Mediastinal Mass

Pepi Granat

Although most mediastinal masses are discovered incidentally on chest radiographs, symptoms can sometimes provide clues enabling the timely ordering of these films. The mediastinum is defined as the extrapleural space within the thorax lying between the lungs. A mass of the mediastinum, by convention, connotes a process with mass effect, whether tumorous, cystic, or vascular. Although two-thirds of all mediastinal tumors are benign and 75% of asymptomatic patients with mediastinal tumors have benign tumors, two-thirds of symptomatic patients will harbor a malignancy. A simple classification (Fraser) into anterior, middle, and posterior mediastinal compartments based on the lateral chest film is clinically useful (1). The more detailed lines and compartments divisions (Felson, Heitzman) are helpful to radiologists (2). Visualizing lung-mediastinal interfaces, where early lesions may be detected, is aided by these lines and signs in both anteroposterior and lateral roentgenograms.

Approach

Not all mediastinal masses perceived on chest radiograph require invasive investigation; although most will require surgery, histologic sampling by fine needle percutaneous biopsy, or thoracoscopy, some can be followed, depending on location and clinical clues. Some will require emergency action (thoracic aortic dissection), either spontaneous or following injury. All require further imaging usually by computerized tomography (CT). The two indications for ordering mediastinal CT are abnormal chest radiograph and clinical suspicion of mediastinal disease.

A. Types of mediastinal masses. These are classified by general rather than by strict anatomic location; they can be further classified by density and behavior on contrast CT or magnetic resonance imaging (MRI). One easy mnemonic for significant mediastinal tumors is “The Terrible Ts”: thymoma, teratoma (embryomal carcinoma), ‘terrible’ lymphoma (Hodgkin’s disease), thyroid carcinoma, neurofibroma (‘tingle’), renal cell carcinoma (‘tinkle’).

 B. Reading the plain films. First, ascertain that the mass is not from lung, pleura, or chest wall. Clues are that masses lying deep to mediastinal vessels are mediastinal in origin; those with irregular, nodular, or spiculated edges arise in the lung; and those broad-based with smooth edge arise in mediastinum or mediastinal pleura. When the rest of the pleura is normal and when no other lung tumors are present, the evidence favors a mediastinal origin. Masses coming from sternum or spine may need CT for better definition of origin. Second, consider anatomic variants such as aortic arch abnormalities, hiatal hernia, and esophageal mass (3). In the anterioposterior projection, look for the paraspinal lines, paraesophageal line, anterior and posterior junction line, paratracheobronchial line, azygos vein, paraaortic line, and widening of the whole mediastinum. In the lateral view, look for aortic arch and tracheal wall profiles and posterior tracheal band. Masses will displace or efface these lines. Not all lines are constant and normal variations are common.

 C. Anatomy and boundaries of the mediastinal compartments (varies slightly with different authors):

1. Anterior mediastinum is defined as the region posterior to the sternum, anterior to the heart and brachiocephalic vessels, extending from the thoracic inlet to the diaphragm. It contains the thymus gland, fat, and lymph nodes.

 2. Middle mediastinum is defined as the space containing the heart and pericardium, including the ascending and transverse aorta, brachiocephalic vessels, vena cavae, main pulmonary arteries and veins, trachea, bronchi and lymph nodes.

 3. Posterior mediastinum is defined as posterior to the heart and trachea, extending to the thoracic vertebral margin, including the paravertebral gutters. It contains the descending thoracic aorta, esophagus, azygos veins, autonomic ganglia and nerves, thoracic duct, lymph nodes, and fat.

 D. Location of mediastinal masses, the most common lesions in various compartments:

1. Anterior mediastinum: aneurysm of ascending aorta, lymphoma, pericardial cyst, retrosternal thyroid, teratoid lesion, and thymic lesion.

 2. Middle mediastinum: aneurysm of aortic arch, azygos vein enlargement, bronchogenic cyst, esophageal lesions, hiatal hernia, lymph node enlargement, thyroid tumor, and hilar vascular dilatation.

