Diagnostic ultrasound ( PDFDrive )

1256 PART IV Obstetric and Fetal Sonography
because of the associated increased risk for hemorrhage, infection,
or malignancy. 131
NEURENTERIC CYST
Neurenteric cysts represent a posterior enteric remnant caused
by incomplete separation of the notochord from the foregut
during embryogenesis. hey typically occur in the posterior
mediastinum or in the spinal canal midline. he cysts can have
a septated or bilobed appearance. Associated spinal abnormalities
are typically present but diicult to identify prenatally. 132-135 MRI
is a useful adjunct in the further evaluation of the spine. Esophageal
duplication cysts should be considered in the diferential
of midline chest cysts.
PLEURAL EFFUSION
Any luid in the pleural space is abnormal. If suiciently large,
pleural efusion may result in mass efect, leading to compression
of the heart and hydrops as well as compression of the lungs,
resulting in pulmonary hypoplasia. 136
Primary pleural efusion is rare, with an incidence of up to
1 in 15,000 pregnancies. 137,138 It is most oten caused by chylothorax,
139 which results from defective development of the
lymphatic system. Any insult to the course of the thoracic duct
in the posterior mediastinum in the fetal chest can result in
chylous fetal pleural efusion. 140 his can be on either the right
or the let side, because the thoracic duct in the posterior
mediastinum crosses from right to let at the ith thoracic level.
Primary pleural efusion is suspected when the efusion is
unilateral or is much larger on one side than the other and when
no other signs of hydrops are present. Primary efusions are
characterized by having high pressures, resolving rapidly ater
thoracentesis and developing hydrops restricted to the upper
fetal body. 141
Primary chylothorax is associated with aneuploidy in 2% to
6% of cases. 142,143 By deinition, chylothorax in neonates is identiied
when luid contains more than 1.1 mmol/L triglycerides
with oral fat intake, with lymphocyte proportion exceeding 80%. 144
However, the fetus is fasting in utero, and the mean percentage
of lymphocytes in the blood of normal fetuses is normally greater
than 80%. 145 herefore these parameters do not apply in utero.
Secondary pleural efusion occurs in association with
aneuploidy (Turner syndrome or trisomy 21), infection (TORCH
[toxoplasmosis, rubella, cytomegalovirus, herpes simplex, HIV]),
genetic syndromes, and other structural malformations (CPAM,
BPS, lymphangiectasia, cardiac anomalies). 142-145 hese syndromes
typically present with bilateral pleural efusions (particularly in
fetuses with hydrops) 140 but occasionally with unilateral
efusion.
Pleural efusions appear on prenatal ultrasound as anechoic
luid collections in the pleural space, leading to the appearance
of the lung loating in the luid, surrounded by the chest wall
and diaphragm 146 (Fig. 36.10, Video 36.2). Small efusions appear
as an anechoic thin rim outlining the lungs and the mediastinum.
Larger unilateral efusions result in mass efect, causing mediastinal
shit and lattening or eversion of the diaphragm. If isolated
and small, pleural efusions have a benign course. If large with
mass efect, untreated fetal pleural efusion has a mortality rate
of 22% to 53%. 137,140,147-149
Small pleural efusions do not shit the mediastinum.
Pleural efusions associated with hydrops may be unilateral
or bilateral, oten beginning as unilateral collections that progress
bilaterally. Once hydrops develops (cardiac compression
from unilateral efusion), distinguishing between primary and
secondary efusion can be diicult. If mediastinal shit is visualized
in association with a small pleural efusion, a chest mass
such as a CDH, CPAM, or BPS should be sought. MRI may
help identify associated abnormalities not seen by ultrasound,
such as an inconspicuous CPAM or BPS. Depending on the
content of the pleural luid (lipid, protein, or blood products),
diferent signal intensities might be seen with MRI in both
T1- and T2-weighted images that may help establish the causal
diagnosis. 150
Prenatal pleural efusion has a variable natural course ranging
from spontaneous resolution to progressive development of
hydrops and polyhydramnios with high risk for perinatal morbidity
and mortality. 140 An efusion ratio can be obtained by
ultrasound (area of efusion divided by area of thorax) and
followed with serial examinations. If it elevates, it increases the
risk of evolution to hydrops, 141 but no cutof ratio has demonstrated
usefulness as a prognostic tool. 151
A fetal assessment for associated anomalies, including echocardiography,
maternal serology for infections, and fetal karyotyping,
should be performed. 141,152 Prognosis depends on the presence
of associated abnormalities, whether it is unilateral or bilateral,
the size of hydrothorax, and severity of mediastinal shit. A small
primary hydrothorax can have spontaneous resolution in 22%
of cases. 142 Unilateral efusions, spontaneously resolved efusions,
and those without mediastinal shit or hydrops have a 73% to
100% survival rate. 140,141
Progression from unilateral to bilateral efusions is associated
with impending hydrops. When large, bilateral, and with mediastinal
shit, the mortality rate increases to 52%. 140 With progression
to hydrops, the mortality rate increases to 62%. 140 Secondary
hydrothorax has a worse outcome. he mortality rate in these
cases can be up to 98% depending on size, progression to hydrops,
and underlying cause. 140
Pleural efusions are treated by drainage if the efusion is
isolated (or asymmetrical) without additional anomalies, typically
in fetuses at risk for developing hydrops (i.e., those with severe
mediastinal shit or with other signs of hydrops already present). 63
Typically, a pleural efusion is drained with a single stick procedure.
153 If it recurs, placement of a thoracoamniotic shunt is
an option. 154 A series of 65 fetuses showed thoracoamniotic shunts
to have a high survival rate in nonhydropic fetuses of 93%, with
survival of 86% in the hydropic group. 4 Risks of prenatal thoracoamniotic
shunts include fetal hemorrhage, blockage or migration
of the shunt, and placental abruption or preterm labor. In cases
of large efusions, drainage immediately before delivery can assist
in airway management at birth. A 2007 systematic review of
prenatal intervention for isolated primary pleural efusion without
hydrops suggested that survival rates ater prenatal intervention
are as high as 60%. 138