Diffuse Mediastinal Abnormalities

Chapter 17 Diffuse Mediastinal Abnormalities

Unlike focal mediastinal masses, which usually can be localized within a single mediastinal compartment, diffuse mediastinal abnormalities almost always involve more than one compartment of the mediastinum and therefore preclude classification by the traditional compartmentalization method. The common feature of these entities is that they all may present with diffuse mediastinal widening on chest radiographs.


Mediastinal Lipomatosis

Mediastinal lipomatosis is the diffuse accumulation of excess unencapsulated fat within the mediastinum. This benign condition is usually seen in adult patients and may be associated with Cushing’s syndrome, exogenous steroid use, and obesity.

Fat accumulation is usually most prominent in the anterior and superior portions of the mediastinum, where it surrounds the great vessels and results in lateral displacement of the pleural reflections. It may be detected in other parts of the mediastinum, including the cardiophrenic angles, paravertebral regions, retrocrural, and subcostal regions.

The appearance on chest radiographs and CT depends on the distribution of excess fat deposition. Accumulation of fat in the anterior and superior portions of the mediastinum results in smooth widening of the anterior and superior mediastinal contours as seen on chest radiographs (Fig. 17-1). An important feature is the lack of mass effect on the trachea and esophagus, structures that are often displaced or compressed by other mediastinal abnormalities. Excess fat deposits within the cardiophrenic angles result in cardiophrenic angle “masses,” and excess fat within the paravertebral regions may result in bilateral lateral displacement of the paraspinal lines.

A definitive diagnosis of mediastinal lipomatosis may be made on CT (Fig. 17-2). Fat is recognized on CT by its low CT numbers, which typically vary from −70 to −130 Hounsfield units (HU). Although CT is considered the imaging modality of choice, the diagnosis also can be made by MRI. On MRI, fat demonstrates bright signal intensity on T1-weighted images. Using a fat-suppression sequence results in suppression of the normally bright T1 signal from fat tissue and helps to differentiate it from other tissues with bright T1 signal. An important feature of mediastinal lipomatosis on CT or MRI is a homogeneous appearance of the mediastinal fat. An inhomogeneous appearance, such as the presence of high-attenuation foci within the fat, should raise the suspicion of a superimposed process, such as mediastinal hemorrhage or neoplastic infiltration.


Diffuse mediastinitis may be acute or chronic. Both forms are most often caused by infections. Acute mediastinitis is often the result of a bacterial infection, and chronic mediastinitis is more often related to a granulomatous infection, such as histoplasmosis. Patients with acute mediastinitis usually present with an acute onset of symptoms, including fever and leukocytosis, whereas patients with chronic mediastinitis are often asymptomatic. If symptoms occur, they usually result from compression of mediastinal structures.

Acute Mediastinitis

Acute mediastinitis may occur after esophageal perforation, from extension of an infectious process from thoracic and extrathoracic structures (especially from the neck), and as an infrequent complication of cardiac surgery (Box 17-1). Most cases are caused by esophageal perforation.

Esophageal Perforation

Patients with esophageal perforation frequently present with fever, leukocytosis, dysphagia, and retrosternal chest pain, which often radiates into the neck. On physical examination, they may demonstrate subcutaneous emphysema and Hamman’s sign, a crunching or rasping sound that is synchronous with the heartbeat and heard on auscultation over the cardiac apex and that is associated with pneumomediastinum.

Chest radiographic findings include diffuse widening of the mediastinum and pneumomediastinum (Fig. 17-3). Associated pleural abnormalities are usually left sided and include pneumothorax and empyema. When the diagnosis is delayed, complications may include mediastinal abscess formation and rupture of the abscess into the adjacent bronchus (i.e., esophagobronchial fistula) and pleura (i.e., esophagopleural fistula, often with subsequent development of empyema). The diagnosis of esophageal perforation can be confirmed by fluoroscopic examination after administration of water-soluble contrast, which demonstrates extravasation of contrast at the site of perforation (Fig. 17-4). In complicated cases that have progressed to mediastinal abscess formation, CT may be helpful in identifying the precise location and extent of fluid collections (Fig. 17-5).

Prompt diagnosis and treatment of esophageal perforation are critical. Very high morbidity and mortality rates are associated with delay in diagnosis beyond 24 hours.

Feb 28, 2016 | Posted by in RESPIRATORY IMAGING | Comments Off on Diffuse Mediastinal Abnormalities

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