Dysgerminoma

A wide variety of lesions occur in the mediastinum in patients of every age. Twenty five to 50 percent of these primary mediastinal masses may be malignant, making early diagnosis and therapy crucial. Since most arise from normal structures in the region, localization of lesions to compartments of the mediastinum may assist in diagnosis. This article reviews imaging techniques for lesions originating in the mediastinum.

Primary mediastinal masses are a diverse group of lesions which present a diagnostic and therapeutic challenge to clinicians, as well as radiologists. In a combined series of 1,000 patients with mediastinal tumors and cysts, the relative incidence was as follows: neurogenic tumors, 24 percent; cysts, 21 percent; germ cell tumors, 17 percent; thymomas, 12 percent; lymphomas, 13 percent; and others, 13 percent.[1] A thorough understanding of mediastinal anatomy is essential for the evaluation of a mediastinal mass, since specific lesions have a predilection for certain sites. In order to formulate reasonable differential diagnoses in the evaluation of mediastinal abnormalities, several methods have been suggested to divide the mediastinum into compartments.[2,3] With the classic (traditional) anatomic method,[2] the anterior mediastinum has been defined as being bounded anteriorly by the sternum and posteriorly by the pericardium, aorta and brachiocephalic vessels; the middle mediastinum contains the pericardium and heart, the ascending and transverse portions of the aorta, the vena cavae, the phrenic and vagus nerves, the trachea, mainstem bronchi and contiguous lymph nodes, and the central pulmonary arteries and veins. The posterior mediastinum is bordered anteriorly by the pericardium and posteriorly by the spine.[2] With the radiologic method of classification, the mediastinum is divided into three compartments based on the lateral chest radiograph. A line drawn from the diaphragm to the thoracic inlet along the back of the heart and anterior to the trachea divides the anterior and middle mediastinum, and a line drawn 1 cm behind the anterior margin of the thoracic vertebral bodies separates the middle and posterior mediastinum. All methods of division are arbitrary but are intended to facilitate understanding of the complex anatomy of the mediastinum. For the purposes of this review, the traditional method of dividing the mediastinum is used.

Nonvascular lesions that tend to occur in each of the compartments of the mediastinum are listed in Table 1. Thymomas, primary mediastinal germ cell tumors, lymphomas, mesenchymal tumors, and substernal extensions of the thyroid are major considerations in the differential diagnosis of primary anterior mediastinal masses. Middle mediastinal masses include lymph node enlargement from a variety of causes, pericardial cysts, and bronchogenic cysts. Posterior mediastinal masses are usually neurogenic in origin, but they may also arise from the esophagus or represent gastroenteric cysts. Nodal enlargement from metastatic disease, including extrathoracic as well as bronchogenic primaries, may occur in any mediastinal compartment.

GENERAL IMAGING CONSIDERATIONS

High kilovoltage posteroanterior and lateral radio-graphs of the chest continue to be the most valuable technique for the initial evaluation of mediastinal masses. Contour distortions of the normal interfaces between the lung and the mediastinum may occur even with small mediastinal masses which, with enlargement, may project into the adjacent hemithorax. Oblique views may also be useful in the evaluation of patients with an equivocal chest radiograph. Careful fluoroscopy may allow optimal determination of obliquity to visualize a lesion better and may assist by demonstrating intrinsic or transmitted pulsations with masses. Occasionally, calcifications within lesions are also identified initially in this way.

Although conventional tomography has been used in the past to evaluate the mediastinum, computed tomography (CT) has now largely replaced conventional tomography in most institutions as the most useful imaging modality following routine radiography.[4] In fact, CT has been shown to be more useful in evaluating the mediastinum than any other region in the thorax. Mediastinal pathology may easily be detected by CT even in the presence of a normal chest radiograph. Superior contrast resolution permits differentiation of normal mediastinal structures from mediastinal masses, allows accurate delineation of the densities of tissues within a mass, and with intravenous contrast, may distinguish between vascular and non-vascular lesions. The transaxial imaging plane of CT allows clear definition of normal structures in the mediastinum, most of which course perpendicular to the imaging plane (eg, major vessels and airways). Computed tomography can also assist in determining the best approach for the biopsy of mediastinal lesions.

