudoaneurysms in adults: Findings at CT and radiography. Am J Roentgenol 188:W126-W134, 2007 27. Shida T, Ohashi H, Nakamura K, et al: Pulmonary varices associated with mitral valve disease: A case report and survey of the literature. Ann Thorac Surg 34(4):452-456, 1982 28. DeBoer DA, Margolis ML, Livornese D, et al: Pulmonary venous aneurysm presenting as a middle mediastinal mass. Ann Thorac Surg 61 (4):1261-1262, 1996 29. Bossert T, Gummert JF, Mohr FW: Giant cystic lymphangioma of the mediastinum. Eur J Cardiothorac Surg 21(2):340, 2002 30. Jougon J, Laborde MN, Parrens M, et al: Cystic lymphangioma of the heart mimicking a mediastinal tumor. Eur J Cardiothorac Surg 22(3):476-478, 2002 31. Okubo T, Okayasu T, Osaka Y, et al: Surgical analysis of mediastinal lymphangioma—analysis of 7 cases. Nippon Kyobu Geka Gakkai Zasshi 40(4):583-586, 1992
B.W. Carter et al. 32. Teramoto K, Suzumura Y: Mediastinal cavernous lymphangioma in an adult. Gen Thorac Cardiovasc Surg 56(2):88-90, 2008 33. Shaffer K, Rosado-de-Christenson ML, Patz Jr EF, et al: Thoracic lymphangioma in adults: CT and MR imaging features. Am J Roentgenol 162:283-289, 1994 34. Davis JM, Mark GJ, Greene R: Benign blood vascular tumors of the mediastinum: Report of four cases and review of the literature. Radiology 126:581-587, 1978 35. Cohen AJ, Sbaschnig RJ, Hochholzer L, et al: Mediastinal hemangiomas. Ann Thorac Surg 43:656-659, 1987 36. Buckner S, McAllister J, D'Altorio R: Case of the season: Hemangioma of the middle mediastinum. Semin Roentgenol 29:98-99, 1994 37. Abe K, Akata S, Ohkubo Y, et al: Venous hemangioma of the mediastinum. Eur Radiol 11:73-75, 2001 38. Klecker RJ, Sinclair DS, King MA: Case 1: Mediastinal hemangioma. Am J Roentgenol 175(866):868-869, 2000 39. McAdams HP, Rosado-de-Christenson ML, Moran CA: Mediastinal hemangioma: Radiographic and CT features in 14 patients. Radiology 193:399-402, 1994 40. Cheung YC, Ng SH, Wan YL, et al: Dynamic CT features of mediastinal hemangioma: More information for evaluation. Clin Imaging 24:276-278, 2000 41. Roach H, Chowdhury P, Adams H: An incidental finding. Br J Radiol 76:753-754, 2003 42. Suster S, Moran CA. Neuroendocrine neoplasms of the mediastinum. Am J Clin Pathol 115:S17-S27 (suppl), 2001 43. Young Jr WF: Paragangliomas: Clinical overview. Ann N Y Acad Sci 1073:21-29, 2006 44. Balcombe J, Torigian DA, Kim W, et al: Cross-sectional imaging of paragangliomas of the aortic body and other thoracic branchiomeric paraganglia. Am J Roentgenol 188:1054-1058, 2007 45. McAdams HP, Rosado-de-Christenson M, Fishback NF, et al: Castleman disease of the thorax: Radiologic features with clinical and histopathologic correlation. Radiology 209:221-228, 1998 46. Johkoh T, Müller NL, Ichikado K, et al: Intrathoracic multicentric Castleman disease: CT findings in 12 patients. Radiology 209:477-481, 1998 47. Ko SF, Hsieh MJ, Ng SH, et al: Imaging spectrum of Castleman's disease. Am J Roentgenol 182(3):769-775, 2004
Introduction
V
ascular lesions of the mediastinum comprise a myriad of disease processes, from abnormalities of the systemic and the pulmonary arteries and veins to benign and malignant primary vascular masses. Although the presence of these lesions may be suggested initially on chest radiography, vascular abnormalities of the mediastinum account for only 10% of all radiographically recognized mediastinal masses.1-3 Therefore, the identification and characterization of vascular lesions using advanced cross-sectional imaging techniques such as multidetector computed tomography (MDCT) and magnetic resonance imaging (MRI) are crucial to ensure appropriate patient management. The combination of clinical information such as sex, age, and symptoms at presentation and radiologic information such as location within the mediastinum and key imaging features usually establish the correct diagnosis. Therefore, it is important for the radiologist to be aware of the most common vascular abnormalities of the mediastinum that can result in abnormal findings on thoracic imaging examinations.
