Although conventional chest radiography remains the main imaging modality for emergency neonatal chest imaging, certain conditions are better evaluated with ultrasonography, computed tomography, and magnetic resonance imaging. This article reviews the radiographic findings and differential diagnoses for tension pneumothorax, congenital lesions in the neonate, and acquired lesions ocurring in the perinatal period.
Drs. Sumner, Cox, and Auringer are from the Department of
Radiology at Wake Forest University Baptist Medical Center in
Usually, emergency neonatal chest imaging is required for causes
of respiratory distress necessitating surgery in the newborn.
Although conventional chest radiography remains the main imaging
modality, certain conditions are better evaluated with
ultrasonography, computed tomography (CT), and magnetic resonance
(MR) imaging. The appearance of the initial chest x-ray determines
which additional imaging procedure(s), if any, will be used. For
the purpose of this article, the three conditions that predispose
to intervention or surgery are: tension pneumothorax, congenital
lesions in the neonate, and acquired lesions occurring in the
Tension pneumothorax may be spontaneous in the newborn or may
develop later as a result of barotrauma or positive pressure
ventilation, frequently associated with pulmonary interstitial
emphysema. Conventional single-view supine radiographs of the chest
are often diagnostic, as pleural air outlines the edge of the lung.
Additional findings include: inversion of the ipsilateral
hemidiaphragm, contralateral mediastinal shift, and herniation of
the parietal pleura across the midline due to mass effect of
tension pneumothorax (figure 1). Because the lung falls
posteriorly, its lateral edge may not be outlined by pleural air in
the supine position. If a pneumothorax is suspected, additional
views, such as cross-table lateral or lateral decubitus chest films
with the side of interest positioned uppermost, are often helpful.
A chest tube should be inserted anteriorly for optimal
decompression of a tension pneumothorax.
In the newborn, congenital lesions requiring intervention or
surgery include three "C" lesions (congenital diaphragmatic hernia
[CDH], congenital cystic adenomatoid malfunction [CCAM], and
congenital lobar emphysema [CLE]), plus sequestration. These "C"
lesions ultimately produce a large lucent or cystic-appearing
hemithorax. Sequestration usually presents as a solid lesion
because it is airless and remains opaque on follow-up radiographs
of the chest.
Congenital diaphragmatic hernia
Bochdalek hernia is a posterolateral developmental defect of the
diaphragm. It results from maldevelopment or failure of fusion of
the pleuroperitoneal membrane (or both). It occurs in approximately
1 of every 2000 to 5000 births and occurs on the left five times as
frequently as on the right.
Initially, CDH may appear as a large intrathoracic mass of
soft-tissue density, progressing to its more characteristic
cystic-mass appearance after several hours (figure 2A and B). Other
classic findings include absence of bowel gas with a scaphoid
abdomen; and Morgagni hernia, which usually develops later in life
and is an anterior hernia that results from failure of fusion of
the septum transversum with the body wall.
Differential diagnosis includes CLE, CCAM, sequestration, and
bronchogenic cysts. Air rapidly fills bowel loops after
air-swallowing, resuscitative efforts, or a combination of these,
thereby eliminating diagnoses other than CDH. If necessary, careful
injection of several cubic centimeters of air through a nasogastric
tube will distinguish CDH from other considerations. Sonography of
the chest is confirmatory in that it reveals peristalsis of
fluid-filled bowel loops and mesenteric vessels in the herniated
Clinically, the infant usually shows symptoms of severe
respiratory compromise. Placement of a nasogastric tube helps to
decompress the bowel and reduces the mass effect. If fetal
circulation persists and pulmonary hypertension ensues,
extracorporeal membrane oxygenation (ECMO) may be necessary for
survival (figure 2C).
Congenital cystic adenomatoid malformation
A developmental abnormality of the lung, CCAM is characterized
by adenomatoid proliferation and bronchial structures forming cysts
at the expense of normal alveoli. Clinical clues include maternal
polyhydramnios and fetal hydrops, anasarca, or both. Polyhydramnios
is secondary to fetal esophageal compression with impaired fetal
swallowing; hydrops may be due to fetal inferior vena cava or heart
compression, and anasarca may also be related to intrauterine vena
cava obstruction. From 50% to 85% of neonates with CCAM have
respiratory compromise that ultimately requires surgery.
CCAM is usually unilateral, occurring in a single lobe in 95% of
It may be airless initially, but unlike sequestration, it
communicates with the tracheobronchial tree. Anatomic and clinical
differences distinguish three types of CCAM. Type 1 (50% of cases
of CCAM) contains few large cysts (3 to 10 cm), type 2 (40% of
cases) contains numerous small- to medium-size cysts (0.5 to 3 cm),
and type 3 (10% of cases) is mostly solid with smaller cysts (<2
cm). The prognosis is best for patients with type 1. With type 2,
the prognosis depends upon associated anomalies (often
genitourinary). Type 3 is associated with the worst prognosis (80%
mortality) because of its large size, with resultant cardiovascular
compromise and pulmonary hypoplasia.
