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Roentgen aspects of mediastinal lesions
Roentgen
Aspects of Mediastinal
Lesions
By TED F. LEIGH, M.D., AND H. STEPHEN WEENS, M.D.
HE MEDIASTINUM is a small area with a lot going on in it. Through it passes all the food you eat, all the air you breath, and all the blood that nourishes your body. And to these structures of transport, plus many others, much can happen. Radiologic examination is the most important diagnostic tool for study of the mediastinum. Any lesion therein should be thoroughly investigated, using selective procedures. And there are a number of these available: conventional chest films, Bucky or grid examinations, fluoroscopy including esophageal examination, tomography, angiography, bronchography, myelography, lymphography and air studies of the mediastinum, pleural space, and peritoneal cavity. At times an isotope study may be necessary. The reader should bear in mind that positive findings elsewhere than in the mediastinum may also give a clue to the correct diagnosis of a mediastinal lesion, e.g., bone lesions in a patient with a parathyroid adenoma, or an enlarged spleen in a patient with mediastinal lymphadenopathy. After a thorough radiologic investigation, the ability to evaluate a given lesion may fall into one of three categories: (1) the lesion can be diagnosed accurately without question; (2) it may defy definite diagnosis, but the possibilities can be narrowed down to only a few conditions; (3) the cause of the lesion is completely unknown and even a good differential diagnosis is not possible. In this paper, the more important masses occurring in the mediastinum will be discussed. The rare conditions are omitted for the sake of brevity. Lesions are described under headings that indicate their usual location within the mediastinum. This is done so that the reader may think in terms of a differential diagnosis when he is investigating a lesion in a specific area.
T
“ANTERIOR”
MEDIASTINUM*
Teratomu Teratomas almost invariably are located in the anterior part of the mediastinum and very commonly occur in the area where the great vessels join the heart; occasionally they are located at higher or lower positions than this. They may project unilaterally to the ,left or right or spread bilaterally. They vary in size from very small to huge, occasionally being so large that they nearly fill the entire chest and markedly compress adjacent structures. Teratomas commonly contain opacities. These may be linear calcifications in the capsule, or they may be skeletal parts such as teeth, mandible, or some other bone. The cystic type contains a fatty substance which is radiolucent, TED F. LEIGH, M.D.: Professor of Radiology, Emory University School of Medicine; Director, Department of Radiology, Emory University Hospital, Atlanta, Ga. H. STEPHEN WEENS, M.D.: Professor and Chairman, Department of Radiology, Emory University School of Medicine; Director, Department of Radiology, Grady Memorial Hospital, Atlanta, Ga.
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but this is difficult to judge in the mediastinum because of the surrounding air in the lungs, bronchi, and trachea. When a horizontal beam is used, the fatty material may layer out on top of fluid of water density, resulting in a fat level on the film (Fig. 1) . An occasional complication is perforation, either into an adjacent air passage (in which case an air-fluid level is likely) or into the mediastinal tissues or pleural space ( the latter resulting in visible pleural fluid).
Thymoma and Thymic Cyst Thymoma, like teratoma, most commonly arises anterior to the juncture of the great vessels and heart. It may widen the mediastinum to the left or right, or in both directions. The outline may be smooth or irregular. Most are small or medium-sized, and they seldom become as large as teratomas. Thymoma, benign or malignant, may calcify either with linear deposits in the wall or conglomerate masses in the substance of the tumor. It does not contain bony parts-a differential point from teratoma. The malignant variety has a tendency to recur after surgical removal. Thymic cysts arise in the same location as the thymoma. They are benign, usually small or medium in size, and occasionally calcify. Since the thymic lesions and teratoma frequently have their origin adjacent to the great vessels, differentiation from a vascular outpouching is frequently necessary, either through opacification of the vascular structures or by diagnostic pneumomediastinography ( Fig. 2).
Lipoma A lipoma usually arises in the “anterior” mediastinum in its midportion, and as it grows in size it tends to broaden the mediastinum on one side only, more commonly the right. Since lipomas are soft and pliable, they grow in the direction of least resistance and are usually quite large when initially discovered. At times such a mass may extend downward to rest on the right hemidiaphragm (Fig. 3). We have encountered 3 such cases with almost identical
Fig. L-Cystic teratoma. Chest films taken with the patient standing (horizontal beam), A level is seen between the lighter fat and the heavier fluid beneath it. (Courtesy of Wendell P. Stampfli, M. D.)
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A Fig. IL.-Benign thymoma. Frontal (A) and lateral (B) tomograms after diagnostic pneumomediastinum show the shape of the left anterior mediastinal mass and prove it is not of vascular origin.
Fig. 3.-Lipoma. PA and the right hemidiaphragm There is no abnormality in because of the pliability of W. B. Saunders C0mpany.l)
lateral films disclose a mass of relative radiolucency on anterior-1 . extending upward to the midmediastinum the adjacent right lung and no cardiac shift, presumab ry the lesion. (Courtesy of Robert M. Lowman, M.D., and
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findings. These masses are relatively radiolucent, particularly the larger lesions, but as previously mentioned, the air in the surrounding lungs and air passages may interfere with its recognition. Liposarcoma also arises in the mediastinum, but is extremely rare, and there is not enough in the literature to formulate a consistent description of its radiologic characteristics. Fibroma Fibroma of the mediastinum is also a rare tumor. It usually arises in the anterior portion and tends to spread to one or both sides. It may grow to relatively large size (Fig. 4). Fibrosarcoma is also rare in the mediastinum, and in the authors’ experience has been mainly confined to the region around the esophagus. Parathyroid
Tumor
The two lower parathyroid glands occasionally migrate into the “anterior” mediastinum along with the thymus. Of course, these are not visible unless hyperplasia or tumor develops, It may then become sufficiently large to broaden the mediastinum on one or both sides. The tumor is usually located in the middle or upper part of the anterior mediastinum. Since most of these are functioning lesions, radiographic signs of hyperparathyroidism may be seen. Blood Vessel Tumor Benign and malignant blood vessel tumors, i.e., hemangioma, hemangiosarcoma, malignant endothelioma, etc., are most commonly located in the “anterior” mediastinum. Their shape and size vary, widening the mediastinum to the left or right, or bilaterally. Some contain phleboliths, which, if identified, are pathognomonic of this tumor (Fig. 5). Some have broad vascular connections and may be opacified on contrast studies. Lymph
Vessel Tumor
Synonyms include lymphangioma and lymphangiosarcoma. Lymphatic tumors are similar to blood vessel tumors in that most have their origin in the “anterior” mediastinum and may broaden it on one or both sides. Their size and shape also vary. Paragangliomu Paraganglioma may occasionally arise from an aorticopulmonary body which lies on the anterior surface of the pulmonary artery and aorta. The tumor may widen the mediastinum bilaterally. Its contour may be smooth or lobulated and it may grow to very large size. Lymphadenopathy Enlargement of one or more lymph nodes in the “anterior” mediastinum, from whatever cause, may present as a mass. The mass may be large or small, smooth or lobulated, noncalci5ed or calcified (the latter a point in favor of
MEDIASTINAL
LESIONS
Fig. 4.-Fibroma. This huge fibrous-tissue tumor, descril 3ed as fibromatosis in the pathology report, weight ed 7% pounds and con&i ted of 2 large masses connec:ted across the midline by ‘an isthmus. It was successfullly removed surgically.
