(Radiographics. 2002;22:S79-S93.)
© RSNA, 2002
MEDIASTINUM, CHEST WALL, AND DIAPHRAGM |
Imaging of Cystic Masses of the Mediastinum1
Mi-Young Jeung, MD,
Bernard Gasser, MD,
Afshin Gangi, MD, PhD,
Adriana Bogorin, MD,
Dominique Charneau, MD,
Jean Marie Wihlm, MD,
Jean-Louis Dietemann, MD and
Catherine Roy, MD
1 From the Departments of Radiology B (M.Y.J., A.G., D.C., C.R.), Pathology (B.G.), Radiology 2 (A.B., J.L.D.), and Thoracic Surgery (J.M.W.), University Hospital of Strasbourg, 1 place de l’Hôpital, 67091 Strasbourg, France. Recipient of a Cum Laude award for an education exhibit at the 2001 RSNA scientific assembly. Received February 25, 2002; revision requested March 28 and received May 30; accepted June 12. Address correspondence to M.Y.J. (e-mail: Mi-Young.Jeung@chru-strasbourg.fr).
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Abstract
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Cystic masses of the mediastinum are well-marginated round lesions that contain fluid and are lined with epithelium. Major cystic masses include congenital benign cysts (ie, bronchogenic, esophageal duplication, neurenteric, pericardial, and thymic cysts), meningocele, mature cystic teratoma, and lymphangioma. Many tumors (eg, thymomas, Hodgkin disease, germ cell tumors, mediastinal carcinomas, metastases to lymph nodes, nerve root tumors) can undergo cystic degeneration—especially after radiation therapy or chemotherapy—and demonstrate mixed solid and cystic elements at computed tomography (CT) or magnetic resonance (MR) imaging. If degeneration is extensive, such tumors may be virtually indistinguishable from congenital cysts. A mediastinal abscess or pancreatic pseudocyst also appears as a fluid-containing mediastinal cystic mass. However, clinical history and manifestations, anatomic position, and certain details seen at CT or MR imaging allow correct diagnosis in many cases. Familiarity with the radiologic features of mediastinal cystic masses facilitates accurate diagnosis, differentiation from other cystlike lesions, and, thus, optimal patient treatment.
© RSNA, 2002
Index Terms: Lymphangioma, 67.3157 • Mediastinum, abscess, 67.272 • Mediastinum, CT, 67.1211 • Mediastinum, cysts, 67.315 • Mediastinum, MR, 67.1214 • Mediastinum, neoplasms, 67.315 • Schwannoma, 67.3161
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LEARNING OBJECTIVES FOR TEST 4
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After reading this article and taking the test, the reader will be able to:
- Recognize the imaging features of a variety of cystic masses of the mediastinum.
- Describe the correlation between these imaging features and the corresponding gross pathologic and histologic findings.
- List various criteria for differentiating cystic masses from other cystlike lesions of the mediastinum.
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Introduction
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Mediastinal cystic masses are well-marginated, round, epithelium-lined lesions that contain fluid. They include a variety of entities with overlapping radiologic manifestations and variable prognoses. Cysts comprise 15%–20% of all mediastinal masses (1) and occur in all compartments of the mediastinum. They include bronchogenic cysts, esophageal duplication cysts, pericardial cysts, neurenteric cysts, meningocele, thymic cysts, cystic teratoma, and lymphangioma. Characterization of these cystic lesions may at times be difficult owing to the variable composition of fluid and associated complications such as hemorrhage or infection. In this article, we present the characteristic radiographic, computed tomographic (CT), and magnetic resonance (MR) findings in major congenital and acquired mediastinal cystic masses, discuss the criteria for differentiating between these cysts and other cystlike lesions, and correlate imaging findings with the underlying pathologic and histologic findings.
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Characteristic Imaging Findings
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Congenital mediastinal cysts include bronchogenic, duplication, neurenteric, pericardial, and thymic cysts. A number of criteria have been described to differentiate benign congenital cysts from other cystlike lesions: shape; cyst wall thickness; intracystic septations; presence of a solid component, fat, or calcification; and infiltration of surrounding structures. On chest radiographs, benign mediastinal cysts appear as a sharply marginated, round or oval area of increased opacity. Their appearance is similar to that of other cystlike lesions, but their location in the mediastinum can suggest the diagnosis and guide subsequent imaging procedures. The CT features of benign mediastinal cyst are (a) a smooth, oval or tubular mass with a well-defined thin wall that usually enhances after intravascular administration of contrast material, (b) homogeneous attenuation, usually in the range of water attenuation (0–20 HU), (c) no enhancement of cyst contents, and (d) no infiltration of adjacent mediastinal structures. Masses that show most or all of these features are invariably benign (2,3). Cysts that contain serous fluid typically have long T1 and T2 relaxation values, which produce low signal intensity on T1-weighted MR images and high signal intensity on T2-weighted images, parallel to that of cerebrospinal fluid (Fig 1). Because cysts containing nonserous fluid can have high attenuation at CT, they may be mistaken for solid lesions, especially when intravenous contrast material cannot be administered. MR imaging can be useful in showing the cystic nature of these masses because these cysts continue to have characteristically high signal intensity when imaged with T2-weighted sequences regardless of the nature of the cyst contents (4). If a malignant neoplasm is suspected because the CT or MR imaging findings are atypical or because the mass has increased in size, surgery or percutaneous or transbronchial-transesophageal aspiration may be required for diagnosis (5). Radionuclide imaging can be helpful in detecting functioning thyroid tissue (iodine-123 or I-131) or parathyroid tissue (technetium-99m sestamibi) in the mediastinal cystic mass (6). gallium-67 scintigraphy may show increased radiotracer uptake in the cystic malignancy owing to necrosis such as lymphoma or metastatic carcinoma. Ultrasonography (US) can be useful in evaluating a mass adjacent to the pleural surface or cardiophrenic (cardiodiaphragmatic) angle. At US, the benign cysts typically appear as anechoic thin-walled masses with increased through transmission.