Classification of Vascular Lesions Vascular lesions of the mediastinum are typically classified based on the vascular tissue or organ from which they arise.3-5 Following this algorithm, vascular abnormalities may be classified as systemic arterial, systemic venous, pulmonary arterial, pulmonary venous, or lymphatic in nature. Other classification schemes characterize vascular abnormalities as posttraumatic, neoplastic, congenital, or acquired in etiology. *Department of Diagnostic Radiology, The University of Texas MD Anderson Cancer Center, Houston, TX. †Department of Diagnostic Imaging, The Chaim Sheba Medical Center, Tel Hashomer, Israel. Address reprint requests to Brett W. Carter, MD, Department of Diagnostic Radiology, The University of Texas MD Anderson Cancer Center, 1515 Holcombe Blvd, Unit 1478, Houston, TX 77030. E-mail: [email protected]
http://dx.doi.org/10.1053/j.ro.2015.01.015 0037-198X/& 2015 Elsevier Inc. All rights reserved.
For the purposes of this review, we have divided vascular lesions of the mediastinum into 2 groups: (1) abnormalities and normal variants of systemic and pulmonary arteries and veins and (2) benign and malignant vascular masses.
Imaging Techniques Although mediastinal abnormalities may initially be detected on chest radiography, contrast-enhanced MDCT and MRI are the imaging modalities of choice for the identification and characterization of these lesions as vascular in origin. The use of intravenous (IV) contrast material greatly improves the detection of vascular lesions, which may be otherwise difficult to distinguish from nonvascular soft tissue attenuation masses on noncontrast MDCT. Contrast-enhanced MDCT is best for demonstrating enhancement of vascular lesions and delineating connections with parent and branch vessels, which typically enhance to a similar degree. Abnormalities of the thoracic aorta and systemic arteries are optimally evaluated in studies timed for the evaluation of the aorta, whereas anomalies of the systemic veins are best characterized on routine contrastenhanced MDCT. Abnormalities of the pulmonary arteries are optimally evaluated on studies timed for evaluation of the pulmonary arteries, typically performed as a CT pulmonary angiogram. Use of multiple phases may be necessary to appropriately identify lesions of vascular origin (Fig. 1). MRI can be performed when contraindications to contrastenhanced MDCT are present, such as renal failure or severe allergy to iodinated contrast material. In the setting of renal insufficiency, noncontrast MR techniques can be used to characterize the abnormality and assess the adjacent vasculature. Angiography may be performed in certain situations, such as trauma, in which endovascular therapy may be necessary during the procedure.
Systemic Arteries Abnormalities or anatomical variants involving the systemic arteries represent a heterogeneous group of congenital and 241
B.W. Carter et al.
242
Figure 1 (A) A contrast-enhanced axial MDCT image timed for evaluation of the thoracic aorta demonstrates a lobular hypodense mass (arrow) in the anterior mediastinum anterior to the transverse thoracic aorta. (B) The routine contrastenhanced axial MDCT image shows contrast opacification of the anterior mediastinal mass (arrow). Multiplanar reformatted images (not shown) revealed a broad-based connection to the left innominate vein in this case of a venous varix. This case illustrates the importance of administering intravenous contrast material and obtaining images in multiple phases when evaluating mediastinal masses, as the vascular nature of lesions may be overlooked.
acquired lesions, most of which involve the thoracic aorta. Other vessels such as the innominate, subclavian, and coronary arteries and coronary artery bypass grafts may also be affected.
Thoracic Aorta: Right Aortic Arch Right aortic arch (RAA) is an uncommon anomaly that occurs in 0.1% of the population.6 RAA can be classified into 3 types according to the branching pattern of the arch vessels: (1) RAA with an aberrant left subclavian artery (ALSA), (2) RAA with mirror-image branching, and (3) RAA with isolation of the LSA. The most common type is RAA with ALSA and is typically asymptomatic, although dysphagia due to the retroesophageal course of the LSA has been reported. RAA with mirror-image branching is strongly associated with congenital heart disease and is thus usually diagnosed in neonates or children. On chest radiography, RAA usually manifests as a rounded masslike opacity in the right upper mediastinum, specifically the right paratracheal region (Fig. 2). Leftward deviation of the trachea and rightward deviation of the superior vena cava (SVC) may be present.4 Unless a double aortic arch is present, a normal left aortic arch cannot be visualized. A diverticulum of Kommerell can result in focal opacity in the expected position of the left arch. An ALSA may appear as retroesophageal opacity on the lateral radiograph. On contrast-enhanced MDCT and MRI, the RAA can be seen passing to the right of the trachea and all vessels arising from the anomalous vessel can be determined. Crosssectional imaging is also beneficial for identifying other anomalies that may be associated with RAA with mirror-
image branching such as tetralogy of Fallot and truncus arteriosus.7
Thoracic Aorta: Aneurysms and Pseudoaneurysms Thoracic aortic aneurysms, defined as permanent abnormal dilatation of the thoracic aorta, are the most common abnormalities to affect the thoracic aorta in adult patients.8 These aneurysms result from atherosclerosis, trauma, inflammation or infection, and cystic medial necrosis.3 The thoracic aorta below the level of the ligamentum arteriosus is the most commonly affected segment, followed by the transverse thoracic aorta and the ascending aorta. Chronic posttraumatic pseudoaneurysms usually affect the thoracic aorta at the isthmus. On chest radiography, 80%-90% of affected patients have abnormal findings, including mediastinal widening and enlargement of the affected portion of the aorta (Fig. 3). Contrast-enhanced MDCT accurately demonstrates the size and number of aneurysms and can identify any potential complications. MRI and contrast-enhanced MR angiography can alternatively be used and lack ionizing radiation.