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benignancy). Enlargement may be isolated or occur with nodal enlargements elsewhere in the mediastinum. At times lymphadenopathy may resemble a single mass lesion such as a thymoma. Differential diagnosis is aided by radiologic investigation of other areas of the body for such findings as retroperitoneal adenopathy or splenomegaly.
Vascular Lesions The most common vascular lesion in the “anterior” mediastinum is enlargement of the ascending aorta. The widening is usually diffuse and results in broadening of the right mediastinal border in its midportion, as seen on the frontal view. Linear calcification is occasionally deposited in the wall. Fluoroscopy and a study of the pulsations may aid in identifying the nature of the enlargement. Aortography will identify the mass as aorta. Superior vena caval enlargement may be congenital or acquired. It causes a smooth bulge of the mediastinum to the right, which usually is fairly long (Fig. 6). If there is enlargement of an associated left superior vena cava (collecting vein), as frequently occurs in anomalous pulmonary venous return to the right heart, there will be a broadening of the left mediastinum as well. Main pulmonary artery dilatation produces an exaggeration of the usual shadow of this structure as observed on frontal projection. Two points help to differentiate the pulmonary artery from other causes for hilar enlargement: it is exactly at hilar level and it is continuous with the left main pulmonary artery (best seen by tomography).
Fig. 5.-Blood vascular tumor. This radiographic study of a surgical specimen removed from the mediastinum discloses multiple phleboliths within the lesion. (Courtesy of Benjamin Felson, M.D., and W. B. Saunders Companyl and Charles C Thomas Publisher.2)
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LESIONS
Fig. 6.-Aneurysmal dilatation of the superior vena cava, thought to be congenital. Surgical exploration did not reveal any associated lesion. (Courtesy of Charles C Thomas Publisher.‘)
“POSTERIOR”
MEDIASTINUM
Neurogenic Tumors This category includes neurilemoma, neurofibroma, schwannoma, ganglioneuroma, sympathicoblastoma ( neuroblastoma) , pheochromocytoma, and paraganglioma (chemodectoma). These tumors arise far posteriorly against the spine, and as they grow they spread laterally and anteriorly. Unilateral growth is the rule. They may be located at any level from the inlet to the outlet, may be large or small, variable in shape, localized or invasive. Calcification is seldom seen, A neurogenic tumor may involve one or more ribs and vertebrae. The ribs may be displaced, eroded, or destroyed. In the spine, the pattern is usually that of unilateral body and/or foraminal destruction or erosion (Fig. 7). Some tumors, notably neurofibromas, are dumbbell in shape, with a spinal canal component connected to the mediastinal mass by an isthmus. The value of myelography in suspected cases of this type is thus apparent.
Lateral Meningocele This anomaly resulting from outpouching of the leptomeninges may present as single or multiple fluid-filled masses in the mediastinum. Its roentgen characterics are similar to those of the solid neurogenic tumor in that it presents as a unilateral mass, variable in size, well circumscribed, with associated bony Iesions. It does not calcify. On myelography, it is likely that some of the contrast medium will pass into the mediastinal sac. Neurofibromatosis is commonly present.
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Fig. ‘I.-Neurofibroma of the posterior mediastinum, eroding the 9th, lOth, and 11th dorsal vertebrae, and the right 10th rib. (Courtesy of Richard A. Elmer, M.D., and Charles C Thomas Publisher.“)
Neurenteric
Cyst
This lesion is usually discovered in early life, and if adequate roentgen investigation is made, can be diagnosed with reasonable certainty. The mediastinal mass is usually large and widens the mediastinum unilaterally or bilaterally. In addition, there is an associated anomaly of the dorsal spine. If the lesion is connected to the intestinal tract by a patent tube, the mass is likely to contain air. A more detailed discussion of this entity can be found in the article by Benton and Silverman in this issue. Extramedulla
y Hematopoksis
Characteristically, extramedullary hematopoiesis presents as bilateral masses in the lower “posterior” mediastinum immediately adjacent to the ribs and spine (Fig. 8). These masses may be lobulated or smooth in contour, single or multiple, and are of homogeneous density without calcium. Because of their paravertebral position, they may be visible only on the frontal view and, since they are most frequently in the retrocardiac area, it is important that penetration be adequate for their perception, Splenomegaly and hepatomegaly are frequent and important associated findings. Bone and Cartilage
Tumors
Tumors of one or more of the dorsal vertebrae are fairly common and generally destroy the vertebrae to a varying degree without causing mediastinal enlargement. A small percentage, however, may expand the vertebrae, grow through it into the adjacent paravertebral area, or extend eccentrically producing a mass which is visible on the ordinary chest study and on special studies as well (Fig. 9). This includes such lesions as sarcomas, myeloma, Ewing’s
MEDIASTINAL
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tumor, aneurysmal bone cyst, and metastatic disease. Tumors may also arise from the posterior aspects of the ribs and present as mediastinal masses. The important thing is to remember that spine lesions can do this and include them in a differential diagnosis. A thorough roentgen investigation of such lesions, including Bucky films, tomography, myelography, and possibly angiography is indicated.
