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The mediastinum is strategically located from the thoracic inlet to the diaphragm between the left and right pleural cavities and contains vital structures of the circulatory, respiratory, digestive, and nervous systems. Embryologic development leads to cells from ectodermal, mesodermal, and endodermal origin, ultimately residing in the small mediastinal compartment. Clinically, the mediastinum may be divided into superior and inferior compartments, with the inferior mediastinum being subdivided into anterior, middle, and posterior sections. The topographic landmarks in each division of the mediastinum allow for directed investigative, diagnostic, and therapeutic strategies. GENERAL MEDIASTINAL EMBRYOLOGY The original intraembryonic coelem (primordium of the body cavities) gives rise to three well-defined body cavities, in the 4th week of gestation, that ultimately form the boundaries of the mediastinum?" The cavities consist of the pericardial cavity, peritoneal cavity, and two pericardioperitoneal canals connecting the pericardial and peritoneal cavities. The cavities are lined with mesodermal mesothelium, which ultimately develops into the pleural and peritoneal surfaces. As the headfold forms and grows ventrocaudally, the dorsal pericardial cavity and embryonic heart are pushed inferiorly toward their ultimate residing place in the mediastinum.21 The lateral borders of the mediastinum are formed as the pleuropericardial

From the Section of General Thoracic Surgery, Division of Cardiothoracic Surgery, Department of Surgery, Emory University School of Medicine, Atlanta, Georgia






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canals grow laterally to the foregut. In this region, the foregut creates the esophagus later in gestation. Partitions that separate the pericardium from the pleural cavities and the peritoneum arise in these canals at the end of the 4th week of gestation. The growth of bronchial lung buds into the canals pushes the superior pleuropericardial surfaces upward and inferior surfaces downward to create membranes that further define the pleural cavities and create a space for the mediastinal structures. By the 7th week of gestation, the pleuropericardial membranes fuse with the mesoderm ventral to the esophagus, forming a defined area called the primitive mediastinum,21which houses the pericardial cavity and is distinct from the pleural cavities at this time. The embryonic mediastinum consists of a mass of mesenchyme from the sternum to the primitive vertebral column and between (the future site of) the lungs. If one accepts the philosophy of Langeba~tel,'~ the adult dorsal and ventral mesentery of the esophagus is responsible for the genesis of the mediastin~m,'~ so surgeons must keep in mind the embryologically and anatomically related entities contained within this space. The mediastinum, filled with mesenchyme, is the anatomic space between the two pleural cavities and contains important anatomic entities, such as the thoracic aorta, pericardium, heart, and esophagus. Individual structures in the mediastinum develop at different stages of embryonic life. The primitive trachea is present early in gestation, whereas the bronchi and lung buds develop much later. Similarly, the primitive foregut, which develops into the proximal gastrointestinal tract, including the esophagus, is noticeable at 7 weeks of gestation but does not canalize or become functional until the middle of the embryonic period. Cardiac development is first indicated in the 3rd week of gestation, and contractions can be detected by day 21 or 22 of gestation?' Rotation of the primitive atrioventricular canal turns a tuba1 structure into a four-chambered organ approximately 2 weeks later. The details of specific embryologic development of mediastinal structures, as they pertain to diagnosis and surgical treatment of disease processes, are discussed in the following sections but a detailed embryologic discussion is beyond the scope of this article. ANATOMY AND ALGORITHMS FOR THE INVESTIGATION OF MEDIASTINAL MASSES

The basic investigative approaches to the identification, diagnosis, and treatment of mediastinal masses are defined by the anatomic relationships of mediastinal structures and the compartments in which various organs lie. A diagnostic algorithm for mediastinal masses is shown in Figure 1. All approaches begin with a thorough history and physical examination focusing on symptoms of respiratory, circulatory, and digestive complaints that guide the direction of diagnostic tests. Typically, the first intervention is posteroanterior and lateral chest radiography looking for a mediastinal mass. If a mass is present, a CT scan of the chest is generally indicated, but MR imaging may be more useful if a neurologic or vascular process is suspected. On the basis of a CT scan, the primary lesion can be classified as being in the superior, anterior, middle, or posterior mediastinal compartment. Figure 2 is a potential algorithm for the diagnosis of the primary lesion based on the mediastinal anatomic compartment in which it is located. When a diagnosis has been entertained, endoscopy or biopsy may be warranted. The clinical presentation of mediastinal masses also varies according to