Thoracic Aorta: Dissection Aortic dissection is a well-described disease process characterized by separation of the aortic intima and adventitia secondary to splitting of the media by circulating blood.9,10 The most common risk factor is hypertension, followed by cystic medial necrosis and diseases that can affect the aortic
Imaging of the mediastinum
243
Figure 2 (A) A PA chest radiograph of an asymptomatic 39-year-old man demonstrates a lobular opacity (arrow) in the right paratracheal region that results in a slight leftward deviation of the trachea. The absence of a normal left aortic arch should be noted. (B) The contrast-enhanced axial MDCT image shows that the opacity in the right paratracheal region on radiography represents a right aortic arch (white arrow). The aberrant left subclavian artery arising from a diverticulum of Kommerell (black arrow) should be noted.
wall, such as atherosclerosis and connective tissue diseases.11 Thoracic aortic dissection is typically classified into Stanford types A and B based on the affected portion of the thoracic aorta. Stanford type A involves the ascending aorta, with or without extension into the descending aorta, and represents 60%-70% of cases.10 Stanford type B involves the descending aorta distal to the LSA and represents 30%-40% of all cases.10 Type A dissections are treated surgically to prevent propagation into the aortic root, pericardium, or coronary arteries, whereas
type B dissections are treated medically unless complications such as end-organ ischemia are present.12 Thoracic aortic dissection can result in a variety of nonspecific findings on chest radiography that can mimic a mediastinal mass.3 For instance, widening of the mediastinum was seen in 61.1% of cases and abnormal cardiac contour was noted in 14.1% of cases in a study.11 Enlargement of the cardiac silhouette can be seen in the setting of pericardial effusion, complicating dissection. Contrast-enhanced MDCT, which may
Figure 3 (A) A PA chest radiograph of a 48-year-old man presenting with chest pain demonstrates an elongated and lobular opacity (arrows) along the inferior aspect of the left mediastinum. (B) A contrast-enhanced axial MDCT image shows that the opacity corresponds to aneurysmal dilatation of the descending thoracic aorta (arrow). The peripheral thrombus should be noted. Atherosclerosis is the most common etiology of thoracic aortic aneurysms, followed by infection and cystic medial necrosis. As this patient's aneurysm measured greater than 6.5 cm, an endovascular stent graft was placed because of the risk of rupture.
B.W. Carter et al.
244 be performed with or without Electrocardiography (ECG) gating, is the best method of identifying and characterizing aortic dissection and potential intrathoracic complications. MRI and contrast-enhanced MR angiography may be used in medically stable patients or individuals with chronic dissections.
Innominate and Subclavian Arteries Prominence or tortuosity of the innominate arteries can be seen in older patients and is associated with hypertension and atherosclerosis. In this setting, the affected artery can manifest as a superior mediastinal or apical lung mass,13 reflecting the prominent vessel or the displaced SVC.4 Aneurysmal dilatation affects approximately 8% of aberrant right subclavian arteries and can result in a masslike opacity in the upper right mediastinum (Fig. 4). On MDCT and MRI, the presence of the aberrant vessel as it arises as the last branch of the posterior margin of the arch and travels posterior to the esophagus can be seen.
Coronary Arteries Aneurysms of the coronary arteries, most of which are associated with atherosclerosis, infection, or Kawasaki disease, occur in 0.4%-0.5% of patients undergoing angiography.14 The right coronary artery is the most frequently affected coronary vessel. Although many affected patients are asymptomatic, these aneurysms can rupture and result in myocardial ischemia or infarction. Therefore, surgical resection is typically performed. On chest radiography, coronary artery aneurysms typically manifest as paracardiac masses and may be located on the right or left depending on which vessel is involved. Contrast-enhanced MDCT and ECG-gated cardiac CT angiography (CTA) optimally evaluate these aneurysms and demonstrate the vessel from which they originate.
Coronary Artery Bypass Grafts Aneurysms of coronary artery bypass grafts, usually involving the saphenous vein graft, are rare. These aneurysms, which may be true or false and can grow very large, may develop as early as 10 days following surgery.15 On chest radiography, bypass graft aneurysms manifest as paracardiac masses. Contrast-enhanced MDCT and ECG-gated cardiac CTA effectively demonstrate the size and location of these aneurysms, as well as potential complications such as rupture.
