JC- Expanding upon the Unilateral Hyperlucent Hemithorax in Children1

Dillman et. al

RadioGraphics 2011; 31:723–741

PRESENTED – DR. ANNIE AGARWAL

Unilateral hyperlucent hemithorax is a common pediatric chest radiographic finding .

It may result from congenital or acquired conditions involving the pulmonary parenchyma, airway, pulmonary vasculature, pleural space, and chest wall, as well as from technical factors such as patient rotation.

When evaluating a patient with this finding, it is important to establish whether the apparent unilateral hyperlucent hemithorax is truly too lucent (hypoattenuating) or if the contralateral hemithorax is too opaque (hyperattenuating).

Lung defect depends upon the pulm vsl abnormality n not on the size of the lung.

Introduction

When detected at frontal radiography, further evaluation with additional radiography, computed tomography (CT), or bronchoscopy may be required.

Pulmonary Parenchymal Conditions

Rare in children, with both lungs affected in most cases.

CAUSES: ◦ idiopathic bullous emphysema, ◦ late sequelae of chronic lung disease associated

with premature birth (bronchopulmonary dysplasia),

◦ pulmonary interstitial emphysema (as well as persistent pulmonary interstitial emphysema) in neonates.

Unilateral Emphysematous or Bullous Disease

Emphysematous changes in bronchopulmonary dysplasia may appear asymmetric, an appearance that sometimes is due to the presence of large bullae

Unilateral hyperlucent hemithorax in an 18-year-old man with a history of chronic lung disease associated with premature birth (at 26 weeks gestation) and severe right lung emphysema.

Pulmonary interstitial emphysema, a form of barotrauma that results from positive pressure ventilation, appears as numerous cystic lucencies within the interstitium at both radiography and CT.

It may be segmental, lobar, unilateral, or bilateral Left lung barotrauma due to positive pressure ventilation in

a 13-day-old neonate.

discrete, thin-walled, gas-containing collections within the lung parenchyma.

They may be Post-infectious or post-traumatic, or result from positive pressure ventilation– related barotrauma and ingestion of caustic material (eg, hydrocarbons).

Postinfectious pneumatoceles are most common among infants and young children, (70% in children under the age of 3 years) and most frequently complicate staphylococcal pneumonia.

Less common causative organisms include Pneumococcus, Klebsiella pneumoniae, E. coli, and H. influenzae.

Pneumatoceles typically appear within 1 week of onset of infection, and most spontaneously disappear within weeks to months after the infection has resolved.

Rarely, persistent pneumatoceles may require percutaneous catheter drainage or surgical management.

Pneumatocele

Post-traumatic pneumatoceles result from blunt trauma, with gas becoming entrapped within areas of pulmonary parenchymal laceration. These are observed within hours of the trauma, noted at initial posttraumatic chest radiography, and spontaneously resolve within 3 weeks. These may be solitary or multiple and generally spare the lung apices.

At chest radiography and CT, pneumatoceles appear as

well-defined pulmonary parenchymal cystic structures, usually with a thin wall. They may be entirely filled with gas, or an air-fluid level may be seen.

C/L mediastinal shift - large pneumatocele. Compressive atelectasis - result of mass effect, may affect

adjacent pulmonary parenchyma or the contralateral lung. Rupture of large pneumatoceles complicated by tension

pneumothorax. A coexisting pulmonary contusion is commonly observed in

the setting of posttraumatic pneumatoceles.

Pneumatocele in a 3-month-old girl with a history of chronic lung disease associated with premature birth and methicillin-resistant Staphylococcus aureus (MRSA) pneumonia. She was born at 26 wk gestation.

Airway Conditions

most common between 6 months and 3 years of age, but it may occur earlier or later in childhood.

Most are diagnosed within hrs to a few days after the event, rarely, weeks to months later.

Most aspirated foreign bodies are located within the right main-stem bronchus :◦ larger diameter◦ more vertical orientation compared with the left bronchus ◦ the carina is usually shifted to the left of the midline.

less commonly located within the trachea or larynx.

may be life threatening, and children may present with cough, respiratory difficulty, wheezing, hemoptysis, or recurrent pneumonia.

Most aspirated foreign bodies are organic (eg, food) and are not radiopaque at chest radiography

Foreign Body Aspiration

secondary radiographic signs:◦ ipsilateral pulmonary hyperinflation due to air trapping, ◦ ipsilateral pulmonary hyperlucency ◦ pulmonary vasoconstriction, and ◦ ipsilateral postobstructive atelectasis or pneumonia.