Paravertebral Masses Paravertebral
enlargement may result from several conditions. A spinal tumor
Fig. 8.-Extramedullary hematopoiesis in a patient with myelofibrosis. There are multiple masses of blood-forming tissue adjacent to the lower dorsal spine. (Courtesy of M. Paul Capp, M.D.)
Fig. 9.-Multiple myeloma involving the 10th dorsal vertebra and having an associated paravertebral mass of fusiform confIguration, presumed to be tumor tissue extending from the confines of the vertebral body. (Courtesy of Charles C Thomas Publisher2 and W. B. Saunders Company.l)
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that extends beyond the confines of the vertebrae, as stated earlier, will broaden the paraspinal space unilaterally or bilaterally, usually with greatest expansion at the level of the involved vertebrae (Fig. 9). Spinal osteomyelitis, tuberculosis or nontuberculous, almost invariably has an associated bilateral fusiform-shaped mass of pus in the paravertebral space, and the diameter is also usually greatest at the level of the lesion; characteristically, the spine itself shows erosion or destruction of one or more vertebrae (frequently in apposition), particularly on the articular surfaces. Fractures of the spine are often accompanied by unilateral or bilateral collections of blood in the paraspinal area, the diameter of the hematoma being broadest at the level of the injury. Again, it is important that adequate radiographic study be made to determine the characteristics of the paravertebral mass and of the spinal lesion as well. Cyst of the Thoracic
Duct
This is an extremely rare type of mass of the mediastinum; only several have been reported. These have been characterized by a soft-tissue mass in the “posterior” mediastinum, but their association with the thoracic duct is not apparent. In one case, upon opening the cyst, a duct was identified at its cephalic end, and after injection of this duct with contrast material, a radiograph taken in the operating room proved that the cyst was continuous with a normal thoracic duct which passed into the cervical area. Vascular Lesions In the “posterior” mediastinum vascular lesions are mainly of the descending aorta. These can be suspected by their roentgen appearance, particularly if there is associated vertebral or rib erosion (as happens occasionally). They can be proved by aortography. “MIDDLE”
MEDIASTJXUM
Included in this area are bronchogenic cyst, enlargement of the paratracheal lymph nodes, esophageal lesions, tracheal tumor, and certain vascular lesions. Bronchogenic
Cyst
The majority of these cysts are adjacent to the trachea or bronchi. Their size varies and they may broaden the mediastinum unilaterally or bilaterally. The contour is usually smooth or lobulated. They are of homogeneous density and do not calcify. Compression or displacement of the trachea may result, and if the cyst is on the posterior side, the esophagus may be similarly affected (Fig. 10). A bronchogenic cyst located in the subcarinal area may widen the bronchial angle. An occasional one communicates with the trachea or one of the bronchi and will contain air as well as fluid within its lumen. Paratracheal
Lymphadenopathy
The most common group of mediastinal lymph nodes that enlarge are those located around the trachea. These present as a smooth or lobulated mass, widening the mediastinum most often to the right, but sometimes to the left
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Fig. IO.-Bronchogenic cyst in an adult. On this spot film made in lateral projection, the lesion is outlined by air in the trachea and barium in the esophagus-
or bilaterally. Such enlargement may be of any size, from a subtle localized bulge to massive widening. Adjacent structures such as the trachea or bronchi may be compressed or displaced. Calcification seen within nodes is a good sign that the enlargement is benign. Noncalcified nodes can be benign or malignant. Esophageal
Lesions
The esophagus must always be remembered in the investigation of the mediastinum. Not only may an esophagram aid in establishing the characteristics of an extraesophageal mass, but there are also certain lesions of the esophagus itself that produce an abnormal mediastinum. These include megaesophagus, benign and malignant tumors, divert&da, and duplication cysts. To these can be added hiatus hernia. Megaesophugus almost invariably widens the mediastinum to the right, not to the left (except in the superior mediastinum). This widening can extend throughout the entire length of the mediastinum, or only partially. The widening may be smooth or lobulated. The esophageal shadow on a routine chest examination may be of homogeneous density, radiolucent, mottled with air, or show an air-fluid level (when a horizontal beam is used) ; each of these pictures depends on the contents of the structure and the patient’s position in relation to the X-ray tube during examination ( Fig. 11) . Benign tumors of the esophagus may be of sufficient size to widen the mediastinum locally at any level. It is usually a unilateral smooth enlargement. Contrast study shows a characteristic smooth deformity of the esophageal lumen with preservation of the esophageal mucosa. Malignant tumor infrequently widens the mediastinum, but, depending on size and level, may be visible on routine chest films. Again, contrast studies aid in the diagnosis and frequently show characteristic shelving margfns, mucosa1 destruction, fusiform narrowing, fungating filling defect, and UIC~E+ tion. Epiphrenic diuerticula are located just above the diaphragm, USU~IY to the
LEIGH AND WEENS
Fig. Il.-Megaesophagus an air-fluid
level. The patient
broadening the mediastinum is in upright position.
to the right
and showing
right of the midline. They are of variable size and shape and usually contain air and fluid. With contrast studies, some of the media frequently runs into the pocket while the remainder outlines a normal esophagus above the neck of the diverticulum and a narrowed segment below it. Pharyngeal diuerticula (Zenker’s), if of sufficient size, will present as a midline superior mediastina1 mass containing fluid, or air and fluid. Contrast study usually shows the diverticulum and demonstrates its position posterior to the esophagus, compressing the adjacent esophageal segment. Duplication of the esophagus may occur at any level of the mediastinum. They are of variable size, usually rounded or oval in conhguration, and usually widen the mediastinum to one side only. Most are homogeneous because of their fluid content, but if they communicate with the esophageal lumen (congenitally or secondary to perforation) they will likely contain some air as well. Contrast studies show luminal deformities similar to the ones produced by benign tumors. When the lesion communicates, some media will probably enter the sac. EsophugeaE hi&us hernia most commonly involves the stomach and for the most part presents as a midline mass just above the diaphragm, but occasionally it may be to the left or right. On routine chest examination, it can be seen as a retrocardiac mass of variabIe size, usually containing both air and fluid. Occasionally, a segment of small intestine or colon, or both, may herniate through the hiatus, with or without the stomach, and cause multiple air and fluid pockets in the lower mediastinum. Rarely there may be hemiation of another structure, such as omentum, liver, or spleen.