History and Physical Examination Chest Radiograph (Posteroanterior and Lateral)

1 Mediastinal Mass

1 CT Scan of Thorax MR image (If Indicated) Angiography (If Indicated)

Endoscopy (If Indicated)

1 Suspect Mediastinal Tumor

/ Biopsy 1. Scalene node 2. Mediastinoscopy 3. Fine needle aspiration

\ Surgery 1. Median sternotomy 2. Lateral thoracotomy

Figure 1. Evaluation of mediastinal masses.

anatomic location. Many patients are asymptomatic with smaller lesions, but as lesions grow to invade the tracheobronchial tree, esophagus, or sensory nervous system or compress vascular structures, symptoms help to localize the disease process. Consequently, approximately 55% to 65% of patients are symptomatic at pre~entation.~~ Patients with benign lesions are more likely to be asymptomatic than are patients with malignant processes. Symptoms of mediastinal lesions occur in 48% to 62% of patients at the time of diagnosis, with anterior lesions more commonly causing symptoms than middle or posterior lesion^.^, ", This article presents mediastinal diseases by the anatomic mediastinal compartment in which they are located. They are described in the context of symptoms and radiographic findings relevant to other processes and structures in the mediastinum. Treatment of mediastinal diseases is discussed briefly in this article, but an in-depth analysis of therapies is left to discussion elsewhere. SUPERIOR MEDIASTINUM

The superior mediastinum lies between the left and right pleural surfaces and is limited superiorly by the thoracic inlet and extends caudal to a line extending from the sternal angle anteriorly to the upper part of the vertebral body of T4 posteriorly (Fig. 3). Contained in the superior mediastinum are the thymic remnants; brachiocephalic veins; superior vena cava; aortic arch and its branches; trachea; and the phrenic, vagus, left recurrent laryngeal, and autonomic nerves. Figure 4 is a cross-section of the superior mediastinum and all of its vital structures. The thymus is the major culprit of most lesions in the superior mediastinum, with vascular anomalies and injuries being less common. The thymus originates as a large gland that lies directly below the superior


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Chest Radiograph

1 Mediastinal Mass

1 Dynamic CT Scan Differential Diagnosis @ased on mediastinal compartment) Superior Thymoma Thyroid (Substernal)

Anterior Teratoma Lymphoma Germ cell tumor

Middle Posterior Pericardial cyst Neurogenic tumor Bronchogenic cyst Esophageal disease Enteric Cyst

Thyroid Lvmohonia Pericardial Cvst Neuroaenic tumors 1. Thoracic Inlet 1. Anterosuperior 1. Usually right- 1. Obtain MR image 2. Look for intraspinal 2. Smooth, frequently 2. Smooth, Homogeneous sided extension 3. Frequently surrounds symmetric great vessels Teratoma

Bronchoaenic Cyst 1. Frequently anterior Compartment subcarinal 2. May contain calcium Enteric Cyst 1. Differential diagnosis with bronchogenic cyst; need pathology 1. Lower superior or

Figure 2. Diagnosis of mediastinal mass by anatomic location.

aspect of the sternum and anterior to the great vessels at birth. It may also extend cephalad into the neck or inferiorly into the anterior mediastinum. Embryologically, the thymus arises primarily from the third pharyngeal pouch but may also contain tissue from the fourth pharyngeal pouch. The pouches contribute endodermal tissue from the ventral aspect of the third pouch and ectodermal tissue from the floor of the branchial The thymic tissue elongates beginning in the 7th week of gestation, and each lobe migrates toward the midline by the 8th week. From this point, the lobes remain distinct, with only a small connection until birth, so during their descent, the right and left thymic primordia are in apposition, without a true and complete fusion of this lobulated organ. The thymus continues to mature until puberty, although it reduces in size during this period. Following puberty, the gland becomes dramatically smaller until it is only a remnant later in life. This reduction is probably a result of increased T-lymphocyte production throughout the body, making thymic production of T cells unnecessary. The surgical anatomy of the thymus is crucial to the successful removal of the gland in pathologic conditions. The structure of the thymus is roughly an H-shaped configuration lying anterior to the great vessels. The upper portion typically lies on the anterior surface of the left innominate vein as the vein



