the purpose an an ultrasound survey of fetal anatomy, examination of the lungs
in the same section used for the four-chamber view of the fetal heart is sufficient.
Under normal condition, the fetal lungs are uniformly echogenic. At 18-23
weeks, the central third of the thoracic area at the level of the four chamber
view is occupied by the heart, and the remaining two thirds by the lungs,
that are normally uniformly echogenic. This scanning plane can also be used
for the measurement of the thoracic circumference, that is correlated with
the development of the lungs.
sagittal plane of the fetal trunk usually allows to identify the diaphragm
as a thin sonolucent line separating the abdominal from the thoracic cavity.
ADENOMATOID MALFORMATION (CAM)
adenomatoid malformation of the lung is a developmental abnormality arising
from an overgrowth of the terminal respiratory bronchioles. The condition
may be bilateral involving all lung tissue, but in the majority of cases it
is confined to a single lung or lobe. The lesions are either macrocystic (cysts
of at least 5 mm in diameter) or microcystic (cysts less than 5 mm in diameter).
In 85% of cases, the lesion is unilateral with equal frequency in the right
and left lungs and equal frequency in the microcystic and macrocystic types.
adenomatoid malformation of the lung is found in about 1 in 4000 births.
is a sporadic abnormality. In about 10% of cases, there are other abnormalities,
mainly cardiac and renal.
is based on the ultrasonographic demonstration of a hyperechogenic pulmonary
tumor which is cystic (CAM type 1), mixed (CAM type 2), or solid – microcystic
(CAM type 3). Microcystic disease results in uniform hyperechogenicity of
the affected lung tissue. In macrocystic disease, single or multiple cystic
spaces may be seen within the thorax. Both microcystic and macrocystic disease
may be associated with deviation of the mediastinum.
there is compression of the heart and major blood vessels in the thorax, fetal
hydrops develops. Polyhydramnios is a common feature and this may be a consequence
of decreased fetal swallowing of amniotic fluid due to esophageal compression,
or increased fluid production by the abnormal lung tissue. Prognostic features
for poor outcome include major lung compression causing pulmonary hypoplasia,
polyhydramnios and development of hydrops fetalis irrespective of the type
of the lesion.
a 180K clip of a CAM
a 18K clip of a CAM
a 140K clip of a CAM
is lethal either in utero, due to progressive hydrops, or in the neonatal
period. Isolated unilateral cystic adenomatoid malformation without hydrops
is associated with a good prognosis; in about 70% of cases, the relative size
of the fetal tumor remains stable, in 20% of cases there is antenatal shrinkage
or resolution, and in 10% of cases there is progressive increase in mediastinal
compression. In symptomatic neonates, thoracotomy and lobectomy are carried
out and survival is about 90%. It is uncertain whether surgery is also needed
for asymptomatic neonates.
intrathoracic cysts causing major mediastinal shift and associated hydrops
can be treated effectively by the insertion of thoraco-amniotic shunts. The
role of more invasive intervention, such as hysterotomy and excision of solid
tumors in cases of fetal hydrops, remains to be defined. Although good results
have been reported after such surgery in a small number of cases, the potential
risks to the mother both during the pregnancy and in subsequent confinements
should not be underestimated.
the diaphragm is usually completed by the 9th week of gestation. In the presence
of a defective diaphragm, there is herniation of the abdominal viscera into
the thorax at about 10–12 weeks, when the intestines return to the abdominal
cavity from the umbilical cord. However, at least in some cases, intrathoracic
herniation of viscera may be delayed until the second or third trimester of
hernia is found in about 1 per 4000 births.
hernia is usually a sporadic abnormality. However, in about 50% of affected
fetuses there are associated chromosomal abnormalities (mainly trisomy 18,
trisomy 13 and Pallister–Killian syndrome – mosaicism for tetrasomy 12p),
other defects (mainly craniospinal defects, including spina bifida, hydrocephaly
and the otherwise rare iniencephaly, and cardiac abnormalities) and genetic
syndromes (such as Fryns syndrome, de Lange syndrome and Marfan syndrome).
the diaphragm is imaged by ultrasonography as an echo-free space between the
thorax and abdomen. Diaphragmatic hernia can be diagnosed by the ultrasonographic
demonstration of stomach and intestines (90% of the cases) or liver (50%)
in the thorax and the associated mediastinal shift to the opposite side. Herniated
abdominal contents, associated with a left-sided diaphragmatic hernia, are
easy to demonstrate because the echo-free fluid-filled stomach and small bowel
contrast dramatically with the more echogenic fetal lung. In contrast, a right-sided
hernia is more difficult to identify because the echogenicity of the fetal
liver is similar to that of the lung, and visualization of the gall bladder
in the right side of the fetal chest may be the only way of making the diagnosis.
(usually after 25 weeks) is found in about 75% of cases and this may be the
consequence of impaired fetal swallowing due to compression of the esophagus
by the herniated abdominal organs. The main differential diagnosis is from cystic
lung disease, such as cystic adenomatoid malformation or mediastinal cystic
processes, e.g. neuroenteric cysts, bronchogenic cysts and thymic cysts. In
these cases, a fluid-filled structure causing mediastinal shift may be present
within the chest. However, in contrast to diaphragmatic hernia, the upper abdominal
anatomy is normal.
prediction of pulmonary hypoplasia remains one of the challenges of prenatal
diagnosis because this would be vital in both counselling parents and also
in selecting those cases that may benefit from prenatal surgery. Poor prognostic
signs are, first, increased nuchal translucency thickness at 10–14 weeks,
second, intrathoracic herniation of abdominal viscera before 20 weeks, and,
third, severe mediastinal compression suggested by an abnormal ratio in the
size of the cardiac ventricles and the development of polyhydramnios.
the human, the bronchial tree is fully developed by the 16th week of gestation,
at which time the full adult number of airways is established. The alveoli
continue to develop even after birth, increasing in number and size until
the growth of the chest wall is completed in adulthood. The growth of blood
vessels supplying the acinus (intra-acinar vessels) parallels alveolar development,
while the growth of pre-acinar vessels follows the development of the airways.