In the newborn, radiographs of the chest reveal an opaque
hemithorax that, in type 1 and type 2 malformations, has
fluid-filled cysts becoming air-filled over the course of hours,
days, or weeks to produce a cystic-appearing hemithorax (figure
3A). Chest sonography in patients with type 1 or type 2 CCAM may
demonstrate fluid-filled cystic spaces (figure 3B). Chest
radiographs in type 3 malformation differ from type 1 and type 2
malformations by showing a persistent opacity (figure 3C); chest
sonography reveals a solid structure (figure 3D). Computed
tomography reveals cystic changes associated with abnormal soft
tissue in types 1 and 2 (figure 3E).
Congenital lobar emphysema
Congenital lobar emphysema consists of progressive lobar
overdistension without destruction of alveolar septae. CLE usually
produces respiratory compromise in the newborn. It has a
male:female incidence of 3:1. The left upper lobe is involved in
43% of cases, right middle lobe in 32%, and the right upper lobe in
The etiology of CLE is unknown in more than 50% of cases; often it
is believed to be secondary to a congenital bronchial abnormality
that causes a high-grade partial obstruction. The involved lobe may
be fluid-filled at birth, appearing as a large opaque hemithorax
(figure 4A). Subsequent chest radiographs reveal increasing
radiolucency as fetal lung fluid is replaced by air (figure 4B). If
an entire lung appears overinflated, a contrast swallow may help to
exclude a bronchogenic cyst or obstructing vascular abnormality. CT
demonstrates the hyperlucent lobe with attenuated or thin vascular
structures (figure 4C).
Definitive treatment of CLE is lobectomy to prevent progression of
symptoms and repeated infections.
The term sequestration was introduced by Pryce in 1946 to
describe a disconnected bronchopulmonary mass or cyst with an
anomalous arterial supply.
Thus, sequestration has no normal connection with the
tracheobronchial tree or with the pulmonary arteries. It may result
from an abnormally caudal accessory budding of the foregut,
dissociating it from the trachea while retaining its embryonic
systemic arterial connection.
Classically, intralobar sequestration (ILS) and extralobar
sequestration (ELS) are defined according to their relationship to
lung parenchyma. Shanji et al
support the theory that ILS occurs earlier and results in
incorporation of the sequestered lung within the lung without a
separate pleural covering; ELS occurs later and has its own pleural
ILS is usually drained by pulmonary veins, whereas ELS is usually
drained by the azygos venous system; however, this distinction is
variable. Arterial supply to ILS derives from the thoracic aorta in
80% to 90% of cases, whereas ELS may be supplied by the thoracic
aorta or supraceliac infradiaphragmatic aorta. ILS, the most common
form, accounts for 75% of cases. It most often manifests during
childhood or early adulthood with recurrent infection; its vascular
supply is usually best demonstrated with MR imaging. ELS is
encountered frequently in the neonate with respiratory distress,
cyanosis, and feeding disorders. Associated congenital anomalies
occur in more than 50% of patients with ELS; the most common is
diaphragmatic hernia (30%).
Associated congenital anomalies are rare with ILS.
Demonstrating the vascular anatomy in ILS may be difficult with CT
because the vessels are small; Doppler sonography or MR imaging may
Sequestration may appear as solid or hyperlucent areas on chest
radiographs. ILS frequently is hyperlucent and may be difficult to
distinguish from types 1 and 2 CCAM. ELS is usually solid and,
therefore, is distinguishable from types 1 and 2 CCAM; but it may
be difficult to distinguish from type 3 CCAM. Because ELS is the
most common type of sequestration in neonates and it occurs most
commonly on the left side (90%), usually in a subpulmonic location,
it should be the primary differential consideration for a solid
lower-lung mass in a neonate (figure 5). Surgical resection is
usually performed for confirmation and to prevent recurrent
Acquired lesions occurring in the perinatal period are pulmonary
interstitial emphysema (PIE) and bronchopulmonary dysplasia
Pulmonary interstitial emphysema
PIE results from air dissection into the perivascular and
peribronchial spaces. It occurs most often in neonates requiring
assisted ventilation for severe respiratory distress syndrome
caused by rupture of overdistended alveoli into the pulmonary
interstitium. Chest radiographs reveal linear lucencies radiating
from the hilar regions; because they are located within the
noncompliant lung, these lucencies usually do not empty on
expiration (figure 6).