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Figure 1a. Typical benign pericardial cyst with serous content in a 46-year-old woman. (a) Coronal T1-weighted MR image shows a round low-signal-intensity cyst with a regular thin wall. (b) T2-weighted MR image shows a homogeneous high-signal-intensity cyst without septation or a mural nodule.
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Figure 1b. Typical benign pericardial cyst with serous content in a 46-year-old woman. (a) Coronal T1-weighted MR image shows a round low-signal-intensity cyst with a regular thin wall. (b) T2-weighted MR image shows a homogeneous high-signal-intensity cyst without septation or a mural nodule.
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Cystic Lesions
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Bronchogenic Cyst
Bronchogenic cysts result from abnormal ventral budding or branching of the tracheobronchial tree during embryologic development. They are lined with pseudostratified columnar respiratory epithelium, and their walls usually contain cartilage, smooth muscle, and mucous gland tissue (Fig 2) (7). They may be filled with clear, serous fluid or thick, mucoid material. They may occur in any part of the mediastinum, but most are near the tracheal carina in the middle or posterior mediastinum (Fig 3). Less often, they may occur within the lung parenchyma, pleura, or diaphragm (8). Bronchogenic cysts are sometimes found in association with other congenital pulmonary malformations such as sequestration and lobar emphysema (9) but are uncommon. They may undergo an abrupt increase in size as a result of hemorrhage or infection. The majority are asymptomatic, but they may occasionally cause symptoms secondary to compression of adjacent structures. These symptoms include chest pain, cough, dyspnea, fever, and purulent sputum (10). On conventional chest radiographs, a bronchogenic cyst usually appears as a well-defined solitary mass with homogeneous opacity just inferior to the carina and often protruding slightly toward the right hilar shadow (Fig 2). On CT scans, a bronchogenic cyst appears as a single, smooth, round or elliptic mass with an imperceptible wall and uniform attenuation (Figs 2, 3). The attenuation value is dependent on the contents of the cyst and can vary from water attenuation to soft-tissue attenuation. The value can be more than 100 HU owing to a high protein level or calcium oxalate in the mucoid cyst (11,12). Air within the cyst is uncommon and suggestive of secondary infection and communication with the tracheobronchial tree. Calcification occurs occasionally in the wall or within the cyst contents. At T2-weighted MR imaging, cysts have high signal intensity regardless of the nature of the cyst contents, but variable patterns of signal intensity are seen at T1-weighted MR imaging because of variable cyst contents and the presence of protein, hemorrhage, or mucoid material (Figs 2, 4) (13). A fluid-fluid level within the bronchogenic cyst may be seen (Fig 2) (14).
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Figure 2a. Bronchogenic cyst in a 49-year-old man with a 2-week history of fever and cough. (a) Chest radiograph shows a round mass (arrow) that displaces the right primary bronchus superiorly, as well as pneumonia of the middle lobe and pleural effusion. (b) Contrast material-enhanced CT scan shows a cyst with uniform water attenuation and with an imperceptible wall. (c) Sagittal T1-weighted MR image shows a high-signal-intensity cyst with a fluid-fluid level due to infection (arrow). (d) Photomicrograph (original magnification, x50; hematoxylin-eosin [H-E] stain) shows a portion of the cyst wall with respiratory epithelium (arrow) that overlies fibrous tissue and cartilage.
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Figure 2b. Bronchogenic cyst in a 49-year-old man with a 2-week history of fever and cough. (a) Chest radiograph shows a round mass (arrow) that displaces the right primary bronchus superiorly, as well as pneumonia of the middle lobe and pleural effusion. (b) Contrast material-enhanced CT scan shows a cyst with uniform water attenuation and with an imperceptible wall. (c) Sagittal T1-weighted MR image shows a high-signal-intensity cyst with a fluid-fluid level due to infection (arrow). (d) Photomicrograph (original magnification, x50; hematoxylin-eosin [H-E] stain) shows a portion of the cyst wall with respiratory epithelium (arrow) that overlies fibrous tissue and cartilage.
