Fetal thoracic lesions: MRI insights for safer delivery planning

Fetal thoracic abnormalities range from small, stable lung lesions to life-threatening conditions that obstruct the airway, compress the heart or prevent normal lung development. Ultrasound remains the first-line examination, yet fetal magnetic resonance imaging (MRI) can clarify anatomy when the diagnosis is uncertain or when delivery decisions depend on accurate estimates of lung volume, airway patency and mediastinal displacement. Learn more about Isorc2015.org.

For Australian families, care often involves several services: a local obstetric ultrasound provider, a maternal-fetal medicine team, a tertiary neonatal intensive care unit and, in regional areas, a retrieval network. A clear imaging pathway helps clinicians plan around distance, availability of paediatric surgery and the practical realities of giving birth in centres such as Sydney, Melbourne, Brisbane, Perth or Adelaide.

Which thoracic lesions require closer assessment

Congenital pulmonary airway malformation (CPAM) is among the most frequently recognised fetal lung lesions. It may appear as a microcystic or macrocystic mass, sometimes with a measurable solid component. Bronchopulmonary sequestration usually has a systemic arterial supply, often arising from the thoracic or abdominal aorta. Hybrid lesions can show features of both conditions, making vascular assessment particularly important.

Other important diagnoses include congenital diaphragmatic hernia (CDH), pleural effusion, congenital high airway obstruction syndrome (CHAOS), bronchogenic cysts and mediastinal masses. A lesion that seems modest in size may still cause significant compression if it shifts the heart, narrows the trachea or interferes with venous return. Conversely, a large CPAM may have a relatively favourable outlook if the remaining lung is well developed and hydrops does not occur.

The clinical picture can change during pregnancy. Serial ultrasound should assess lesion size, cyst characteristics, mediastinal shift, amniotic fluid, fetal growth and signs of hydrops. The CPAM volume ratio (CVR) can help estimate risk, although it should be interpreted alongside the lesion’s appearance and the overall condition of the fetus rather than treated as an isolated forecast.

What prenatal MRI adds to ultrasound

Fetal MRI is particularly useful when ultrasound is limited by maternal body habitus, fetal position, oligohydramnios, late gestation or an unusual lesion. It provides a broader view of both lungs, the diaphragm, liver, bowel, heart and central airways. Fast T2-weighted sequences can demonstrate fluid-filled cysts, compressed lung and the degree of mediastinal displacement without requiring fetal sedation.

MRI can support an estimate of observed-to-expected total fetal lung volume, which is especially relevant in suspected CDH. It may show how much of the liver has moved into the chest, whether the contralateral lung is compressed and whether the lesion occupies one hemithorax or crosses the mediastinum. These details help distinguish a potentially resectable pulmonary lesion from a broader pattern of pulmonary hypoplasia.

MRI does not replace expert ultrasound or Doppler imaging. Ultrasound is usually better for real-time assessment of blood flow, fetal movement, cardiac function and a feeding vessel to a sequestration. A useful report combines the strengths of both modalities and explains the level of diagnostic confidence, since delivery planning should account for uncertainty as well as the most likely diagnosis.

Reading airway, vascular and cardiac anatomy

Airway anatomy becomes central when CHAOS, a large cervical or mediastinal mass, or severe thoracic compression is suspected. MRI may show an enlarged, fluid-filled tracheobronchial tree in CHAOS, while ultrasound and MRI together can help establish whether the obstruction is likely to be complete. The position and calibre of the trachea should be described in relation to the lesion and the planned route of delivery.

For CPAM and sequestration, clinicians need to understand the lesion’s internal structure and blood supply. A systemic feeding artery supports sequestration or a hybrid diagnosis, while a cystic mass with no obvious systemic vessel may favour CPAM. Large pleural effusions require assessment of the underlying lung, the heart and the possibility of chylothorax or another cause of fetal hydrops.

Cardiac findings can alter urgency and location of birth. Severe mediastinal shift may reduce cardiac filling, impair venous return and contribute to ascites or skin oedema. Where there is concern about ventricular function, pericardial effusion or abnormal great vessel relationships, a detailed fetal echocardiogram should sit alongside MRI rather than being inferred from cross-sectional images alone.

