NEONATAL RESPIRATORY DISEASES IMAGING

NEONATAL DISEASES IMAGING is very important

Neonatal Respiratory Distress (NRD):

  • RD in the newborn is usually due to one of 4 disease entities:
1.     Respiratory distress syndrome (RDS; hyaline membrane disease, HMD)

2.     Transient tachypnea of the newborn (TTN)

3.     Meconium aspiration

4.     Neonatal pneumonia

The most common complications of RDS are:

  • Pulmonary interstitial emphysema (PIE)
  • Persistent PDA
  • Bronchopulmonary dysplasia (BPD)

Neonatal Respiratory Distress:

Disease Lung Volume Opacities Time Course Complication
RDS:  Low Granular 4-6 days PIE, BPD, PDA
Transient tachypnea: High or normal Linear, streaky* < 48 hours None
Meconium aspiration:  Hyperinflation Coarse, patchy At birth PFC, ECMO
Neonatal pneumonia:  Anything Granular Variable  

*Ground-glass opacity at birth.

ECMO: extracorporeal membrane oxygenation; PFC : persistent fetal circulation;

RDS/ hyaline membrane disease (HMD):

Evolving Terminology:

  • The term hyaline membrane disease is now less commonly used in clinical practice to describe pulmonary surfactant insufficiency in infants.
  • Hyaline membranes are considered a byproduct, not the cause, of respiratory failure in neonates with immature lungs.
  • The term respiratory distress syndrome is currently used to denote surfactant deficiency and should not be used for other causes of respiratory distress.
  • In recognition of the underlying pathogenesis of the disease process, the alternative term surfactant deficiency disorder has been proposed.

Pathogenesis:

  • RDS is caused by surfactant deficiency. Surfactant diminishes surface tension of expanding alveoli. As a result, acinar atelectasis and interstitial edema occur.
  • Hyaline membranes are formed by proteinaceous exudate.
  • Symptoms occur within 2 hours of life.

The incidence of RDS depends on the gestational age at birth:

Birth at Gestational Age (wk) Incidence (%)
27 50
31 16
34 5
36 1

Radiographic Features:

  • In most cases of RDS, the diagnosis is made clinically but may initially be made radiographically. The role of the radiologist is to assess serial chest films.

CXR signs of premature infants:

  • No subcutaneous fat
  • No humeral ossification center
  • Endotracheal tube present

Any opacity in a premature infant should be regarded as RDS until proven otherwise.

o   Lungs are opaque (ground-glass) or reticulogranular (hallmark).

o   Hypoaeration (atelectasis) leads to low lung volumes à bell-shaped thorax (if not intubated).

o   Bronchograms are often present.

o   Absence of consolidation or pleural effusions

o   In contrast to other causes of RDS in neonates, pleural effusions are uncommon.

o   Treatment with surfactant may result in asymmetric improvement

Treatment complication of RDS:

  • Persistent PDA : signs of congestive heart failure (CHF):
  • The ductus usually closes within 1 to 2 days after birth in response to the high Po2 content.
  • Air-trapping : PIE & acquired lobar emphysema
  • Diffuse opacities (whiteout) may be due to a variety of causes:
  • Atelectasis
  • Progression of RDS
  • Aspiration
  • Pulmonary hemorrhage
  • CHF
  • Superimposed pneumonia

Pulmonary interstitial emphysema (PIE):

  • PIE refers to àaccumulation of interstitial air in peribronchial & perivascular spaces.
  • Most common cause à +ve-pressure ventilation.

Complications:

  • Pneumothorax
  • Pneumomediastinum
  • Pneumopericardium

Radiographic Features:

  • Tortuous linear lucencies radiate outward from the hilar regions.
  • The lucencies extend all the way to the periphery of the lung.
  • Lucencies do not change with respiration.

Bronchopulmonary dysplasia (BPD)

  • Caused by oxygen toxicity & barotrauma of respiratory therapy.
  • BPD is now uncommon in larger & more mature infants (gestational age > 30 weeks or weighing >1200 g at birth).

