Mediastinal Diseases

12.1 Mediastinal Lymphadenopathy

This long-standing rule has come under discussion since mediastinal lymph node stations 4R and 7 often contain normal lymph nodes larger than 10 mm. Hence, thresholds of 15 mm for station 4R and 20 mm for station 7 have been suggested.²^,³

For hilar lymph nodes, a short-axis threshold of 3 mm is specified for the majority of lymph node stations.¹ However, that specification is based on a much earlier single publication with single-row CT.⁴ In the age of thin-slice multiple-row detector CT, application of that threshold would lead to many false-positive results for hilar lymphadenopathy. A more appropriate approach is to consider a diagnosis of hilar lymphadenopathy only if there is visible evidence of pronounced lymph node enlargement on CT or MRI.

There are myriad inflammatory and malignant diseases that can potentially cause lymphadenopathy.⁵ The distribution pattern of the affected lymph nodes gives insights into the underlying disease (▶Table 12.1). Both pulmonary hypertension and congestive left heart failure lead to increased fluid filtration in the pulmonary capillaries. The resultant increased lymphatic drainage from the lungs can in turn cause, generally symmetrical, hilar and mediastinal lymph node enlargement.

Homogeneous lymph node calcification is a sign of resolved tuberculosis. Eggshell-like lymph node calcification is seen in silicosis, coal workers’ pneumoconiosis, sarcoidosis, irradiated lymphomas, and less commonly in tuberculosis (▶Fig. 12.1).

12.2 Mediastinitis

Mediastinitis is the term used to describe acute or chronic inflammation of the mediastinal structures. The acute form is almost always caused by bacteria, most commonly as an iatrogenic complication of bypass surgery or due to esophageal perforation.⁶ The third most common cause is descending necrotizing inflammation from the head-neck region, usually from an odontogenic focus. Rarer causes of infection are advanced osteomyelitis, perforation of the trachea or mainstem bronchi, or hematogenous dissemination.⁷^,⁸

Acute mediastinitis is a life-threatening condition associated with considerable mortality. The clinical manifestation includes chest pain, fever, shaking chills, and dyspnea as well as elevated inflammatory lab results. Descending mediastinitis from the neck is often recognized from neck swelling. Acute mediastinitis must be suspected if the clinical symptoms are present and mediastinal enlargement is seen on chest radiography (▶Fig. 12.2). At times, mediastinal gas bubbles may be visible. CT is the method of choice for confirmation of suspected acute mediastinitis, as well as for diagnosis of infection spread and treatment planning.

Table 12.1 Typical distribution patterns of mediastinal or hilar lymphadenopathy and underlying diseases

Clinical symptoms	Typical distribution patterns of lymphadenopathy
Sarcoidosis	Bihilar and bilateral paratracheal (two-thirds of cases)
	Only bihilar, not mediastinal (one-third of cases)
	Almost always symmetrically bihilar
	Rarely, only mediastinal
	Extremely rarely, only in the posterior mediastinum
Pneumonia	Ipsilateral hilar and paratracheal
Tuberculosis	Asymmetrically or symmetrically hilar (depending on lung involvement) and paratracheal
Hodgkin disease and non-Hodgkin lymphomas	Anterior mediastinum
	Paratracheal
	Less frequently, subcarinal or symmetrically hilar
	Rarely, only hilar
Lung cancer	Asymmetrically ipsilateral hilar and paratracheal (stations 2 and 4), less often, contralateral hilar and paratracheal
	Stations 5 and 6 in primary tumors of the left upper lobe
	Station 7 in tumors of the lower lobes
Breast cancer	Along the internal thoracic vessels
Breast cancer	Axillary
Esophageal cancer	Paratracheal (stations 2 and 4) in primary tumors of the upper or middle third
	Supraclavicular and cervical in cervical primary tumors
	Lesser curvature of the stomach in primary tumors of the lower third
Pleural mesothelioma	Along the internal thoracic vessels
	Caudal paraspinal
	Anterior peridiaphragmatic

Fig. 12.1 Eggshell-like calcifications in the mediastinal and hilar lymph nodes in tuberculosis. Radiograph. Sectional magnification of a lateral image.

Fig. 12.2 Acute mediastinitis secondary to tracheal stenosis resection. Radiograph. Considerable enlargement and compression of the upper mediastinum.

Fig. 12.3 Acute suppurative mediastinitis. CT image. Fluid-isodense mediastinal mass with gas bubbles. Small bilateral pleural effusions.