More recently, magnetic resonance imaging (MRI) has been used to evaluate the mediastinum. The lack of ionizing radiation, the availability of direct cross-sectional images in multiple imaging planes, and the ability to distinguish vascular structures without using intravenous contrast has made MRI a potentially valuable alternative to CT scanning. Multiple studies have now shown MRI to be equivalent to CT for detecting mediastinal lymph nodes and masses.[5-7] Although initially it was hoped that differences in signal intensity would allow differentiation between benign and malignant masses, MRI has been unable to discriminate between enlarged benign and malignant nodes. However, there is evidence to suggest that in the future, MRI may prove to be useful in the differentiation of residual tumor from fibrosis.[8] Invasion or encasement of major cardiovascular structures by tumor may be demonstrated better on MRI than CT. The direct sagittal and coronal images afforded by MRI may also allow better evaluation of lesions in the thoracic apex and the diaphragmatic areas than CT. However, because of diminished spatial resolution, inability to detect small calcifications, long scan time, and the current difficulty in imaging the lung parenchyma, the overall utility of MRI for evaluating the thorax remains limited at this time.[7]

A brief discussion follows of diagnostic imaging applications for the major masses which occur in the mediastinum.

THYMOMA

Thymoma is the most frequent tumor occurring in the anterior mediastinum. Although it may occur at any age, it is most common in patients over the age of 40. Thymomas arise from both the epithelial and the thymocytic elements of the gland and can be classified into the following four subtypes based on the predominant cell: (1) lymphocytic; (2) epithelial; (3) mixed lumphoepithelial; and (4) spindle cell. Histologic examination alone does not allow the differentiation of benign from malignant lesions, and the presence at surgery of complete encapsulation or local invasion is used to estimate malignancy and prognosis.

The association between thymic neoplasms and myasthenia gravis is well known. Thymic tumors occur in approximately 8 to 15 percent of patients with myasthenia gravis, and approximately 25 to 50 percent of patients with thymic tumors have been shown to have myasthenia. Other associated conditions that have been reported include red blood cell hypoplasia, hypogammaglobulinemia, and/or Cushing's syndrome.

Radiographically, these lesions appear as round, oval or lobulated masses in the anterior mediastinum, usually just anterior to the junction of the heart and the great vessels (Fig 1). Nearly one-quarter of thymomas may not be detected initially on routine posteroanterior chest radiographs, but diagnostic accuracy is increased to 94 percent when both posteroanterior and lateral views are considered.[9] Calcification has been reported both throughout the lesion and in the periphery of a thymoma, in benign as well as malignant types. While thymomas usually appear as circumscribed soft tissue masses in the mediastinum on CT, this modality cannot reliably differentiate benign from malignant lesions. Thymomas may exhibit fibrous adherence to the mediastinum in the absence of tumor infiltration, causing partial obliteration of the interfaces between tumor and mediastinal fat without tumor invasion.[9] Thymomas typically spread by local invasion and by direct extension to the pleura, major blood vessels and lungs with distant metastases uncommon. Computed tomography remains superior to MRI for imaging the thymus in patients with myasthenia gravis because of better spatial resolution and thymic definition in a shorter scan time.[10]

Thymolipoma is an uncommon benign lesion in the thymus, representing approximately 2 to 9 percent of thymic tumors.[11] This tumor may occur at any age and has no sex predilection. Because the tumor is quite soft in consistency and slowly growing, patients are usually asymptomatic and the tumor can attain a large size. It is usually discovered on routine chest radiography. Large thymolipomas may sag toward the diaphragm and adapt themselves to the diaphragmatic contours. There is no known association between thymolipoma and myasthenia gravis or any other syndrome. On plain chest radiographs, a clear difference between the fatty mass and the adjacent water density structures may often be noted.

GERM CELL TUMORS

The anterior mediastinum is the most frequent site for primary extragonadal germ cell tumors. This category of tumor includes teratoma (benign or malignant), seminoma or dysgerminoma, embryonal cell carcinoma, choriocarcinoma, endodermal sinus (yolk sac) tumors, and benign dermoid cysts. Incomplete migration or persistence of primitive germinal cells during embryogenesis is theorized to account for the presence of these lesions in the mediastinum. The germ cell tumors usually become manifest during adolescence or early adulthood. Eighty percent of primary germ cell tumors in the mediastinum are benign teratomas. Benign lesions occur more often in women and malignant lesions more frequently in men.