Systemic Veins Although vascular lesions of the mediastinum can potentially involve any systemic vein, the most commonly affected vessels include the superior vena cava, innominate vein, and azygos and hemiazygos veins.
Superior Vena Cava Persistent left SVC occurs in 0.5% of normal patients and 5% of patients with congenital heart diseases4,16 such as cor triatriatum.17 Persistent left SVC results from persistence of the left anterior and common cardinal veins and left sinus horn.16,18 The anomalous vessel typically empties into the coronary sinus; drainage into the left atrium is much less common. Chest radiographs typically show widening of the aorta or a left paramediastinal opacity that can mimic abnormalities such as mediastinal lymphadenopathy.19 However, the vascular nature of these lesions is readily identifiable on contrast-enhanced MDCT and MRI. Enlargement or dilatation of the SVC is typically due to an increase in central venous pressure resulting from tricuspid valvular heart disease, heart failure, or pericardial disease.5 Dilatation of the proximal SVC due to partial or complete distal
Figure 4 (A) A PA chest radiograph of a 63-year-old man with chest pain demonstrates a lobular opacity (black arrow) in the upper right mediastinum. Extensive atherosclerosis of the thoracic aorta (white arrow) should be noted. (B) A contrastenhanced axial MDCT image shows marked aneurysmal dilatation of an aberrant right subclavian artery (arrows), which accounts for the opacity seen on chest radiography. As on the radiograph, atherosclerosis of the thoracic aorta should be noted. Rupture of these aneurysms has been associated with atherosclerotic disease.
Imaging of the mediastinum obstruction by mediastinal fibrosis, neoplasm, or lymphadenopathy can also occur.5 Idiopathic aneurysmal dilatation of the SVC has been reported but is rare. SVC aneurysms have been associated with cystic hygromas.20 SVC enlargement manifests as widening of the right aspect of the mediastinum on chest radiography. However, these abnormalities can be readily identified as vascular lesions on contrast-enhanced MDCT and MRI.
Abnormalities of the Pulmonary Arteries and Veins The most common congenital anomalies that produce mediastinal abnormalities include congenital pulmonic stenosis, pulmonary sling, and idiopathic dilatation of the pulmonary artery (PA) and the acquired anomalies include pulmonary hypertension and PA aneurysms and pseudoaneurysms.
Pulmonic Stenosis Pulmonic stenosis is characterized by the fusion of the valve leaflets at the commissures, resulting in restricted opening of the leaflets during systole.21 Overall, 95% of cases are congenital in etiology, and pulmonic stenosis accounts for 10% of patients with congenital heart disease.22 Patients with minimal or mild stenosis are typically asymptomatic, whereas those with moderate or severe stenosis may demonstrate signs and symptoms related to systemic venous congestion. On chest radiography, the most characteristic feature is enlargement of the pulmonary trunk and the left PA because of poststenotic dilatation. The hila may appear asymmetric because of the normal right PA. MDCT demonstrates poststenotic dilatation of the pulmonary trunk and the left PA. Thickening and immobility of the pulmonic valve leaflets may be present on MDCT or cardiac-gated CTA. MRI is beneficial for evaluating pulmonic valve morphology and characterizing the abnormal flow jet associated with pulmonic stenosis.
Pulmonary Hypertension Pulmonary hypertension (PH) is characterized by the mean PA pressure greater than 25 mm Hg at rest or greater than 30 mm Hg during exercise.23 Pulmonary arterial hypertension represents elevation in pulmonary arterial pressure and vascular resistance with normal PA wedge (or left heart) pressure. pulmonary arterial hypertension may be idiopathic or related to human immunodeficiency virus infection, connective tissue diseases, pulmonary veno-occlusive disease, or pulmonary capillary hemangiomatosis. PH can be associated with left heart diseases such as mitral stenosis or left heart failure; congenital left-to-right shunts, including atrial septal defects and ventricular septal defects and patent ductus arteriosus; pulmonary disease, such as interstitial lung disease or chronic obstructive pulmonary disease; chronic pulmonary thromboemboli; and drugs and toxins.24 On chest radiography, the most common finding of PH is a convex opacity in the left aspect of the mediastinum that
245 represents enlargement of the pulmonary trunk. Dilatation of the left or right pulmonary arteries may result in hilar prominence. Enlargement of the pulmonary trunk greater than 29 mm on MDCT is suggestive of PH, with a sensitivity and a specificity of 87% and 89%, respectively.23
PA Aneurysms and Pseudoaneurysms PA aneurysms represent focal dilatation involving all the 3 layers of the affected vessel. The most common causes include congenital heart diseases, particularly those resulting in left-to-right shunts, pulmonary hypertension, pulmonic stenosis, and vasculitides, such as Behçet disease and Hughes-Stovin syndrome. Pseudoaneurysms do not involve all the 3 layers of the affected vessel and are associated with an increased risk of rupture. The most frequent etiologies include pulmonary infections, thoracic malignancies, and iatrogenic causes such as malpositioned Swan-Ganz catheters, thoracic surgery, and biopsy.25 PA aneurysms and pseudoaneurysms may manifest as mediastinal masses when the central vessels are affected and patchy, poorly circumscribed pulmonary opacities due to adjacent hemorrhage when more peripheral vessels are affected. Contrast-enhanced MDCT is the noninvasive imaging modality of choice, as the number, size, and location may be determined.26
Pulmonary Veins Pulmonary Venous Varix A pulmonary venous varix (also referred to as pulmonary varix) represents congenital or acquired dilatation of one or more pulmonary veins, most commonly at the confluence with the left atrium. Patients with congenital varices are usually asymptomatic. However, those with acquired varices typically report clinical symptoms related to the associated disease process, of which mitral valve disease is the most common.27 Pulmonary venous varices manifest as masses in the perihilar or infrahilar regions or middle mediastinum28 on radiographs (Fig. 5). Contrast-enhanced MDCT and MRI can characterize the varix as the cause of the radiographic abnormality.