Chronic mediastinitis is divided somewhat arbitrarily into granulomatous and fibrosing or sclerosing mediastinitis. These conditions probably reflect continuing chronic infections, often caused by tuberculosis or fungi.⁶^,⁷^,⁹ Chronic mediastinitis is also caused by numerous noninfectious diseases, such as sarcoidosis, malignancies, obstruction of the lymphatic drainage system, and autoimmune diseases.⁷ Chest radiography usually shows mediastinal enlargement, including at times a hilar mass. CT characteristically visualizes a diffuse or discrete, often very extensive, mass of soft-tissue density that can be misinterpreted as a malignant tumor or lymphoma. Calcifications may occur. Stenosis of the superior vena cava is a typical clinical manifestation and easily identified on CT (▶Fig. 12.4).

Fig. 12.4 Chronic sclerosing mediastinitis. CT image. Mediastinal and right hilar mass of soft-tissue density. High-grade stenosis of the superior vena cava (arrow). Small right pleural effusion.

12.3 Pneumomediastinum

The characteristic feature of pneumomediastinum is free air surrounding the mediastinal structures. Pneumomediastinum is caused by the following⁸^,¹⁰^,¹¹:

Blunt or penetrating chest injury.
Esophageal perforation.
Perforation of the trachea or mainstem bronchi.
Pneumothorax.
Positive pressure ventilation.
Transmission of pulmonary interstitial emphysema.
Acute mediastinitis with gas-producing bacteria.
Cocaine consumption.

Fig. 12.5 Pneumomediastinum secondary to tear in the left mainstem bronchus. CT image. Furthermore, minor chest wall emphysema.
Asthma attack.
Spontaneous onset, in particular in young adults (cough, vomiting, physical exertion).

Spontaneous pneumomediastinum is a special form of pneumomediastinum usually observed in young adults and which has a benign course and does not require any particular treatment.¹¹ In around two-thirds of cases, pneumomediastinum can be diagnosed from the chest radiograph, showing characteristic linear radiolucent areas in the mediastinum. CT is pathognomonic (▶Fig. 12.5).

Tension pneumomediastinum is a rare complication which, like tension pneumothorax, is caused by a valve mechanism resulting in increased mediastinal pressure. This can have acute, life-threatening consequences due to compression of the heart and central airways.⁸

12.4 Esophageal Tumors

Benign esophageal tumors are 50-fold less common than esophageal carcinomas. These are predominantly leimyomas,¹² which are intramural tumors that originate from the smooth muscle cells and exhibit hardly any circumferential growth. They can become very large and gradually cause progressive dysphagia. On CT and MRI, they manifest as smoothly marginated and homogeneous masses. Occasionally, calcifications are seen.¹³

Duplication cysts, the second most common benign masses, become symptomatic already in childhood. On sectional imaging, the typical features of a fluid-filled cyst can be identified. These are filled with air if they communicate with the esophagus.¹³

In the vast majority of cases, the most common malignant tumor of the esophagus, esophageal carcinoma, is found on histology to be a squamous cell carcinoma or adenocarcinoma (▶Fig. 12.6). Smoking and alcohol abuse are the main risk factors for esophageal carcinoma. This tumor mainly affects men aged 60 to 70 years. It has a poor prognosis, with a 5-year survival of around 10%.¹³ Staging is the main focus of imaging in esophageal carcinoma. CT and PET-CT are required to rule out distant metastasis as well as for evaluation of invasion of surrounding structures. Only endosonography is able to evaluate tumor extension within the esophagus; it is also superior to other cross-sectional imaging techniques for detection of lymph node metastasis. The tumor stage can be derived from the TNM staging classification (▶Table 12.2). For some stages, histologic grading is also used in addition to the imaging findings (▶Table 12.3). Tumor contact with the aorta of more than one-quarter of the vascular circumference (over 90°) is considered a criterion for probable aortic invasion.¹⁴

Fig. 12.6 Esophageal carcinoma. CT image. Circular wall thickening of the distal esophagus. No identifiable invasion of surrounding structures.

12.5 Mediastinal Tumors and Tumor-Like Masses

Anatomic assignment of mediastinal masses to a mediastinal compartment is useful for differential diagnosis. This allows for considerable narrowing of differential diagnoses (▶Table 12.4). Another important consideration is the CT density. Cystic masses can often be reliably identified. Presence of intratumoral fat on CT also serves as a diagnostic pointer. Masses of low density (cysts, fat-containing structures) are discussed in the following sections, followed by solid tumors, i.e., tumors of soft-tissue density.

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