 3. Posterior mediastinum: aneurysm or tortuosity of descending aorta, lymph node enlargement, neurogenic tumor, and paraspinal manifestations of spinal lesions.

 E. Some causes of mediastinal and hilar lymph node enlargement (4): bronchogenic carcinoma; Hodgkin’s disease and non-Hodgkin’s lymphoma; leukemia; immunoblastic lymphadenopathy (a hyperimmune disorder of B lymphocytes); heavy-chain disease (a plasma cell dyscrasia); bronchopulmonary amyloidosis (a plasma cell dyscrasia); lymph node metastasis; Castleman’s disease (giant lymph node hyperplasia); bacterial infections, including primary tuberculosis, tularemia, pertussis, anthrax, plague; viral and rickettsial diseases, including Mycoplasma pneumoniae, rubeola, Epstein-Barr virus, human immunodeficiency virus (HIV) and acquired immune deficiency syndrome, psittacosis, echovirus pneumonia, varicella pneumonia; fungal infections, including histoplasmosis, coccidioidomycosis, sporotrichosis, and tropical eosinophilia; sarcoidosis; silicosis, beryliosis; histiocytosis X; idopathic pulmonary hemosiderosis and Goodpasture’s syndrome, cystic fibrosis, and some are drug-induced.

 F. Some causes of mediastinal widening: mediastinal pseudowidening, including expiratory film, scoliosis; normal thymus (neonate); mesothelial (pericardial or pleuropericardial cysts and diverticula); diverticula of pharynx or esophagus; meningocele; tumors, including thyroid masses and tumors, thymoma, teratoma, germinal cell neoplasms, lipoma, liposarcoma, lipomatosis, fibroma, fibrosarcoma, hemangioma, hemangiosarcoma, hemangioendothelioma, lymphangioma, hygroma, leiomyoma; lymphoma (Hodgkin’s or non-Hodgkin’s), leukemia; metastatic lymph node enlargement; esophageal neoplasms; neurogenic neoplasms; bone and cartilage neoplasms; vascular lesions, including aortic aneurysm, dilatation or aneurysm of innominate artery (right) or subclavian artery (left); aortic arch malformation; mediastinal hemorrhage or hematoma, dilatation of superior vena cava, azygos vein, pulmonary artery; pneumomediastinum; fracture of thoracic vertebra, herniation through foramen of Morgagni, esophageal hiatal hernia, herniation through foramen of Bochdalek, diaphragmatic eventration, diaphragmatic rupture, megaesophagus, and some occur postsurgery (reconstructions).

History

 A. Most mediastinal masses, including lymphomas, do not cause symptoms; however, it is important to pay early attention even to vague symptoms because most symptomatic patients with a mediastinal tumor will have a malignancy. Patients may be completely asymptomatic or their complaints can relate to the underlying disease process: myasthenia gravis or anemia from red cell aplasia, with thymoma; flushing, diarrhea, or Cushing’s syndrome, with thymic carcinoid; fatigue and irritability with parathyroid adenoma; fever, night sweats, and pruritus with lymphoma or Hodgkin’s; cough, wheezing, dysphagia, or chest pain, with compression or invasion of mediastinal organs (5). A personal or family history of cancer or aneurysms might be significant. Be especially alert to patients with prior tumors, even if benign. Some lesions can recur after many years (thymoma).

 B. Possible symptoms include fatigue, general weakness, cough, pruritus, chest pain, fever, night sweats, wheezing, dysphagia, stridor, voice change, hoarseness, weight loss, paresthesias, pain, proximal muscle weakness, swelling of face, and venous distention of neck (superior vena cava syndrome).

Physical examination

A. A general examination before an x-ray study gives clue to a mediastinal mass: vital signs, especially temperature, heart rate, and weight; check for pallor, skin lesions, lymphadenopathy, thyromegaly, splenomegaly, other abdominal or pelvic organomegaly or masses, rashes, weakness; auscultate lungs for wheezes, rales, and rhonchi.