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Figure 2c. Bronchogenic cyst in a 49-year-old man with a 2-week history of fever and cough. (a) Chest radiograph shows a round mass (arrow) that displaces the right primary bronchus superiorly, as well as pneumonia of the middle lobe and pleural effusion. (b) Contrast material-enhanced CT scan shows a cyst with uniform water attenuation and with an imperceptible wall. (c) Sagittal T1-weighted MR image shows a high-signal-intensity cyst with a fluid-fluid level due to infection (arrow). (d) Photomicrograph (original magnification, x50; hematoxylin-eosin [H-E] stain) shows a portion of the cyst wall with respiratory epithelium (arrow) that overlies fibrous tissue and cartilage.
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Figure 2d. Bronchogenic cyst in a 49-year-old man with a 2-week history of fever and cough. (a) Chest radiograph shows a round mass (arrow) that displaces the right primary bronchus superiorly, as well as pneumonia of the middle lobe and pleural effusion. (b) Contrast material-enhanced CT scan shows a cyst with uniform water attenuation and with an imperceptible wall. (c) Sagittal T1-weighted MR image shows a high-signal-intensity cyst with a fluid-fluid level due to infection (arrow). (d) Photomicrograph (original magnification, x50; hematoxylin-eosin [H-E] stain) shows a portion of the cyst wall with respiratory epithelium (arrow) that overlies fibrous tissue and cartilage.
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Figure 3a. Bronchogenic cyst in a 44-year-old woman with a 3-year history of chest pain. (a) CT scan shows a thin-walled water-attenuation cyst in the posterior mediastinum (arrow). (b) Videothoracoscopic image shows a translucent round cyst behind the descending aorta (arrow).
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Figure 3b. Bronchogenic cyst in a 44-year-old woman with a 3-year history of chest pain. (a) CT scan shows a thin-walled water-attenuation cyst in the posterior mediastinum (arrow). (b) Videothoracoscopic image shows a translucent round cyst behind the descending aorta (arrow).
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Duplication Cyst
Esophageal duplication cysts are developmental in origin and are classified as foregut cysts that are either bronchogenic or neurenteric (15). Esophageal duplication cysts are uncommon. Many are asymptomatic, but they may cause dysphagia, pain, or other symptoms owing to compression of adjacent structures (16). The majority are detected in infants or children (16), usually adjacent to or within the esophageal wall. Ectopic gastric mucosa in the cyst may cause hemorrhage or perforation of the cyst, or infection. Their appearance at CT or MR imaging is identical to that of bronchogenic cysts except that the wall of the lesion may be thicker and in more intimate contact with the esophagus (Fig 5) (17,18). Results of barium examination will show extrinsic or intramural compression due to close contact with the esophagus (16). Radionuclide scanning with the use of Tc-99m sodium pertechnetate may be helpful in pediatric patients, in 50% of whom thoracic duplication cysts contain ectopic gastric mucosa (19).
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Figure 5a. Duplication cyst in a 10-year-old girl with cough. (a) Chest radiograph shows a round area of increased opacity that deforms the azygoesophageal recess (arrow). (b) Contrast-enhanced CT scan shows a thin-walled water-attenuation cyst adjacent to the esophagus (arrow).
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Figure 5b. Duplication cyst in a 10-year-old girl with cough. (a) Chest radiograph shows a round area of increased opacity that deforms the azygoesophageal recess (arrow). (b) Contrast-enhanced CT scan shows a thin-walled water-attenuation cyst adjacent to the esophagus (arrow).
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Pericardial Cyst
Pericardial (mesothelial) cysts result from aberrations in the formation of coelomic (somatic) cavities. The cyst walls are composed of connective tissue and a single layer of mesothelial cells (Fig 6), and they usually contain clear fluid. Pericardial cysts are invariably connected to the pericardium, but at surgery, only a few cases show visible communication with the pericardial sac (20). The majority of pericardial cysts arise in the anterior cardiophrenic angle, more frequently on the rightside (20), but they can be seen as high as the pericardial recesses at the level of the proximal aorta and pulmonary arteries (21). Occasionally, cysts are pedunculated. Most patients are asymptomatic. At conventional radiography, these cysts appear as well-defined, round or oval masses in the cardiophrenic angle. US can be used to demonstrate the cystic nature of these lesions. CT and MR imaging features are similar to those of other congenital mediastinal cysts (Fig 6). Pleuropericardial cysts are not always round; they may demonstrate different shapes when studied at different times (22).
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Figure 6a. Pericardial cyst in a 37-year-old asymptomatic man. (a) Chest radiograph shows a sharply defined area of increased opacity in the right cardiophrenic angle (arrow). (b) US image shows a well-defined anechoic cyst that connects to the pericardium (arrow). (c) Contrast-enhanced CT scan shows a thin-walled water-attenuation cyst (arrow). (d) Photomicrograph (original magnification, x100; H-E stain) shows a cyst wall composed of a thin layer of fibrous tissue lined with a single layer of mesothelial cells (arrow).
