Diagnostic ultrasound ( PDFDrive )

1248 PART IV Obstetric and Fetal Sonography
TABLE 36.3 Differential Diagnosis of Echogenic Lesion in Fetal Thorax
Abnormality Location Distinguishing Features
Congenital pulmonary airway
malformation (CPAM)
Unilateral
(2%-3% bilateral)
Multiple cysts may be seen in association with
echogenic lesion
Sequestration Unilateral; left lower lobe most often Systemic blood supply
Congenital lobar overinlation Unilateral; upper lobe most often Similar to microcystic CPAM; enlarged echogenic
lung with mediastinal shift
Congenital diaphragmatic
hernia (CDH)
Congenital high airway
obstruction (CHAOS)
Typically unilateral; left sided most
often
Bilateral
Peristalsis of bowel in chest
Stomach above diaphragm
Absence of part of the diaphragm
Distended trachea and main central airways
Symmetrical bilateral enlarged lungs with eversion
of hemidiaphragms
bronchiolar structures without alveolar diferentiation, except
in the subpleural areas. 41-43 he resulting cystic lesions result in
enlargement of the afected lobe (or segment). If suiciently
large, CPAM will result in mediastinal shit and interfere with
normal alveolar development in the adjacent lung. Communication
with the tracheobronchial tree usually is retained, with
vascular supply and venous drainage to the pulmonary circulation,
unless CPAM is associated with sequestration. In these cases
this is called a “hybrid lesion.”
here are diferent classiication schemes for CPAMs depending
on histology 44 or on prenatal sonographic appearance. 44,45 he
three main types described sonographically are type I (large
cysts measuring 2-10 cm), type II (multiple small cysts), and
type III (microcystic, appearing as echogenic lesions).
Sonographic diagnosis can be made as early as 16 weeks.
CPAM may appear as a solid echogenic lung mass (microcystic)
or as a mixed, cystic and solid mass (Fig. 36.4, Video 36.1). Color
Doppler ultrasound may demonstrate vascular low to the lesion
from branches of the pulmonary artery. Typically, there is no
systemic feeding vessel, although as mentioned, CPAM can occur
in concert with sequestration. he lesions with microcysts appear
solid and echogenic, whereas the macrocystic CPAMs have
demonstrable cysts. Occasionally, only a single large cyst is
visualized.
As with any chest mass, it is important to assess for associated
mediastinal shit, polyhydramnios, and hydrops because these
factors impact prognosis and management. 45,46 It is the size of
the CPAM rather than the size of the cysts that determines whether
or not the fetus develops hydrops. Macrocystic lesions usually
have a more favorable prognosis. Large CPAMs can result in
cardiac and vena cava compression, leading to altered hemodynamics
and hydrops as a result of elevated central venous pressure
that may require in utero intervention. 47
he CPAM volume ratio (CVR), a measurement initially
described by ultrasound, should be measured to assess prognosis
and risk of hydrops. It is obtained by calculating the volume of
the lung mass (height × anteroposterior diameter × transverse
diameter × 0.52) and dividing it by the head circumference. A
CVR less than 1.6 indicates a 14% risk of developing hydrops for
fetuses with macrocystic lesions and 3% for those with
microcystic lesions. If the CVR is greater than 1.6, the risk
increased to 75%. 48 In the absence of hydrops, the prognosis is
good, with reported live birth rates of 95% and higher. 49-51
Untreated hydrops as a result of CPAM, however, has an anticipated
mortality rate of up to 100%. 52-61 Hydrops is therefore an
indication for in utero fetal therapy, and close follow-up in the
second and early third trimesters is important when a high CVR
is encountered. However, if there is luid, such as ascites, in only
a single body cavity, spontaneous regression of the lesion and
improvement in luid status is still possible. 62 Steroids have been
used in an attempt to prevent the development of hydrops or help
speed the regression of the lesion, particularly with microcystic
CPAM. In uncontrolled studies, maternal steroid administration
appeared to reverse hydrops and improve outcome. 55-59 However,
it is possible that fetal thoracic growth and/or CPAM regression
rather than steroids account for the resolution of hydrops.
With macrocystic CPAM, steroid therapy appears to be less
helpful, with in utero therapy generally consisting of either
draining the largest cyst with a single stick procedure 48 (Fig.
36.4G) or, if luid reaccumulates, placing a shunt. 60,61 Rarely is
open fetal surgery indicated. A meta-analysis showed that shunting
of CPAMs improved survival in fetuses with hydrops compared
with no efect on survival in fetuses with chest masses without
hydrops. 63 he success with open fetal surgery in cases of CPAM
ranges between 29% and 62% but has the limitation of expected
preterm delivery. 64
Associated anomalies, most oten renal, intestinal, and cardiac,
are present in up to 26% of cases, 35,44-46,65 more frequently when
CPAM is bilateral. 40 herefore a complete fetal anatomic survey
is indicated. he diferential diagnosis includes BPS, CLO,
bronchogenic cyst, CDH, laryngeal or tracheal occlusion,
neurenteric/enteric cysts, and mediastinal teratomas.
MRI has become a useful adjunct in the evaluation and
management of CPAM 66 (Fig. 36.4H and I). Macrocysts have a
high T2-weighted signal intensity, whereas microcysts have
moderately high signal intensity and are relatively homogeneous.
As the lesions regress, they develop lower signal intensity on
T2-weighted imaging. 67
Longitudinal studies of CPAM have demonstrated that most
CPAMs demonstrate rapid progressive growth from about weeks