Findings: PA view shows a small right hemithorax. There is elevation of the right hemidiaphragm and a small hilum (A, red arrow). The findings are very suggestive of RLL lobectomy. The oblique fissure in the RLL represents the displaced minor fissure (A, white arrow). Previous CT shows a normal-size right lung with a ground-glass opacity in the RLL (B, arrow).

Final diagnosis: RLL lobectomy for adenocarcinoma of the lung

I am showing this case to discuss displacement of the lung fissures, an important finding that can indicate partial collapse of the underlying lobe. Usually, lobar collapse is detected because of the increased opacity of the lobe. Occasionally, the collapsed lobe retains much of its air, so a shift of the fissure may be the only sign of collapse.

A potential pitfall of fissure displacement is previous surgery, as seen in the case presented. In my experience, excluding previous surgery, aerated lobar collapse occurs mainly in the following conditions:

1. Inflammatory peripheral lung disease
2. Central lobar bronchial obstruction
3. Rounded atelectasis

NORMAL ANATOMY
The right minor fissure is visible in about 50% of chest radiographs as a straight horizontal line at the level of the right hilum (Fig. 1, A and B) The right and left major fissures are not visible in the PA film because their course is not tangential to the x-ray beam. (A, curved dotted lines). They are both visible as oblique lines in the lateral view (B).

Inflammatory lesions can cause scarring which diminishes the size of the affected lobe. TB is the most common cause in upper lobes. Bronchiectasis is the predominant cause in lower lobes. Both conditions can show an aerated lobe with loss of volume (Figs. 3-5).

Central lobar bronchial obstruction is occasionally associated with aerated lobar collapse. It is thought to be due to collateral air ventilation through incomplete fissures (Figs. 6-7).

Unenhanced axial CT confirms the marked LUL collapse (C, white arrow) secondary to endobronchial obstruction (C, red arrow). CT taken one year earlier shows an endobronchial lesion (D, red arrow) and discrete forward displacement of the major fissure (D,E, white arrows). These changes were overlooked. Surgical diagnosis: bronchogenic carcinoma

Rounded atelectasis is a common cause of fissure displacement. It occurs secondary to spiral folding of the lung parenchyma when fixed by thickened pleura. The consequence is a peripheral rounded opacity in an aerated collapsed lobe. The volume loss, detected by the displaced fissure, avoids possible confusion with a true nodule in the plain film.

Axial and sagittal CT confirm displacement of the left major fissure (C and D, white arrows), the small LLL, and the posterior rounded atelectasis (C, red arrow).

As a final thought, occasionally you may find fissure displacement without an apparent cause (Fig. 10).

Follow Dr. Pepe’s advice:
1. A displaced fissure may be the only manifestation of aerated lobar collapse (always exclude previous surgery).

2. Most common causes:

a) Peripheral lobar inflammatory disease

b) Central bronchial obstruction

c) Rounded atelectasis