Dr. Pepe’s Diploma Casebook: CASE 144 – SOLVED

Findings: PA radiograph shows increased opacity of the left hilum (A, arrow), which is due to a mass projected over it, as seen in the lateral view (B, arrows). In addition, there is convexity of the aortopulmonary window (A, red arrow)

The increased hilar opacity (C, arrow) was not visible in a PA radiograph taken six months earlier (D, circle). Convexity of the aortopulmonary window (C, red arrow) was not present at that time.

In the lateral view, the mass (E, arrows) was visible six month earlier, albeit smaller (F, arrow). This progression indicates rapid growth.

Enhanced axial and coronal CT confirms a pulmonary mass invading the aortopulmonary window (G and H, arrows). Lung metastases were present (insert, red arrows)

Diagnosis: lung carcinoma invading the aortopulmonary window

I am presenting this case to discuss the aortopulmonary window (APW), which is a small mediastinal space located between the aortic knob and the pulmonary artery in the PA view (Fig 1A). The APW is normally concave; convexity (Fig 1B) suggests an abnormality that should be studied with enhanced CT.

Visibility of the APW is difficult in the elderly, because the superimposed uncoiled descending aorta makes the interpretation more difficult (Fig 2).

Convexity of the APW may be overlooked unless we look specifically at the area (fig 3). The larger the abnormality, the more readily it is detected in the chest radiograph. Subtle changes are more difficult to identify and comparing with previous films is very helpful.

Causes that may alter the APW are: tumors, enlarged lymph nodes, aortic aneurysms and increased mediastinal fat. The phrenic nerve crosses this space and a phrenic neurinoma may also grow in the APW, although I have never seen a case.

Enlarged lymph nodes are by far the most common cause of occupation of the APW. They may occur in malignant and non-malignant diseases. They usually coexist with radiographic manifestations of the primary process (Figs 4 and 5).

In isolated occupation of the APW the etiology cannot be determined in the chest radiograph and enhanced CT should be obtained (fig 6).

Aortic aneurysm is an uncommon cause of convexity of the APW (Fig 7). The abnormality is initially subtle and it becomes more evident as the aneurysm grows (Fig 8).

Radiographs taken five years earlier did not show the abnormality (E and F, circles).

Enhanced axial and coronal CT demonstrate that the mass represents a saccular aneurysm arising from the aortic arch (G and H, arrows).

Comparison with previous films shows a normal APW in 2007 and progression of the opacity over a three-year period (arrows).

Enhanced CT shows that the opacity represents a partially thrombosed aneurysm arising from the inferior aspect of the aortic arch (C-D and E, arrows).

Last but not least, we should remember that mediastinal fat is an innocuous cause of convexity of the APW (Fig 9).

Follow Dr. Pepe’s advice:

1. Convexity of the APW suggests underlying pathology.

2. Enlarged lymph nodes are the most common cause of a convex APW.

3. Aneurysm and mediastinal fat may also enlarge the APW