This document contains 9 figures showing examples of unilateral lobar or localized hyperlucency of the lung seen on radiographs. The figures demonstrate various conditions that can cause one lung or lobe to appear brighter on chest x-ray, including congenital emphysematous bulla, giant emphysematous bulla, compensatory overaeration, Westermark's sign of pulmonary embolism, unilateral hyperlucent lung, congenital lobar emphysema, cystic adenomatoid malformation, hydrocarbon poisoning, and absence of the right pectoralis muscles.

1. 15Unilateral Lobar or Localized
Hyperlucency of the Lung

2. CLINICAL IMAGAGING
AN ATLAS OF DIFFERENTIAL DAIGNOSIS
EISENBERG
DR. Muhammad Bin Zulfiqar
PGR-FCPS III SIMS/SHL

3. • Fig C 15-1 Congenital emphysematous bulla.
Large thin-walled air cyst (arrows) in the mid-
portion of the right lung.

4. • Fig C 15-2 Giant emphysematous bulla. The
air-containing mass fills most of the left
hemithorax.

5. • Fig C 15-3 Compensatory overaeration in agenesis of the left lung. There is
virtually total absence of aerated lung in the left hemithorax. The right
lung is markedly overinflated and has herniated across the midline. The
entire mediastinum lies within the left hemithorax. The chest wall is
asymmetric, and the ribs are somewhat close together on the left.

6. • Fig C 15-4 Westermark's sign of pulmonary embolism. (A) Baseline
chest radiograph demonstrates normal vascularity in the left upper
lobe. (B) Striking hyperlucency of the left upper lobe coincided with
the onset of the patient's symptoms. (C) Arteriogram performed on
the same day the film in (B) was made shows an occluding clot in
the left upper lobe and multiple emboli in the right lung.

7. • Fig C 15-5 Unilateral hyperlucent lung. (A) Frontal
radiograph exposed at total lung capacity reveals a
marked discrepancy in the radiolucency of the two
lungs, with the left showing severe oligemia but
normal lung volume. (B) Frontal radiograph at residual
volume after bronchography demonstrates severe air
trapping in the left lung and little change in volume
from total lung capacity. Because the deflation of the
right lung is normal, the mediastinum has swung
sharply to the right. (C) A pulmonary arteriogram
shows the discrepancy in blood flow to the two lungs.
The left pulmonary artery is present, although
diminutive, differentiating this appearance from
congenital absence of the left pulmonary artery.7

8. • Fig C 15-6 Congenital lobar emphysema. Severe overdistension of
the left upper lobe causes marked radiolucency of the left
hemithorax along with depression of the ipsilateral hemidiaphragm
and displacement of the mediastinum into the right hemithorax.
The hyperinflated left upper lobe has herniated into the right side
of the chest (arrows). Note the small and widely separated
bronchovascular markings in the lucent left lung.

9. • Fig C 15-7 Cystic adenomatoid malformation. Frontal
radiograph of an infant's chest and abdomen at 1 hour
of age demonstrates a large lucent mass in the right
hemithorax with shift of the mediastinal structures to
the left. In the lower right chest, the mass appears
multicystic and resembles air-filled loops of bowel.
Ascites is also present.33

10. • Fig C 15-8 Hydrocarbon poisoning. (A) Large
thin-walled pneumatocele (arrows). (B)
Multiple thin-walled pneumatoceles bilaterally
but more marked on the right.

11. • Fig C 15-9 Absence of the right pectoralis muscles.
Asymmetry of the thoracic cage with hypoplasia of the
anterior ribs (arrows). The lower portion of the right
lung appears hyperlucent, whereas the apex seems
comparatively opaque.