Both the location and size of lesions within the aortic-pulmonic window have been reported to influence their visibility on the PA radiograph. Larger masses are more easily identified, as expected. Earlier detection is facilitated when pathology is situated laterally in the window and the reflection projects beyond the aortic arch (13), although the visibility of a lesion is reduced when it becomes associated with left upper lobe volume loss (14). Inferior displacement of the left pulmonary artery may be appreciated as an enlarging mass becomes restricted above by the aortic arch. A mass or adenopathy developing within the medial aspect of the window may eventually begin to displace the esophagus and trachea away from the aortic arch. A posterior lesion may deviate the preaortic recess reflection.
Like the aortic-pulmonary reflection, the aortic-pulmonic window reflection is essentially viewed en face on the lateral radiograph (Fig. 6D). Pathology may be perceived more quickly on the PA view because reflecting pleura is imaged tangentially to the x-ray beam, and subaortic nodes lie in close proximity to the reflection (15). An abnormal opacity will be identified on the lateral radiograph as a lesion grows and protrudes deeper into the left hemithorax, and an edge will become well-defined once it is presented in tangent to the x-ray beam. Early detection of pathology is facilitated by correlation with previous radiographs, along with careful evaluation for change in appearance of the inferior margin of the aortic arch and the superior margin of the left pulmonary artery bordering the window. A margin may be clearly defined (Fig. 9A) while lung inserts into the window, and then later become indistinct (Fig. 9B) as a mass or adenopathy prohibits contact with adjacent lung.
Once the question of an abnormality in the region of the aortic-pulmonic window is raised on a conventional radiograph, computed tomography should generally be the next study performed to help characterize it, and to define its extent and relationship to other mediastinal structures. CT should also be used to evaluate the aortic-pulmonic window when the conventional radiograph appears normal but there is high clinical suspicion for pathology. The height of the window may appear reduced on CT images performed with the patient supine (16). Care should be taken to differentiate nodes from volume averaging of adjacent vessels. Magnetic resonance (MRI) imaging is also of value in certain situations, such as when CT does not clarify findings, iodinated contrast is necessary but contraindicated, or the multiplanar capability of MRI is needed.
The preaortic recess is present in individuals whose left lung is able to extend anterior to the descending aorta. It can be considered analogous to the extension of the right lower lobe in front of the azygous vein, which occurs more commonly and is identified as the azygoesophageal recess. The preaortic recess is more prominent in the presence of emphysema, kyphosis, or a tortuous aorta. The interface formed once left lung and visceral pleura extend medially and contact the mediastinum may be identified on the PA radiograph as the preaortic recess reflection.
The normal preaortic recess reflection typically parallels the descending thoracic aorta, projecting slightly to the right of its left lateral margin. It disappears inferiorly as the aorta courses toward the midline to enter the abdomen. The relevance of this reflection to a discussion of the left superior mediastinum relates specifically to its superior continuation (Fig. 5). It must terminate beneath the left pulmonary artery when posterior closure of the aortic-pulmonic window is accomplished by approximation of the pulmonary artery and the descending aorta. However, when able to continue superiorly toward the aortic arch, it then becomes responsible for closure of the posterolateral aspect of the window (Fig. 7). Subsequently, it either deviates laterally to merge with pleura along the aorta or it terminates directly beneath the arch. If it abuts the esophagus medially, it becomes synonymous with the left pleuroesophageal stripe (Fig. 11).
Understanding the preaortic recess reflection enhances appreciation of the interrelated anatomy of the left superior mediastinum. The aortic-pulmonic window not only relates anterolaterally to the paraaortic region and aortic-pulmonary reflection, but also (potentially) posterolaterally to the left lower lobe and preaortic recess reflection. A mass displacing the preaortic recess reflection on a conventional radiograph may subsequently be shown in cross-section to arise directly from the aortic-pulmonic window. The lateral margin of a left lower lobe mass tucked within the preaortic recess might also simulate a displaced reflection. Indeed, radiographic analysis is enriched through developing a three-dimensional perspective of the relationships of normal mediastinal structures, along with an understanding of the nuances of anatomy and the often subtle changes produced by disease. Our ability to extract information from conventional radiographs can be refined by taking advantage of opportunities that promote correlation with cross-sectional images.
The author thanks Drs. Jon Dalton, Marvin Chasen, Mark Kransdorf, Thomas Berquist, and Stephen Carmichael for their assistance, Laura Newman for secretarial support, and Irma Lyndsey-Parker and Daniel Hubert for support in graphics and photography.
1. Blank N, Castellino RA. Patterns of pleural reflections
of the left superior mediastinum
– normal anatomy
and distortions produced by adenopathy. Radiology 1972; 102:585–89.
2. Keats, TE. The aortic-pulmonary mediastinal stripe. Am J Roentgenol 1972; 116:107–9.
3. Heitzman ER. The Mediastinum–Radiologic Correlations with Anatomy and Pathology
. Heidelberg: Springer-Verlag, l988.
4. Proto, AV. Mediastinal anatomy
: emphasis on conventional images with anatomic and computed tomographic correlations. J Thor Imaging 1987; 2 (1):1–48.
5. Mountain CF, Dressler CM. Regional lymph node classification for lung cancer staging. Chest 1977; 111:1718–23.
6. Mountain CF, Lipshitz HI, Hermes KE. Lung cancer: a handbook for staging, imaging, and lymph node classification—Revised international system for staging and regional lymph node classification. Bristol-Myers Squibb, l999.
7. Shin MS, Jolles PR. Computed tomography of the aortopulmonary window–normal anatomy
and pathology. J Computed Tomography 1987; 11:111–22.
8. Parkinson J, Bedford E. The aortic triangle–a radiological landmark in the left (or II) oblique position. Lancet 1936; 2:909–11.
9. Heitzman ER, Lane EJ, Hammack DB, et al. Radiological evaluation of the aortic-pulmonic window. Radiology 1975; 116:513–18.
10. Tuddenham, WJ. Glossary of terms for thoracic radiology–recommendations of the nomenclature committee of the Fleischner Society. AJR 1984; 143:509–17.
11. Naidich DP, Webb WR, Muller NL, et al. Computed Tomography and Magnetic Resonance of the Thorax
. Philadelphia: Lippincott Williams and Wilkins, l999.
12. Woodring JH, Daniel TL. Mediastinal analysis emphasizing plain radiographs and computed tomograms. Medical Radiography
and Photography 1986; 1:62.
13. Jolles PR, Shin MS, Jones WP. Aortopulmonary window lesions–detection with chest radiography
. Radiology 1986; 159:647–51.
14. Muller NL, Nichols DM. Accuracy of the plain radiograph in the detection of aortopulmonary lymphadenopathy. J Can Assoc Radiol
15. Blank N, Castellino RA. Mediastinal lymphadenopathy. Semin Roentgenol
16. Moss AA, Gamsu G, Genant HK. Computed Tomography of the Body—with Magnetic Resonance Imaging
. Philadelphia: WB Saunders, 1992.
Editor: Jeffrey S. Klein
Associate Editors: Ann Leung, MD
David Lynch, MD, Jung-Gi Im, MD
Michio Kono, MD, Charles White, MD
Guest Editor: William Stanford, M.D.