Left lower lobe collapse

Lobar or segmental collapse occurs in large airway obstruction and subsequent absorbtion of air from the affected lung. Causes are listed below. Bronchogenic malignancy is one of the commonest causes and the case study illustrates the subtle signs on plain X-ray. Subsequent CT imaging of this patient demonstrated a malignant neoplasm originating in the left lower lobe bronchus.

Table 1.1 Causes of lobar collapse

• Neoplasm (carcinoma, carcinoid)

• Mucus plug/inflammatory exudate

• Endoluminal metastasis

• Misplaced endotracheal tube (ITU ventilated patients)

■ Bronchial wall

• Inflammation (TB, sarcoid)

■ Extrinsic compression

In children, bronchial malignancy is rare and the causes of lobar collapse differ from those in adults. Inflammatory exudate in pneumonia or mucus plugging (in patients with cystic fibrosis and asthma) are much more common causes (Table 1.1).

The five lobes collapse in different directions to produce different patterns although there are some common features (see below). If the vessels within the collapsed lobe remain perfused, then a wedge-shaped opacity is more clearly identified. In lower lobe collapse (both right and left lower lobe), the lung collapses posteriorly and medially. This is well illustrated by the CT scan (see Fig. 1.18). In left lower lobe collapse, the silhouette of the medial aspect of the hemidiaphragm and the descending

Fig. 1.18 CT left lower lobe collapse. Note how the left lower lobe collapses tight against the descending aorta.
Fig. 1.19 Right lower lobe collapse. Loss of volume in the right lung, the right hemithorax is hypertranslucent.

aorta is lost because it is no longer outlined by adjacent aerated lung. A triangular opacity is seen projected through the cardiac outline. In right lower lobe collapse (Fig. 1.19), the hemidiaphragm silhouette remains clearly seen as the middle lobe is in contact with it. On a lateral projection the collapsed lower lobe may be identified as a triangle of increased density in the posterior costophrenic recess.

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