Consolidation

Lobar Consolidation

Definition

Consolidation on CT scans refers to a pattern of pulmonary abnormality that appears as a homogeneous increase in lung parenchymal attenuation that obscures the margins of vessels and airway walls. Air-bronchogram sign may be present within the lesion [1] (Fig. 3.1). Pathologically, the consolidation consists of an exudate or other product of disease that replaces alveolar air, rendering the lung solid (as in infective pneumonia) [2].

Diseases Causing the Pattern

Lobar consolidation is the representative pattern of lobar pneumonia. The lobar pneumonia is one of the two morphologic classiÞcations of pneumonia (the other being bronchopneumonia) (Figs. 3.1 and 3.2). The most common organisms causing lobar pneumonia are Streptococcus (Pneumococcus) pneumoniae, Hemophilus influenzae, and Moraxella catarrhalis. Mycobacterium tuberculosis may also cause lobar pneumonia [3] (Table 3.1).

Tumorous conditions such as invasive mucinous adenocarcinoma [4] (Figs. 3.3 and 3.4) and bronchus-associated lymphoid tissue lymphoma [5] (Fig. 3.5) also occur with lobar consolidation.

The lobar consolidation may also be associated with obstructive pneumonia, cicatricial or passive atelectasis, and pulmonary infarction [6] (Fig. 3.6).

Distribution

Lobar consolidation in lobar pneumonia tends to be located at the middle and outer thirds of the lung. In contrast, atypical

pneumonia frequently shows centrilobular nodules or acinar opacity and lobular consolidation or lobular ground-glass opacity and tends to be distributed at the inner third of the lung in addition to the middle and outer thirds [7].

Clinical Considerations

The presence of acute pneumonia symptoms and signs favors the diagnosis of lobar pneumonia. Also the rapid development of symptoms and signs may help diagnose acute lobar pneumonia.

MRI examination with ultrafast Òwater-sensitiveÓ sequence depicts bright signal, the so-called MR white lung sign, from lung consolidative lesions in patients with mucinous adenocarcinoma [8].

Key Points for Differential Diagnosis

1.The presence of acute pneumonia symptoms and signs and their development speed help diagnose acute lobar pneumonia.

2.Stretching, squeezing, and widening of the branching angle of CT air-bronchogram sign and bulging of the surrounding interlobar Þssure suggest the diagnosis of lobar mucinous adenocarcinoma [4].

3.Indolent and slow progressive nature of consolidative lesion may help make a diagnosis of bronchusassociated lymphoid tissue lymphoma [5].

4.When mucinous adenocarcinoma is suspected, MR imaging may be conducted to see whether or not the so-called MR white lung sign is present [6, 8].

5.Central lucencies in peripheral consolidations on lung window images (a kind of reversed halo sign) are highly suggestive of pulmonary infarction [9, 10].