Vascular Masses of the Mediastinum Numerous lesions of vascular origin can present as mediastinal masses separate from the systemic and pulmonary vasculature. There are also mediastinal masses that, although not of vascular origin, are vascular in nature and may result in strong enhancement similar to vessels. These abnormalities can be neoplastic or developmental, as well as benign or malignant. For the purposes of this review, we consider several of the most common primary vascular masses of the mediastinum.
B.W. Carter et al.
246
Figure 5 (A) A lateral chest radiograph of an asymptomatic 39-year-old man demonstrates a lobular opacity (arrow) in the right hilar or infrahilar region. (B) A contrast-enhanced axial MDCT image shows focal dilatation at the confluence of the right inferior pulmonary vein and the left atrium. These findings are characteristic of a pulmonary venous varix.
Lymphangioma Lymphangiomas, also known as cystic hygromas, are benign lesions that arise as abnormal collections of lymphatic channels and are most commonly encountered in the neck. However, they may also be identified in the mediastinum, where they affect the anterior and mediastinal compartments and rarely the heart.29,30 Primary mediastinal lymphangiomas have been described in a wide age range, from 5 months to 74 years.31 Most patients with lymphangiomas are usually asymptomatic. When symptoms are present at presentation, they are usually secondary to mass effect exerted on mediastinal structures.
On chest radiography, lymphangiomas typically manifest as smooth or lobular mediastinal masses. MDCT and MRI optimally demonstrate these lesions. Although these lesions usually grow around normal tissues, they can infiltrate adjacent organs and prevent complete surgical excision when large.32 On MDCT, lymphangiomas manifest as uniform cystic mass. Regions of internal high attenuation may be due to proteinaceous components. Following the administration of IV contrast material, most lymphangiomas do not enhance. However, hemangiomatous elements or associated aneurysms may enhance33 (Fig. 6). On MRI, lymphangiomas are hyperintense to muscle on T1-weighted images and demonstrate high signal intensity on T2-weighted images.
Figure 6 (A) A PA chest radiograph of a child presenting with dyspnea demonstrates marked widening of the mediastinum and loss of the normal mediastinal contours. (B) A contrast-enhanced axial MDCT image shows a large low attenuation mass encasing the mediastinal vessels without evidence of obstruction or invasion. Biopsy revealed lymphangioma. Multiple regions of enhancement (arrows) represent hemangiomatous elements.
Imaging of the mediastinum
Hemangioma Hemangiomas are uncommon benign lesions that account for less than 0.5% of all mediastinal masses and may represent true neoplasms or developmental vascular abnormalities.34,35 Young patients are typically affected, with 75% of lesions identified before 35 years of age, and men and women are affected equally.34,36 Most patients are asymptomatic at the time of clinical presentation. When symptoms are present, they are typically due to local mass effect and include cough, stridor, hoarseness, chest pain, or dysphagia.36 Hemangiomas may be classified as capillary, cavernous, or venous types based on the size of the vascular spaces.37 Most hemangiomas occur in the anterior mediastinum.38 On chest radiography, hemangiomas typically manifest as well-circumscribed mediastinal masses. Small foci of calcification representing phleboliths may be seen on 10% of radiographs; however, calcification is better visualized on MDCT.39 The appearance of hemangiomas on cross-sectional imaging depends on the stromal content and thrombosed vascular channels. On noncontrast MDCT, hemangiomas are typically heterogeneous. Following the administration of IV contrast material, hemangiomas typically demonstrate heterogeneous enhancement,39 with increasing and persistent enhancement present on dynamic contrast-enhanced studies.40 Prominent vessels may be identified, particularly on the delayed images41 (Fig. 7).