Teratomas are the most common primary mediastinal germ cell tumor. These anterior mediastinal lesions are comprised of all three embryonic layers and may be either cystic or solid. They are malignant in approximately 30 percent of cases. Radiographically, the solid lesions often appear lobulated and the cystic lesions more smooth and circumscribed. Peripheral calcification may occur and rarely ossification, with skeletal parts or teeth, allowing a definitive diagnosis. Malignant teratomas are less likely to demonstrate well differentiated structures. Computed tomography is particularly useful in evaluating these lesions, since the sensitivity to contrast differences allows for the identification of fat and calcifications.[12]

Primary mediastinal seminomas or dysgerminomas are much more frequent in young men and appear roentgenographically as lobulated anterior mediastinal masses. These lesions are radiosensitive and potentially radiocurable, as compared to the nonseminomatous malignancies.[13] Primary embryonal cell carcinomas, choriocarcinomas, and endodermal sinus tumors are highly malignant lesions and also occur in young men. There are no radiographic features that allow their differentiation from other mediastinal masses on chest radiography. On CT scanning, these lesions appear as lobulated anterior mediastinal masses. While obliteration of normal mediastinal fat planes may suggest malignancy, this finding may also occur with fibrous adherence of benign masses to vessels.[14] Because of differences in prognosis and therapy, differentiation between seminomas and non-seminomatous tumors is crucial, and biopsy is essential for diagnosis.

MEDIASTINAL THYROID

Mediastinal extension of cervical thyroid tissue is a frequent cause of a mediastinal mass. Intrathoracic thyroid tissue is usually located in the anterior mediastinum, but occasionally it may be middle or posterior mediastinal in location. Mediastinal thyroid tissue is rarely malignant. Radionuclide scanning with iodine [sup.131]I, [sup.125]I, or [sup.99m]Tc is the usual method for identifying intrathoracic thyroid tissues, and contiguity with cervical thyroid is usually present. False negative radionuclide scans may occur because of nonfunctioning thyroid within the thorax, and CT scanning may be a useful adjunct to radionuclide scanning. Characteristic features that may be identified on CT and aid in a specific diagnosis include the following: (1) anatomic continuity with the cervical thyroid; (2) high attenuation on the CT scan; (3) rise in attenuation after bolus administration of IV contrast with prolonged enhancement; and (4) focal calcification which may occur in approximately 25 percent of cases.[15]

MESENCHYMAL TUMORS

Primary mesenchymal tumors of the mediastinum are an unusual and heterogeneous group of tumors arising from connective tissue, fat, muscle, blood vessels and/or lymphatics. Lipomas are the most frequent of these lesions and are usually benign, originating in the anterior mediastinum. They are usually asymptomatic. Roentgenographically, they are lobulated lesions, and because of the lower radiographic density of fat, may appear less dense than other mediastinal masses and also less dense than the adjacent mediastinal soft tissues. Liposarcomas may lead to symptoms when they invade contiguous structures, and they occur most often in the posterior mediastinum. On CT scans, islands of soft tissue density may be interspersed within fat density in these mass lesions.

Fibromas may occur anywhere in the mediastinum but are more frequently found in the anterior mediastinum. Fibrosarcomas are more often posterior in location. Radiographically, they appear as soft tissue masses without any distinguishing radiographic features.

Neoplasms arising from mediastinal blood vessels are all rare and include hemangiomas, endotheliomas, hemangiopericytomas, and hemangiosarcomas. Hemangioma is the most common mediastinal blood vessel tumor and is located most often in the anterior mediastinum. When visible radiographically, phleboliths are a useful diagnostic sign. The spinal canal and vertebral bodies may be involved in posterior lesions, requiring evaluation with myelography, CT with intrathecal contrast, or MRI.

Lymphangiomas may be cystic or cavernous and occur in an anterior location. Continuity with a neck mass in children may be evident. With recent advances in ultrasound technology and performance, intrauterine diagnosis has become possible.

