What’s the cause of this woman’s chest x-ray abnormality?
Vol.18, No.04, April 2010

This 27-year-old woman presented to the emergency department with an 8-day history of persistent cough, fever and chest pain. Routine lab values were unremarkable apart from mild leukocytosis. A chest x-ray was performed (Fig. 1a, 1b).

The most likely diagnosis in this young woman is:

a) right middle lobe pneumonia

b) Hampton’s hump sign from pulmonary embolism

c) Westermark’s sign from pulmonary embolism

d) lingular pneumonia

e) right breast abscess

d) right lung hydro-pneumothorax, with air-fluid level

ANSWER
Solution to Analyze This!

The answer is a) right middle lobe pneumonia.

The chest x-ray images reveal hazy increased opacity in the region of the mid and lower right lung on the PA film (Fig. 1a), and triangular wedge-like opacification of the anterior mid-aspect of the chest on the lateral view (Fig. 1b). The appearance on the lateral view is classic for either a right middle lobe pneumonia, or a lingular pneumonia (although the triangular opacity for the latter is usually smaller in height than seen in Fig. 1b). Since the PA film reveals the abnormality to be on the right side (note the ‘L’ marker at the top right of Fig. 1a indicating the patient’s left side), then combining the findings from both exams places the abnormality in the right middle lobe (the lingula consists of two antero-inferior segments of the left upper lobe). The right middle lobe consists of medial and lateral segments. In this case, the consolidation is situated in the lateral segment. When the consolidation involves the medial segment, there is secondary obscuration of the right heart border on the frontal chest x-ray, as a result of loss of the normal pericardial-air interface. Figure 2 provides a summary of the various lung lobes and segments.


Figure 2: Segmental lung anatomy (from: www.medcyclopaedia.com).

The Hampton’s hump sign refers to a pleural-based wedge-shaped opacity in the lung on a chest x-ray suggesting focal lung infarction from pulmonary embolus. Although the finding on Figure 1 could in theory represent a large Hampton’s hump, and the history is not entirely against an embolic phenomenon, it’s unlikely for pulmonary embolic disease to cause localized infarction of a complete lung lobe segment (in this case, the lateral segment of the right middle lobe). The Westermark sign for pulmonary embolism refers to relative reduced regional lung vascularity (oligemia) secondary to blockage of pulmonary blood flow from the embolic filling defect. This results in increased lung lucency, not increased opacity. This isn’t a good option for this case. Lingular pneumonia is not an option, as the abnormality is on the right side; the lingula represents two segments of the left upper lobe (see Fig. 2). Although the increased opacity overlies the right breast on the PA chest x-ray, the lateral projection confirms the location within the lung, and as such the option of right breast abscess is not viable. On the frontal PA chest x-ray, it does look like there’s a straight line along the superior aspect of the opacity, which could then represent the interface of a right hydro-pneumothorax. However, the superior margin of the opacity is seen on the lateral view to be slightly convex and in fact represents the pneumonia consolidation abutting the minor fissure of the right lung. There’s no pneumothorax present and no pleural effusion. The straight line appearance on the PA view is spurious.

References

  1. Shah RM, Miller W Jr. AJR 2003;180:965-8.
  2. Kim SJ et al. AJR 2003;180:1251-4.
  3. Magnussen JS et al. AJR 2000;174:1333-6.
  4. Worsley D et al. Radiology 1993;189:133-6.
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Figure 1a: posterior-anterior (PA) chest x-ray; 1b: lateral chest x-ray
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