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Figure 6b. Pericardial cyst in a 37-year-old asymptomatic man. (a) Chest radiograph shows a sharply defined area of increased opacity in the right cardiophrenic angle (arrow). (b) US image shows a well-defined anechoic cyst that connects to the pericardium (arrow). (c) Contrast-enhanced CT scan shows a thin-walled water-attenuation cyst (arrow). (d) Photomicrograph (original magnification, x100; H-E stain) shows a cyst wall composed of a thin layer of fibrous tissue lined with a single layer of mesothelial cells (arrow).
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Figure 6c. Pericardial cyst in a 37-year-old asymptomatic man. (a) Chest radiograph shows a sharply defined area of increased opacity in the right cardiophrenic angle (arrow). (b) US image shows a well-defined anechoic cyst that connects to the pericardium (arrow). (c) Contrast-enhanced CT scan shows a thin-walled water-attenuation cyst (arrow). (d) Photomicrograph (original magnification, x100; H-E stain) shows a cyst wall composed of a thin layer of fibrous tissue lined with a single layer of mesothelial cells (arrow).
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Figure 6d. Pericardial cyst in a 37-year-old asymptomatic man. (a) Chest radiograph shows a sharply defined area of increased opacity in the right cardiophrenic angle (arrow). (b) US image shows a well-defined anechoic cyst that connects to the pericardium (arrow). (c) Contrast-enhanced CT scan shows a thin-walled water-attenuation cyst (arrow). (d) Photomicrograph (original magnification, x100; H-E stain) shows a cyst wall composed of a thin layer of fibrous tissue lined with a single layer of mesothelial cells (arrow).
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Meningocele
An intrathoracic meningocele is an anomalous herniation of the leptomeninges through an intervertebral foramen or a defect in the vertebral body. This abnormality is frequently associated with neurofibromatosis. Most meningoceles are detected in adults (23). On conventional radiographs, they appear as sharply defined round, smooth, or lobulated paraspinal masses. However, they demonstrate no specific features that distinguish them from neurogenic neoplasms. At CT, they appear as well-defined, homogeneous, low-attenuation paravertebral masses (Fig 7). Other findings may include enlargement of intervertebral foramina and associated vertebral and rib anomalies or scoliosis (5). CT or myelography performed after intraspinal injection of contrast material shows filling of the meningocele and helps confirm the diagnosis (Fig 7) (24).
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Figure 7a. Lateral thoracic meningocele in a 37-year-old man with neurofibromatosis. (a) CT scan shows a low-attenuation mass protruding from the enlarged left intervertebral foramen. (b) On a myelogram, contrast medium is seen to pass into the meningocele (arrow).
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Figure 7b. Lateral thoracic meningocele in a 37-year-old man with neurofibromatosis. (a) CT scan shows a low-attenuation mass protruding from the enlarged left intervertebral foramen. (b) On a myelogram, contrast medium is seen to pass into the meningocele (arrow).
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Thymic Cyst
Thymic cysts are uncommon and represent 1% of all mediastinal masses (25). They can be congenital or acquired. Congenital thymic cysts are rare and derive from a patent thymopharyngeal duct. Approximately 50% of congenital thymic cysts are incidentally discovered during the first 2 decades of life (26). Acquired thymic cysts may occur in patients after radiation therapy for Hodgkin disease (27), in association with thymic tumors (28), and after thoracotomy (29). They may be unilocular or multilocular (26). Multilocular thymic cysts are the sequelae of a variety of inflammatory processes and usually occur in asymptomatic men (30,31). Large multilocular thymic cysts are seen in approximately 1% of children with human immunodeficiency virus infection (32). On chest radiographs, thymic cysts are indistinguishable from other nonlobulated thymic masses. At CT, simple congenital thymic cysts usually appear as well-defined water-attenuation masses with imperceptible walls (Fig 8). Multilocular thymic cysts may appear as well-defined, heterogeneous, unilocular or multilocular cystic masses with a clearly seen wall (31). However, some thymic cysts may have increased CT attenuation if hemorrhage or infection occurs as a complication and may be misdiagnosed as solid masses. Curvilinear calcification of the cyst wall occurs in a minority of cases (26). At MR imaging, the contents of thymic cysts demonstrate the typical characteristics of fluid (ie, low signal intensity on T1-weighted images, uniform high signal intensity on T2-weighted images) (Fig 8). If hemorrhage or infection occurs, the cysts can demonstrate high signal intensity on both T1- and T2-weighted images (25).
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Figure 8a. Thymic cyst in a 70-year-old asymptomatic woman. (a) Contrast-enhanced CT scan shows a thin-walled water-attenuation cyst (arrow). (b) Sagittal T1-weighted MR image shows a low-signal-intensity cyst (arrow) in a thymic location. (c) Photograph obtained at surgery shows a translucent round cyst protruding from the thorax.
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Figure 8b. Thymic cyst in a 70-year-old asymptomatic woman. (a) Contrast-enhanced CT scan shows a thin-walled water-attenuation cyst (arrow). (b) Sagittal T1-weighted MR image shows a low-signal-intensity cyst (arrow) in a thymic location. (c) Photograph obtained at surgery shows a translucent round cyst protruding from the thorax.
