Pneumonia at superior segment of right lower lobe (hidden area)
Presentation
Generally healthy 20 years old male. Presented with backache for the last 3 days, accompanied by mild fever (37.5 ºC). No dyspnea or cough. Normal lung auscultation. Normal white blood cell count (8,110 per microliter) with mildly elevated CRP (23.1 mg/l).
Patient Data
A subtle increased density over the right hilum is shown on the frontal chest x-ray.
The edges of the hilar vessels are recognized, and therefore the density represents a pathology that is either anterior or posterior to the right hilum (hilum overlay sign).
As the right heart border is clearly visualized without loss of silhouette sign, a consolidation posterior to the right hilum (at the superior segment of the right lower lobe) was suspected.
A correlation with a lateral chest x-ray was recommended.
The lateral x-ray projection shows clearly the consolidation at the superior segment of the right lower lobe, adjacent to the oblique fissure.
Case Discussion
Hidden frontal chest x-ray areas refer to areas where lesions may be overlooked due to the superimposition of different anatomical structures. These areas are the: apical zones, hilar zones, retro-cardiac zone, and the zone below the dome of the diaphragm.
This case shows the process of evaluation of right hilar density on the frontal chest x-ray. Hilum overlay sign and lack of loss of silhouette sign with the medial cardiac border are observed, keeping with superior segment of the right lower lobe consolidation. These signs are very helpful in analyzing the frontal chest x-ray hilar density. While the density is quite subtle on the frontal x-ray projection, due to the superimposition of the hilar vessels, on the lateral projection the consolidation is seen much more clearly.
The peripheral location of the consolidation in this case explains the atypical clinical presentation of the patient with backache (representing a pleuritic pain) rather than the classical segmental pneumonia sign of a cough.
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