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MEDIASTINAL LESIONS
Tracheal
Tumor
These are very rare. A tumor growing eccentrically off the trachea may reach sufficient size to enlarge the mediastinum locally. The mass may encroach on the tracheal lumen and deform the air column; tomography is valuable in such instances. Va.sc&r
Lesions
Azygos vein enlargement characteristically produces, on frontal view of the chest, a hemispherically shaped mass of homogeneous density resting in the angle between the trachea and the right main stem bronchus. A rare lesion is aneurysmal dilatation of the hemiazygos vein, which has been seen once by the authors. It presented as a left-sided retrocardiac mass on chest roentgenograms. Greatly enlarged esophageal varices may aIso produce lobulated shadows in the middle mediastinum on the routine chest film. All suspected vascular masses should have a thorough fluoroscopic investigation, and in doubtful cases angiography as well. With the latter, an accurate diagnosis can be made in almost every case. SUPERIOR PART OF THE MEDIASTINUM
Several types of lesions are invariably seen in the superior part of the mediastinum. These include mediastinal extension of a thyroid tumor, enlargement of the innominate or subclavian artery, pseudocoarctation of the aorta; and pharyngeal diverticula of the esophagus (already discussed). Thyroid
Lesions
Thyroid enlargement of various types (adenoma, cyst, benign and malignant tumors) is usually confined to the cervical area, but occasionally it extends downward into the superior mediastinum, particularly if it arises from one of the inferior poles of the gland. It may broaden the mediastinum unilaterally or bilaterally. The borders are sharply defined and smooth or lobulated. Linear, flocculent, or conglomerate calcium deposits may be seen. Frequently the trachea and esophagus are displaced, and separation of the two may result if the lesion is interposed between them. If a thyroid mass is attached to the trachea, upward movement with swallowing may be observed Auoroscopically. The superior mediastinal mass of thyroid is almost invariably continuous with an enlarged part of the gland in the neck, but the latter cannot be seen well because its borders are not surrounded by air. Vascular Lesions Usually these are caused by aneurysmal dilatation of the innominate artery on the right or subclavian artery on the left by an aneurysm arising from the superior aspect of the aortic arch, or by pseudocoarctation. A mass of this type may show linear intramural calcium deposits. It may or may not displace the trachea and esophagus, depending upon its location and size. Its true nature can be identified by angiography.
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Other Lesions Several other lesions may be seen in this area. These include blood vessel tumor, lymphatic tumor, thymoma, teratoma, bronchogenic cyst, duplication of the esophagus, parathyroid enlargement, neurogenic lesions, tracheal tumor, abscess and hematoma. INFERIOR PART OF THE MEDIASTINUM
The inferior part of the mediastinum may be the site of a pericardial celomic cyst, foramen of Morgagni hernia, epiphrenic diverticulum, or esophageal hiatus hernia (the latter two already discussed). Pericardial
Celomic Cyst
These vary from 1 to 15 cm. in diameter, the majority being relatively small. They are smooth or slightly lobulated, and rounded, oval, or tear-drop in configuration. Most are located in the right cardiophrenic angle, but an occasional one is found at any point along the pericardium. They do not calcify. They may strongly resemble omental hemiation through the foramen of Morgagni, and a diagnostic pneumoperitoneum may be necessary for differentiation. Foramen of Morgagni
Herniation
Abdominal contents, such as a portion of omentum, liver, small intestine, colon, or stomach may herniate into the lower mediastinum through the right or left foramen of Morgagni. The hernia usually 08ccurs on the right since the left foramen is protected by the pericardium. Most often it contains a portion of omenturn, and presents on the chest film as a smooth oval-shaped mass of homogeneous density adjacent to the right heart border. If a diagnostic pneumoperitoneum is performed, and films are made with a horizontal beam, air usually will be seen in the sac between the peritoneal covering and the fat. A segment of colon, small intestine, or stomach that herniates through one foramen of Morgagni will usually show one or more pockets of air or air-fluid levels along with shadows of homogeneous density which represent the wall of the viscus. Barium studies will reveal the exact segment involved. Mediastinal lesions of many other types may at times be located in the inferior part of the mediastinum, but are not necessarily confined to this area. LESIONS THAT VARY IN LOCATION
Mediastinitis and hematoma demonstrate no proclivity for any specific location, but it should be borne in mind that many of the other mass lesions discussed in this paper can at times be found in areas other than their usual sites. Mediastinitis Inflammation may be localized or diffuse, A localized abscess may be of almost any size or configuration, and may be located at practically any point in the mediastinum. It may be unilateral or bilateral. Those resulting from perforation of a hollow structure like the esophagus or trachea will probably contain air as well as pus (Fig. 12)) and this point should be investigated by examination of the esophagus or trachea with water-soluble or oily media (in
MEDIASTINAL
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Fig. 12.-Localized mediastinal abscess secondary to perforation of the upper esophagus by a fish bone. This examination, made with the patient in upright position, reveals a small collection of air at the superior aspect of the mass. The trachea is displaced anteriorly. (Courtesy of E. H. Wood, M.D. and C. A. Bream, lM.D., and W. B. Saunders Company.‘)
case of spillage). When an abscess is located in the superior mediastinum, the cervical area should be investigated with soft-tissue technic for abnormal collections of air. Diffuse mediastinal inflammation, if of sufficient magnitude, will widen the mediastinum bilaterally and cause loss of sharpness of the borders.
Hematomu Like mediastinitis, hematoma may be localized or diffuse. The localized form may be of any size or shape and located at any level. Frequently it is caused by trauma and thus can be suspected from the history. It has a tendency to change in size on serial examination because of blood absorption or further bleeding. Diffuse hematoma usually widens the mediastinum bilaterally and, like the localized blood collections, gives a changing picture. In both the localized and diBuse forms, ancillary findings such as fracture in the sternum, ribs, or dorsal spine, surgical clips, and metallic sutures, etc., may aid in the evaluation of these lesions. REFERENCES 1. Leigh, T. F.: Mass lesions of the mediastinum. Radiol. Clin. N. Amer. 1:377, 1963. 2. Leigh, T. F., and Weens, H. S.: The
Mediastinum. Springfield, Thomas Publisher, 1959.
