MR imaging in the prenatal diagnosis of fetal chest masses: effects on diagnostic accuracy, clinical decision making, parental understanding, and prediction of neonatal respiratory health outcomes

Highlights on MRI of the fetal body

Fetal MRI is a level III diagnostic tool performed subsequently a level II prenatal ultrasound (US), in cases of inconclusive ultrasonographic diagnosis or when a further investigation is required to confirm or improve the diagnosis, to plan an appropriate pregnancy management. Fetal MRI plays an increasingly important role in the prenatal diagnosis of fetal neck, chest and abdominal malformations, even if its role has been amply demonstrated, especially, in the field of fetal CNS anomalies. Due to its multiparametricity and multiplanarity, MRI provides a detailed evaluation of the whole fetal respiratory, gastrointestinal and genitourinary systems, especially on T2-weighted (W) images, with a good tissue contrast resolution. In the evaluation of the digestive tract, T1-W sequences are very important in relation to the typical hyperintensity of the large intestine, due to the presence of meconium. The objective of this review is to focus on the application of fetal MRI in neck, chest and abdominal diseases.

Congenital diaphragmatic hernia

The incidence of congenital diaphragmatic hernia (CDH) may be as high as 1 in 2000. Over the past two decades, antenatal diagnosis rates have increased, the pathophysiology of CDH has become better understood, and advances in clinical care, including foetal surgery, have occurred. However, there remains a paucity of randomised controlled trials to provide evidence-based management guidelines. Reports of improved survival rates appear to be confined to a select subset of CDH infants, surviving to surgical repair, while the overall mortality, at over 60%, appears to be unchanged, largely due to the often forgotten 'hidden mortality' of CDH. The significant long-term morbidity in surviving infants has become apparent, and the need for long-term multidisciplinary follow up established. A total of 10% of cases may present later in life, and misdiagnosis on initial chest X-ray may lead to significant morbidity.

Percent predicted lung volumes as measured on fetal magnetic resonance imaging: a useful biometric parameter for risk stratification in congenital diaphragmatic hernia

PURPOSE

This study was aimed at determining whether a new method of analyzing lung volumes on fetal magnetic resonance (MR) imaging could be used to predict the degree of pulmonary compromise in congenital diaphragmatic hernia (CDH).

METHODS

Seventeen fetuses with CDH were prospectively evaluated by MR. Lung volumes were measured using an established technique and expressed as a percentage of the predicted lung volume (PPLV). Predicted lung volume was determined by subtracting measured mediastinal volume from total measured thoracic volume. The PPLV was correlated with postnatal outcomes. Statistical analyses were performed using the Mann-Whitney, Spearman correlation, or Fisher exact tests (P < .05).

RESULTS

Of the 14 liveborn patients, the PPLV was 20.3+/-10.4 (gestational age at MR, 22.3 +/- 5.7 weeks). The PPLV was significantly associated with extracorporeal membrane oxygenation (ECMO) use, hospital length of stay, and survival. All patients with a PPLV of less than 15 required prolonged ECMO support and had a 40% survival rate. In contrast, only 11% of patients with a PPLV of greater than 15 required ECMO, and survival was 100%.

CONCLUSION

The PPLV as measured by fetal MR imaging can accurately predict disease severity in CDH. A value of less than 15 is associated with a significantly higher risk for prolonged support and/or death, despite aggressive postnatal management.

Prenatal prognosis of congenital diaphragmatic hernia using magnetic resonance imaging measurement of fetal lung volume

OBJECTIVES

To investigate the correlation between fetal lung volume (FLV), measured with magnetic resonance imaging (MRI), and postnatal mortality in newborns with prenatally diagnosed isolated congenital diaphragmatic hernia (CDH).

METHODS

In a 4-year prospective multicenter study, 77 fetuses with isolated CDH diagnosed between 20 and 33 weeks' gestation underwent fast spin-echo T2-weighted lung MRI. These MRI-FLV measurements were compared with a previously published normative curve obtained in 215 fetuses without thoracoabdominal malformations and with normal ultrasound biometric findings. FLV measurements were correlated with postnatal survival. The mean gestational age at MRI was 31.3 weeks.