There are specific techniques that may help accentuate air trapping related to foreign body aspiration. ◦ In older, cooperative children, inspiratory and expiratory phase images

may demonstrate failure of the affected lung to collapse at expiration. ◦ In younger, less cooperative children, lateral decubitus images may

depict failure of the affected lung to collapse when in a dependent position

20%–35% children have normal chest radiograph.

Chronic aspiration complicated by bronchiectasis and abscess formation.

Although chest CT with virtual bronchoscopy has been

described as a useful tool for depicting aspirated foreign bodies, it is not commonly employed.

Aspirated foreign body in a 19-month-old boy with a persistent cough.

PA chest radiograph Right lateral decubitus

Left lateral decubitus

Thought to be secondary to infectious obliterative bronchiolitis and distal airspace destruction in infancy or childhood

Adenovirus, respiratory syncytial virus, and Mycoplasma organisms.

may be either unilateral (affecting one or more lobes) or bilateral .

C/F -chronic cough, wheezing, or recurrent pneumonia, although some individuals may be asymptomatic.

At pulmonary function testing, an obstructive lung disease pattern seen.

In appropriate clinical setting, radiography and CT usually are sufficient to diagnose the condition.

detected as early as 9 months after the initial infectious insult.

Swyer-James Syndrome/ Macleod syndrome

Affected lung parenchyma appears hyperlucent, a result of air trapping due to bronchiolar obstruction, and blood vessels within the affected lung are decreased in number and caliber.

Affected lung commonly appears small, although hyperexpansion due to collateral ventilation and air trapping may be seen.

Incomplete filling of ipsilateral peripheral bronchioles with contrast material at bronchography.

Ipsilateral bronchiectasis also is a common finding.

The use of high-resolution CT during expiration may help determine the extent of disease (which is seen as air trapping) which the chest radiography fails to depict.

Affected pulmonary parenchyma also may demonstrate a mosaic attenuation pattern, a result of areas of preserved normal lung.

Presumed Swyer-James syndrome in a 16-year-old girl with a history of severe viral respiratory infection as a child and fixed obstructive airway disease at pulmonary function testing.

or congenital pulmonary overinflation,

most commonly affects a single lobe of the lung, although multiple lobes or specific lobar segments may be involved.

The left upper lobe is most commonly affected, although the right middle and upper lobes are also commonly involved.

Causes:◦ deficient bronchial cartilage (bronchomalacia), ◦ endobronchial lesions (eg, mucosal web), ◦ extrinsic bronchial compression (eg, an anomalous vascular structure or

mass)—all of which result in airway luminal narrowing and obstruction.

The obstructed lung becomes hyperinflated by collateral air drift. 15% have ass. congenital heart disease such as PDA & VSD.

C/F- respiratory distress during early childhood, with 50% presenting during the first 2 days of life.

Congenital Lobar Emphysema

On chest radiographs obtained immediately after birth: appears as a hazy masslike opacity, a result of trapped fetal lung fluid.

Congenital lobar emphysema of the right upper lobe in a 1-day-old boy. Chest radiograph at 1 day. Sagittal reformation CT acquired 6 mths later.

A few hours to several days after birth, this fluid is replaced with air, and affected lung appears hyperlucent and hyperexpanded at both X ray and CT.

Atelectatic collapse of adjacent pulmonary parenchyma andC/L mediastinal shift may be present, a result of mass effect of the hyperinflated lung.

Vascular structures within the affected lung appear attenuated and displaced.

Left-upper-lobe congenital lobar emphysema in a 2-day-old boy

Pediatric endobronchial tumors are rare

Tumors that may arise from the tracheobronchial tree- carcinoid tumor (most common), mucoepidermoid carcinoma, and inflammatory (myofibroblastic) pseudotumor.

At radiography, a circumscribed central parahilar mass may or may not be present in the setting of carcinoid tumor.

80% endobronchial carcinoid tumors are central in location. Endobronchial tumors rarely are peripheral (manifesting as SPN).

Secondary signs: ipsilateral air trapping, mucus plugging (seen as branching V- and Y-shaped areas of opacification), and postobstructive atelectasis or pneumonia.

At CT, bronchial and endobronchial carcinoid tumors usually are parahilar and well defined with homogeneous hyperenhancement, and eccentric calcifications may be present.