LYMPHOMA

Nodal enlargement from lymphomatous involvement is one of the most frequent causes of a mediastinal mass. Accurate localization of the extent of tumor and a tissue diagnosis may both be crucial in determining therapy. Anterior mediastinal, paratracheal, or tracheobronchial adenopathy is seen in approximately 90 percent of those with intrathoracic involvement in Hodgkin's disease.[16] In patients with intrathoracic involvement in non-Hodgkin's lymphoma, these lymph node groups are affected in approximately 46 percent. Posterior mediastinal and pericardial nodal groups, as well as the lung parenchyma, are more frequently involved in non-Hodgkin's lymphoma.

Mediastinal lymph node enlargement can be detected on initial chest radiography in approximately 50 percent of patients with Hodgkin's disease. Calcification is not seen within the enlarged nodes initially, but it may be demonstrated following radiation therapy or chemotherapy. Computed tomography can confirm mediastinal involvement in patients with equivocal findings on chest radiography and can detect additional sites of disease not demonstrated on the initial plain films. In one study, occult disease was demonstrated by CT in one-third of patients with "normal" chest radiographs.[17] Modifications in treatment were based on these findings in approximately 9 percent of the patients, with the most significant changes occurring in those patients undergoing radiation therapy alone.

Serial CT studies may also be useful in the evaluation of response to therapy and for detection of recurrent disease (Fig 2). Persistent soft tissue masses in the mediastinum do not necessarily represent residual tumor, but may be secondary to one or more fibrotic, sterilized lymph nodes. Nodal calcifications may be detected on CT scan following therapy. Thymic cysts have also been reported following therapy in patients with Hodgkin's disease.[18] Magnetic resonance imaging may prove to be useful in the future to differentiate residual or recurrent tumor from fibrosis following therapy.[8]

PERICARDIAL CYSTS

Pericardial cysts are relatively uncommon lesions and are presumed to arise from congenital defects related to ventral and parietal pericardial recesses.[19] They are lined by a single layer of mesothelial cells and are most often unilocular. These cysts are usually asymptomatic, but occasionally patients may present with chest pain, dyspnea, or cough. Approximately 70 percent of pericardial cysts arise in the right cardiophrenic angle, but lesions remote from the cardiophrenic angle may occur and may be more difficult to diagnose.

Typically, pericardial cysts appear on plain radiographs as smooth, round homogeneous soft tissue masses in the cardiophrenic angle, contiguous with the anterior chest wall and the hemidiaphragm. Calcification may rarely occur within the wall of the cyst. Occasionally, a pointed superior contour is identified, presumably due to drooping of the thin-walled cyst from its point of origin. Fluoroscopic examination may show changes in the contour of a cyst with changes in patient position.

Cardiac ultrasound may allow determination of the cystic nature of the mass if the lesion is adjacent to the chest wall. Computed tomography is diagnostic when the mass is in a classic location, does not enhance with intravenous contrast, and has an attenuation coefficient consistent with a cystic lesion.[20] A pointed contour and variations in shape with changes in position also point to a cystic lesion.[21] When the clinical and radiographic presentation is consistent with pericardial cyst, thoracotomy is generally not required in the asymptomatic patient.

FOREGUT DUPLICATION CYSTS

Foregut duplication cysts are rare congenital anomalies, accounting for approximately 10 percent of mediastinal masses in the adult.[23] Bronchogenic cysts, esophageal duplication cysts, and enurenteric cysts are part of the spectrum of malformations which are thought to share a common embryogenesis arising from the primitive foregut early in fetal development.

Bronchogenic cysts are the most common form of foregut cysts.[1] They result from abnormal budding of the ventral lung bud or abnormal branching of the tracheobronchial tree.[22,23] These lesions may occur either within the mediastinum or the lung parencyma, with the mediastinal cysts resulting from earlier abnormal branching during embryogenesis. The cysts are lined by secretory epithelium; depending on whether a communication remains with the tracheobronchial tree, they may vary from being completely fluid-filled to completely air-filled.

Mediastinal bronchogenic cysts typically are asymptomatic and are usually discovered on routine chest radiography. Symptoms, when present, frequently result from compression of neighboring structures and include chest discomfort or pain, nonproductive cough, wheezing, or dysphagia.

