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Recognizing Other Diseases of the Chest


In this chapter, you will learn how to recognize mediastinal masses, benign and malignant pulmonary neoplasms, pulmonary thromboembolic disease, and selected airway diseases.

Case Quiz 10 Question

This is a view of the lung apices in a 73-year-old male with shoulder pain, a drooping eyelid, and constricted pupil on one side. You can deduce which side from the x-ray. What is the most likely diagnosis from the clinical history and this chest radiograph? See the correct answer at the end of this chapter.

  • Several chest abnormalities are discussed in other chapters ( Table 10.1 ).

    TABLE 10.1
    Chest Abnormalities Discussed Elsewhere in This Text
    Topic Appears in
    Atelectasis Chapter 6
    Pleural effusion Chapter 7
    Pneumonia Chapter 8
    Pneumothorax, pneumomediastinum, and pneumopericardium Chapter 24
    Cardiac and thoracic aortic abnormalities Chapter 11
    Chest trauma Chapter 24

  • A discussion of all of the diseases imaged in the chest fills multivolume textbooks so we will concentrate on mediastinal masses and work our way outward to some of the most common lung diseases.

Mediastinal Masses

  • The mediastinum is an area whose lateral margins are defined by the medial borders of each lung , whose anterior margin is the sternum and anterior chest wall, and whose posterior margin is the spine , usually including the paravertebral gutters.

  • The mediastinum has been arbitrarily subdivided into three compartments based on the lateral chest x-ray : the anterior, middle, and posterior compartments and each contains its favorite set of diseases. The superior mediastinum, roughly the area above the plane of the aortic arch, is a division that is now usually combined with one of the other three compartments mentioned previously ( Fig. 10.1 ).

    Fig. 10.1, The Mediastinal Compartments.

  • A newer classification, based primarily on CT, defines virtually the same three compartments mentioned previously but names them the prevascular, visceral, and paravertebral compartments. The new system was designed to be a universal classification system accepted by all specialties and based on cross-sectional imaging rather than chest radiography. For the purposes of this text, we will use the terms anterior, middle, and posterior mediastinum.

Diagnostic Pitfalls

  • Since these compartments have no true anatomic boundaries, diseases from one compartment may extend into another compartment.

  • When a mediastinal abnormality becomes widespread or a mediastinal mass becomes quite large, it is often impossible to determine which compartment was its site of origin.

  • Differentiating a mediastinal mass from a parenchymal lung mass on frontal and lateral chest radiographs can be difficult. Some helpful clues include:

    • If a mass is completely surrounded by lung tissue on both the frontal and lateral projections, it lies within the lung, not the mediastinum.

    • In general, the margin of a mediastinal mass is sharper than a mass originating in the lung.

    • Mediastinal masses frequently displace, compress, or obstruct other mediastinal structures (e.g., the trachea or esophagus).

  • Ultimately, CT imaging of the chest is more accurate in determining the location and nature of a mediastinal mass than conventional radiographs.

Anterior Mediastinal Masses

  • The anterior mediastinum is the compartment that extends from the back of the sternum to the anterior border of the heart and great vessels. In the newer classification, the term anterior mediastinum is replaced by the term prevascular compartment but contains almost the same elements.

  • There is a differential diagnosis for anterior mediastinal masses that most often includes:

    • Substernal thyroid masses

    • Lymphoma

    • Thymoma , and

    • Teratoma

    • As a helpful way of remembering these four diseases, lymphoma is referred to as “Terrible lymphoma” in this list so that all of the diseases “start” with the letter “T” ( Table 10.2 ).

      TABLE 10.2
      Anterior Mediastinal Masses (“Four T’s”)
      Mass What to Look for
      Thyroid goiter The only anterior mediastinal mass that routinely deviates the trachea
      Lymphoma (lymphadenopathy) Lobulated, polycyclic mass; frequently asymmetric; may occur in any compartment of the mediastinum
      Thymoma Look for a well-marginated mass that may be associated with myasthenia gravis
      Teratoma Well-marginated mass that may contain fat and calcium visible on CT scans

Thyroid Masses

  • In everyday practice, enlarged substernal thyroids are the most frequently encountered anterior mediastinal mass. The vast majority of these masses are multinodular goiters and the mass is called a substernal goiter, substernal thyroid, or substernal thyroid goiter.

    • Multinodular goiters usually present as a mass in the neck, mostly in females. After a few decades, most patients with a multinodular goiter will develop hyperthyroidism. It is uncommon for them to be malignant.

  • Substernal goiters characteristically displace the trachea either to the left or right above the level of the aortic arch , a tendency the other anterior mediastinal masses do not typically demonstrate.

Important Points

  • Classically, substernal goiters do not extend below the top of the aortic arch ( Fig. 10.2 ).

    Fig. 10.2, Substernal Thyroid Mass.

  • You should think of an enlarged substernal thyroid whenever you see an anterior mediastinal mass that displaces the trachea.

  • On occasion, the isthmus or lower pole of either lobe of the thyroid may enlarge but project downward into the upper thorax rather than anteriorly into the neck. About three out of four thyroid masses extend anterior to the trachea; the remaining 25% (almost all of which are right-sided) descend posterior to the trachea.

  • Radioisotope thyroid scans are the study of first choice in confirming the diagnosis of a substernal thyroid as virtually all of them will display some uptake of the radioactive tracer that can be imaged and recorded with a special camera (see e-Appendix A. Nuclear Medicine: Understanding the Principles and Recognizing the Basics ).

  • On CT , substernal thyroid masses are part of and contiguous with the thyroid gland , frequently contain calcification, and avidly take up intravenous contrast but with a mottled, inhomogeneous appearance ( Fig. 10.3 ).

    Fig. 10.3, CT of a Substernal Thyroid Goiter Without and With Contrast Enhancement.