Ill.,
Charles C
Aspects of Mediastinal
Lesions
By TED F. LEIGH, M.D., AND H. STEPHEN WEENS, M.D.
HE MEDIASTINUM is a small area with a lot going on in it. Through it passes all the food you eat, all the air you breath, and all the blood that nourishes your body. And to these structures of transport, plus many others, much can happen. Radiologic examination is the most important diagnostic tool for study of the mediastinum. Any lesion therein should be thoroughly investigated, using selective procedures. And there are a number of these available: conventional chest films, Bucky or grid examinations, fluoroscopy including esophageal examination, tomography, angiography, bronchography, myelography, lymphography and air studies of the mediastinum, pleural space, and peritoneal cavity. At times an isotope study may be necessary. The reader should bear in mind that positive findings elsewhere than in the mediastinum may also give a clue to the correct diagnosis of a mediastinal lesion, e.g., bone lesions in a patient with a parathyroid adenoma, or an enlarged spleen in a patient with mediastinal lymphadenopathy. After a thorough radiologic investigation, the ability to evaluate a given lesion may fall into one of three categories: (1) the lesion can be diagnosed accurately without question; (2) it may defy definite diagnosis, but the possibilities can be narrowed down to only a few conditions; (3) the cause of the lesion is completely unknown and even a good differential diagnosis is not possible. In this paper, the more important masses occurring in the mediastinum will be discussed. The rare conditions are omitted for the sake of brevity. Lesions are described under headings that indicate their usual location within the mediastinum. This is done so that the reader may think in terms of a differential diagnosis when he is investigating a lesion in a specific area.
T
“ANTERIOR”
MEDIASTINUM*
Teratomu Teratomas almost invariably are located in the anterior part of the mediastinum and very commonly occur in the area where the great vessels join the heart; occasionally they are located at higher or lower positions than this. They may project unilaterally to the ,left or right or spread bilaterally. They vary in size from very small to huge, occasionally being so large that they nearly fill the entire chest and markedly compress adjacent structures. Teratomas commonly contain opacities. These may be linear calcifications in the capsule, or they may be skeletal parts such as teeth, mandible, or some other bone. The cystic type contains a fatty substance which is radiolucent, TED F. LEIGH, M.D.: Professor of Radiology, Emory University School of Medicine; Director, Department of Radiology, Emory University Hospital, Atlanta, Ga. H. STEPHEN WEENS, M.D.: Professor and Chairman, Department of Radiology, Emory University School of Medicine; Director, Department of Radiology, Grady Memorial Hospital, Atlanta, Ga.
*See footnote, page 55. SEMINARS
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but this is difficult to judge in the mediastinum because of the surrounding air in the lungs, bronchi, and trachea. When a horizontal beam is used, the fatty material may layer out on top of fluid of water density, resulting in a fat level on the film (Fig. 1) . An occasional complication is perforation, either into an adjacent air passage (in which case an air-fluid level is likely) or into the mediastinal tissues or pleural space ( the latter resulting in visible pleural fluid).
Thymoma and Thymic Cyst Thymoma, like teratoma, most commonly arises anterior to the juncture of the great vessels and heart. It may widen the mediastinum to the left or right, or in both directions. The outline may be smooth or irregular. Most are small or medium-sized, and they seldom become as large as teratomas. Thymoma, benign or malignant, may calcify either with linear deposits in the wall or conglomerate masses in the substance of the tumor. It does not contain bony parts-a differential point from teratoma. The malignant variety has a tendency to recur after surgical removal. Thymic cysts arise in the same location as the thymoma. They are benign, usually small or medium in size, and occasionally calcify. Since the thymic lesions and teratoma frequently have their origin adjacent to the great vessels, differentiation from a vascular outpouching is frequently necessary, either through opacification of the vascular structures or by diagnostic pneumomediastinography ( Fig. 2).
Lipoma A lipoma usually arises in the “anterior” mediastinum in its midportion, and as it grows in size it tends to broaden the mediastinum on one side only, more commonly the right. Since lipomas are soft and pliable, they grow in the direction of least resistance and are usually quite large when initially discovered. At times such a mass may extend downward to rest on the right hemidiaphragm (Fig. 3). We have encountered 3 such cases with almost identical
Fig. L-Cystic teratoma. Chest films taken with the patient standing (horizontal beam), A level is seen between the lighter fat and the heavier fluid beneath it. (Courtesy of Wendell P. Stampfli, M. D.)
MEDIASTINAL
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61
A Fig. IL.-Benign thymoma. Frontal (A) and lateral (B) tomograms after diagnostic pneumomediastinum show the shape of the left anterior mediastinal mass and prove it is not of vascular origin.
Fig. 3.-Lipoma. PA and the right hemidiaphragm There is no abnormality in because of the pliability of W. B. Saunders C0mpany.l)
lateral films disclose a mass of relative radiolucency on anterior-1 . extending upward to the midmediastinum the adjacent right lung and no cardiac shift, presumab ry the lesion. (Courtesy of Robert M. Lowman, M.D., and
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findings. These masses are relatively radiolucent, particularly the larger lesions, but as previously mentioned, the air in the surrounding lungs and air passages may interfere with its recognition. Liposarcoma also arises in the mediastinum, but is extremely rare, and there is not enough in the literature to formulate a consistent description of its radiologic characteristics. Fibroma Fibroma of the mediastinum is also a rare tumor. It usually arises in the anterior portion and tends to spread to one or both sides. It may grow to relatively large size (Fig. 4). Fibrosarcoma is also rare in the mediastinum, and in the authors’ experience has been mainly confined to the region around the esophagus. Parathyroid
Tumor
The two lower parathyroid glands occasionally migrate into the “anterior” mediastinum along with the thymus. Of course, these are not visible unless hyperplasia or tumor develops, It may then become sufficiently large to broaden the mediastinum on one or both sides. The tumor is usually located in the middle or upper part of the anterior mediastinum. Since most of these are functioning lesions, radiographic signs of hyperparathyroidism may be seen. Blood Vessel Tumor Benign and malignant blood vessel tumors, i.e., hemangioma, hemangiosarcoma, malignant endothelioma, etc., are most commonly located in the “anterior” mediastinum. Their shape and size vary, widening the mediastinum to the left or right, or bilaterally. Some contain phleboliths, which, if identified, are pathognomonic of this tumor (Fig. 5). Some have broad vascular connections and may be opacified on contrast studies. Lymph
Vessel Tumor
Synonyms include lymphangioma and lymphangiosarcoma. Lymphatic tumors are similar to blood vessel tumors in that most have their origin in the “anterior” mediastinum and may broaden it on one or both sides. Their size and shape also vary. Paragangliomu Paraganglioma may occasionally arise from an aorticopulmonary body which lies on the anterior surface of the pulmonary artery and aorta. The tumor may widen the mediastinum bilaterally. Its contour may be smooth or lobulated and it may grow to very large size. Lymphadenopathy Enlargement of one or more lymph nodes in the “anterior” mediastinum, from whatever cause, may present as a mass. The mass may be large or small, smooth or lobulated, noncalci5ed or calcified (the latter a point in favor of
MEDIASTINAL
LESIONS
Fig. 4.-Fibroma. This huge fibrous-tissue tumor, descril 3ed as fibromatosis in the pathology report, weight ed 7% pounds and con&i ted of 2 large masses connec:ted across the midline by ‘an isthmus. It was successfullly removed surgically.
