Clinical History
Normal chest x-tay film. No lung lesions seen. Cardiac shadows and bony structers are normal.
In the right upper region an opaque thin curved line is seen. This linear shadows end inferiorly with an oval smooth opacity. The curved line is concave superiorly and medially.
Imaging Findings
Intermittent cough in a young male patient.
PA erect chest x-ray.
Discussion
The azygous fissure originates from an anomaly in the migration of the posterior cardinal vein during intra-uterine life.
It is not a true fissure as it is composed of four layers of pleura (two visceral and tow parietal layers), while fissures are formed by only the two visceral layers.
It is seen in 0.4% of chest radiographs (ref. 1).
It leaves a portion of lung parenchyma of the anterior and/or posterior segment of the upper lobe (ref. 2) between the adventitia of the vessel itself and the mediastinum, maintaining always an extra-pleuric position.
In the standard PA (postero-anterior) chest radiograph this normal variant is seen as an upper lobe linear opacity, concave superiorly and medially, ending inferiorly with an oval opacity, given by the horizontal portion of the azygous vein converging on the superior vena cava.
It can also have a more vertical course.
The differential diagnosis is with the apical fissures of the upper lobe segments, with scars of previous lung and pleuric lesions, and with the walls of bullous lung lesions (ref. 3).
In differential diagnosis it is helpful to check the absence of the regular mediastinal azygous vein.
While in cases of presence of azygous fissure the diagnosis is given by the usual position of it, that is near the superior vena cava, the trachea and the right main bronchus, and by its usually curved course, with superior and medial concavity, ending with an oval smooth opacity with sharp margins.
Differential Diagnosis List
