Ground glass opacity on CT scanning of the chest: What does it mean?

FIGURE 10. Bronchiolitis obliterans organizing
pneumonia. Image is of a 50-year-old
man with increasing shortness of breath after
bilateral lung transplantation. HRCT (1.0 mm
collimation) shows bilateral patchy areas of
GGO in both a bronchovascular and peripheral
distribution.
FIGURE 11. Contusions. Image is of a 22year-old
man involved in a motor vehicle accident.
Helical CT scan (10 mm collimation)
shows bilateral areas of GGO and consolidation
in a typical peripheral non-segmental distribution.
There are both posterior and anterior
rib fractures adjacent to the sites of contusion.
peripheral ring of hemorrhage or hemorrhagic
infarction surrounding target
lesions of pulmonary aspergillosis (figure
9). Several infectious and noninfectious
causes of the CT halo sign have
since been reported. 24 In most patients,
hemorrhagic nodules can be distinguished
from nonhemorrhagic nodules
by the presence of a halo of GGO.
Another cause of focal GGO, or a
nodule with a surrounding halo of GGO,
is the post-biopsy pseudo nodule. These
pseudo nodules have been described in
Causes of a “halo” pattern of
GGO on CT scanning
• Invasive pulmonary aspergillosis
• Neoplasm, hemorrhagic
• Post-biopsy pseudo nodule
Table 4
FIGURE 12. Desquamative interstitial pneumonitis.
Image is of a 77-year-old man with a
3-month history of increasing shortness of
breath. HRCT (1.5 mm collimation) shows
bilateral areas of GGO and consolidation in a
peripheral distribution without evidence of
honeycombing or traction bronchiectasis.
patients who have undergone lung transplantation
and transbronchial lung
biopsy, 25 but they may be seen in any
patient after lung biopsy.
A peripheral pattern of GGO—
Processes that are known to result in a
peripheral lung distribution of GGO
with HRCT scanning are listed in table
5. This particular distribution pattern
can be very helpful in narrowing the differential
diagnosis, especially when
combined with other clinical data and
associated CT scan findings.
Bronchiolitis obliterans organizing
pneumonia (BOOP) is a disease characterized
histologically by the presence of
granulation tissue plugs within respiratory
bronchioles and alveolar ducts, and
organizing pneumonia extending into
the surrounding alveoli. 26 CT scans
show patchy GGO (in 8 to 75% of
patients), nodules, or areas of consolidation
with a predominantly peripheral
(50% of patients), bilateral, and nonsegmental
distribution (figure 10). 27-29
Collagen vascular diseases are multisystem
disorders characterized by
vascular changes, fibrosis, and inflammation
of connective tissue. Specific
diseases include progressive systemic
sclerosis (scleroderma), systemic lupus
erythematosus, polymyositis/dermatomyositis,
rheumatoid arthritis, and Sjogren’s
syndrome. GGO is seen on CT
scanning in 63 to 100% of these
patients, 30 and is a sign of active inflammation
in the absence of significant honeycombing,
bronchiectasis, or other
signs of lung fibrosis. 31
Pulmonary contusion results from
trauma to the chest wall and lung, with
Causes of a peripheral pattern of
GGO on CT scanning
• Bronchiolitis obliterans organizing
pneumonia (BOOP)
• Collagen vascular disease
• Contusion
• Desquamative interstitial
pneumonitis
• Drug toxicity
• Eosinophilic pneumonia
• Fibrosis
• Sarcoidosis
Table 5
bleeding into the air spaces and lung
interstitium. Generally, the cause is a
compression injury with significant
kinetic energy absorption adjacent to the
site of chest wall injury. The CT scan
appearance of lung contusion is that of
ill-defined areas of GGO, consolidation,
or both, usually with a peripheral, nonanatomic
distribution (figure 11). 32,33
Desquamative interstitial pneumonitis
is characterized by alveolar filling with
macrophages. The HRCT scan findings
consist of GGO with a lower lung zone
(73%) and a peripheral (59%) predominant
distribution (figure 12). Usual interstitial
pneumonitis, or idiopathic
pulmonary fibrosis, results in a similar
distribution of GGO on CT scanning but
typically with more areas of honeycombing
and traction bronchiectasis
(figure 13).
Pulmonary toxicity has been associated
with numerous drugs and a variety
of radiographic and CT patterns. CT
scanning shows nodular areas of GGO
and consolidation, often with a peripheral
distribution. 35,36
Pulmonary eosinophilia occurs with a
variety of conditions or diseases, or can
be idiopathic. Chronic idiopathic
eosinophilic pneumonia is characterized
by multiple dense areas of <strong>opacity</strong> on
chest radiographs and CT scans. In one
study of patients with chronic
eosinophilic pneumonia, the most common
HRCT finding was GGO, usually
adjacent to areas of consolidation, with
a peripheral distribution. 37 Acute idiopathic
eosinophilic pneumonia is characterized
by diffuse GGO and
micronodules on chest radiographs and
CT scans, often in a bronchovascular
distribution. 38
20 APPLIED RADIOLOGY, December 1998