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Figure 8c. Thymic cyst in a 70-year-old asymptomatic woman. (a) Contrast-enhanced CT scan shows a thin-walled water-attenuation cyst (arrow). (b) Sagittal T1-weighted MR image shows a low-signal-intensity cyst (arrow) in a thymic location. (c) Photograph obtained at surgery shows a translucent round cyst protruding from the thorax.
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Mature Cystic Teratoma
Mature cystic teratomas (dermoid cysts) are cystic tumors composed of well-differentiated derivations from at least two of the three germ cell layers (ectoderm, mesoderm, and endoderm). Ectodermal elements may be represented by skin, teeth, and hair; mesodermal elements by bone, cartilage, and muscle; and endodermal elements by bronchial and gastrointestinal epithelium and pancreatic tissue. Cyst formation is typical, and cysts are usually lined by tall, mucus-secreting epithelial cells (33). The cysts are filled with sebaceous material and may contain hair (Fig 9). Hair follicles, skin glands, muscle, and other tissues lie within the wall. Mature cystic teratomas are the most common germ cell neoplasm. They occur more frequently in young adults. Most are asymptomatic and are incidentally discovered, but large tumors may cause chest pain, dyspnea, cough, or other symptoms of compression (26). The majority of dermoid cysts are in the anterior mediastinum, with only 3%–8% occurring in the posterior mediastinum (33).
At radiography, cystic teratomas usually appear as a sharply marginated, round or lobulated anterior mediastinal mass that extends to one side of the midline. Calcification, ossification, or even teeth may be visible on chest radiographs (34). At CT, these tumors are heterogeneous, well-defined masses with walls of variable thickness that may enhance (26,35). They may contain all four tissue types, including soft tissue, fluid, fat, and calcium, but fluid-containing cystic components are usually prominent (Fig 10) (35). Recently, Moeller et al (34) reported that mediastinal mature teratomas contain soft tissue in virtually all cases, fluid in 88%, fat in 76%, and calcium in 53%. All these elements are present in the same lesion in 39% of cases. In 15% of cases, teratomas consist only of cystic lesions that contain neither fat nor calcification. Most cystic teratomas are multilocular, but unilocular cystic lesions also occur. Calcifications may be focal, rimlike, or, in rare cases, representative of teeth or bone. A fat-fluid level within the mass is a highly specific finding but is seen less frequently (34,36). Complications such as tumor rupture may occur. Ruptured teratomas show a higher prevalence of (a) inhomogeneity of the internal component of the mass and (b) adjacent consolidation, atelectasis, and pleural or pericardial effusion than do unruptured teratomas (37). The most common MR imaging appearance is that of a heterogeneous mediastinal mass containing a variable admixture of fat, fluid, soft tissue, and calcification (25,38). The sebaceous component of the mass has high signal intensity on T1-weighted images and variable signal intensity on T2-weighted images, usually approximating that of fat (Fig 10) (39). However, this combination of signal intensities on T1- and T2-weighted images is not specific for fat; some hemorrhagic cystic lesions may have a similar MR imaging appearance. A fat-saturation MR imaging technique (phase-shift gradient-echo imaging or proton-selective fat-saturation imaging) can be used to detect fat and distinguish it from hemorrhage (40).
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Figure 10a. Mature cystic teratoma in a 31-year-old man who had chest discomfort and dyspnea at exertion. (a) Radiograph shows a large, well-defined mediastinal mass (arrow). (b) Contrast-enhanced CT scan shows a heterogeneous anterior mediastinal mass with areas of fat (long arrow), calcification (short arrow), fluid attenuation, and thin soft-tissue septa. (c, d) T1-weighted (c) and T2-weighted (d) MR images show a mass with a high-signal-intensity area of fat (arrow), low-signal-intensity calcification, and a high-signal-intensity multilocular cyst. (e) Photograph of the surgical specimen shows an oval mass with sebaceous material (long arrow), cartilage, and nerve tissue (short arrow).
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Figure 10b. Mature cystic teratoma in a 31-year-old man who had chest discomfort and dyspnea at exertion. (a) Radiograph shows a large, well-defined mediastinal mass (arrow). (b) Contrast-enhanced CT scan shows a heterogeneous anterior mediastinal mass with areas of fat (long arrow), calcification (short arrow), fluid attenuation, and thin soft-tissue septa. (c, d) T1-weighted (c) and T2-weighted (d) MR images show a mass with a high-signal-intensity area of fat (arrow), low-signal-intensity calcification, and a high-signal-intensity multilocular cyst. (e) Photograph of the surgical specimen shows an oval mass with sebaceous material (long arrow), cartilage, and nerve tissue (short arrow).