 B. Focused reexamination after a mass is detected. Vital signs, especially temperature, heart rate, and documentation of weight loss; check carefully for cervical adenopathy (suitable for biopsy), evidence of thyromegaly, voice quality, airway patency sitting and supine; and observe the swallowing function. Auscultate the lungs for wheezes, rales, rhonchi; the heart for pericardial rubs; recheck for adenopathy (total body), check skin for melanoma, check testes for masses, and repeat the pelvic examination for ovarian masses.

Testing

 A. Clinical laboratory tests will depend on the index of suspicion, based on the most common diagnoses in the anatomic location. These may include complete blood count, erythrocyte sedimentation rate, lactic dehydrogenase, alpha fetoprotein, beta fraction human growth hormone, serum calcium, parathormone, gamma globulins, serum antiacetylcholine receptor antibody, purified protein derivative skin test, and HIV antibody screening.

 B. Imaging studies. Any patient, but especially smokers or exsmokers, with unexplained peripheral adenopathy, unexplained cough, or any of the aforementioned symptoms, should have a chest x-ray study after no more than 2 to 3 weeks of symptomatic treatment. Any mediastinal mass seen requires a CT with iodinated bolus. The indications for mediastinal MRI are suspected vascular lesion, equivocal CT findings, posterior or paravertebral masses and neurogenic tumors, and suspected tumor recurrence so that scarring can be delineated from tumor. The MRI should be ordered with T1- and T2-weighted images and gadolinium-enhanced T1 images.

Diagnostic assessment

Correlation of the clinical and imaging picture is paramount in deciding the extent of the investigation of a mediastinal mass, because of the fairly predictable location pattern of various lesions. A patient with acute, searing chest pain and mediastinal widening will need emergent attention for thoracic aortic dissection. An anterior solid mass in a patient with cough and weight loss demands a tissue diagnosis and, if operable, surgical extirpation. A posterior cystic mass in a healthy patient may allow close follow-up. However, much overlap is seen (6), and diagnostic accuracy is better based on direct clues (e.g., tissue diagnosis) and on solid clinical judgment to include surgical diagnosis or treatment or medical or oncologic methods, if inoperable.

References

1. Strollo DC, Rosado-de-Christenson ML, Jett JR. Primary mediastinal tumors. Part I: Tumors of the anterior mediastinum. Chest 1997;12(2):511–522.

2. Giron J, Fajadet P, Sans N, et al. Diagnostic approach to mediastinal masses. Eur J Radiol 1998;27(1):21–42.

3. Laurent F, Latrabe V, Lecesne R, et al. Mediastinal masses: diagnostic approach. Eur Radiol 1998;8(7):1148–1159.

4. Mediastinal or hilar enlargement. In: Burgener FA, Kormano M. Differential diagnosis in conventional radiology, 2nd revised ed. London: Thieme Medical Publishers, 1991.

5. Strollo DC, Rosado-de-Christenson ML, Jett JR. Primary mediastinal tumors. Part II. Tumors of the middle and posterior mediastinum. Chest 1997;112(5):
1344–1357.

6. Ahn JM, Lee KS, Goo JM, Song KS, Kim SJ, Im JG. Predicting the histology of anterior mediastinal masses: comparison of chest radiography and CT. J Thorac Imaging 1996;11(4):265–271.

Book Source Details

• Book Title: The 10-Minute Diagnosis Manual: Symptoms and Signs in the Time-Limited Encounter
• Author(s): Robert B. Taylor (editor)
• Year of Publication: 2000
• Copyright Details: The 10-Minute Diagnosis Manual: Symptoms and Signs in the Time-Limited Encounter, Copyright © 2000 Lippincott Williams & Wilkins.

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More About This Book: Title: The 10-Minute Diagnosis Manual: Symptoms and Signs in the Time-Limited Encounter Authors: Robert B. Taylor (editor) Publisher: Lippincott Williams & Wilkins Copyright: 2000 ISBN: 0-78172-094-X

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