What is the management plan for a fetus with multiple cystic spaces on the lung detected on ultrasound during the second or third trimester of pregnancy?

Management of Multiple Cystic Spaces on Fetal Lung

When multiple cystic spaces are detected on fetal lung ultrasound, perform a detailed ultrasound examination immediately or schedule it for the near future to characterize the lesion and identify any associated anomalies, as this finding most likely represents congenital pulmonary airway malformation (CPAM, formerly called CCAM) which requires serial monitoring and delivery planning. 1

Initial Diagnostic Approach

Detailed Ultrasound Examination

• Perform a comprehensive detailed fetal anatomic ultrasound to confirm the finding is isolated and to look for additional structural anomalies, particularly cardiac defects, hydrops fetalis, and other thoracic abnormalities 1
• Characterize the cystic lung lesion by documenting: location, size, number of cysts, presence of macrocysts (>5mm) versus microcysts (<5mm), and degree of mediastinal shift 2, 3, 4
• Assess for polyhydramnios, as this finding is associated with 50% mortality in non-aborted fetuses compared to 100% survival with normal amniotic fluid 4
• Evaluate for non-immune fetal hydrops (NIFH), which is the single most important negative prognostic indicator - all cases with hydrops in published series resulted in fetal death 3

Advanced Imaging Considerations

• Fetal MRI is indicated when ultrasound information is incomplete or additional anatomic details are needed for prenatal or postnatal intervention planning 1
• MRI should ideally be performed at or after 22 weeks gestation, though it may provide value between 18-22 weeks in certain clinical scenarios 1
• MRI is particularly helpful for thoracic anomalies and planning airway management 1

Antenatal Surveillance Strategy

Serial Ultrasound Monitoring

• Perform serial ultrasound examinations throughout pregnancy to monitor lesion size, development of hydrops, mediastinal shift, and amniotic fluid volume 1, 2, 3
• The natural history shows that 53% of lung masses decrease in size during gestation, and some may completely resolve prenatally 4
• Monitor specifically for increasing mediastinal shift, as 90% of fetuses with no mediastinal shift survive compared to only 50% of non-aborted fetuses with severe mediastinal shift 4

Prognostic Indicators to Track

• Absence of hydrops is the most critical favorable prognostic factor - counseling should emphasize the prevalence of positive outcomes when hydrops is absent 3
• Polyhydramnios development indicates worse prognosis and requires closer monitoring 4
• Complete prenatal resolution or significant size reduction suggests excellent prognosis 2, 3

Genetic and Associated Anomaly Evaluation

• Screen for additional structural abnormalities, as 8% of fetuses with chest masses have other structural abnormalities and may be karyotypically abnormal 4
• If associated anomalies are present, offer genetic testing including karyotype, FISH studies, and/or chromosomal microarray analysis 5
• Obtain detailed family history, as genetically transmitted disorders account for approximately one-third of cases with multiple anomalies 5

Delivery Planning and Postnatal Management

Delivery Considerations

• Transfer care to a high-risk obstetrical center with immediate access to pediatric surgery and neonatal intensive care for urgent intervention if the infant develops respiratory distress at birth 6
• Plan delivery at a tertiary care center even if the fetus appears stable, as 69% of liveborns in one series had no respiratory symptoms at birth but some required urgent intervention 4
• Arrange multidisciplinary consultation with pediatric surgery, neonatology, and potentially cardiothoracic surgery prior to delivery 5

Postnatal Evaluation

• Obtain chest X-ray immediately after birth to confirm the lesion 2
• CT scan is the technique of choice to confirm resolution or persistence of the lesion after birth 2
• Even if the chest X-ray appears normal at birth, obtain CT imaging as one case series reported a false negative chest X-ray with CT confirmation of CPAM 2

Surgical Decision-Making

• Surgical resection is preferable over conservative management, even for asymptomatic lesions, though the optimal timing remains debated 2
• In published series, approximately 56% of survivors underwent surgical resection while others are followed conservatively 4
• Intraoperative pulmonary function measurements have demonstrated significant improvement after resection of the affected lobe 6

Fetal Intervention Considerations

• Fetal intervention (thoracoamniotic shunting, fetal thoracotomy, or EXIT procedure) is reserved exclusively for cases developing hydrops fetalis, as this is life-saving with acceptable maternal morbidity 7
• Without hydrops, expectant management with serial surveillance is appropriate 7, 3
• Refer immediately to a fetal intervention center if hydrops develops 7

Critical Pitfalls to Avoid

• Do not dismiss the finding even if it appears to resolve on prenatal ultrasound - obtain postnatal CT imaging to confirm true resolution, as chest X-rays can be falsely negative 2
• Do not delay transfer to a tertiary center - diagnosis can be made as early as 18-24 weeks gestation, allowing time for appropriate planning 6
• Do not assume all cystic lung lesions are CPAM - differential diagnosis includes bronchopulmonary sequestration (25% of cases in one series), hybrid lesions, congenital lobar emphysema, esophageal duplication cysts, and rarely thoracic neuroblastoma 7, 4
• Do not recommend routine invasive testing for isolated lung cysts without other anomalies, as the aneuploidy risk is low (8%) and only present when additional structural abnormalities exist 4