Figure 3. Sagittal section of the mediastinum identifying superior, anterior, middle, and posterior mediastinal regions.

courses across the mediastinum to join the right innominate and forms the superior vena cava, so an enlarged thymus may lie adjacent to the superior vena cava and the aorta. Additional thymic tissue may be ectopic and reside anywhere in the neck or other regions of the mediastinum. The arterial blood supply to the thymus most often arises from the inferior thyroid and internal thoracic arteries. In some cases, the superior thyroid arteries and branches of the subclavian and carotid arteries add to the blood supply of the organ. This phenomenon results from the similar embryologic origin of the

Figure 4. Cross-sectional anatomy of superior mediastinurn at the level oi the fourth thoracic vertebra. v = vein; n = nerve; a = artery. /




Paratracheal and mediastinal lymph

Thymic remnants


Fourth thoracic vertebra

Thoracic duct

Left recurrent

Left subclavian a

Left brachiocephalic v

Brachiocephalic trunk Left common carotid a



thyroid, parathyroid, and thymus glands, all of which share similar vascular supply. Other sources of oxygenated blood for the thymus are laterally from small branches of the internal mammary arteries and inferiorly from pericardiophrenic arteries. Venous drainage is predominantly central, through the great vein of Keynes, a vein on the posterior aspect of the gland that directly empties into the left innominate vein. Smaller, venous vessels accompany the arterial supply, and multiple posterior vessels are often found in enlarged glands. Sympathetic and parasympathetic nerves enter the thymus but primarily regulate vascular tone. Lymphatic drainage of the thymus is to the nodes of the pulmonary hilum and internal mammary chains, but the thymus has no afferent lymphatics. Thymomas are the most common primary neoplasm in the superior mediastinum and the second most common neoplasm in the mediastinurn? The peak incidence is from the third to fifth decade of life, but they can occur any time throughout adulthood. Histologically, thymomas can be classified as predominantly lymphocytic, epithelial, or spindle cell, but more than 80% are of the lymphoepithelial variety, whereas only 5% to 12% are purely of the spindle type.I7 The determination of malignancy with thymomas is by their degree of invasiveness. Microscopic evaluation of thymoma does not differentiate between benign versus malignant thymomas, but rather the invasive characteristics at surgery are the principal determinants of malignancy. Thymomas rarely metastasize distantly, but approximately 20% may be associated with local pleural or pericardial metastatic disease.I2,17, 31 Nearly 45% of thymomas are associated with myasthenia gravis, but only thymomas develop in 5% to 15%of myasthenic patients, whereas thymic hyperplasia without evidence of malignancy develops in as many as 75% of patients. Approximately 50% of thymomas are asymptomatic, and those that are symptomatic are commonly associated with thymoma-related syndrome^.'^. 29 The most common related symptoms are cough, dyspnea, and chest pain, highlighting the anatomic relationships of the thymus that directly influence the symptoms of an enlarged gland. The recommended treatment for thymic tumors is surgical excision, with an extended thymectomy to include accessory mediastinal fat tissue, including ectopic thymus glands. Depending on the stage of the tumor, adjuvant radiation or chemotherapy might be required. Thymic cysts are another common indication for surgical intervention in the superior mediastinum. Cysts may be uniloculated or multiloculated and are lined with various epithelia, including squamous, cuboidal, pseudocolumnar, and transitional. The symptoms of thymic cysts vary widely depending on their location. Some cysts are associated with a lateral neck mass, extend inferiorly into the mediastinum, and require sternotomy. These patients can present with compression or irritation of the structures adjacent to the cyst, including cough, dyspnea, and chest pain. Other structures contained in the superior mediastinurn are the aortic arch and great vessels, trachea, and numerous nerves traversing the compartment and connecting the head with the trunk. Primary abnormalities of the great vessels in this region are unusual. A right-sided or aneurysmal aortic arch may be present and distort the normal surrounding anatomy. Anomalous attachments of the great vessels to the aorta also occur but are rare. The gold standard for identifying these abnormalities is angiography, which helps to further clarify any undiscernible vascular defects found on CT scans. Abnormalities of the trachea are common and can be numerous, but their discussion is beyond the scope of this article.


