Chapter 6

Abnormal Mediastinum

Abnormalities localized to the mediastinum include mass, enlargement, fluid, or air. For a brief description and graphic of the normal mediastinum CXR, see the mediastinal anatomy in chapter 3.

Mediastinal masses and other abnormalities occur in areas defined by anterior, middle, or posterior [1].

Each region has its own unique differential diagnosis, with some overlap such as vascular abnormalities. The other pages in the “Mediastinum” section of this book describe a method of systematically identifying abnormalities of the mediastinum, localizing more specifically, and provide simple mnemonics for recalling differentials in each region.

Radiological signs: Any disturbance of previously described mediastinal lines or edges could indicate an abnormality of the mediastinum.

Mechanism: Mass or other process can occur from many processes, depending on the anatomy in each area. Since vessels are in all three anatomic locations, tortuous or anomalous vessels can be included in each differential presented. Like with lung patterns, keep in mind that “mass” is a radiological finding and not synonymous with tumor. For example, a mass-like finding could be an aortic aneurism or enlarged pulmonary artery.

Anterior Mediastinal Mass

The anterior mediastinal region includes the following:

•Anterior to trachea, aorta, and arch vessels; superior to the pericardium; and is posterior to sternum. It contains fat, thymic remnants, internal mammary vessels, and lymph nodes.

You can use the six “T”s to help you remember the causes of anterior mediastinal masses.

•Thyroid lesions

•Thymic lesions (and parathyroid masses)

•Teratomas (and other germ cell tumors, see below mnemonic)

•“Terrible” lymphoma (Lymphadenopathy)

•Tortuous vessels (dissecting aorta, right arch)

•Trauma

To take this a step further, you can use the mnemonic YES CT to help you remember the types of germ cell tumors (under Teratoma, above). Some use ChESTY instead of YES CT.

Y – Yolk Sac

E – Endodermal Sinus Tumor (Yolk Sac)

S – Seminoma

C – Choriocarcinoma

T – Teratoma (most common in chest)

Case 6.1

Figure 6.1 is that of a 22-year-old active duty Marine Corps female smoker with chronic persistent cough and scattered wheezes. There was no significant medical or family history.

Findings: Well-rounded opacity overlying lateral left margin of the aorta and pulmonary artery. On lateral there is filling-in of the usually dark area behind the sternum (sometimes called RSCS or the RetroSternal Clear Space). Note that there are also calcifications in the mass.

Fig. 6.1a Left hilar mass on PA (arrows). Note the hilar overlay sign (non-obliteration of aorta or main pulmonary artery)

Fig. 6.1b Mass on lateral anteriorly located

(large arrows), note absence of RSCS and calcifications (small arrows)

Fig. 6.1c CT of the same patient, which reveals a mass (arrows) in the anterior mediastinum. In the soft tissue window on the right, note the fat density as well as calcification representing a tooth

Fig. 6.1d Axial CT bone algorithm highlighting tooth morphology (arrow)