Aortopulmonary window (radiograph)

The aortopulmonary (aortic-pulmonary or AP) window (also known as APW, but see 'Terminology' below) is a radiological mediastinal space seen on frontal chest radiographs.

Terminology

The term should also not be confused with an aortopulmonary septal defect, which is occasionally also - unfortunately - called an aortopulmonary window, referring to a rare form of congenital heart disease where there is an opening between the aorta and the pulmonary trunk ⁴. It is usually referred to with the acronym APW instead of AP window.

Also, be careful not to confuse the AP window with the aortic-pulmonary stripe. 

Gross anatomy

Boundaries

The AP window boundaries are ^1,2,5:

• superior: inferior wall of the aortic arch

• inferior: superior wall of the left pulmonary artery

• anterior: posterior wall of the ascending aorta

• posterior: anterior wall of the descending aorta

• medial: trachea; lateral wall of the left main bronchus; esophagus (anterior to posterior)

• lateral: pleural surface of the left lung contacting the superior boundary (aortic arch) and extending to the inferior boundary (left pulmonary artery)

The ligamentum arteriosum separates the AP window into medial and lateral parts ⁵.

Contents

A variety of structures are contained within or traverse the AP window ^1-3,5:

• connective tissue/fat

• lymph node(s)

• left phrenic nerve

• left vagus nerve

• left recurrent laryngeal nerve

• left bronchial arteries

• ligamentum arteriosum

Radiographic appearance

Plain radiograph

The AP window normally has a concave lateral border. A straight lateral border can be considered normal if unchanged from the previous chest x-ray. A newly straightened or convex lateral border is considered abnormal and has a number of causes ^1,2:

• mediastinal lymphadenopathy (most common ³)

• prominent mediastinal fat (normal variant ³)

• aortic or bronchial artery aneurysms

• malignancy, e.g. nerve sheath tumor