Definition of BPD & Diagnostic Criteria:

Diagnostic Criterion Gestational Age < 32 wk Gestational Age > 32 wk
Time point of assessment o   36 wk PMA* or

o   discharge to home, whichever comes first;

o   treatment with >21% oxygen for at least 28 days plus

o   >28 days but <56 days postnatal age or

o   Discharge to home, whichever comes first;

o   Treatment with >21% oxygen for at least 28 days plus

Mild BPD o   Breathing room air at 36 wk PMA or

o   discharge, whichever comes first

o   Breathing room air by 56 days postnatal age or

o   discharge, whichever comes first

Moderate BPD o   Need* for <30% oxygen at 36 wk PMA or

o   discharge, whichever comes first

o   Need* for <30% oxygen at 56 days postnatal age or

o   discharge, whichever comes first

Severe BPD o   Need* for ≥30% oxygen and/or positive pressure (PPV* or nasal CPAP) at 36 wk PMA or

o   discharge, whichever comes first

o   Need* for ≥30% oxygen and/or positive pressure (PPV or nasal CPAP) at 56 days postnatal age or

o   discharge, whichever comes first

*Using a physiologic test (pulse oximetry saturation range) to confirm the oxygen requirement.

  • BPD : bronchopulmonary dysplasia.
  • CPAP: continuous positive airway pressure.
  • PMA : postmenstrual age (gestational age at birth plus chronologic age).
  • PPV : positive-pressure ventilation.
  • There are 4 stages in the development; the progression of BPD àthrough all 4 stages is now rarely seen because of the awareness of this disease entity.
  • Stages of Bronchopulmonary Dysplasia:
Stage Time Pathology Imaging
1 o   < 4 days o   Mucosal necrosis o   Similar to RDS
2 o   1 week o   Necrosis, edema, exudate o   Diffuse opacities
3 o   2 weeks o   Bronchial metaplasia o   Bubbly lungs*
4 o   1 month o   Fibrosis o   Bubbly lungs*

*Bubbly lungs (honeycombing): rounded lucencies surrounded by linear densities; hyperaeration.

Prognosis of Stage 4:

  • Mortality, 40%
  • Minor handicaps, 30%
  • Abnormal pulmonary function tests in almost all in later life
  • Clinically normal by 3 years, 30%

Meconium aspiration syndrome:

  • Meconium (mucus, epithelial cells, bile, debris) à the 1.st stool that is evacuated within 12 hours after delivery.
  • In fetal distress, evacuation may occur into the amniotic fluid (up to 10% of deliveries).
  • However, in only 1% does this aspiration cause respiratory symptoms.
  • Only meconium aspirated to below the vocal cords is clinically significant.
  • Meconium aspiration sometimes clears in 3 to 5 days.
  • CXR nearly always returns to normal by 1 year of age.

Radiographic Features:

o   Patchy, bilateral opacities, may be “rope-like”

o   Atelectasis

o   Hyperinflated lungs

o   Pneumothorax, pneumomediastinum, 25%

Complication:

  • Mortality (25%) from persistent fetal circulation

Neonatal pneumonia (NP):

  • Pathogenesis:

Trans-placental infection: ·        TORCH:

ü Pulmonary manifestation of TORCH is usually less severe than other manifestations.

Perineal flora: ·        Group B streptococci, enterococci, Escherichia coli:

ü Ascending infection

ü Premature rupture of membranes

ü Infection while passing through birth canal

Radiographic Features:

  • Patchy asymmetrical opacities in a term infant represent neonatal pneumonia until proven otherwise.
  • Hyperinflation

Transient tachypnea of the newborn (TTN):

  • TTN (wet lung syndrome) is a clinical diagnosis.
  • It is caused by a delayed resorption of intrauterine pulmonary liquids.
  • Normally, pulmonary fluids are cleared by:

Bronchial squeezing during delivery, 30%

Absorption, 30%: lymphatics, capillaries

Suction, 30%

Causes:

  • Cesarean section, premature delivery, maternal sedation (no thoracic squeezing)
  • Hypoproteinemia, hypervolemia, erythrocythemia

Radiographic Features:

o   Fluid over-load àsimilar appearance as non-cardiogenic pulmonary edema.

o   Prominent vascular markings

o   Pleural effusion

o   Fluid in fissure

o   Alveolar edema

o   Lungs clear in 24 48 hours.

Extracorporeal membrane oxygenation (ECMO):

  • Technique of providing prolonged extracorporeal gas exchange.

Indications:

  • Any severe respiratory failure with predicted mortality rates of > 80%.

Exclusion criteria for ECMO include:

  • < 34 weeks of age
  • >10 days of age
  • Serious intracranial hemorrhage
  • Patients who require epinephrine

Complications:

  • Late neurologic sequelae; developmental delay, 50%
  • Intracranial hemorrhage, 10%
  • Pneumothorax, pneumomediastinum
  • Pulmonary hemorrhage (common)
  • Pleural effusions (common)
  • Catheter complications

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