Fig. 1

PA and lateral radiographs show an ill-defined opacity at the right lung base (white arrows). The clue to the diagnosis is a small air-fluid level at the costophrenic angle (red arrow). This finding is known as the V line and it is highly suspicious for pneumothorax. A thin line visible in the PA view (yellow arrow) marks the edge of the lung.

CT confirms the basal pneumothorax (A, arrow), which has caused segmental collapse of the right lower lobe (B, arrows). In the axial view, the pneumothorax is seen to extend to the lung apex (C, arrow). There are bullae throughout both lungs.

Fig. 2

Final diagnosis: basal pneumothorax with secondary segmental lung collapse

The V line is described as two intersecting lines forming a V, with the apex pointing laterally. It represents a small amount of pleural bleeding secondary to separation of the two pleural layers. One of the lines of the V is sometimes absent, as in the case presented.

The V line is not always seen in pneumothorax, but when it is present, it is a useful indicator of a small or overlooked pneumothorax. A confirmatory expiration film should then be performed.

Fig. 3

Typical V line. Note the two branches of the V, better seen in the cone down view (red arrows), where the pneumothorax is more evident (white arrows).

Fig. 4

Two cases in which the V line alerts to a small pneumothorax (A, B arrows). The V line has two branches in A (arrows) and only one in B (arrow).

Fig. 5

Pneumothorax poorly seen in the inspiration film, but suspected because of a tiny V line (A, red arrow). Expiration film shows the pneumothorax to better advantage (B, white arrows).

Follow Dr. Pepe’s advice

Follow Dr. Pepe’s advice:

• A small pneumothorax may be missed because the free lung edge is barely discernible.
• The V line is a useful ancillary finding to suspect a pneumothorax. Confirm with an expiratory film.

Case prepared by Dr. Pepe