Masses arising from the airway may have a substantial extrabronchial component.

Endobronchial Mass

Carcinoid tumor in a 16-year-old boy. Axial CECT image shows a hyperenhancing mass (arrows) arising from the central right bronchial tree (*). A branching Y-shaped area of the right lung with peripheral areas of low attenuation (arrowheads) is also seen, a result of mucus impaction within the airway.

Mucoepidermoid carcinoma arising from the left main-stem bronchus in a 15-year-old girl. (a) Axial CECT image shows a hyperenhancing mass (arrow) within the left main-stem bronchus. (b) Volume-rendered CT image shows air trapping within the left lung and an endobronchial filling defect (arrow). (c) Reconstructed endobronchial CT image shows the mass (*) within the left main-stem bronchus.

result from both congenital and acquired extrinsic bronchial compression of various causes, and a variety of mediastinal masses may exert substantial mass effect on the airway with resultant air trapping.

Pericardial lipoblastoma : PA chest radiograph (a) and axial

CT image (b) show a hyperexpanded, hyperlucent, hypovascular left lung.

Axial CT image shows the mass (*) extrinsically compressing the left main-stem bronchus (arrow).

Extrinsic Bronchial Compression

Several vascular structures also may cause substantial bronchial narrowing and manifest with either air trapping or atelectasis, such as major aortopulmonary collateral arteries, dilated or anomalous pulmonary arteries (including pulmonary slings), and repaired interrupted aortic arch .

Tetralogy of Fallot, pulmonary atresia, and major aortopulmonary collateral arteries in a 1-month-old boy. (a) AP chest radiograph shows a hyperlucent, hyperexpanded, hypovascular right lower lobe. (b) Coronal reformatted contrast-enhanced CT image shows multiple large aortopulmonary collateral arteries, which surround and compress the right main-stem bronchus (arrow).

Accidental bronchial endotracheal-tube intubation is a common cause of unilateral hyperlucent hemithorax.

Hyperaeration of the i/l lung, and the c/l lung may appear collapsed, a result of generalized hypoaeration and occlusion of its main-stem bronchial orifice.

Complications: ipsilateral barotrauma from positive pressure ventilation (eg, pneumothorax) and hypoxia.

Bronchial Endotracheal-Tube Intubation

focal congenital obstruction of the airway, typically occurs at the segmental level and

most commonly affects the apicoposterior segment of the left upper lobe,

C/F - asymptomatic, and the condition is incidentally discovered at imaging.

At radiography and CT, hyperinflation and hyperlucency of the affected lung due to air trapping, with a relative paucity of pulmonary blood vessels.

a branching, nonenhancing parahilar masslike (or tubular) abnormality is commonly observed, a result of mucus impacted within more peripheral dilated airways.

Bronchial Atresia

Vascular Conditions

complete, unilateral absence of lung parenchyma and associated blood vessels and airways.

results from an insult during the 4th wk of gestation.

Failure of the lung to develop- left > right

patients with an absent right lung have a worse prognosis. associated with pulmonary sling (passage of the left

pulmonary artery between the trachea and esophagus) and complete tracheal rings.

C/F – asymptomatic in childhood and the condition may manifest in adulthood.

Unilateral Pulmonary Agenesis

opaque hemithorax. At both radiography

and CT, resultant I/L mediastinal shift and marked C/L pulmonary hyperexpansion and hyperlucency are seen.

CHEST RADIOGRAPHY :

CT : I/L lung parenchyma, blood vessels, and airways are absent.

Volume-rendered images of the airway may depict narrowing due to tracheal kinking from mediastinal shift, extrinsic impression from a pulmonary sling, and complete tracheal rings.

CECT image shows hyperinflation of the right lung and absence of the left lung and left pulmonary artery. White * = main pulmonary artery, black * = right pulmonary artery.

Right pulmonary agenesis in a 3-day-old girl. (a) Axial CECT image shows absence of the right lung. The left

lung is hyperinflated, and the left pulmonary artery (*) courses between the trachea and esophagus, findings indicative of pulmonary sling. The trachea is narrowed by the anomalous left pulmonary artery.

(b) Volume-rendered CT image (posterior view) of the airway and left lung shows kinking of the trachea (arrow), a result of mediastinal shift. Complete tracheal rings (arrowheads) also are seen.

associated with decreased numbers and sizes of alveoli, airways, and blood vessels, and it results from incomplete lung development.

