Mensuration of the arch of the azygos vein and its application to the study of cardiopulmonary disease.

Abstract

The normal range and size of the arch of the azygos vein in the standard upright chest film has been variously stated. Felson (4) indicates a maximum dimension of 10 mm. Fleischner and Udis (5), in their excellent article, point out that in their experience the upper limits of normal for the transverse dimension of the arch are 5 mm and, in rare instances, 6 mm. These authors, however, fail to describe their technic for measurement and provide no information concerning possible variation with age and sex. Doyle et al. (2) and Swart (7) do give some statistical data but they used horizontal tomography to visualize the azygos arch. This method is inconvenient and the data obtained cannot be translated to the upright 72-inch postero-anterior chest film because of differing target-film distances and the recognized increase in the width of the azygos arch which occurs with assumption of the supine position. This study was undertaken to provide more easily available, useful data. Method The azygos arch appears as a spindle-shaped shadow in the right tracheobronchial angle and was seen in 56 per cent of the normal patients we surveyed (Fig. 1). In order to determine a normal value, we measured the transverse dimension of the azygos arch in standard chest films of 200 normal men and women between the ages of nineteen and sixty-three years. To standardize our method of measurement, we selected the widest diameter of the vein as measured perpendicularly to the wall of the trachea. Because the tracheal wall blends imperceptibly with the azygos vein, the measurement by necessity includes the tracheal wall (Fig. 2). It's inclusion in the measurement, however, does not introduce a significant error since it should be relatively uniform from subject to subject. Early in the study we discovered that the azygos arch is frequently dilated in pregnant women, so we undertook the same measurement in 100 normal pregnant women as well. The results are shown in Table I. Comment Dilatation of the azygos arch is known to occur in cases of venous congestion including congestive heart failure, right ventricular strain, organic and functional tricuspid insufficiency, pericarditis, both constrictive and with effusion, and obstruction of the superior vena cava above the junction of the azygos vein. Dilatation of the azygos arch has also been described in portal hypertension as a result of collateral flow to the azygos system (1–3, 6) (Fig. 3). We have found that knowledge of the normal dimension of the azygos arch is useful in the differentiation of inflammatory and neoplastic pulmonary infiltration from acute congestive pulmonary interstitial edema. These entities may radiographically resemble one another closely and present a difficult differential diagnosis, particularly when presented without knowledge of prior medical history.