Radiographically, the mediastinal lesions present as smooth, homogeneous round or ovoid masses of water density in close association with the trachea or major bronchi. While they may be located in the middle, posterior or superior mediastinum, the most typical location is subcarinal with extension inferiorly. Mediastinal bronchogenic cysts rarely have a patent communication with the tracheobronchial tree and are usually filled with mucoid material. Calcification within the wall of the cyst is rare.

Computed tomography is invaluable in characterizing these congenital cystic lesions. On CT, these cysts appear as well-defined, rounded masses without infiltration of adjacent mediastinal structures. Although they are typically of water density, they may contain sufficient mucoid material to give a high CT number[24,25] and do not enhance following intravenous contrast administration.

Ultrasound may also be helpful in evaluating these congenital lesions because of its ability to establish the cystic nature of a mass. Lesions contiguous with the chest wall, in the anterior mediastinum, or in the subcarinal region may be imaged using standard cardiac projections. Cysts in the posterior mediastinum are not assessible by ultrasound because of the absence of an acoustic window. Diagnostic cyst puncture may be approached percutaneously with CT or ultrasound guidance or by bronchoscopy.

Esophageal duplications are presumed to result from a diverticulum of the dorsal bud of the primitive foregut or aberrant recanalization of the gut during embryogenesis.[23] While they are usually found adjacent to or within the esophageal wall, these duplication cysts may migrate with the lung bud and develop remote from the esophagus. Simple enteric cysts have variable radiographic apperances and are not always distinguishable from bronchogenic cysts.[26] They are usually located in the posterior mediastinum and tend to be larger than respiratory cysts. Barium esophagram may show extrinsic compression of the esophagus by the cyst.

Neurenteric cysts originate earlier in embryonic life and result from incomplete separation of the endoderm and notocord, resulting in the development of a diverticulum of the endoderm.[23] Normal fusion of vertebral ossification centers is prevented and associated vertebral anomalies including hemivertebra, butterfly vertebra, and scoliosis may occur. These lesions also occur typically in the posterior mediastinum.

NEUROGENIC TUMORS

Neurogenic tumors arise most often in the posterior mediastinum and include benign and malignant neoplasms arising from the intercostal nerves or components of the autonomic system. They are commonly divided into the following three groups: (1) those of peripheral nerve origin (neurilemomas, neurofibromas, malignant schwannomas); (2) those of sympathetic nervous origin (ganglioneuromas, neuroblastomas, ganglioneuroblastomas); and (3) those of parasympathetic system origin (pheochromocytomas, paragangliomas).

Nerve sheath tumors are the most common and are usually benign. Neurogenic tumors may occur at any age, but are most common in younger age groups. Neurilemoma (schwannoma) is the most common benign tumor.[27]

Radiographically, these lesions are similar in appearance with a smooth, round or oval mass in a paravertebral location. Ganglia-related tumors tend to have an elongated or triangular density with a broad base towards the mediastinum and tapering superior and inferior margins, distinguishing them from the more oval nerve sheath tumors.[27] Erosion, destruction, or spreading of the ribs may occur, as may vertebral abnormalities, including enlargement of the neural foramina, erosion of the pedicles, and scoliosis. Myelography is recommended when neurologic symptoms or vertebral body changes occur in the presence of a posterior mediastinal mass. Also, MRI can be used now to evaluate intraspinal extension of these tumors,[7] and additional imaging planes may better define the origin of the tumor (Fig 3).[28]

VASCULAR LESIONS

Vascular lesions may simulate mediastinal neoplasms and may occur in any mediastinal compartment.[29,30] Clinical symptoms and physical examination may not distinguish vascular lesions from other mediastinal abnormalities, and an accurate radiographic diagnosis prior to intervention is crucial to prevent inappropriate therapy.