Carcinoid Carcinoid tumors are rare primary neuroendocrine neoplasms of the mediastinum which may arise from the thymus gland, paraganglionic structures, or neoplastic transformation of
247 misplaced embryonal rests.42 Thymic carcinoid is the most common type to affect the mediastinum and is usually encountered in the anterior compartment. Thymic carcinoids tend to behave more aggressively than carcinoids of the lung and the gastrointestinal tract do. On chest radiography, these tumors can result in nonspecific mediastinal widening, loss of normal contours, or focal mass. The most common appearance on contrast-enhanced MDCT is a well-circumscribed anterior mediastinal mass. Regions of internal heterogeneity are due to internal vascularity and intratumoral thrombus. Following the administration of IV contrast material, most lesions demonstrate heterogeneous enhancement. On MRI, carcinoid tumors demonstrate low to intermediate signal intensity on T1-weighted images and high signal intensity on T2-weighted images. As on MDCT, lesion enhancement is typically heterogeneous (Fig. 8). Internal cystic regions show low signal intensity on T1-weighted images and high signal intensity on T2-weighted images.
Paraganglioma Most (90%) of the tumors of chromaffin cell origin arise from the adrenal glands and are designated as pheochromocytomas. The remainder (10%) may originate as primary tumors called paragangliomas from the neck, chest, elsewhere in the abdomen, and pelvis. When paragangliomas arise from the chest, most involve the mediastinum and can originate from paraaortic and paravertebral sympathetic chain ganglia in the middle and the posterior mediastinum, respectively.43,44 Unlike pheochromocytomas, they are rarely functional, and clinical presentation is often delayed until compression of nearby structures causes pain or shortness of breath.
Figure 7 (A) A PA chest radiograph of a 57-year-old man presenting with chest pain demonstrates a masslike opacity (arrow) projecting over the left lower lung zone and silhouetting the left heart border. Because of the history of previous median sternotomy and coronary artery bypass grafting, this opacity was concerning for a left ventricular pseudoaneurysm. (B) A contrast-enhanced axial MDCT image shows a large heterogeneous mass in the left mediastinum adjacent to the left ventricle. Extensive internal vascularity, some of which demonstrates enhancement (white arrow) and some of which does not (black arrow), should be noted. Although most hemangiomas demonstrate enhancement, the pattern may be highly variable.
B.W. Carter et al.
248
Figure 8 (A) A PA chest radiograph of a 45-year-old man presenting with chest pain and shortness of breath demonstrates a large right mediastinal mass. Presence of the “hilum overlay sign,” indicating that the mass is located within the anterior or posterior mediastinum, should be noted. (B) A contrast-enhanced T1-weighted MR image demonstrates a large heterogeneous mass in the anterior mediastinum with regions of internal enhancement (arrows). Biopsy revealed neuroendocrine tumor, specifically carcinoid of thymic origin.
Paragangliomas can result in focal mediastinal abnormalities on chest radiography depending on their size and location. On contrast-enhanced MDCT, these tumors manifest as mass lesions near the bifurcation of the great vessels and demonstrate intense and homogeneous enhancement44 (Fig. 9). Heterogeneous enhancement can be seen in the setting of necrosis. On MRI, paragangliomas demonstrate intermediate signal intensity on T1-weighted images and high signal intensity on T2weighted images.44
Castleman Disease Castleman disease (CD) is an uncommon benign lymphoproliferative disorder.45,46 It is classified based on histopathology and distribution. Hyaline vascular type represents 90% of all CD and is the most common type; plasma cell and mixed forms are less common. CD may also be localized or multicentric in distribution. The middle and posterior mediastinal compartments are involved more commonly than the anterior mediastinal compartment is.
Figure 9 (A) A PA chest radiograph of a 32-year-old man presenting with chest pain shows widening of and masslike opacity in the mediastinum (arrows). (B) A contrast-enhanced axial MDCT image demonstrates a large mass involving the anterior and middle mediastinum, most of which exhibits intense enhancement. The vessels (arrows) within the mass should be noted. Biopsy revealed paraganglioma.
Imaging of the mediastinum
249
Figure 10 (A) A PA chest radiograph of a 22-year-old man presenting with chest pain shows a lobular masslike opacity (arrow) in the right hilum. (B) A contrast-enhanced axial MDCT image demonstrates a lobular, enhancing mass (asterisk) in the right hilum that corresponds to the opacity seen on radiography. Histopathologic findings at the time of surgical resection were consistent with unicentric Castleman disease.
