1- Pulmonary Parenchymal Conditions:
Emphysema and Bullous Disease: Fig. 1 Fig. 2
Emphysema and bullae are related to patients who have a smoking habit or alpha-1 antitrypsin deficiency.
There are also congenital entities that can manifest as emphysema and bullous disease.
When the distribution of this affectation is asymmetric,
affecting one lobe more than others,
the imaging findings can give a hyperlucent lung image.
Pneumatocele: Fig. 3 and Fig. 4
Pneumatoceles can occur after infection,
trauma or barotrauma.
The most frequent with post-infectious pneumatoceles.
They usually affect children under 3 years old secondary to staphylococcal pneumonia.
They appear after a week of the beginning of the infection and usually disappear a few weeks after treatment.
On radiography and CT,
they are observed as a well-defined fine-walled cystic structure in the pulmonary parenchyma.
It can be filled only with gas or have an air-fluid level inside it.
The main complication is the rupture that a tension pneumothorax can produce.
2- Airway Conditions:
Swyer-James Syndrome or MacLeod Syndrome:
It is a syndrome characterized by a unilateral hyperlucent lung,
a small pulmonary artery and an incomplete filling of the peripheral bronchioles with contrast material in bronchography.
Fig. 5
It is a pathology acquired,
secondary to infectious obliterative bronchiolitis with destruction of the distal air space in infancy or childhood.
Microorganisms such as the respiratory syncytial virus,
adenovirus and mycoplasma are usually involved.
The affectation can be unilateral,
affecting one or more lobes,
or bilateral.
The affected lung parenchyma appears hyperlucent,
due to the air trapping,
produced by the bronchiolar obstruction.
It is associated with a decrease in the number and size of the blood vessels.
The formation of bronchiectasis can also be observed.
Fig. 6
The high-resolution CT during the expiration helps to determine more precisely the extent of the affectation,
which can be underestimated in the radiography.
Bronchial Atresia: Fig. 7
It is a lung affectation at segmental level,
being the apicoposterior segment of the left upper lobe the most frequently affected.
It is usually an incidental finding at imaging in asymptomatic patients.
At radiography or CT,
hyperinflation and hyperlucency of the affected lung due to air trapping is observed,
associated with a relative decrease of the pulmonary blood vessels.
In the airways there is usually impacted mucus that mimic a nonenhancing perihilar mass.
Other causes: foreign bodies in airway,
endobronchial mass.
3- Vascular Conditions:
Unilateral Pulmonary Agenesis:
It is a congenital anomaly that consists of the absence of unilateral development of pulmonary parenchyma,
airways and pulmonary artery.
It is more frequent on the left side,
however,
it has a worse prognosis if it affects the right lung.
Some patients may be asymptomatic at birth and present symptoms only from childhood.
On radiography and CT,
unilateral pulmonary agenesis is seen as an opaque hemithorax with a marked hyperexpansion and hyperlucency of the contralateral lung.
In some cases the agenesis is only of the pulmonary artery; in this case there is a collateral vascularization that irrigates the affected lung.
Anyway,
there is a decrease in blood vessels which manifests as a more hyperlucent lung (contrary to what happens if the agenesis is complete). Fig. 8
Scimitar Syndrome: Also called Hypogenetic lung syndrome or pulmonary venolobar syndrome
It is a form of abnormal pulmonary venous drainage that can affect an entire lung,
typically the right lung,
which is usually hypoplastic.
The anomalous vein (Scimitar vein) can drain to different sites: infradiaphragmatic inferior vena cava,
suprahepatic veins,
portal vein,
azygo vein,
coronary sinus or right atrium.
On radiography and CT,
a small ipsilateral lung and a contralateral hyperinflation and hyperlucent lung are observed.
The Scimitar vein may appear as a curvilinear tubular opacity along the border of the right side of the heart.
Other causes: Unilateral pulmonary central embolism,
Pulmonary hypoplasia.
4- Involvement of the pleural or chest wall:
Poland Syndrome: ( Fig. 9 ; Fig. 10 )
Corresponds to a congenital anomaly characterized by the partial or complete absence of the pectoralis major,
pectoralis minor,
latissimus dorsi,
anterior serratus,
and intercostal muscles,
ipsilateral rib anomalies such as hypoplasia or absence of ribs; and mammary tissue hypoplasia or aplasia.
On radiography the affected hemithorax is more hyperlucent,
similar to the findings visualized in a mastectomy.
CT or MRI confirm the absence of unilateral development of the muscles of the thoracic wall and / or ribs.
Anterior Pneumothorax: Fig. 3 and Fig. 4
Corresponds to the extrapulmonary gas located in the anterior pleural space,
visualized on a supine chest radiograph.
Other causes: scoliosis,
unilateral mastectomy.
5- Technical Defects:
The most frequent cause is the rotation of the patient and is due to the asymmetric absorption of x-rays in the thorax.