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Figure 10c. Mature cystic teratoma in a 31-year-old man who had chest discomfort and dyspnea at exertion. (a) Radiograph shows a large, well-defined mediastinal mass (arrow). (b) Contrast-enhanced CT scan shows a heterogeneous anterior mediastinal mass with areas of fat (long arrow), calcification (short arrow), fluid attenuation, and thin soft-tissue septa. (c, d) T1-weighted (c) and T2-weighted (d) MR images show a mass with a high-signal-intensity area of fat (arrow), low-signal-intensity calcification, and a high-signal-intensity multilocular cyst. (e) Photograph of the surgical specimen shows an oval mass with sebaceous material (long arrow), cartilage, and nerve tissue (short arrow).
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Figure 10d. Mature cystic teratoma in a 31-year-old man who had chest discomfort and dyspnea at exertion. (a) Radiograph shows a large, well-defined mediastinal mass (arrow). (b) Contrast-enhanced CT scan shows a heterogeneous anterior mediastinal mass with areas of fat (long arrow), calcification (short arrow), fluid attenuation, and thin soft-tissue septa. (c, d) T1-weighted (c) and T2-weighted (d) MR images show a mass with a high-signal-intensity area of fat (arrow), low-signal-intensity calcification, and a high-signal-intensity multilocular cyst. (e) Photograph of the surgical specimen shows an oval mass with sebaceous material (long arrow), cartilage, and nerve tissue (short arrow).
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Figure 10e. Mature cystic teratoma in a 31-year-old man who had chest discomfort and dyspnea at exertion. (a) Radiograph shows a large, well-defined mediastinal mass (arrow). (b) Contrast-enhanced CT scan shows a heterogeneous anterior mediastinal mass with areas of fat (long arrow), calcification (short arrow), fluid attenuation, and thin soft-tissue septa. (c, d) T1-weighted (c) and T2-weighted (d) MR images show a mass with a high-signal-intensity area of fat (arrow), low-signal-intensity calcification, and a high-signal-intensity multilocular cyst. (e) Photograph of the surgical specimen shows an oval mass with sebaceous material (long arrow), cartilage, and nerve tissue (short arrow).
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Lymphangioma
Lymphangiomas are rare, benign congenital malformations consisting of focal proliferations of well-differentiated lymphatic tissue that are present in a multicystic or spongelike accumulation (41). They represent 0.7%–4.5% of all mediastinal tumors (42). The majority of lymphangiomas are discovered during the first 2 years of life. They are most common in the neck and axilla, and about 10% extend into the mediastinum (41,43). Approximately 1% of all lymphangiomas are confined to the chest (44). They are classified histologically as simple (capillary), cavernous, or cystic (hygroma), depending on the size of the lymphatic channels they contain. Cystic lymphangiomas are most common. They may occur in two clinical forms: a cavernous or cystic variety that often extends into the neck and occurs in infants (hygroma), and a variety that occurs later in life and is confined to the mediastinum. Because of their soft, yielding consistency, they seldom produce symptoms. However, compression of the mediastinal structures can result in chest pain, cough, and dyspnea. Complications of lymphangioma include infection, airway compromise, chylothorax, and chylopericardium (35).
On chest radiographs, lymphangiomas appear as well-defined, round, lobular masses (Fig 11). Unilateral or bilateral pleural effusions, which are often chylous, may be present. CT usually shows a smooth, lobulated mass, which may mold to or envelop, rather than displace, the adjacent mediastinal structures (43). Lymphangiomas usually have homogeneous low attenuation similar to that of water, but can have higher attenuation or consist of a combination of fluid, solid tissue, and fat (Fig 11). Calcification is rare. Lymphangiomas may be either unilocular or multilocular. Thin septations within the mass can sometimes be seen (42,43). At MR imaging, the lesions have heterogeneous signal intensity on T1-weighted images. They usually have high signal intensity on T2-weighted images, a finding that reflects their fluid content (42). It is sometimes easier to recognize serpentine, vessel-like septa at MR imaging than at CT (Fig 11). Because of their insinuating nature, complete surgical resection of lymphangiomas may be difficult, and follow-up may be needed to exclude recurrence (44).
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Figure 11a. Lymphangioma in a 35-year-old man with a history of multiple resections of cystic hygroma since infancy. (a) Chest radiograph shows a large mediastinal mass. (b) Contrast-enhanced CT scan shows a low-attenuation mass (arrow) that extends to all mediastinal compartments. (c) Coronal T2-weighted MR image shows a high-signal-intensity cystic mass with multiple septa (arrows).
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Figure 11b. Lymphangioma in a 35-year-old man with a history of multiple resections of cystic hygroma since infancy. (a) Chest radiograph shows a large mediastinal mass. (b) Contrast-enhanced CT scan shows a low-attenuation mass (arrow) that extends to all mediastinal compartments. (c) Coronal T2-weighted MR image shows a high-signal-intensity cystic mass with multiple septa (arrows).
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Figure 11c. Lymphangioma in a 35-year-old man with a history of multiple resections of cystic hygroma since infancy. (a) Chest radiograph shows a large mediastinal mass. (b) Contrast-enhanced CT scan shows a low-attenuation mass (arrow) that extends to all mediastinal compartments. (c) Coronal T2-weighted MR image shows a high-signal-intensity cystic mass with multiple septa (arrows).