On chest radiography, unicentric CD affecting the mediastinum usually manifests as a mediastinal or hilar mass with smooth margins or lobular contours, whereas multicentric CD may result in bilateral hilar and mediastinum enlargement.46 On contrast-enhanced MDCT, unicentric CD can manifest as a solitary, noninvasive mass; a dominant mass with involvement of contiguous structures; or matted lymphadenopathy, limited to a single mediastinal compartment45-47 (Fig. 10). As CD is hypervascular in nature, intense contrast enhancement is characteristic. In multicentric CD, bilateral hilar and mediastinal lymphadenopathy is the most common manifestation of mediastinal involvement.46
Conclusions Vascular lesions of the mediastinum include a wide variety of abnormalities of systemic and pulmonary vessels and primary mediastinal masses of vascular origin. The correct identification and characterization of these lesions using advanced crosssectional imaging techniques such as MDCT or MRI are crucial to ensure appropriate patient management. Failure to recognize the vascular nature of these lesions can lead to potentially life-threatening complications such as excessive bleeding during biopsies. Therefore, it is important for the radiologist to be aware of the most common vascular abnormalities of the mediastinum that can result in abnormal findings on thoracic imaging examinations.
References 1. Gozdziuk K, Czekajska-Chehab E, Wrona A, et al: Saccular aneurysm of the superior vena cava detected by computed tomography and successfully treated with surgery. Ann Thorac Surg 78(6):e94-e95, 2004 2. Lyons HA, Calvy GL, Sammons BP: The diagnosis and classification of mediastinal masses. 1. A study of 782 cases. Ann Intern Med 51:897-932, 1959
3. Boateng P, Anjum W, Wechsler AS: Vascular lesions of the mediastinum. Thorac Surg Clin 19(1):91-105, 2009 4. Kelley MJ, Mannes EJ, Ravin CE: Mediastinal masses of vascular origin. A review. J Thorac Cardiovasc Surg 76(4):559-572, 1978 5. Shields TW, LoCicero III J, Ponn RB, et al: Vascular masses of the mediastinum. In: Shields TW, Ponn JB, Rusch VW (eds) ed 6: General Thoracic Surgery, Vol 2. Philadelphia: Lippincott Williams & Wilkins, 2523-2544, 2005 6. McElhinney DB, Hoydu AK, Gaynor JW, et al: Patterns of right aortic arch and mirror-image branching of the brachiocephalic vessels without associated anomalies. Pediatr Cardiol 22:285-291, 2001 7. Hastreiter AR, D'Cruz IA, Cantez T, et al: Right-sided aorta. Part I. Occurrence of right aortic arch in various types of congenital heart disease. II. Right aortic arch, right descending aorta, and associated anomalies. Br Heart J 28:722-725, 1966 8. Green CE, Klein JF: Multidetector row CT angiography of the thoracic aorta. In: Boiselle PM, White CS (eds): New Techniques in Cardiothoracic Imaging. New York, NY: Informa Healthcare, 105-126, 2007 9. Dähnert W: Cardiovascular disorders: Aortic dissection, Radiology Review Manual, ed 5. Philadelphia, PA: Lippincott Williams & Wilkins, 607-609, 2003 10. McMahon MA, Squirrell CA: Multidetector CT of aortic dissection: A pictorial review. Radiographics 30(2):445-460, 2010 11. Hagan PG, Nienaber CA, Isselbacher EM, et al: The International Registry of Acute Aortic Dissection (IRAD): New insights into an old disease. J Am Med Assoc 283(7):897-903, 2000 12. Castañer E, Andreu M, Gallardo X, et al: CT in nontraumatic acute thoracic aortic disease: Typical and atypical features and complications. Radiographics 23:S93–S110 (suppl), 2003 13. Smyth PT, Edwards JE: Pseudocoarctation, kinking, or buckling of the aorta. Circulation 46(5):1027-1032, 1972 14. Syed M, Lesch M: Coronary artery aneurysm: A review. Prog Cardiovasc Dis 40(1):77-84, 1997 15. Trop I, Samson L, Cordeau MP, et al: Anterior mediastinal mass in a patient with prior saphenous vein coronary artery bypass grafting. Chest 115(2):572-576, 1999 16. Gandhi SK, Siewers R: Anomalies of systemic venous drainage. In: Kaiser LR, Kron IL, Spray TL (eds): Mastery of Cardiothoracic Surgery. Philadelphia: Lippincott Williams & Wilkins, 708-715, 2007