Kelley et al[30] divided mediastinal vascular abnormalities into the following four groups depending on their sites of origin; (1) systemic venous system; (2) pulmonary arterial system; (3) pulmonary venous system; and (4) systemic arterial system. Abnormalities of the systemic veins including the superior vena cava and the azygos, hemiazygos, and innominate veins, usually occur in the middle or superior mediastinum. Abnormalities of the pulmonary arterial system, including abnormalities of the pulmonary trunk and main pulmonary arteries, present as middle mediastinal or perihilar masses and include pulmonary valve stenosis, congenital absence of the pulmonary valve, pulmonary arterial hypertension of any cause, anomalous left pulmonary artery, or aneurysm of the ductus arteriosus. Pulmonary venous system abnormalities including partial anomalous pulmonary venous return and pulmonary vein varix may present as masses in the middle or superior mediastinum.[30]

The most common vascular lesions to be confused with mediastinal neoplasms are abnormalities of the thoracic aorta and its branches. These lesions typically occur in elderly patients with hypertension and arteriosclerosis. Aneurysms of the thoracic aorta may occur from a variety of causes, including arteriosclerosis, trauma, syphilis, or cystic medial necrosis. The majority are discovered on routine radiographs. Peripheral calcification of a mass may suggest a vascular etiology, and fluoroscopy has been used to evaluate intrinsic pulsations. Contrast-enhanced CT should allow differentiation of vascular lesions and soft tissue masses, but aneurysms filled with thrombus may fail to show contrast enhancement. Angiography is performed in most cases prior to definitive therapy.

Magnetic resonance imagining has been shown to be an excellent modality for the evaluation of the thoracic aorta and its major branches. The advantages of MRI include lack of ionizing radiation, multiplanar imaging capability, and excellent contrast between vascular structures and soft tissues without the use of intravenous contrast agents. While differentiation between slow-flowing blood and mural thrombus may be difficult, and small calcifications are not detectable, our experience suggests that MRI may eventually supplant arteriography for evaluating lesions of the thoracic aorta.[31]

The innominate artery commonly undergoes elongation, tortuosity, and buckling, and may appear radiographically as a curvilinear density coursing above the right clavicle. While true aneurysms of this vessel are less common, they are more likely to be symptomatic.

An aberrant right subclavian artery originating from a normal left-sided aortic arch is the most common congenital anomaly of the aortic arch. The aberrant and courses posterior to the trachea and esophagus. While individuals with this abnormality are usually asymptomatic, dysphagia due to compression of the esophagus has been described ("dysphagia lusoria"). A barium esophagram classically will demonstrate anterior displacement of the posterior wall of the esophagus at the level of the aortic arch. Aortogram, CT scan, or MRI are diagnostic. Aneurysms of an aberrant right subclavian artery have been reported but are rare.[32]

A right aortic arch, cervical aortic arch, coarctation, or pseudocoarctation may all simulate a mediastinal neoplasm in isolated individuals.

REFERENCES

[1] Oldham HN. Mediastinal tumors and cysts. Ann Thorac Surg 1971; 11:246-75

[2] Fraser RG, Pare JAP, Pare PD, Fraser RS, Genereux GP. Diagnosis of diseases of the chest, ed 3. Philadelphia: WB Saunders, 1988

[3] Heitzman ER. The mediastinum: radiologic correlations with anatomy and pathology. St. Louis: CV Mosby, 1977

[4] Webb WR. Advances in computed tomography of the thorax. Radiol Clin North Am 1983; 21:723-39

[5] Levitt RG, Glazer HS, Roper CL, Lee JKT, Murphy WA. Magnetic resonance imaging of mediastinal and hilar masses: comparison with CT. AJR 1985; 145:9-14

[6] Heelan RT, Martin N, Westcott JL, Bains MS, Watson RC, Caravelli JF, et al. Carcinomatous involvement of the hilum and mediastinum: computed tomographic and magnetic resonance evaluation. Radiology 1985; 156:111

[7] Gefter WB. Chest applications of magnetic resonance imaging: an update. Radiol Clin North Am 1988; 26:573-88

[8] Glazer HS, Levitt RG, Lee JKT, Emami B, Gronemeyer S, Murphy WA. Differentation of radiation fibrosis from recurrent pulmonary neoplasm by magnetic resonance imaging. AJR 1984; 143:729-30

[9] Brown LR, Muhm JR, Gray JE. Radiographic detection of thymoma. AJR 1980; 134:1181-88