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Cystlike Lesions
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Many tumors can undergo cystic degeneration and demonstrate mixed solid and cystic elements at CT or MR imaging. If degeneration is extensive, the CT and gross appearances of the lesion are indistinguishable from those of a congenital cyst. This category includes thymomas (Fig 12), Hodgkin disease (Fig 13), germ cell tumors (Fig 14), mediastinal carcinomas, metastases to lymph nodes, and nerve root tumors, especially schwannomas (Fig 15) and neurofibromas. Cystic degeneration of a solid mass is more likely to occur after radiation therapy or chemotherapy but may be seen prior to treatment. A mediastinal abscess or pancreatic pseudocyst appears as a fluid-containing mediastinal cystic mass, but clinical features usually permit differentiation from true cysts or neoplasms.
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Figure 12a. Cystic thymoma in a 50-year-old man with a 2-month history of myasthenia. (a) Contrast-enhanced CT scan shows a solid mass (arrow) in a thymic location. (b) CT scan obtained at a lower level than a shows a thin-walled water-attenuation cystic lesion. (c) Sagittal T2-weighted MR image shows a thin-walled high-signal-intensity cystic lesion with mural nodules (arrow). The nodules are better seen at MR imaging than at CT. (d) Photograph of the resected surgical specimen shows a thymoma with cystic degeneration and solid mural nodules.
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Figure 12b. Cystic thymoma in a 50-year-old man with a 2-month history of myasthenia. (a) Contrast-enhanced CT scan shows a solid mass (arrow) in a thymic location. (b) CT scan obtained at a lower level than a shows a thin-walled water-attenuation cystic lesion. (c) Sagittal T2-weighted MR image shows a thin-walled high-signal-intensity cystic lesion with mural nodules (arrow). The nodules are better seen at MR imaging than at CT. (d) Photograph of the resected surgical specimen shows a thymoma with cystic degeneration and solid mural nodules.
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Figure 12c. Cystic thymoma in a 50-year-old man with a 2-month history of myasthenia. (a) Contrast-enhanced CT scan shows a solid mass (arrow) in a thymic location. (b) CT scan obtained at a lower level than a shows a thin-walled water-attenuation cystic lesion. (c) Sagittal T2-weighted MR image shows a thin-walled high-signal-intensity cystic lesion with mural nodules (arrow). The nodules are better seen at MR imaging than at CT. (d) Photograph of the resected surgical specimen shows a thymoma with cystic degeneration and solid mural nodules.
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Figure 12d. Cystic thymoma in a 50-year-old man with a 2-month history of myasthenia. (a) Contrast-enhanced CT scan shows a solid mass (arrow) in a thymic location. (b) CT scan obtained at a lower level than a shows a thin-walled water-attenuation cystic lesion. (c) Sagittal T2-weighted MR image shows a thin-walled high-signal-intensity cystic lesion with mural nodules (arrow). The nodules are better seen at MR imaging than at CT. (d) Photograph of the resected surgical specimen shows a thymoma with cystic degeneration and solid mural nodules.
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Figure 13. Hodgkin disease in a 16-year-old girl with a 1-month history of chest pain and general weakness. Axial T2-weighted MR image shows a mass with mixed solid and cystic components (arrow).
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Figure 14a. Recurrent choriocarcinoma in a 37-year-old man who had undergone radiation therapy and chemotherapy 4 years earlier. Contrast-enhanced CT scan (a) and T2-weighted MR image (b) show a lobulated mass with mixed solid and cystic components (arrow in b) in the anterior mediastinum.
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Figure 14b. Recurrent choriocarcinoma in a 37-year-old man who had undergone radiation therapy and chemotherapy 4 years earlier. Contrast-enhanced CT scan (a) and T2-weighted MR image (b) show a lobulated mass with mixed solid and cystic components (arrow in b) in the anterior mediastinum.
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Figure 15a. Cystic schwannoma in a 17-year-old asymptomatic boy. (a) Chest radiograph shows a well-defined round mass (arrow) in the left part of the superior mediastinum. (b) Contrast-enhanced CT scan shows a thin-walled low-attenuation cystic lesion in the paravertebral region. (c) Axial T2-weighted MR image shows a homogeneous high-signal-intensity cystic lesion (arrow) that is indistinguishable from a congenital cyst. (d) Photomicrograph (original magnification, x25; H-E stain) shows a portion of tumor wall composed of spindle cells with a relatively compact architecture (arrow) as well as fibrous tissue.
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Figure 15b. Cystic schwannoma in a 17-year-old asymptomatic boy. (a) Chest radiograph shows a well-defined round mass (arrow) in the left part of the superior mediastinum. (b) Contrast-enhanced CT scan shows a thin-walled low-attenuation cystic lesion in the paravertebral region. (c) Axial T2-weighted MR image shows a homogeneous high-signal-intensity cystic lesion (arrow) that is indistinguishable from a congenital cyst. (d) Photomicrograph (original magnification, x25; H-E stain) shows a portion of tumor wall composed of spindle cells with a relatively compact architecture (arrow) as well as fibrous tissue.