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ANTERIOR MEDIASTINUM The anterior mediastinum is often referred to as the prevascular compartment. It extends from the posterior surface of the sternum to the pericardium and is bound superiorly by the inferiormost aspect of the superior mediastinum and inferiorly by the diaphragm (see Fig. 3). The major primary lesions of the anterior mediastinum are of lymphatic origin. Germ-cell tumors and vascular lesions are also found in the anterior mediastinum but are less common. Secondary processes include mediastinitis, which has potentially high morbidity and mortality rates. Because the most common cause of acute mediastinitis is postoperative infection of the anterior mediastinum following median sternotomy, mediastinitis is discussed in this section of the article, with the understanding that mediastinitis can originate or progress to any mediastinal compartment. The most common primary anterior mediastinal lesion is lymphoma. In general, mediastinal lymphoma presents as part of a systemic disseminated disease present in multiple sites. Primary mediastinal lymphoma occurs in only 5% to 10% of patients with l y m p h ~ m aApproximately .~ 60% to 75% occur in the anterior mediastinum, with the remainder in the middle and superior mediastinum. Lymphomas include Hodgkin’s disease and non-Hodgkin’s lymphomas and represent approximately 10% to 20% of primary mediastinal tumors.’7,22 Most patients (60-70%) present with local symptoms, whereas as many as 30% of patients are asymptomatic at diagnosis.3o,33 Principal symptoms include chest heaviness, cough, fatigue, fever, sweats, weight loss, and pruritus. Palpable lymph nodes are present in 10% to 15% of patients. When lymphoma is suspected, definitive diagnosis can be made by mediastinoscopy, mediastinotomy, or, for infra-aortic nodes, video-assisted thoracoscopy. Fine-needle aspiration is often inadequate for definitive diagnosis, and node biopsy is needed for maximal diagnostic accuracy. Occasionally, when the supraclavicular lymph nodes are palpable, biopsy is diagnostic. When the diagnosis has been established by tissue biopsy, therapy is predominantly medical with radiation, chemotherapy, or both. Hodgkin’s lymphoma in the chest presents an overall 5-year survival rate of 75%, whereas non-Hodgkin’s lymphoma presents a 5-year survival rate of approximately 50%, depending on the stage at the time of presentation? Earlier stages of Hodgkin’s disease (i.e., stages I and IIA) are primarily treated with high-dose radiation. In higher stages (i.e., stages IIB, 111, and IV), chemotherapy is the modality of choice. Non-Hodgkin’s lymphoma is usually treated with combined radiation and chemotherapy. Similar to mediastinal lymphomas, mediastinal germ-cell tumors usually arise extrathoracically. When in the mediastinum, germ-cell tumors occur primarily in the anterior mediastinum and comprise approximately 15% of anterior mediastinal masses and 8% to 10% of all primary mediastinal tumors.3O The mediastinum is the second most common site of germ-cell tumors following gonadal locations. Tumors are common in this location because of abnormal embryologic migration of primitive germ cells that began in the fetal region destined to become the anterior mediastinum. Mediastinal germ-cell tumors can be benign or malignant. Teratomas are the most common type of germ-cell tumor in the mediastinum and can be benign or malignant. Malignant tumors are classified as seminomatous or nonseminomatous. Benign teratomas of the mediastinum account for approximately 10% of mediastinal tumors.16Most of these occur in young adults aged 15 to 20 years. They are typically slow growing and cause symptoms based on a mass effect on surrounding anatomic structures. When symptomatic (approximately 50% of