It may be either primary or secondary to intrauterine processes that affect lung growth, such as congenital diaphragmatic hernia, and it may be complicated by recurrent infection and atelectasis.

At chest radiography and CT, the affected lung appears small and may be hyperlucent due to oligemia.

The contralateral lung may appear hyperlucent, a result of compensatory hyperexpansion.

The ipsilateral pulmonary artery usually appears diminutive, and ipsilateral mediastinal shift is present.

Unilateral Pulmonary Hypoplasia

Right pulmonary hypoplasia in a 1-week-old boy. (a) AP chest radiograph shows a hyperexpanded, hyperlucent left lung and dextroposition of the heart. (b) Axial contrast-enhanced CT image shows a small right pulmonary artery (arrowhead). The left pulmonary artery (arrow) is normal in caliber.

there is unilateral absence of a central pulmonary artery.

abnormal development of the sixth aortic arch in utero, and the affected side typically is opposite the aortic arch.

More peripheral ipsilateral pulmonary arteries are supplied by systemic collateral arteries including the patent ductus arteriosus (PDA), aortopulmonary and bronchial arteries, subclavian artery, internal mammary artery, and intercostal arteries.

Ass. with other cardiovascular anomalies, such as TOF. PDA and pulmonary arterial hypertension are associated with

decreased survival during infancy.

Proximal Interruption of the Pulmonary Artery (Absent Pulmonary Artery)

At chest radiography and CT: ipsilateral lung usually appears small, a finding likely due

to hypoplasia, and the contralateral lung appears hyperlucent and hyperexpanded.

I/L shift of the mediastinum and anterior junction line often is present.

Other findings:◦ i/l absent or diminutive appearance of pulmonary hilum, ◦ i/l narrowed intercostal spaces, ◦ occasionally, rib notching.

Other CT findings:◦ nonvisualization of the i/l central pulmonary artery,

reconstitution of more peripheral pulmonary arteries from collateral vessels, and linear areas of opacification perpendicular to the pleura, a finding thought to represent transpleural collateral blood vessels.

Proximal interruption of the left pulmonary artery PA chest radiograph shows mild hyperexpansion and associated hyperlucency of

the right lung. The mediastinum is shifted to the left, and the aortic arch is right sided.

(b) CECT volume-rendered image shows absence of the mediastinal portion of the left pulmonary artery, with a relative paucity of more peripheral left pulmonary arterial structures (*). These structures are reconstituted from collateral vessels, including a PDA (arrow).

also known as hypogenetic lung syndrome or pulmonary venolobar syndrome

is a form of partial anomalous pulmonary venous connection that involves all or a portion of the right lung.

The anomalous pulmonary vein (the scimitar vein) may drain into a variety of structures, including the infradiaphragmatic inferior vena cava (IVC), suprahepatic IVC, hepatic veins, portal vein, azygos vein, coronary sinus, and right atrium.

The ipsilateral lung typically is hypoplastic, and the affected hemithorax almost always is on the right side.

The clinical significance- relates in part to the degree of left-to-right shunting of blood and associated congenital heart disease.

Scimitar Syndrome

At chest radiography and CT, the ipsilateral lung typically appears small, and the contralateral lung usually is hyperinflated and hyperlucent.

At radiography, the scimitar vein may appear as a curvilinear tubular opacity along the border of the right side of the heart.

The mediastinum and heart are shifted toward the affected side (typically the right side), and the ipsilateral pulmonary hilum may appear small, a finding due to pulmonary artery hypoplasia or aplasia.

Systemic arterialization of the right lung (without sequestration) also may be present, with the anomalous artery arising from the abdominal aorta or a visceral artery.

Scimitar syndrome. (a) AP chest radiograph shows mild hyperinflation of the left lung with slightly increased vascularity, a small right lung, and rightward mediastinal shift.

(b) Axial CECT image in another child with scimitar syndrome shows mild hyperinflation of the left lung. The right lung and pulmonary artery (arrowhead) are small, and an anomalous pulmonary vein (arrow) is seen within the right posterior hemithorax.

Unilateral congenital pulmonary lymphangiectasia has also been reported to be a cause of a unilateral hyperlucent hyperexpanded lung in neonates.

A massive central pulmonary embolus may cause considerable unilateral pulmonary oligemia, and it also may manifest with a unilateral hyperlucent hemithorax at radiography.

