Page 222 - Concise Pathology for Exam Preparation ( PDFDrive )

8 Genetic and Paediatric Disorders 207

Clinical Features

• Dyspnoea, tachypnea, hypoxia and cyanosis.
• May be fatal in severe cases.

Morphology

Gross: Lung or its part(s) are normal in size, solid, airless, reddish purple in colour and
sink(s) in water.
Microscopic features: Collapsed alveoli, neutrophilic infiltration, eosinophilic hyaline
membrane in the terminal bronchioles and alveolar ducts/alveoli.
Q. Define fetal hydrops. Enumerate and describe the two types of
hydrops.

Ans. Fetal hydrops refer to accumulation of oedema fluid in the fetus during intrauterine
growth
Fluid accumulation may vary from progressive generalized oedema of the fetus (hydrops)
to a more localized isolated pleural/peritoneal collection
It may be immune or nonimmune in origin.
1. Immune hydrops (erythroblastosis fetalis; haemolytic disease of newborn):
• Haemolytic disease in the newborn is caused by blood group incompatibility be-
tween mother and child.
• Occurs when the fetus inherits red cell antigenic determinants from the father that
are foreign to the mother.
• Immunization of the mother by blood group antigens on fetal red cells and the free
passage of antibodies from the mother through the placenta to the fetus is the basis
of the disease.
• Antigens may reach maternal circulation in the last trimester when the cytotropho-
blast is no longer present as a barrier or during childbirth (fetomaternal bleed).
• Most common incompatibility is Rh (D), followed by ABO blood group:
Rh incompatibility:
- When the mother is Rh-negative and the fetus is Rh-positive, the first child is
usually unaffected; but all pregnancies in the future producing an Rh-positive
fetus will be affected. Immunoglobulin containing anti-D antibodies should be
administered within 72 h of delivery and/or at 28th week of pregnancy to
Rh-negative mothers to prevent complications in the subsequent pregnancies.
- If an Rh-negative mother has already been sensitized by Rh-positive blood due

to prior transfusion, even the first Rh-positive child may be affected.
- Such sensitized mothers form antibodies against Rh antigens.
- Antibodies (Abs) cross placenta during the first pregnancy but usually in late
third trimester; IgM isotype is the first antibody to be formed, which does not
cross placenta, so the first child is mostly unaffected; but if there is heavy and
early sensitization of mother, then haemolytic symptoms are visible in the first
child due to IgG formation (which is capable of crossing placenta).

- Second Rh-positive fetus causes large amount of IgG antibody formation. These
antibodies cross placenta and attach to Rh-positive fetal RBCs.
- Destruction of such RBCs leads to anaemia and haemolytic jaundice. In severe
cases, jaundice may lead to kernicterus and mental retardation; anaemia may
cause extramedullary hematopoiesis and/or cardiac decompensation leading to
hydrops fetalis.
ABO incompatibility:
- This is less common compared to Rh incompatibility because anti-A and anti-B
antibodies are IgM type, they do not cross the placenta.
- Neonatal RBCs express blood group antigens A and B poorly, resulting in less
sensitization of the mother.
- ABO haemolytic disease occurs exclusively in infants born to ‘O’ blood group
mothers (IgG type anti-A and anti-B antibodies).

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