patients), chronic cough and substernal chest pain are the most common symptoms.lb Pain originates from the encapsulation of anterior mediastinal sensory nerves, whereas cough occurs secondary to bronchial irritation with lateral extension of the mass. In some cases, posterior extension of a large teratoma can directly compress the pericardium or indirectly create a reactive pericardial effusion, resulting in tamponadelike symptoms. Calcification of teratomas can be seen in as many as 30% of patients with the 1esi0n.I~Serum P-human chorionic gonadotropin (P-HCG) and a-fetoprotein (aFP) are typically normal at the time of presentation. The treatment of choice for teratoma is excision. Surgical approach depends on the location of the tumor, but whenever possible, radical excision of the tumor and surrounding structures should be accomplished. With complete excision, the 5-year survival rate of patients with benign teratomas is near loo%, with almost no recurrence, but the 5-year survival rate of patients with malignant teratomas is 35% to 50%.16 Malignant mediastinal germ-cell tumors are much less common than are teratomas and germinal tumors arising in the testis. Only 1%to 5% of germinal neoplasms are found in the m e d i a s t i n ~ mOf . ~ ~these primary malignant mediastinal germ-cell tumors, pure seminoma is the most common histologic subtype, accounting for approximately 10% to 35% of these tumors. The other 65% have some element of nonseminomatous histopathology.2 Many malignant germ-cell tumors are large at the time of presentation, and they commonly invade the pericardium and local mediastinal structures, including lung, pleura, and chest wall. Symptomatology is dependent on these anatomic relations and varies widely among patients. The development of specific serum immunoassays for P-HCG and aFP allows for more accurate serum and histologic diagnosis. Approximately 10% of seminomas have elevated PHCG, whereas the aFP is always normal in pure semi no ma^,^ but elevations in aFP level do correlate with the presence of nonseminomatous elements of mediastinal germ-cell neoplasms. Lactate dehydrogenase levels are also elevated in mediastinal seminomas. Almost 90% of patients with nonseminomatous tumors have significant elevations in P-HCG and aFP levels.23 Before management, classification of tumor type and staging of tumor are imperative to direct therapy. Although the in-depth treatment of mediastinal germ-cell tumors is beyond the scope of this article, seminomas are highly radiosensitive and are treated with radiation alone or combination therapy using radiation therapy and chemotherapy. Nonseminomatous neoplasms are typically treated with cisplatin-based chemotherapy with or without radiation depending on the protocol. The prognosis for nonseminomatous tumors has improved over time and is associated with a cure rate of approximately 50%. Similar to neoplasms of the anterior mediastinum, infection of the mediastinal space is a severe and potentially fatal process. Because of Boerhaave’s51724 description in graphic detail of the morbid results of spontaneous esophageal rupture, acute mediastinitis has been recognized by physicians as a devastating disease that is commonly unresponsive to valiant treatment efforts, but with early disease recognition, appreciation of the anatomic extent of the disease, and aggressive therapy, the infection may be contained and treated, with an improved patient survival rate. The following are common causes of acute mediastinitis: Postoperative (sternotomy, open heart) Esophageal perforation (endogenous, iatrogenic) Idiopathic Head and neck infection


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Lung infection Subphrenic infection Post-traumatic Rib or sternal osteomyelitis Datafrom Baue AE, Geha AS, Laks H, et a1 (eds): Glenn’s Thoracic and Cardiovascular Surgery, ed 6. Stamford, CT, Appleton & Lange, 1996.

