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AN52.1-8 | Histology & Embryology (Abdomen & Pelvis) — Part 3
SELF-CHECK
A. Pyloric stenosis — hypertrophy of pyloric smooth muscle due to neonatal inflammation
B. Duodenal atresia — failure of recanalisation of the solid cord phase of duodenal development; associated with Down syndrome in 30%
C. Malrotation — incomplete counterclockwise rotation of the midgut loop leading to Ladd's bands
D. Meckel's diverticulum — persistent vitellointestinal duct causing luminal obstruction
Reveal Answer
Answer: .
The 'double-bubble' sign (gas in stomach + proximal duodenum with no distal gas) is pathognomonic of duodenal atresia (or severe duodenal stenosis). Embryological basis: during weeks 5–6, the duodenum becomes a solid cord of proliferating endoderm, then recanalises. Failure = complete obstruction. Check for Down syndrome (trisomy 21) in 30% of cases. Bilious vomiting confirms the obstruction is below the ampulla of Vater (bile duct opens here). Management: duodenoduodenostomy.
SELF-CHECK
A. Autosomal dominant polycystic kidney disease (ADPKD) — accumulation of cysts in adults from defective cystogenesis
B. Horseshoe kidney — fusion of inferior poles preventing ascent
C. Autosomal recessive polycystic kidney disease (ARPKD) — defect in tubular differentiation; presents in infancy/childhood
D. Wilms' tumour (nephroblastoma) — malignant kidney tumour of childhood
Reveal Answer
Answer: .
ARPKD (autosomal recessive PKD) presents in the neonatal period or early childhood — bilateral flank masses, oligohydramnios (Potter sequence if severe), hypertension, renal failure. Consanguinity increases the risk. The defect is in PKHD1 (fibrocystin) → abnormal tubular differentiation with diffuse microcrysts in collecting ducts. ADPKD presents in adults (3rd–5th decade) with fewer, larger cysts.
CLINICAL PEARL
Hirschsprung's disease — remembering the embryological basis: Neural crest cells migrate craniocaudally along the bowel wall from weeks 5–12. The LAST segment to be colonised is the distal rectum/sigmoid. In Hirschsprung's, migration stops prematurely → the distal segment (beyond the migration arrest) is aganglionic. The aganglionic bowel remains tonically contracted (no Auerbach's/Meissner's plexus → no peristaltic relaxation) → functional obstruction. The dilated proximal bowel (which IS ganglionic and functions normally but cannot empty) is what the surgeon sees — not the aganglionic segment — hence the pull-through operation (resect the aganglionic segment, anastomose ganglionic bowel to the anus). Rectal suction biopsy confirms aganglionosis.