In diaphragmatic hernia, the reduced thoracic space available to the developing
lung leads to reduction in airways, alveoli and arteries. Furthermore, there
is an increase in arterial medial wall thickness and extension of muscle peripherally
into the small pre-acinar arteries, offering an explanation for the pulmonary
hypertension and persistent fetal circulation observed after neonatal repair.
Thus, although isolated diaphragmatic hernia is an anatomically simple defect,
which is easily correctable, the mortality rate is about 50%. The main cause
of death is hypoxemia due to pulmonary hypertension, resulting from the abnormal
development of the pulmonary vascular bed.
animal studies have suggested that pulmonary hypoplasia and hypertension due
to intrathoracic compression are reversible by in utero surgical repair.
However, such therapy is likely to have limited success in the human because
the bronchial tree is fully developed by the 16th week of gestation. For a
fetus with a sonographically demonstrable large diaphragmatic hernia at 16–18
weeks, irreversible maldevelopment of the bronchial tree and vasculature is
likely. However, in fetuses with a diaphragmatic defect which allows the intrathoracic
herniation of abdominal viscera only after mid-gestation (when the bronchial
tree and pre-acinar vessels are fully developed), prenatal correction, by
allowing further development of the alveoli and intra-acinar vessels, may
well prevent pulmonary hypoplasia and neonatal death. In a few cases of diaphragmatic
hernia, hysterotomy and fetal surgery have been carried out but this intervention
has now be abandoned in favor of minimally invasive surgery. Animal studies
have demonstrated that obstruction of the trachea results in expansion of
the fetal lungs by retained pulmonary secretions. Endoscopic occlusion of
the fetal trachea has also been carried out in human fetuses with diaphragmatic
hernia, but the number of cases is too small for useful conclusions to be
drawn as to the effectiveness of such treatment.
pleural effusions, which may be unilateral or bilateral, may be an isolated
finding or they occur in association with generalized edema and ascites.
a 50K clip of a hydrothorax
of the underlying cause, infants affected by pleural effusions usually present
in the neonatal period with severe, and often fatal, respiratory insufficiency.
This is either a direct result of pulmonary compression caused by the effusions,
or due to pulmonary hypoplasia secondary to chronic intrathoracic compression.
The overall mortality of neonates with pleural effusions is 25%, with a range
from 15% in infants with isolated pleural effusions to 95% in those with gross
hydrops. The mortality rate in cases of antenatally diagnosed chylothorax
is about 50%. Isolated pleural effusions in the fetus may either resolve spontaneously
or they can be treated effectively after birth. Nevertheless, in some cases,
severe and chronic compression of the fetal lungs can result in pulmonary
hypoplasia and neonatal death. In others, mediastinal compression leads to
the development of hydrops and polyhydramnios, which are associated with a
high risk of premature delivery and perinatal death.
at prenatal therapy by repeated thoracocenteses for drainage of pleural effusions
have been generally unsuccessful in reversing the hydropic state, because
the fluid reaccumulates within 24–48 h of drainage. A better approach is chronic
drainage by the insertion of thoracoamniotic shunts. This is useful both for
diagnosis and treatment. First, the diagnosis of an underlying cardiac abnormality
or other intrathoracic lesion may become apparent only after effective decompression
and return of the mediastinum to its normal position. Second, it can reverse
fetal hydrops, resolve polyhydramnios and thereby reduce the risk of preterm
delivery, and may prevent pulmonary hypoplasia. Third, it may be useful in
the prenatal diagnosis of pulmonary hypoplasia because, in such cases, the
lungs often fail to expand after shunting. Furthermore, it may help to distinguish
between hydrops due to primary accumulation of pleural effusions, in which
case the ascites and skin edema may resolve after shunting, and other causes
of hydrops such as infection, in which drainage of the effusions does not
prevent worsening of the hydrops. Survival after thoracoamniotic shunting
is more than 90% in fetuses with isolated pleural effusions and about 50%
in those with hydrops.
OF THE LUNGS
lung sequestration, a portion of the lung develops without connection to the
airways. The blood supply to the abnormal lung tissue is through arteries
that arise from the descending aorta rather than from the pulmonary artery.
This condition is classically divided in the radiological literature into
intralobar (about 75%) and extralobar (about 25%), but the difference (which
is based on the presence or absence of a separate pleural covering from the
normal lung) cannot be accurately determined with prenatal ultrasound.
of the lungs is rare and the prevalence is less than 5% of congenital pulmonary
of the lungs is a sporadic abnormality.
sequestrated portion of the lung appears as a homogeneous, brightly echogenic
mass in the lower lobes of the lungs or in the upper abdomen (infradiaphragmatic
sequestration). The diagnosis is confirmed by color Doppler demonstration
that the vascular supply of the sequestered lobe arises from the abdominal
lung sequestration may act as an arteriovenous fistula and cause high-output
heart failure and hydrops.
sequestrations are usually isolated, whereas more than 50% of extralobar sequestrations
are associated with other abnormalities (mainly diaphragmatic hernia and cardiac
outcome depends on the presence of associated abnormalities, and hemodynamic
disturbances. In general, intralobar sequestration has an excellent prognosis,
whereas extralobar sequestration has a poor prognosis because of the high
incidence of other defects and hydrops.
© 2000 by Pilu, Nicolaides, Ximenes & Jeanty