The most common cause of acute mediastinitis is postoperative infection following median sternotomy for open heart surgery. The incidence of mediastinitis following coronary surgery ranges from 1%to 6%, depending on premorbid and postoperative conditions, with a mean of approximately 2%.4 Factors predisposing patients to mediastinitis include obstructive pulmonary disease, obesity, diabetes mellitus, chronic debilitation, and long-term corticosteroid therapy. Hazelrigg et a19’ reported that intraoperative use of unilateral or bilateral internal mammary arteries for coronary bypass can increase the risk for mediastinitis threefold to fivefold compared with saphenous vein bypass grafting without internal mammary arteries use? Postoperatively, closed chest cardiac massage, increased intrathoracic bleeding, prolonged cardiopulmonary bypass time, necessity for re-exploration, prolonged mechanical ventilation, other systemic infections, and requirement for tracheostomy increase the incidence of mediastinal infection. As would be expected of an infection that begins locally following surgery, staphylococci and other skin flora are the major organisms responsible for postoperative mediastinitis. Specifically, S tuphylococcus epidermidis and Staphylococcus aureus are responsible for as many as 75% of all mediastinal infections? The gram-negative bacilli, usually Enterobacter or Pseudomonas sp., are responsible for the remainder of the infections. The diagnosis of mediastinitis is often difficult, and early signs may be subtle. Infection is marked by fever, leukocytosis, sternal instability, and superficial sternal wound drainage. A high suspicion of infection is necessarpto prevent a delay in diagnosis. The mortality rate is significantly decreased with early recognition and prompt, aggressive treatment. When the diagnosis has been made, surgical and antibiotic therapy is required. Three methods of treatment can be used for deep-seeded mediastinitis of the anterior mediastinum. The open method of sternal opening and tissue d6bridement with healing by secondary intention is largely of historical interest because of poor toleration and a high mortality rate of patients. The second method, made popular by Shumaker6 in 1963 and later by Bryant et a1,6 is the closed technique with dhbridement and wound closure over an irrigation system with simultaneous administration of systemic antibiotic therapy. The third method is muscle flap closure of the opened and dkbrided anterior mediastinal compartment. Starting in 1980 after an initial report by Jurkiewicz et alrn muscle flap closure of postbypass mediastinal infection has been used as the authors’ primary treatment modality, with good results and a low morbidity rate (2%). Because of anatomic proximity and adequate vascular supply, pectoralis major flaps are used either as an advancement flap o r rotational turnover flap. MIDDLE MEDIASTINUM The middle mediastinum is composed primarily of the heart and pericardium but also contains the pulmonary trunk, phrenic nerves, and tracheal bifurcation (see Fig. 3). This is an impressive list of structures that contain a wide variety of abnormalities that are often of severe consequence. Myocardial



embryology, anatomy, and surgical approach are complex and are not described in this article. Most noncardiac abnormalities of the mediastinum are mediastinal cysts. Mediastinal cysts of the middle mediastinum are classified as pericardial, bronchogenic, and enteric. Primary mediastinal cysts constitute 20% of mediastinal masses.32Most of these cysts are asymptomatic because of their small size and failure to compress their surrounding anatomic structures. They also rarely cause significant complications. Bronchogenic cysts are the most common primary mediastinal cysts and comprise approximately 35% to 60% of all The most common location is in the subcarinal area or adjacent to the trachea or mainstem bronchi. Diagnosis is generally confirmed by CT scanning following suspicion by chronic cough, hemoptysis, or abnormal chest radiographs. Symptoms may be present in as many as 67% of patients because of the proximity of the lesion to the respiratory tree, causing cough and dyspnea.'Q 26 Surgical excision is recommended for all patients to provide a definitive diagnosis and prevention of potential malignant degeneration. A fine-needle aspirate can confirm the diagnosis of a bronchogenic cyst. Pericardial cysts are the second most common cysts of the mediastinum (approximately 33%). Embryologically, these cysts probably arise from failure of fusion of one of the mesenchymal lacunae that normally fuse to form the pericardial sac.I3 These most commonly occur at the pericardiophrenic angles, with greater than 70% occurring on the right.25They are easily seen on CT scanning, and diagnosis can be confirmed with echocardiography. In general, these cysts do not require excision, and serial radiographic follow-up is often sufficient therapy. Surgical excision is required for diagnosis or confirmation that the lesions are not malignant, but as long as they remain stable in size and are asymptomatic, surgical excision is not indicated. Enteric cysts are the final type of middle mediastinal cyst and account for only approximately 3% of primary mediastinal masses.3oThey are traditionally lined with either stratified squamous or gastric or intestinal mucosa. Enteric cysts are usually found in children, but as many as 30% are diagnosed in adults.3O In general, they lie anterior to the esophagus in the middle mediastinal compartment but can also occur in the posterior mediastinum. Approximately two thirds are to the right of midline and lie in the right hemithorax region. Surgical excision is the treatment of choice for these lesions to prevent bleeding and infectious complications. POSTERIOR MEDIASTINUM