[10] Batra P, Herrmann C, Jr., Mulder D. Mediastinal imaging of myasthenia gravis: correlation of chest radiography, CT, MR, and surgical findings. AJR 1987; 148:515-19

[11] Teplick JG, Nedwich A, Haskin ME. Roentgenographic features of thymolipoma. AJR 1973; 117:873-77

[12] Suzuki M, Takashima T, Itoh H, Choutoh S, Kawamura I, Watanabe Y. Computed tomography of mediastinal teratomas. J Comput Assist Tomogr 1983; 7:74-76

[13] Economou JS, Trump DL, Holmes EC, Eggleston JE. Management of primary germ cell tumors of the mediastinum. J Thorac Cardiovasc Surg 1982; 83:643-49

[14] Levitt RG, Husband JE, Glazer HS. CT of primary germ-cell tumors of the mediastinum. AJR 1984; 142:73-78

[15] Glazer GM, Axel L, Moss AA. CT diagnosis of mediastinal thyroid. AJR 1982; 138:495-98

[16] Filly R, Blank N, Castellino RA. Radiographic distribution of intrathoracic disease in previously untreated patients with Hodgkin's disease and non-Hodgkin's lymphoma. Radiology 1976; 120:227-81

[17] Castellino RA, Blank N, Hoppe RT, Cho C. Hodgkin disease: contributions of chest CT in the initial staging evaluation. Radiology 1986; 160:603-05

[18] Baron RL, Sagel SS, Baglan RJ. Thymic cysts following radiation therapy for Hodgkin disease. Radiology 1981; 141:593-97

[19] Feigin DS, Fenoglio JJ, McAllister HA, Madewell JE. Pericardial cysts; a radiologic-pathologic correlation and review. Radiology 1977; 125:15-20

[20] Pugatch RD, Braver JH, Robbins AH, Faling LJ. CT diagnosis of pericardial cysts. Am J Roentgenol, 1978; 131:515-16

[21] Demos TC, Budorick NE, Posniak HV. Benign mediastinal cysts: pointed appearance in CT. J Comput Assist Tomogr 1989; 13:132-33

[22] Rogers LF, Osmer JC. Bronchogenic cyst. Am J Roentgenol Radium Ther Nucl Med 1964; 91:273-83

[23] Fitch SJ, Tonkin IL, Tonkin AK. Imaging of foregut duplication cysts. RadioGraphics 1986; 6:189-201

[24] Kuhlman JE, Fishman EK, Wang KP, Zerhouni EA, Siegelman SS. Mediastinal cysts: diagnosis by CT and needle aspiration. AJR 1988; 150:75-78

[25] Mendelson DS, Rose JS, Efremidis SC, Kirschner PA, Cohen BA. Bronchogenic cysts with high CT numbers. AJR 1983; 140:463-65

[26] Reed JC, Sobonya RE. Morphologic analysis of foregut cysts in the thorax. Am J Roentgenol Radium Ther Nucl Med 1974; 120:851-60

[27] Reed JC, Haller KK, Feigin DS. Neural tumors of the thorax: subject review from the AFIP. Radiology 1978; 126:9-17

[28] Batra P, Brown K, Steckel RJ, Collins JD, Ovenfors CO, Aberle DR. MR imaging of the thorax: a comparison of axial, coronal, and sagittal imagining planes. J Comput Assist Tomogr 1988; 12:75-81

[29] Shahian DM, Javid H, Faber LP, Kittle CF, Matthew GR. Lesions of the thoracic aorta and its arch branches simulating neoplasm. J Thorac Cardiovasc Surg 1981; 81:251-63

[30] Kelly MJ, Mannes EJ, Ravin CE. Mediastinal masses of vascular origin. J Thorac Cardiovasc Surg 1978; 76:559-72

[31] Lois JF, Gomes AS, Brown K, Mulder DG, Laks H. Magnetic resonance imaging of the thoracic aorta. Am J Cardiol 1987; 60:358-62

[32] Brown K, Batra P. MR imaging of aneurysm of an aberrant right subclavian artery. J Comput Assisted Tomogr 1987; 11(6) 1071-1073

COPYRIGHT 1990 American College of Chest Physicians
COPYRIGHT 2004 Gale Group