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benignancy). Enlargement may be isolated or occur with nodal enlargements elsewhere in the mediastinum. At times lymphadenopathy may resemble a single mass lesion such as a thymoma. Differential diagnosis is aided by radiologic investigation of other areas of the body for such findings as retroperitoneal adenopathy or splenomegaly.
Vascular Lesions The most common vascular lesion in the “anterior” mediastinum is enlargement of the ascending aorta. The widening is usually diffuse and results in broadening of the right mediastinal border in its midportion, as seen on the frontal view. Linear calcification is occasionally deposited in the wall. Fluoroscopy and a study of the pulsations may aid in identifying the nature of the enlargement. Aortography will identify the mass as aorta. Superior vena caval enlargement may be congenital or acquired. It causes a smooth bulge of the mediastinum to the right, which usually is fairly long (Fig. 6). If there is enlargement of an associated left superior vena cava (collecting vein), as frequently occurs in anomalous pulmonary venous return to the right heart, there will be a broadening of the left mediastinum as well. Main pulmonary artery dilatation produces an exaggeration of the usual shadow of this structure as observed on frontal projection. Two points help to differentiate the pulmonary artery from other causes for hilar enlargement: it is exactly at hilar level and it is continuous with the left main pulmonary artery (best seen by tomography).
Fig. 5.-Blood vascular tumor. This radiographic study of a surgical specimen removed from the mediastinum discloses multiple phleboliths within the lesion. (Courtesy of Benjamin Felson, M.D., and W. B. Saunders Companyl and Charles C Thomas Publisher.2)
MEDIASTINAL
65
LESIONS
Fig. 6.-Aneurysmal dilatation of the superior vena cava, thought to be congenital. Surgical exploration did not reveal any associated lesion. (Courtesy of Charles C Thomas Publisher.‘)
“POSTERIOR”
MEDIASTINUM
Neurogenic Tumors This category includes neurilemoma, neurofibroma, schwannoma, ganglioneuroma, sympathicoblastoma ( neuroblastoma) , pheochromocytoma, and paraganglioma (chemodectoma). These tumors arise far posteriorly against the spine, and as they grow they spread laterally and anteriorly. Unilateral growth is the rule. They may be located at any level from the inlet to the outlet, may be large or small, variable in shape, localized or invasive. Calcification is seldom seen, A neurogenic tumor may involve one or more ribs and vertebrae. The ribs may be displaced, eroded, or destroyed. In the spine, the pattern is usually that of unilateral body and/or foraminal destruction or erosion (Fig. 7). Some tumors, notably neurofibromas, are dumbbell in shape, with a spinal canal component connected to the mediastinal mass by an isthmus. The value of myelography in suspected cases of this type is thus apparent.
Lateral Meningocele This anomaly resulting from outpouching of the leptomeninges may present as single or multiple fluid-filled masses in the mediastinum. Its roentgen characterics are similar to those of the solid neurogenic tumor in that it presents as a unilateral mass, variable in size, well circumscribed, with associated bony Iesions. It does not calcify. On myelography, it is likely that some of the contrast medium will pass into the mediastinal sac. Neurofibromatosis is commonly present.
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Fig. ‘I.-Neurofibroma of the posterior mediastinum, eroding the 9th, lOth, and 11th dorsal vertebrae, and the right 10th rib. (Courtesy of Richard A. Elmer, M.D., and Charles C Thomas Publisher.“)
Neurenteric
Cyst
This lesion is usually discovered in early life, and if adequate roentgen investigation is made, can be diagnosed with reasonable certainty. The mediastinal mass is usually large and widens the mediastinum unilaterally or bilaterally. In addition, there is an associated anomaly of the dorsal spine. If the lesion is connected to the intestinal tract by a patent tube, the mass is likely to contain air. A more detailed discussion of this entity can be found in the article by Benton and Silverman in this issue. Extramedulla
y Hematopoksis
Characteristically, extramedullary hematopoiesis presents as bilateral masses in the lower “posterior” mediastinum immediately adjacent to the ribs and spine (Fig. 8). These masses may be lobulated or smooth in contour, single or multiple, and are of homogeneous density without calcium. Because of their paravertebral position, they may be visible only on the frontal view and, since they are most frequently in the retrocardiac area, it is important that penetration be adequate for their perception, Splenomegaly and hepatomegaly are frequent and important associated findings. Bone and Cartilage
Tumors
Tumors of one or more of the dorsal vertebrae are fairly common and generally destroy the vertebrae to a varying degree without causing mediastinal enlargement. A small percentage, however, may expand the vertebrae, grow through it into the adjacent paravertebral area, or extend eccentrically producing a mass which is visible on the ordinary chest study and on special studies as well (Fig. 9). This includes such lesions as sarcomas, myeloma, Ewing’s
MEDIASTINAL
LESIONS
67
tumor, aneurysmal bone cyst, and metastatic disease. Tumors may also arise from the posterior aspects of the ribs and present as mediastinal masses. The important thing is to remember that spine lesions can do this and include them in a differential diagnosis. A thorough roentgen investigation of such lesions, including Bucky films, tomography, myelography, and possibly angiography is indicated.