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Figure 15c. Cystic schwannoma in a 17-year-old asymptomatic boy. (a) Chest radiograph shows a well-defined round mass (arrow) in the left part of the superior mediastinum. (b) Contrast-enhanced CT scan shows a thin-walled low-attenuation cystic lesion in the paravertebral region. (c) Axial T2-weighted MR image shows a homogeneous high-signal-intensity cystic lesion (arrow) that is indistinguishable from a congenital cyst. (d) Photomicrograph (original magnification, x25; H-E stain) shows a portion of tumor wall composed of spindle cells with a relatively compact architecture (arrow) as well as fibrous tissue.
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Figure 15d. Cystic schwannoma in a 17-year-old asymptomatic boy. (a) Chest radiograph shows a well-defined round mass (arrow) in the left part of the superior mediastinum. (b) Contrast-enhanced CT scan shows a thin-walled low-attenuation cystic lesion in the paravertebral region. (c) Axial T2-weighted MR image shows a homogeneous high-signal-intensity cystic lesion (arrow) that is indistinguishable from a congenital cyst. (d) Photomicrograph (original magnification, x25; H-E stain) shows a portion of tumor wall composed of spindle cells with a relatively compact architecture (arrow) as well as fibrous tissue.
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Cystic Schwannoma
Schwannoma is a peripheral nerve sheath tumor composed of spindle cells densely packed together or organized more loosely in association with a myxoid stroma; areas of infarction are common. At CT, schwannoma appears as a well-marginated, smooth, rounded or elliptic mass in the paravertebral region (Fig 15) or along the courses of intercostal nerves. Schwannomas have heterogeneous attenuation, including low-attenuation areas caused by the coalescence of interstitial fluid, xanthomatous change, or cystic degeneration secondary to infarction (45). Enlargement of neural foramina with or without extension into the spinal canal may be associated with paravertebral tumors. MR imaging is the preferred modality for demonstrating the intraspinal extension of the tumor or the presence of an associated spinal cord abnormality. Schwannomas may have low to intermediate signal intensity on T1-weighted MR images and inhomogeneous high signal intensity throughout the lesion on T2-weighted images, findings that correspond to cystic degeneration (Fig 15) (46,47).
Mediastinal Pancreatic Pseudocyst
Extension of a pancreatic pseudocyst into the mediastinum is uncommon. A cystic posterior mediastinal mass that develops over a short time in a patient with evidence of pancreatitis is likely to be a pseudocyst (48). A pseudocyst represents an encapsulated collection of pancreatic secretion, blood, and necrotic material. A mediastinal pseudocyst almost always occurs in the lower part of the posterior mediastinum, having gained access to the chest via the esophageal or aortic hiatus (49). CT shows a thin, cystic, low-attenuation mass in the posterior mediastinum or adjacent thoracic cavity associated with compression or displacement of the esophagus or splaying of the diaphragmatic crura (Fig 16) (48). Cyst contents can be isoattenuating or hyperattenuating relative to water, depending on the presence of hemorrhage or infection. An abdominal component is common but is not invariably present (50). MR imaging demonstrates the cystic nature of the mass (Fig 16).
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Figure 16a. Pancreatic pseudocyst in a 45-year-old woman with a 2-week history of dysphagia and chest pain. (a) Contrast-enhanced CT scan shows bilateral pleural effusion and a thin-walled periaortic cystic lesion that displaces the esophagus (arrow) anteriorly. (b) Axial T1-weighted MR image shows a low-signal-intensity cyst (arrow).
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Figure 16b. Pancreatic pseudocyst in a 45-year-old woman with a 2-week history of dysphagia and chest pain. (a) Contrast-enhanced CT scan shows bilateral pleural effusion and a thin-walled periaortic cystic lesion that displaces the esophagus (arrow) anteriorly. (b) Axial T1-weighted MR image shows a low-signal-intensity cyst (arrow).
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Mediastinal Abscess
Mediastinal abscesses are uncommon and are usually related to surgery (eg, median sternotomy), esophageal perforation, or spread of infection from an adjacent region. Sepsis may develop, and the fatality rate is high. The abscesses may appear as a low-attenuation mass at CT owing to fluid content. Air bubbles, contiguity or communication with an empyema or subphrenic abscess, and clinical features usually permit differentiation from true cysts or neoplasms (5). However, percutaneous needle aspiration may be required to distinguish an abscess from an uninfected postoperative seroma or hematoma.
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Conclusions
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A variety of mediastinal masses contain cystic areas and have variable prognoses. They include bronchogenic cysts, esophageal duplication cysts, neurenteric cysts, meningocele, pericardial cysts, thymic cysts, cystic teratoma, and lymphangioma. Although these masses have similar imaging appearances, clinical history, anatomic position, and certain details seen at CT or MR imaging allow correct diagnosis in many cases. Familiarity with the radiologic features of these lesions facilitates accurate diagnosis, differentiation from other cystlike lesions, and, thus, optimal patient treatment.
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Footnotes
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Abbreviation: H-E = hematoxylin-eosin
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References
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