Connecting imaging findings with prognosis

Prognosis depends on more than lesion diameter. Hydrops, bilateral disease, marked pulmonary hypoplasia, severe airway obstruction and significant cardiac compromise are adverse features. A unilateral CPAM with preserved growth, stable amniotic fluid and no hydrops may have a far better outlook, even when it appears conspicuous on an ultrasound image.

The timing of diagnosis also matters. Some lesions grow rapidly in the mid-trimester and then plateau or become less prominent later. Others become more clinically important near term as the fetus has less room to compensate for compression. Repeated imaging should compare the same measurements where possible, while acknowledging that technical differences can produce apparent changes in volume.

Families need an explanation that separates prenatal uncertainty from postnatal treatment. A lesion may require neonatal respiratory support, drainage, bronchoscopy, surgery or observation. The neonatal course can also involve issues outside the thorax, including thrombocytopenia in critically unwell infants; a practical review of neonatal platelet disorders can provide useful background when broader neonatal risks are being discussed.

Building a delivery plan in Australia

The place of birth should match the anticipated level of intervention. A fetus with a stable, isolated CPAM and no evidence of airway compromise may be delivered near term in a hospital with neonatal respiratory support and access to paediatric consultation. Suspected severe pulmonary hypoplasia, hydrops, CHAOS or a large mediastinal mass generally warrants delivery in a tertiary perinatal centre with neonatal intensive care, paediatric surgery, anaesthesia and advanced imaging.

Australian geography makes this decision particularly practical. A family in northern Queensland, regional New South Wales or Western Australia may need accommodation near a tertiary hospital well before delivery, with retrieval timing considered if birth occurs unexpectedly. Public maternity services and private hospitals can have different arrangements for fetal MRI, neonatal surgery and intensive care, so the referral pathway should be confirmed rather than assumed.

For selected airway-obstructing lesions, an ex utero intrapartum treatment procedure, commonly called EXIT, may maintain placental oxygenation while the team secures the airway. EXIT is highly specialised and requires coordinated obstetrics, anaesthesia, neonatology, otolaryngology and paediatric surgery. It is not a routine response to every thoracic lesion; the decision depends on predicted airway obstruction, gestation, maternal considerations and local expertise.

The archived FAOPS 2020 site reflects the wider international focus on perinatal and neonatal medicine that supports this multidisciplinary approach. In Australia, discussions may involve maternal-fetal medicine specialists, neonatologists, paediatric surgeons, fetal cardiologists, radiologists, genetic counsellors, retrieval clinicians and social workers. Early coordination is often more valuable than a last-minute change of hospital.

Preparing for the newborn period

Delivery-room planning should translate imaging into specific actions. The team should decide who attends the birth, whether delayed cord clamping is appropriate, what respiratory support is available and how quickly intubation, drainage or surgery can be performed. A neonate with suspected CDH may require gentle ventilation to avoid overdistending the hypoplastic lung, while a baby with pleural effusion may need urgent thoracentesis or chest drainage.

A suspected airway lesion requires an explicit airway algorithm. This may include flexible or rigid bronchoscopy, video laryngoscopy, equipment for emergency tracheostomy and, in exceptional cases, continuation of placental support through EXIT. The plan should state what happens if the airway cannot be secured and whether cardiopulmonary bypass or extracorporeal membrane oxygenation is available at that hospital.

After birth, chest radiography, echocardiography, CT or postnatal MRI may refine the diagnosis. Surgical resection is often considered for symptomatic CPAM, recurrent infection or a lesion with concerning anatomy, while selected asymptomatic infants may undergo structured observation. Sequestration and hybrid lesions require attention to the systemic arterial supply, particularly before an operation.

Families benefit from a written summary that includes the imaging diagnosis, expected complications, planned hospital, transport arrangements and key contacts. In metropolitan centres, this may be coordinated across multiple departments; in rural and remote communities, telehealth and the regional retrieval service can help keep parents and clinicians aligned.

Clinicians caring for suspected fetal thoracic lesions should review ultrasound and MRI together, document the degree of uncertainty and convene the relevant specialists early. Families can ask their care team for a plain-language birth plan, clarification of the nearest appropriate tertiary centre and an explanation of possible neonatal procedures. Access to coordinated fetal medicine and neonatal expertise gives each pregnancy the best opportunity for a safe, prepared delivery.