Paravertebral Masses Paravertebral
enlargement may result from several conditions. A spinal tumor
Fig. 8.-Extramedullary hematopoiesis in a patient with myelofibrosis. There are multiple masses of blood-forming tissue adjacent to the lower dorsal spine. (Courtesy of M. Paul Capp, M.D.)
Fig. 9.-Multiple myeloma involving the 10th dorsal vertebra and having an associated paravertebral mass of fusiform confIguration, presumed to be tumor tissue extending from the confines of the vertebral body. (Courtesy of Charles C Thomas Publisher2 and W. B. Saunders Company.l)
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that extends beyond the confines of the vertebrae, as stated earlier, will broaden the paraspinal space unilaterally or bilaterally, usually with greatest expansion at the level of the involved vertebrae (Fig. 9). Spinal osteomyelitis, tuberculosis or nontuberculous, almost invariably has an associated bilateral fusiform-shaped mass of pus in the paravertebral space, and the diameter is also usually greatest at the level of the lesion; characteristically, the spine itself shows erosion or destruction of one or more vertebrae (frequently in apposition), particularly on the articular surfaces. Fractures of the spine are often accompanied by unilateral or bilateral collections of blood in the paraspinal area, the diameter of the hematoma being broadest at the level of the injury. Again, it is important that adequate radiographic study be made to determine the characteristics of the paravertebral mass and of the spinal lesion as well. Cyst of the Thoracic
Duct
This is an extremely rare type of mass of the mediastinum; only several have been reported. These have been characterized by a soft-tissue mass in the “posterior” mediastinum, but their association with the thoracic duct is not apparent. In one case, upon opening the cyst, a duct was identified at its cephalic end, and after injection of this duct with contrast material, a radiograph taken in the operating room proved that the cyst was continuous with a normal thoracic duct which passed into the cervical area. Vascular Lesions In the “posterior” mediastinum vascular lesions are mainly of the descending aorta. These can be suspected by their roentgen appearance, particularly if there is associated vertebral or rib erosion (as happens occasionally). They can be proved by aortography. “MIDDLE”
MEDIASTJXUM
Included in this area are bronchogenic cyst, enlargement of the paratracheal lymph nodes, esophageal lesions, tracheal tumor, and certain vascular lesions. Bronchogenic
Cyst
The majority of these cysts are adjacent to the trachea or bronchi. Their size varies and they may broaden the mediastinum unilaterally or bilaterally. The contour is usually smooth or lobulated. They are of homogeneous density and do not calcify. Compression or displacement of the trachea may result, and if the cyst is on the posterior side, the esophagus may be similarly affected (Fig. 10). A bronchogenic cyst located in the subcarinal area may widen the bronchial angle. An occasional one communicates with the trachea or one of the bronchi and will contain air as well as fluid within its lumen. Paratracheal
Lymphadenopathy
The most common group of mediastinal lymph nodes that enlarge are those located around the trachea. These present as a smooth or lobulated mass, widening the mediastinum most often to the right, but sometimes to the left
MFDIASTINAL
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69
Fig. IO.-Bronchogenic cyst in an adult. On this spot film made in lateral projection, the lesion is outlined by air in the trachea and barium in the esophagus-
or bilaterally. Such enlargement may be of any size, from a subtle localized bulge to massive widening. Adjacent structures such as the trachea or bronchi may be compressed or displaced. Calcification seen within nodes is a good sign that the enlargement is benign. Noncalcified nodes can be benign or malignant. Esophageal
Lesions
The esophagus must always be remembered in the investigation of the mediastinum. Not only may an esophagram aid in establishing the characteristics of an extraesophageal mass, but there are also certain lesions of the esophagus itself that produce an abnormal mediastinum. These include megaesophagus, benign and malignant tumors, divert&da, and duplication cysts. To these can be added hiatus hernia. Megaesophugus almost invariably widens the mediastinum to the right, not to the left (except in the superior mediastinum). This widening can extend throughout the entire length of the mediastinum, or only partially. The widening may be smooth or lobulated. The esophageal shadow on a routine chest examination may be of homogeneous density, radiolucent, mottled with air, or show an air-fluid level (when a horizontal beam is used) ; each of these pictures depends on the contents of the structure and the patient’s position in relation to the X-ray tube during examination ( Fig. 11) . Benign tumors of the esophagus may be of sufficient size to widen the mediastinum locally at any level. It is usually a unilateral smooth enlargement. Contrast study shows a characteristic smooth deformity of the esophageal lumen with preservation of the esophageal mucosa. Malignant tumor infrequently widens the mediastinum, but, depending on size and level, may be visible on routine chest films. Again, contrast studies aid in the diagnosis and frequently show characteristic shelving margfns, mucosa1 destruction, fusiform narrowing, fungating filling defect, and UIC~E+ tion. Epiphrenic diuerticula are located just above the diaphragm, USU~IY to the
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Fig. Il.-Megaesophagus an air-fluid
level. The patient
broadening the mediastinum is in upright position.
to the right
and showing
right of the midline. They are of variable size and shape and usually contain air and fluid. With contrast studies, some of the media frequently runs into the pocket while the remainder outlines a normal esophagus above the neck of the diverticulum and a narrowed segment below it. Pharyngeal diuerticula (Zenker’s), if of sufficient size, will present as a midline superior mediastina1 mass containing fluid, or air and fluid. Contrast study usually shows the diverticulum and demonstrates its position posterior to the esophagus, compressing the adjacent esophageal segment. Duplication of the esophagus may occur at any level of the mediastinum. They are of variable size, usually rounded or oval in conhguration, and usually widen the mediastinum to one side only. Most are homogeneous because of their fluid content, but if they communicate with the esophageal lumen (congenitally or secondary to perforation) they will likely contain some air as well. Contrast studies show luminal deformities similar to the ones produced by benign tumors. When the lesion communicates, some media will probably enter the sac. EsophugeaE hi&us hernia most commonly involves the stomach and for the most part presents as a midline mass just above the diaphragm, but occasionally it may be to the left or right. On routine chest examination, it can be seen as a retrocardiac mass of variabIe size, usually containing both air and fluid. Occasionally, a segment of small intestine or colon, or both, may herniate through the hiatus, with or without the stomach, and cause multiple air and fluid pockets in the lower mediastinum. Rarely there may be hemiation of another structure, such as omentum, liver, or spleen.