PIE occurs in two forms: acute and chronic (persistent). Acute
PIE can resolve or persist. Recognition of PIE itself is important,
but its clinical significance is that it may be the precursor of
such air-block complications as pneumothorax, pneumomediastinum,
and pneumoperitoneum. Alveolar rupture may also permit air to enter
the pulmonary venous system, causing fatal systemic air
As previously mentioned, pneumothorax may produce mass effect
requiring decompression with a chest tube. Emergency exploratory
surgery is frequently required to determine the cause of
pneumoperitoneum. Pneumomediastinum is more often self-limiting
and, therefore, less likely to necessitate surgical
Persistent PIE (PPIE) is much less common than acute PIE. It
typically occurs in neonates with surfactant deficiency, but can
occur in those with no history of lung disease or assisted
Chest radiographs show progressive expansile cystic areas (figure
7A and B). The air cysts are usually isolated to one or two lobes,
can be as large as 3 cm, and can produce mediastinal shift and
CT may help to differentiate PPIE from other causes of multicystic
abnormality seen on chest radiographs, such as CCAM and CLE.
In patients with PPIE, abnormal air collections are located in the
interstitial space, and CT shows interstitial air surrounding
bronchovascular bundles, thereby documenting the interstitial
location of the cystic air spaces. The bronchovascular bundles
appear as soft-tissue-attenuation nodular or linear densities in
the center of the air-filled cyst(s) (figure 7C).
By contrast, chest CT in patients with CCAM shows cystic changes
associated with abnormal soft tissue (figure 3E). Chest CT in those
with CLE shows attenuated thinned vascular structures at the
periphery of the expanded air spaces, rather than in the center as
with PPIE (figure 4C). Initial treatment of PPIE with decubitus
positioning or selective intubation may be sufficient; however, in
some cases, surgical resection is required to relieve respiratory
Bronchopulmonary dysplasia (BPD)
A distinct pulmonary disease, BPD results from prolonged oxygen
or respirator therapy for causes of respiratory distress, including
hyaline membrane disease, neonatal pneumonia, and meconium
The combination of high oxygen concentration and barotrauma of
respirator therapy ultimately injures alveolar epithelium and
results in overdistended alveoli and acini within scarred lungs.
Corresponding chest radiographs show hyperexpansion with irregular
aeration and a "soap-bubble" appearance that resembles multiple
cysts (figure 8A). The bubbly lucencies are due to overdistended
alveoli, which alternate with curvilinear strands of soft-tissue
density representing scarred lung. Associated hyperaeration is
often most marked at the bases. CT may be helpful in distinguishing
BPD from other causes of cystic-appearing lungs. Changes associated
with BPD typically demonstrated on CT scans of the chest include:
volume loss (especially in the upper and middle lobes), fibrosis,
retraction, and bronchial dilatation (figure 8B).
Occasionally, development of a focal large interstitial cyst or
acquired emphysema produces increasing respiratory distress; CT may
again prove helpful by defining the type and severity of
involvement with PPIE or lobar emphysema.
Finally, some extrapulmonary conditions may mimic lung masses
and produce respiratory distress in the neonate. Two such processes
are pleural fluid and mass lesions. Pleural fluid is detected
easily on a chest radiograph; a large amount may produce
significant respiratory distress, necessitating aspiration, an
indwelling chest tube, or both. However, imaging may exclude a
solid mass lesion before intervention with aspiration or drainage.
Sonography of the chest may suffice in this regard; CT will also
differentiate fluid from a solid mass lesion (figure 9). The most
common cause of a large pleural effusion in the newborn is
chylothorax. The etiology of spontaneous chylothorax is usually
unknown; thoracic duct rupture secondary to birth trauma and
transient central venous hypertension during delivery are two
possible causes. Fifty percent of infants with spontaneous
chylothorax have symptoms within the first day of life, and 70%
have symptoms by the end of the first week. Right-sided effusion is
more common than left-sided effusion.
Treatment consists of single or multiple thoracentesis; chest-tube
drainage may be required. Medium-chain triglycerides are often
therapeutic and thoracic duct exploration is rarely necessary;
prognosis is excellent. Other etiologies of pleural effusion in the
newborn include Turner's syndrome, congestive heart failure,
infantile polycystic kidney disease, polycythemia, CCAM, idiopathic
hypervolemia, iatrogenic hypervolemia, obstructed pulmonary venous
return, esophageal rupture, erosion by gastroenteric cyst, and
Rarely, respiratory distress may be secondary to an
extrapulmonary mass lesion producing cardiovascular compromise.
Figure 10A illustrates respiratory distress in an infant whose
chest radiograph suggested the possibility of a cardiac or
pericardial mass lesion. Ultrasonography demonstrated an echogenic
mass within the pericardium (figure 10B). Subsequent surgical
exploration revealed the mass to be a pericardial teratoma.
The conditions described above may produce respiratory distress
requiring intervention or surgery. Diagnosis may be possible with
conventional radiography, which is undoubtedly the most rapid
imaging technique. However, ultrasonography followed by CT or MR
imaging may also be necessary to establish the diagnosis.
We thank David H. Binstadt, MD, St. John's Hospital,
Springfield, IL, for providing the images in figure 4.