RESULTS

The measured/expected FLV ratio was significantly lower in the newborns with CDH who died compared with those who survived (23.6 +/- 12.2 vs. 36.1 +/- 13.0, P < 0.001). When the ratio was below 25%, there was a significant decrease in postnatal survival (19% vs. 40.3%, P = 0.008). Survival was significantly lower for neonates when one lung could not be seen by fetal MRI compared with those fetuses with two visible lungs on MRI (17.9% vs. 62.1%, P < 0.001).

CONCLUSION

In isolated CDH, FLV measurement by MRI is a good predictor of postnatal mortality due to pulmonary hypoplasia.

Antenatal diagnosis of congenital diaphragmatic hernia

Congenital diaphragmatic hernia occurs in approximately 1 of 2200 live births and is associated with a high degree of morbidity and mortality. Poor outcome in these cases is primarily related to the presence of additional anomalies or abnormal karyotype and the development of pulmonary and cardiovascular complications. Prenatal diagnosis occurs in approximately 50% of cases. Multiple ultrasound markers have been identified as being predictive of outcome. Three-dimensional ultrasound, fetal echocardiography, and magnetic resonance imaging have been identified as additional imaging modalities that can assist in making the antenatal diagnosis and accurately assessing perinatal outcome.

Prenatal diagnosis of pulmonary sequestration using three-dimensional power Doppler ultrasound

OBJECTIVE

To investigate the contribution of three-dimensional power Doppler ultrasound to the prenatal diagnosis of pulmonary sequestration.

METHODS

Prenatal three-dimensional power Doppler ultrasound was used to screen for an abnormal pulmonary blood supply in eight fetuses with hyperechogenic lung lesions and to image the pulmonary blood supply in 50 normal controls. A comparison was made with postnatal findings.

RESULTS

Postnatally the eight pulmonary lesions were found to be an isolated pulmonary sequestration (n = 3), a microcystic congenital adenomatoid malformation (n = 4), and a mixed (macrocystic and microcystic) congenital adenomatoid malformation (n = 1). Prenatal three-dimensional power Doppler ultrasound demonstrated an abnormal blood supply in all cases of pulmonary sequestration and in none of the other cases. Among the three cases that turned out to be pulmonary sequestrations, conventional two-dimensional ultrasound failed to identify the feeding vessel in one case and identified it at a later stage of gestation than did three-dimensional power Doppler in the other two.

CONCLUSION

Prenatal three-dimensional power Doppler ultrasound may be useful in identifying the feeding vessel and thus establishing the diagnosis of pulmonary sequestration in the presence of a hyperechogenic pulmonary lesion, allowing its differentiation from congenital cystic adenomatoid malformation.

Volume contrast imaging: A new approach to identify fetal thoracic structures

OBJECTIVE

To assess the potential of volume contrast imaging for evaluation of fetal intrathoracic structures.

METHODS

Volume contrast imaging is a new ultrasonographic method that increases the contrast between tissues. It consists of a 5- to 10-mm-thick slice-shaped volume image projected on a 2-dimensional screen. The rendering process applied on the slice smoothens the speckle pattern of the image by filling up the gaps with tissue information from the adjacent layers. To evaluate the potential of volume contrast imaging for enhancing the contrast between fetal lungs and surrounding tissues, we compared the ability of volume contrast imaging and conventional ultrasonography to image the fetal thymus in 50 controls. We also applied volume contrast imaging to prenatal imaging of 6 thoracic abnormalities (2 left congenital diaphragmatic hernias, 1 right diaphragmatic hernia, 2 congenital adenomatoid lung malformations, and 1 lung sequestration).

RESULTS

In controls, the thymus was identified in all cases by volume contrast imaging and in 42 cases (84%) by conventional 2-dimensional ultrasonography. Clear images of macrocystic and microcystic congenital adenomatoid malformations were obtained by volume contrast imaging, which provided precise contouring of the lesions. In cases with congenital diaphragmatic hernias, volume contrast imaging provided clear images of the limits of the lungs ipsilateral to the hernia.

CONCLUSIONS

Volume contrast imaging may enhance the contrast between fetal lungs and surrounding organs and can be applied to prenatal imaging of intrathoracic structures in cases with thoracic fetal abnormalities.