Meconium Aspiration Syndrome
The most likely diagnosis is C) Meconium aspiration syndrome (MAS), given the combination of fetal distress on CTG, pneumomediastinum, increased anteroposterior diameter (indicating hyperinflation), and flattened diaphragm—all classic radiographic features of air trapping and barotrauma from meconium-obstructed airways.
Clinical Reasoning
Key Diagnostic Features Present
Fetal distress on CTG: This indicates intrauterine stress, which is the primary trigger for in utero meconium passage in term or near-term infants 1
Pneumomediastinum: Among neonatal conditions, the most significant predisposing factors for pneumomediastinum are mixed lung diseases such as pneumonia or meconium aspiration syndrome, with coexisting atelectasis and airway obstruction 1. This air leak occurs when meconium creates a ball-valve mechanism—allowing air in but preventing complete exhalation, leading to alveolar rupture and air dissection into the mediastinum 2, 3
Increased AP diameter with flattened diaphragm: These radiographic findings indicate severe hyperinflation from air trapping, which is pathognomonic for obstructive airway disease rather than surfactant deficiency or fluid retention 1, 2
Why Other Diagnoses Are Less Likely
A) Transient Tachypnea of the Newborn (TTN):
- TTN results from delayed clearance of fetal lung fluid and typically presents with perihilar streaking on chest X-ray, not pneumomediastinum 4
- TTN does not cause air trapping, hyperinflation, or air leak syndromes 4, 5
- The presence of pneumomediastinum essentially excludes TTN as the primary diagnosis
B) Respiratory Distress Syndrome (RDS):
- RDS predominantly affects preterm infants <30 weeks gestation due to surfactant deficiency 6, 7
- The question describes a term infant delivered by SVD (spontaneous vaginal delivery implies adequate gestational age)
- RDS causes diffuse atelectasis and ground-glass appearance on X-ray, not hyperinflation with flattened diaphragm 6
- While air leak syndromes can complicate RDS, they occur in the context of mechanical ventilation with high pressures, not immediately after spontaneous vaginal delivery 8
D) Tracheoesophageal Fistula (TEF):
- TEF presents with excessive oral secretions, choking with feeds, and aspiration pneumonia—not acute pneumomediastinum at birth 8
- The clinical scenario lacks the typical feeding intolerance and polyhydramnios history associated with TEF
- Pneumomediastinum is not a primary feature of TEF
Pathophysiology of MAS
Meconium aspiration creates a ball-valve obstruction in the airways:
- Air enters during inspiration but cannot fully escape during expiration 1, 2
- This leads to progressive air trapping, alveolar overdistension, and eventual rupture 2, 3
- Air dissects along bronchovascular bundles into the mediastinum, creating pneumomediastinum 3
- The increased intrathoracic pressure flattens the diaphragm and increases the AP diameter on chest X-ray 2
Clinical Pitfalls to Avoid
Do not dismiss pneumomediastinum as benign: While most pneumomediastinum resorbs spontaneously, in the context of MAS it indicates severe disease with significant air trapping requiring close monitoring 2
Recognize the air leak risk: The presence of pneumomediastinum in MAS signals high risk for progression to pneumothorax, which can cause acute decompensation and may mimic cardiac tamponade 8, 2
Avoid aggressive positive pressure ventilation: In MAS with existing air leak, excessive ventilatory pressures can worsen barotrauma 8
Immediate Management Considerations
- Confirm diagnosis with chest X-ray showing hyperinflation, flattened diaphragm, and air in the mediastinum 1, 3
- Monitor closely for pneumothorax progression with serial clinical assessments and consider lung ultrasound for early detection 1
- Provide supportive respiratory care with gentle ventilation strategies if needed, avoiding high peak pressures 8
- Maintain adequate oxygenation while minimizing barotrauma risk 8