Congenital Malformations of the Lungs (CTM)

1. Introduction & Classification

Congenital Thoracic Malformations (CTM) are a spectrum of developmental anomalies of the lower respiratory tract. They are often diagnosed antenatally due to widespread ultrasonography.

Classification (Key Entities):
The spectrum is often overlapping, but the four major entities are:

1. Congenital Pulmonary Airway Malformation (CPAM/CCAM): Hamartomatous lesions replacing normal lung tissue.
2. Bronchopulmonary Sequestration (BPS): Non-functioning lung tissue with anomalous systemic blood supply and no connection to the tracheobronchial tree.
3. Congenital Lobar Emphysema (CLE/CLO): Over-distension of a lobe (usually LUL) due to air trapping (ball-valve obstruction).
4. Bronchogenic Cysts: Foregut duplication cysts arising from abnormal budding.

2. Description of Specific Malformations

A. CPAM (formerly CCAM)

Based on Stocker’s Classification (Histological):

• Type 0: Tracheal origin (lethal).
• Type 1 (Most Common, 65%): Large cysts (>2cm). Good prognosis. Risk of malignancy (BAC).
• Type 2 (20%): Small cysts (<2cm). Often associated with other anomalies (renal/cardiac).
• Type 3: Solid/microcystic (echo-bright on USG). Poor prognosis if large (hydrops).
• Type 4: Large peripheral cysts. High association with Pleuropulmonary Blastoma (PPB). Associated with DICER1 mutation

B. Bronchopulmonary Sequestration (BPS)

Crucial feature: Systemic arterial supply (usually thoracic/abdominal aorta).

C. Congenital Lobar Emphysema (CLE)

• Pathology: Cartilage deficiency or extrinsic compression causing air entry but preventing exit (Air trapping).
• Site: Left Upper Lobe (43%) > Right Middle Lobe > RUL. (Lower lobes rarely affected).
• Feature: Massive hyperinflation causes mediastinal shift and compression of normal lung.

D. Bronchogenic Cysts

• Solitary cysts lined by respiratory epithelium.
• Location: Mediastinal (near carina) or Intraparenchymal.
• Risk: Infection, compression of airway, malignant transformation.

3. Diagnosis

A. Antenatal Diagnosis (Routine USG)

• Appearance: Hyperechoic lung mass (microcystic) or hypoechoic cysts (macrocystic).
• Prognostic Factor: CPAM Volume Ratio (CVR).
  • Formula: $(L\times H\times W\times 0.52)÷\text{Head Circumference}$.
  • CVR > 1.6: High risk of Hydrops Fetalis (indicator for fetal intervention).
  • CVR < 1.6: Favorable prognosis.

B. Postnatal Presentation

• Asymptomatic: Increasing number detected due to antenatal screening.
• Symptomatic: Respiratory distress (neonates), Recurrent pneumonia, failure to thrive (infants/children).
• CLE specific: Rapidly worsening distress with hyper-resonance and mediastinal shift.

C. Postnatal Imaging

1. CXR (Initial):
   • CPAM: Multicystic air-filled lesion.
   • CLE: Hyperlucent lobe with herniation across midline; depressed diaphragm.
   • BPS: Triangular opacity in lower lobes.
2. CT Chest with Angiography (Gold Standard):
   • Mandatory for surgical planning.
   • Crucial: Identifies the aberrant systemic artery in Sequestrations (prevents intra-op hemorrhage).
   • Delineates anatomical extent.

4. Management

A. Fetal Management

• No Hydrops: Serial USG. Many lesions regress in 3rd trimester.
• Hydrops Present / CVR > 1.6:
  • Maternal Steroids (Betamethasone) - shrinks lesion (Type 3/microcystic).
  • Thoraco-amniotic shunt (for macrocystic).
  • Rare: Fetal surgery or EXIT procedure.

B. Postnatal Management (Symptomatic)

• Immediate Surgery: Indicated for respiratory distress.
• CLE Caution: Do NOT needle aspirate a CLE (unless in extremis code situations). It creates a tension pneumothorax. Selective intubation of the healthy lung may be needed.
• Procedure: Lobectomy (preferred) or segmentectomy. Thoracoscopic (VATS) approaches are now standard.

C. Postnatal Management (Asymptomatic) - The Debate

Current consensus favors Elective Resection.

• Timing: Between 6 to 12 months of age (allows lung growth, reduces anesthetic risk).
• Rationale for Surgery:
  1. Infection Risk: Cysts eventually get infected (abscess).
  2. Malignancy Risk: Small but definite risk of Bronchioloalveolar Carcinoma (BAC) or Rhabdomyosarcoma (in CPAM Type 1/4) and Pleuropulmonary Blastoma.
  3. Compensatory Growth: Early resection allows compensatory alveolar growth of remaining lung.
• Conservative: Watchful waiting (CT surveillance) is an alternative but carries risk of lost follow-up and late complications.

D. Prognosis

• Excellent after surgical resection.
• Lung function is usually normal in long-term follow-up due to compensatory growth.