250 17. Kouchoukos NT, Blackstone EH, Doty DB, et al: Cor triatriatum, Kirklin/ Barratt-Boyes Cardiac Surgery, ed 3. Philadelphia: Churchill Livingstone, 781-789, 2003 18. Pahwa R, Kumar A: Persistent left superior vena cava: An intensivist's experience and review of the literature. South Med J 96(5):528-529, 2003 19. Wong PS, Goldstraw P: Left superior vena cava: A pitfall in computed tomographic diagnosis with surgical implications. Ann Thorac Surg 50 (4):656-657, 1990 20. Joseph AE, Donaldson JS, Reynolds M: Neck and thorax venous aneurysm: Association with cystic hygroma. Radiology 170(1 Pt 1):109-112, 1989 21. Ryan R, Abbara S, Colen RR, et al: Cardiac valve disease: Spectrum of findings on cardiac 64-MDCT. Am J Roentgenol 190(5):W294-W303, 2008 22. Waller BF, Howard J, Fess S: Pathology of pulmonic valve stenosis and pure regurgitation. Clin Cardiol 18(1):45-50, 1995 23. Frazier AA, Galvin JR, Franks TJ, et al: From the archives of the AFIP: Pulmonary vasculature—hypertension and infarction. Radiographics 20:491-524, 2000 24. Peña E, Dennie C, Veinot J, et al: Pulmonary hypertension: How the radiologist can help. Radiographics 32(1):9-32, 2012 25. Bartter T, Irwin RS, Nash G: Aneurysms of the pulmonary arteries. Chest 94:1065-1075, 1988 26. Nguyen ET, Silva CI, Seely JM, et al: Pulmonary artery aneurysms and pseudoaneurysms in adults: Findings at CT and radiography. Am J Roentgenol 188:W126-W134, 2007 27. Shida T, Ohashi H, Nakamura K, et al: Pulmonary varices associated with mitral valve disease: A case report and survey of the literature. Ann Thorac Surg 34(4):452-456, 1982 28. DeBoer DA, Margolis ML, Livornese D, et al: Pulmonary venous aneurysm presenting as a middle mediastinal mass. Ann Thorac Surg 61 (4):1261-1262, 1996 29. Bossert T, Gummert JF, Mohr FW: Giant cystic lymphangioma of the mediastinum. Eur J Cardiothorac Surg 21(2):340, 2002 30. Jougon J, Laborde MN, Parrens M, et al: Cystic lymphangioma of the heart mimicking a mediastinal tumor. Eur J Cardiothorac Surg 22(3):476-478, 2002 31. Okubo T, Okayasu T, Osaka Y, et al: Surgical analysis of mediastinal lymphangioma—analysis of 7 cases. Nippon Kyobu Geka Gakkai Zasshi 40(4):583-586, 1992
B.W. Carter et al. 32. Teramoto K, Suzumura Y: Mediastinal cavernous lymphangioma in an adult. Gen Thorac Cardiovasc Surg 56(2):88-90, 2008 33. Shaffer K, Rosado-de-Christenson ML, Patz Jr EF, et al: Thoracic lymphangioma in adults: CT and MR imaging features. Am J Roentgenol 162:283-289, 1994 34. Davis JM, Mark GJ, Greene R: Benign blood vascular tumors of the mediastinum: Report of four cases and review of the literature. Radiology 126:581-587, 1978 35. Cohen AJ, Sbaschnig RJ, Hochholzer L, et al: Mediastinal hemangiomas. Ann Thorac Surg 43:656-659, 1987 36. Buckner S, McAllister J, D'Altorio R: Case of the season: Hemangioma of the middle mediastinum. Semin Roentgenol 29:98-99, 1994 37. Abe K, Akata S, Ohkubo Y, et al: Venous hemangioma of the mediastinum. Eur Radiol 11:73-75, 2001 38. Klecker RJ, Sinclair DS, King MA: Case 1: Mediastinal hemangioma. Am J Roentgenol 175(866):868-869, 2000 39. McAdams HP, Rosado-de-Christenson ML, Moran CA: Mediastinal hemangioma: Radiographic and CT features in 14 patients. Radiology 193:399-402, 1994 40. Cheung YC, Ng SH, Wan YL, et al: Dynamic CT features of mediastinal hemangioma: More information for evaluation. Clin Imaging 24:276-278, 2000 41. Roach H, Chowdhury P, Adams H: An incidental finding. Br J Radiol 76:753-754, 2003 42. Suster S, Moran CA. Neuroendocrine neoplasms of the mediastinum. Am J Clin Pathol 115:S17-S27 (suppl), 2001 43. Young Jr WF: Paragangliomas: Clinical overview. Ann N Y Acad Sci 1073:21-29, 2006 44. Balcombe J, Torigian DA, Kim W, et al: Cross-sectional imaging of paragangliomas of the aortic body and other thoracic branchiomeric paraganglia. Am J Roentgenol 188:1054-1058, 2007 45. McAdams HP, Rosado-de-Christenson M, Fishback NF, et al: Castleman disease of the thorax: Radiologic features with clinical and histopathologic correlation. Radiology 209:221-228, 1998 46. Johkoh T, Müller NL, Ichikado K, et al: Intrathoracic multicentric Castleman disease: CT findings in 12 patients. Radiology 209:477-481, 1998 47. Ko SF, Hsieh MJ, Ng SH, et al: Imaging spectrum of Castleman's disease. Am J Roentgenol 182(3):769-775, 2004