The posterior mediastinum is bound anteriorly by the pericardium and extends to the spinal column, with the pleural sacs being the lateral boundaries. The posterior mediastinum contains longitudinal structures that run the length of the compartment. Included are the descending aorta, azygous vein, esophagus, sympathetic chains, splanchnic nerves, thoracic duct, and lymphatics. Posterior mediastinal abnormalities are most commonly of neural or esophageal origin. For the purposes of this article, esophageal abnormalities are not described. Neurogenic tumors are the most common primary lesions of the mediastinum and make up approximately 20% to 35% of all primary mediastinal abnormalities? They most commonly arise from the sympathetic chains or intercostal nerves of the posterior mediastinum. They may be characterized into neurolemmas or schwannomas, ganglioneuromas or ganglioneuroblastomas, neurofibro-


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mas, or paraganglionic tumors. Most of these lesions are asymptomatic and are identified incidentally on routine chest radiography. The most characteristic radiographic finding in the adult is a smooth, rounded, homogeneous density adjacent to the vertebral column and posterior on the lateral film. In general, CT scanning or MR imaging is confirmatory of the diagnosis, with MR imaging being superior to identify intraspinal extension, which occurs in approximately 10% of patients2” 28 The most common type of neurogenic tumor is a neurolemma. Ganglioneuromas and ganglioneuroblastomas arise most commonly from the nerve cells of the sympathetic ganglia running parallel to the vertebral column in the costovertebral sulcus. They represent approximately one third of neurogenic mediastinal tumors.’ Ganglioneuroma is more common than is ganglioneuroblastoma, and it is usually benign. Treatment consists of surgical resection. Neurofibromas contain elements of nerve cells and sheaths. They make up less than 10% of neurogenic tumors, and they are commonly associated with neurofibromatosis, which includes caf6-au-lait spots and cutaneous neurofibromas. Paraganglionic tumors are extremely rare and make up less than 1% of posterior mediastinal tumors.24 Mediastinal neurogenic tumors are generally asymptomatic but can cause pain if they erode into the paravertebral foramina. Surgery remains the treatment of choice for posterior mediastinal neurogenic tumors. For dumbbell-type tumors (approximately loyo), combined thoracotomy and neurosurgical techniques are necessary for complete excision. References 1. Adams GA, Schochat SJ, Smith EL, et al: Thoracic neuroblastoma: A pediatric oncology group study. J Pediatr Surg 28:372-378, 1993 2. Adkins RB Jr, Maples MD, Hainsworth JD: Primary malignant mediastinal tumors. Ann Thorac Surg 38:648, 1984 3. Azanow KS, Pearl RH, Zurcher R, et al: Primary mediastinal masses: A comparison of adult and pediatric populations. J Thorac Cardiovasc Surg 106:67-72, 1993 4. Baue AE, Geha AS, Laks H, et a1 (eds): Glenn’s Thoracic and Cardiovascular Surgery, ed 6. Stamford, CT, Appleton & Lange, 1996 5. Boerhaave H: Atrocis, nec descripti prius, morbi historia (1724). Translated in Bull Med Libr Assoc 43:217, 1955 6. Bryant LR, Spencer FC, Trinkle JK: Treatment of median sternotomy infection by mediastinal irrigation with an antibiotic solution. Ann Surg 169:914, 1969 7. Castlemen B, Norris EH: The pathology of the thymus gland in myasthenia gravis: A study of 35 cases. Medicine 28:27, 1949 8. Cohen AJ, Thompson L, Edwards FH, et al: Primary cysts and tumors of the mediastinum. Ann Thorac Surg 41:378-386, 1991 9. Davis RD Jr, Oldham HN Jr, Sabiston DC Jr: Primary cysts and neoplasms of the mediastinum: Recent changes in clinical presentation, methods of diagnosis, management and results. Ann Thorac Surg 44:229-237, 1987 9a. Hazelrigg SR, Wellons HA Jr, Schneider SA, et al: Wound complications after median sternotomy: Relationship to internal mammary grafting. J Thorac Cardiovasc Surg 98:1096-1099, 1989 10. Johnston SR, Adam A, Allison DJ, et al: Recurrent respiratory obstruction from mediastinal bronchogenic cysts. Thorax 47660-662, 1992 11. Jurkiewicz MJ, Bostwick J, Hester RT, et al: Infected median sternotomy wound: Success of treatment by muscle flaps. Ann Surg 191:738, 1980 12. Kornstein MJ, Curran WJ Jr, Turrisi AT 111, et al: Cortical versus medullary thymoma: A useful morphologic classification? Hum Pathol 19:1335, 1988



