Pathogenesis and types of potter’s sequence md pathology exam question give robbins based answer
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Potter sequence pathogenesis types renal agenesis oligohydramnios authoritative pathology
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"Potter Sequence"
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https://www.ncbi.nlm.nih.gov/books/NBK430685
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Potter sequence (Oligohydramnios sequence)
Definition:
Potter sequence is a sequence of congenital abnormalities resulting from prolonged oligohydramnios. A sequence means that one primary abnormality produces a cascade of secondary defects. It is not a malformation syndrome.
Potter sequence is a sequence of congenital abnormalities resulting from prolonged oligohydramnios. A sequence means that one primary abnormality produces a cascade of secondary defects. It is not a malformation syndrome.
Pathogenesis
Initiating event: Severe, persistent reduction in amniotic fluid.
Amniotic fluid normally cushions the fetus and is required for normal expansion of the developing lungs and chest wall. In the second half of pregnancy, fetal urine is a major source of amniotic fluid.
Causes of oligohydramnios:
- Chronic leakage of amniotic fluid due to rupture of the fetal membranes. This is the commonest cause.
- Fetal renal causes, particularly:
- Bilateral renal agenesis
- Severe renal dysplasia/cystic dysplasia
- Obstructive uropathy, for example posterior urethral valves
- Any cause of markedly reduced fetal urine output
- Uteroplacental insufficiency, such as that associated with severe maternal hypertension or preeclampsia/toxemia.
Cascade of abnormalities
Primary cause
↓
Oligohydramnios
↓
Loss of fluid cushion and fetal compression
↓
↓
Oligohydramnios
↓
Loss of fluid cushion and fetal compression
↓
- Flattened facial appearance, called Potter facies
- Low-set ears
- Receding chin/retrognathia
- Limb deformities due to restricted fetal movement: club foot (talipes), abnormal positioning of hands and feet
- Hip dislocation
↓
Impaired thoracic expansion and lung growth
↓
Pulmonary hypoplasia, often severe and lethal due to respiratory failure at birth.
Thus, death in severe Potter sequence is usually caused by pulmonary hypoplasia, rather than renal failure alone.
Types / etiologic variants of Potter sequence
A practical pathology classification is by the mechanism producing oligohydramnios:
| Type | Underlying lesion | Mechanism |
|---|---|---|
| Type I | Bilateral renal agenesis | Absent fetal urine production |
| Type II | Renal dysplasia, especially bilateral multicystic dysplastic kidneys | Markedly reduced urine production |
| Type III | Obstructive uropathy, such as posterior urethral valves | Impaired urine outflow, often with renal dysplasia |
| Type IV | Chronic rupture of membranes | Persistent loss of amniotic fluid |
| Type V | Uteroplacental insufficiency | Reduced fetal perfusion and urine output |
Important note: The term Potter syndrome was traditionally used especially for Potter phenotype caused by bilateral renal agenesis. The preferred term is Potter sequence or oligohydramnios sequence, because many different initiating abnormalities can lead to the same final phenotype.
Exam conclusion
Potter sequence is a pattern of deformations caused by long-standing oligohydramnios. The typical features are Potter facies, limb and hip deformities, and pulmonary hypoplasia. It may result from renal agenesis, severe renal dysplasia or obstruction, chronic rupture of membranes, or uteroplacental insufficiency. Bilateral renal agenesis is the classic fetal cause.
Robbins & Kumar Basic Pathology, Congenital Anomalies, p. 124.
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