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MEDIASTINAL LESIONS
Tracheal
Tumor
These are very rare. A tumor growing eccentrically off the trachea may reach sufficient size to enlarge the mediastinum locally. The mass may encroach on the tracheal lumen and deform the air column; tomography is valuable in such instances. Va.sc&r
Lesions
Azygos vein enlargement characteristically produces, on frontal view of the chest, a hemispherically shaped mass of homogeneous density resting in the angle between the trachea and the right main stem bronchus. A rare lesion is aneurysmal dilatation of the hemiazygos vein, which has been seen once by the authors. It presented as a left-sided retrocardiac mass on chest roentgenograms. Greatly enlarged esophageal varices may aIso produce lobulated shadows in the middle mediastinum on the routine chest film. All suspected vascular masses should have a thorough fluoroscopic investigation, and in doubtful cases angiography as well. With the latter, an accurate diagnosis can be made in almost every case. SUPERIOR PART OF THE MEDIASTINUM
Several types of lesions are invariably seen in the superior part of the mediastinum. These include mediastinal extension of a thyroid tumor, enlargement of the innominate or subclavian artery, pseudocoarctation of the aorta; and pharyngeal diverticula of the esophagus (already discussed). Thyroid
Lesions
Thyroid enlargement of various types (adenoma, cyst, benign and malignant tumors) is usually confined to the cervical area, but occasionally it extends downward into the superior mediastinum, particularly if it arises from one of the inferior poles of the gland. It may broaden the mediastinum unilaterally or bilaterally. The borders are sharply defined and smooth or lobulated. Linear, flocculent, or conglomerate calcium deposits may be seen. Frequently the trachea and esophagus are displaced, and separation of the two may result if the lesion is interposed between them. If a thyroid mass is attached to the trachea, upward movement with swallowing may be observed Auoroscopically. The superior mediastinal mass of thyroid is almost invariably continuous with an enlarged part of the gland in the neck, but the latter cannot be seen well because its borders are not surrounded by air. Vascular Lesions Usually these are caused by aneurysmal dilatation of the innominate artery on the right or subclavian artery on the left by an aneurysm arising from the superior aspect of the aortic arch, or by pseudocoarctation. A mass of this type may show linear intramural calcium deposits. It may or may not displace the trachea and esophagus, depending upon its location and size. Its true nature can be identified by angiography.
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Other Lesions Several other lesions may be seen in this area. These include blood vessel tumor, lymphatic tumor, thymoma, teratoma, bronchogenic cyst, duplication of the esophagus, parathyroid enlargement, neurogenic lesions, tracheal tumor, abscess and hematoma. INFERIOR PART OF THE MEDIASTINUM
The inferior part of the mediastinum may be the site of a pericardial celomic cyst, foramen of Morgagni hernia, epiphrenic diverticulum, or esophageal hiatus hernia (the latter two already discussed). Pericardial
Celomic Cyst
These vary from 1 to 15 cm. in diameter, the majority being relatively small. They are smooth or slightly lobulated, and rounded, oval, or tear-drop in configuration. Most are located in the right cardiophrenic angle, but an occasional one is found at any point along the pericardium. They do not calcify. They may strongly resemble omental hemiation through the foramen of Morgagni, and a diagnostic pneumoperitoneum may be necessary for differentiation. Foramen of Morgagni
Herniation
Abdominal contents, such as a portion of omentum, liver, small intestine, colon, or stomach may herniate into the lower mediastinum through the right or left foramen of Morgagni. The hernia usually 08ccurs on the right since the left foramen is protected by the pericardium. Most often it contains a portion of omenturn, and presents on the chest film as a smooth oval-shaped mass of homogeneous density adjacent to the right heart border. If a diagnostic pneumoperitoneum is performed, and films are made with a horizontal beam, air usually will be seen in the sac between the peritoneal covering and the fat. A segment of colon, small intestine, or stomach that herniates through one foramen of Morgagni will usually show one or more pockets of air or air-fluid levels along with shadows of homogeneous density which represent the wall of the viscus. Barium studies will reveal the exact segment involved. Mediastinal lesions of many other types may at times be located in the inferior part of the mediastinum, but are not necessarily confined to this area. LESIONS THAT VARY IN LOCATION
Mediastinitis and hematoma demonstrate no proclivity for any specific location, but it should be borne in mind that many of the other mass lesions discussed in this paper can at times be found in areas other than their usual sites. Mediastinitis Inflammation may be localized or diffuse, A localized abscess may be of almost any size or configuration, and may be located at practically any point in the mediastinum. It may be unilateral or bilateral. Those resulting from perforation of a hollow structure like the esophagus or trachea will probably contain air as well as pus (Fig. 12)) and this point should be investigated by examination of the esophagus or trachea with water-soluble or oily media (in
MEDIASTINAL
73
LESIONS
Fig. 12.-Localized mediastinal abscess secondary to perforation of the upper esophagus by a fish bone. This examination, made with the patient in upright position, reveals a small collection of air at the superior aspect of the mass. The trachea is displaced anteriorly. (Courtesy of E. H. Wood, M.D. and C. A. Bream, lM.D., and W. B. Saunders Company.‘)
case of spillage). When an abscess is located in the superior mediastinum, the cervical area should be investigated with soft-tissue technic for abnormal collections of air. Diffuse mediastinal inflammation, if of sufficient magnitude, will widen the mediastinum bilaterally and cause loss of sharpness of the borders.
Hematomu Like mediastinitis, hematoma may be localized or diffuse. The localized form may be of any size or shape and located at any level. Frequently it is caused by trauma and thus can be suspected from the history. It has a tendency to change in size on serial examination because of blood absorption or further bleeding. Diffuse hematoma usually widens the mediastinum bilaterally and, like the localized blood collections, gives a changing picture. In both the localized and diBuse forms, ancillary findings such as fracture in the sternum, ribs, or dorsal spine, surgical clips, and metallic sutures, etc., may aid in the evaluation of these lesions. REFERENCES 1. Leigh, T. F.: Mass lesions of the mediastinum. Radiol. Clin. N. Amer. 1:377, 1963. 2. Leigh, T. F., and Weens, H. S.: The
Mediastinum. Springfield, Thomas Publisher, 1959.
Ill.,
Charles C