Other Vascular Conditions

In unilateral pulmonary venous atresia, the affected lung typically appears small and hyperattenuating, a result of pulmonary venous congestion, and the unaffected lung generally appears relatively hyperlucent and may be hyperinflated.

Congenital left pulmonary venous atresia in a 2-day-old boy. Coronal reformatted CT image shows unilateral pulmonary edema in the left lung, with interlobular septal thickening (Kerley lines) and relative hyperlucency of the right lung.

Pleural Space Conditions

Gas located within the anterior pleural space on a supine chest radiograph may have - “large hyperlucent hemithorax sign” and most common in neonates.

The ipsilateral hemithorax may also appear slightly enlarged.

This finding should not be dismissed as a result of artifact

It may be confirmed with either a lateral or decubitus radiograph.

Anterior Pneumothorax

Dependent, layering fluid within the pleural space may cause the contralateral hemithorax to appear hyperlucent, a false finding.

The presence of a c/l layering pleural effusion may be confirmed by obtaining a lateral decubitus radiograph (with the more radiopaque hemithorax positioned down), which will depict layering pleural fluid along the dependent lateral chest wall,

or at ultrasonography.

C/L Layering Pleural Effusion

a 9-day-old girl who underwent surgical repair of TOF and open median sternotomy. AP chest radiograph shows an apparent hyperlucent right lung, due to a layering left pleural effusion. A left apical cap is seen, as well as fluid tracking along the left lateral chest wall .

may be either congenital or acquired.

Congenital diaphragmatic hernias are most commonly left-sided and posterior in location (so-called Bochdalek hernias). Intraabdominal structures, including the stomach and small and large intestines, as well as solid organs, may pass through these diaphragmatic defects and reside (either partially or completely) within the thorax.

When gas-filled stomach or bowel loops are present within the chest, the affected hemithorax may appear hyperlucent.

Gastrothorax is a rare complication of upper abdominal trauma and may also manifest as a unilateral hyperlucent hemithorax that mimics an ipsilateral tension pneumothorax.

Congenital Diaphragmatic Hernia and Traumatic Diaphragm Rupture

Congenital left diaphragmatic hernia in a 1-day-old girl.

Chest radiograph shows the left mid and lower hemithorax, which appear hyperlucent due to herniation of gas-filled loops of bowel and stomach into the left thoracic cavity (arrowheads).

A ng tube is seen within the intrathoracic stomach, and the left lung is hypoplastic (*).

Chest Wall Conditions

associated with a variety of congenital chest wall anomalies including ◦ unilateral partial or complete absence of muscles

such as the pectoralis major, pectoralis minor, latissimus dorsi, serratus anterior, and intercostal muscles;

◦ ipsilateral rib anomalies such as hypoplasia or absence of ribs;

◦ mammary tissue hypoplasia or aplasia.

Scoliosis and upper extremity anomalies such as syndactyly also may be present.

Poland Syndrome

At chest radiography, the affected hemithorax often appears hyperlucent, an appearance that mimics that of radical mastectomy in adults.

Both chest radiography and CT depict absent or hypoplastic ipsilateral ribs and scoliosis when present.

At CT, ipsilateral partial or complete absence of chest wall musculature is seen.

Ipsilateral mammary tissue may appear hypoplastic (compared with the contralateral breast) or completely absent.

Thoracic spine scoliosis is a rare cause of unilateral hyperlucent hemithorax .

Hyperlucency is due to substantial axial rotation of the spinal curvature, which leads to asymmetric absorption of the x-ray beam by the chest wall.

Scoliosis

Patient rotation - most common cause. The area of hyperlucency is always on the side

toward which the patient rotates (independent of AP or PA technique) and results from asymmetric absorption of the x-ray beam by the chest wall .

Evaluation of the appearance of the ribs, clavicles, spinous processes, sternal ossification centers, and sternal wires (when present) on frontal chest radiographs may help determine the extent of patient rotation.

Lateral decentering (positioning the x-ray tube lateral to the patient’s midline) also may cause a unilateral hyperlucent hemithorax to be seen.

Technical Causes

Hyperlucent right hemithorax resulting from patient rotation in a 2-week-old boy who underwent cardiac surgery. (a) AP chest radiograph shows a hyperlucent right hemithorax. The asymmetric appearance of the ribs and clavicles indicates that the patient is rotated to the right. Midline sternotomy wires are also displaced to the right. (b) Follow-up AP radiograph obtained 6 hours later, with the patient in a more appropriate position, shows no abnormal hyperlucent right hemithorax.

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