Lymphoma

  • Lymphadenopathy, whether from lymphoma, metastatic carcinoma, sarcoid, or tuberculosis, is the most common cause of mediastinal masses overall.

  • Anterior mediastinal lymphadenopathy is most common in Hodgkin lymphoma, especially the nodular sclerosing variety. Hodgkin lymphoma is a malignancy of the lymph nodes, more common in females, which most often presents with painless, enlarged lymph nodes in the neck.

  • Unlike teratomas and thymomas, which are presumed to expand outward from a single abnormal cell, lymphomatous masses are frequently composed of several contiguously enlarged lymph nodes. As such, lymphadenopathy frequently presents with a border that is lobulated or polycyclic in contour due to the conglomeration of enlarged nodes that make up the mass.

Important Points

  • On chest radiographs, this lobulation may help differentiate lymphadenopathy from other mediastinal masses that may demonstrate a smoother contour .

  • Mediastinal lymphadenopathy in Hodgkin lymphoma is usually bilateral and asymmetric ( Fig. 10.4 ). In addition, asymmetric hilar adenopathy is associated with mediastinal adenopathy in many patients with Hodgkin lymphoma.

    Fig. 10.4, Mediastinal Adenopathy from Hodgkin Lymphoma.

  • In general, mediastinal lymph nodes that exceed about 1 cm measured along their short axis on CT scans of the mediastinum are considered to be enlarged.

  • Lymphoma will produce multiple, lobulated soft-tissue masses or one large, soft-tissue mass from lymph node aggregation.

  • The mass is usually homogeneous in density on CT ( Fig. 10.5 ) but may be heterogeneous when it achieves a sufficient size to undergo necrosis (areas of lower attenuation, i.e., blacker) or hemorrhage (areas of higher attenuation, i.e., whiter).

    Fig. 10.5, Anterior Mediastinal Adenopathy in Hodgkin Lymphoma.

  • Some findings of lymphoma may mimic those of sarcoidosis since both produce thoracic adenopathy. Table 10.3 contains several key points to differentiate the two diseases.

    TABLE 10.3
    Sarcoidosis vs. Lymphoma
    Sarcoid Lymphoma
    Bilateral hilar and right paratracheal adenopathy are the classic combination More often dominated by mediastinal adenopathy, but is associated with asymmetric hilar enlargement
    Enlarged bronchopulmonary nodes are more peripheral Enlarged hilar nodes are more central
    Pleural effusion in about 5% Pleural effusion more common, in about 30%
    Anterior mediastinal adenopathy is uncommon Anterior mediastinal adenopathy is common

Thymic Masses

  • Normal thymic tissue can be visible on CT throughout life , although the gland begins to involute after age 20.

  • Thymomas are neoplasms of thymic epithelium and lymphocytes. They occur most often in middle-aged adults , generally at an older age than those with teratomas. Most thymomas are benign.

Important Points

  • Thymomas are associated with myasthenia gravis about 35% of the time they are present.

  • Conversely, about 15% of patients with clinical myasthenia gravis will be found to have a thymoma.

  • The importance of identifying a thymoma in patients with myasthenia gravis lies in the more favorable prognosis for patients with myasthenia after thymectomy.

  • On CT scans, thymomas classically present as a smooth or lobulated mass that arises near the junction of the heart and great vessels and which, like a teratoma, may contain calcification ( Fig. 10.6 ).

    Fig. 10.6, Thymoma, Chest Radiograph and CT Scan.

  • Other lesions that can produce enlargement of the thymus are rare and include thymic cysts, thymic hyperplasia, thymic lymphoma, carcinoma, or lipoma.

Teratoma

  • Teratomas are germinal tumors that typically contain all three germ layers (ectoderm, mesoderm, and endoderm). Most teratomas are benign and occur earlier in life than thymomas. Usually asymptomatic and discovered serendipitously, about 30% of mediastinal teratomas are malignant and have a poor prognosis.

  • The most common variety of teratoma is cystic , produces a well-marginated mass near the origin of the great vessels, and characteristically contains fat, cartilage, and possibly bone on CT examination ( Fig. 10.7 ).

    Fig. 10.7, Mediastinal Teratoma.

Middle Mediastinal Masses

  • The middle mediastinum is the compartment that extends from the anterior border of the heart and aorta to the posterior border of the heart and contains the heart , the origins of the great vessels, trachea, and main bronchi along with lymph nodes (see Fig. 10.1 ). In the newer CT classification, the term middle mediastinum is replaced by the term visceral compartment and it extends farther posteriorly to include part of the mediastinum overlying the vertebral column.

  • Lymphadenopathy produces the most common mass in this compartment. While Hodgkin lymphoma is the most likely cause of mediastinal adenopathy, other malignancies and several benign diseases can produce such findings.

    • Other malignancies that produce mediastinal lymphadenopathy include small cell lung carcinoma and metastatic disease such as from primary breast carcinoma ( Fig. 10.8 ).

      Fig. 10.8, Middle Mediastinal Lymphadenopathy.

    • Benign causes of mediastinal lymphadenopathy include infectious mononucleosis and tuberculosis, the latter usually producing unilateral mediastinal adenopathy.

Posterior Mediastinal Masses

  • The posterior mediastinum is the compartment that extends from the posterior border of the heart to the anterior border of the vertebral column. For imaging purposes, however, it is considered to extend to either side of the spine into the paravertebral gutters (see Fig. 10.1 ).

  • The posterior mediastinum contains the descending aorta, esophagus, lymph nodes, is the site of masses representing extramedullary hematopoiesis, and, most importantly, is the home of tumors of neural origin. In the newer classification, the term posterior mediastinum is replaced by the term paravertebral compartment and contains almost exclusively neurogenic lesions.

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