HYDROPS FETALIS IMAGING STUDIES

hydrops fetalis imaging studies:
• Once the possibility of fetal hydrops is considered or suspected, sophisticated and complete fetal imaging studies are an initial absolute necessity. Hydrops is defined by the presence of serous effusion(s) in a fetus with subcutaneous tissue edema. Some authors have distinguished the presence of a single effusion (pleural, peritoneal) as an entity distinct from hydrops; however, recent evidence suggests that an isolated effusion often (if not usually) progresses to overt fetal hydrops. Exceptions appear to be isolated chyloperitoneum/ascites (usually associated with obstructive uropathy and, thus, not true hydrops) and pleural or peritoneal effusions that regress spontaneously. Thus, careful and complete imaging is required to establish the diagnosis and the extent of the hydrops.

• Equipment employed must be capable of providing high-resolution images at large depth.
o Linear array transducers are commonly used; however, sector scanners provide better views of the heart and many other structures.
o Range-gated Doppler capability is optimal for functional physiologic assessments. Use of high-frequency transvaginal 2-dimensional and pulsed-wave/color Doppler flow mapping particularly has been promising.

• The initial imaging study may provide important clues concerning the origin of the fetal
condition. For example, most arrhythmias and anomalies may be detected even in the process of establishing the initial diagnosis. However, in most cases, more complex, serially repeated studies may be required to accurately define the constellation of findings in the fetus.

• Specific echocardiographic assessment of fetal cardiac structure and function is required in most cases of fetal hydrops. Essential elements of this examination should include definitive results concerning (1) assessment of biventricular outer dimensions in diastole and of the cardiothoracic ratio, (2) presence or absence of AV valve regurgitation, and (3) umbilical vessel blood flow velocities and pulsations.

o Biventricular diameter in diastole had 100% sensitivity and 86% specificity for detection of cardiac failure in one study. These observations, confirmed by results from several other reports, address the basic underlying pathophysiologic disturbance in faltering cardiac output of the fetus with hydrops and increased CVP.

o Presence of AV valve regurgitation is a common finding, suggesting right-heart failure or increased preload. Persistence of serious functional AV valve incompetence following treatment interventions is ominous, particularly in terms of fetal outcome. The proportion of atrial area taken up by the regurgitant jet is related to hydrops. The proportion of systolic time during which AV valve insufficiency is demonstrated is also related to hydrops. In one study, AV valve insufficiency was pansystolic in all babies with hydrops.

o Umbilical and fetal abdominal vessel pulsations, flow velocities, and waveforms have been studied by several investigators in hydrops caused by tachyarrhythmias, alpha-thalassemia, and twin-twin transfusion.
􀂃 Because sensitivity, specificity, and predictive values are not available, the practical clinical value of these studies is uncertain.
􀂃 However, the results available to date suggest that they may provide valuable quantitative and qualitative pathophysiologic information and may even be predictive of fetal deterioration prior to the development of overt hydrops in some situations.

o Umbilical venous (UV) blood flow, normally nonpulsatile, demonstrates pulsatile (or double-pulsatile) flow, a finding consistent with an increased fetal CVP.
􀂃 Pulsed Doppler duplex ultrasound studies demonstrate higher UV and inferior vena cava (IVC) blood velocity and blood flow, suggesting an increase in the preload (cardiac) index. Studies of IVC, hepatic vein, and ductus venosus blood flow demonstrate similar results.
􀂃 In hydrops caused by sustained tachycardia, reversal of blood flow (or increased retrograde flow) with systolic forward flow and diastolic reverse flow is present at heart rates exceeding 220 bpm; these abnormalities are reversed by successful fetal treatment with return of the heart rate to 210 bpm or less. Great interindividual differences exist in the time required for this reversal.

o Myocardial function is impaired with hydrops, and the severity of this functional cardiomyopathy is reflected by the degree and persistence of AV valve incompetence and UVC/IVC flow patterns in the fetus.

o Abnormalities in umbilical artery (UA) blood flow are also found. UA early-diastolic blood flow velocity is absent, and end-diastolic UA velocity is reversed. The UA pulsatility index (PI) is increased in feto-fetal transfusion hydrops, and, most importantly, this abnormal finding usually precedes and predicts the development of hydrops in the recipient/hydropic twin. PI also improves parallel to clinical improvement in fetal condition. Abnormal UA blood flow patterns in alpha-thalassemia hydrops include an increased acceleration slope, more linear decline from maximum systole to end diastole, and reduced spectral broadening; fetal aortic waveforms also demonstrate distorted systolic peaks, flow turbulence, and greatly elevated diastolic frequencies.

o Elevated umbilical venous pressures, found in approximately two thirds of individuals with fetal hydrops, return to normal with successful treatment. Such measurements, obtained by cordocentesis at time of fetal treatment, may be useful in assessing the success of fetal therapies that require a direct invasive approach.