13. Lambert AVS: Etiology of thin-walled thoracic cysts. J Thorac Surg l O : l , 1940 14. Langebartel DA: The Anatomical Primer. Baltimore, University Press, 1977 15. Levine BA, Copeland E 111, Howard RJ, et al: Current Practice of Surgery, vol 1. New York, Churchill Livingstone, 1994 16. Lewis ED, Hurt RD, Payne WS, et al: Benign teratomas of the mediastinum. J Thorac Cardiovasc Surg 86:727, 1983 17. Lewis JE, Wick MR, Scheithauer BW, et al: Thymoma: A clinicopathologic review. Cancer 602727, 1987 18. Maggi G, Giaccone G, Donadio M, et al: Thymomas: A review of 169 cases with particular reference to results of surgical treatment. Cancer 58:765, 1986 19. Manelbaum I: Germ cell tumors of the mediastinum. Chest Surg Clin North Am 2203-211, 1992 20. Moon WK, Jung-Gi I, Hau MC: Malignant schwannomas of the thorax: CT findings. J Comput Assisted Tomogr 17274-276, 1993 21. Moore KL, Persaud TVN: The Developing Human, ed 5. Philadelphia, WB Sanders, 1993 22. Mullen B, Richardson JD: Primary anterior mediastinal tumors of children and adults. Ann Thorac Surg 42:338, 1986 23. Nichols CR: Mediastinal germ cell tumors: Clinical features and biologic correlates. Chest 99:472479, 1991 24. Olsen JL, Salyer WR: Mediastinal paragangliomas (aortic body tumor): A report of four cases and a review of the literature. Cancer 412405-2412, 1978 25. Ochsner JL, Ochsner SF: Congenital cysts of the mediastinum. Ann Surg 163:909, 1966 26. Patel SR, Meeker DP, Biscotti CV, et al: Preservation and management of bronchogenic cysts in the adult. Chest 106:79-85, 1994 27. Patton EM: Human Embryology, ed 3. New York, McGraw-Hill, 1968, p 438 28. Ricci C, Redina EA, Venuto F, et al: Diagnostic imaging and surgical treatment of dumbbell tumors of the mediastinum. Ann Thorac Surg 50:586-589, 1990 29. Rosenow EC 111, Hurley BT Disorders of the thymus: A review. Arch Intern Med 1444:763, 1984 30. Shields TW General Thoracic Surgery, ed 4. Baltimore, Williams & Wilkins, 1994 31. Verley JM, Hollmann KH: Thymoma: A clinical study of clinical stages, histologic features, and survival in 200 cases. Cancer 55:1074, 1985 32. Wychulis AR, Panye WS, Clagett OT, et al: Surgical treatment of mediastinal tumors. J Thorac Cardiovasc Surg 62379, 1971 33. Yellin. A, Rosen A, Reichert N, et al: Superior vena cava syndrome: The myth-the facts. Ann Rev Respir Dis 14:1114, 1990

Address reprint requests to Joseph I. Miller, MD Section of General Thoracic Surgery Division of Cardiothoracic Surgery Department of Surgery Emory University School of Medicine 25 Prescott Street, NE Suite 3420 Atlanta, GA 30308