HY lecture notes:
Person who’s vomiting; what’s the biochemical disturbance? –> hypokalemic hypochloremic metabolic alkalosis –> low K, low Cl, high pH, high bicarb, low H, anion gap normal (even though it’s alkalosis, not acidosis, the USMLE will still ask an arrow for the anion gap here).
2-week-old male + forceful non-bilious vomiting; Dx? –> hypertrophic pyloric stenosis.
Dx of pyloric stenosis? –> abdominal ultrasound to show olive-shaped hypertrophied pylorus.
Tx of pyloric stenosis? –> myomectomy.
Who gets pyloric stenosis? –> first-born males (weird, but it’s on an old NBME) + neonates taking oral erythromycin for chlamydial ophthalmia neonatorum (erythromycin is a motilin-receptor agonist).
2-week-old male + bilious vomiting; Dx? –> duodenal atresia, annular pancreas, congenital midgut volvulus, or Hirschsprung (correct, Hirschsprung can present with bilious vomiting).
2-week-old + Down syndrome + bilious vomiting + passed meconium ok; Dx? –> duodenal atresia.
2-week-old + Down syndrome + bilious vomiting + slow to pass meconium; Dx? –> Hirschsprung.
How do you Dx duodenal atresia? –> abdominal x-ray (AXR) showing double-bubble sign (very HY).
2- week-old + bilious vomiting + triple bubble sign; Dx? –> jejunal atresia.
How do you Dx Hirschsprung? –> rectal manometry, followed by confirmatory rectal biopsy showing absence of ganglion cells.
Mechanism for Hirschsprung? –> failure of migration of neural crest cells distally to the rectum.
How do you Dx congenital midgut volvulus? –> upper-GI series (AXR + contrast follow-through of esophagus, stomach, and duodenum with barium or gastrografin).
Failure to pass meconium at birth. Most likely cause overall? –> cystic fibrosis.
18-month-old + intermittent abdominal pain + crying + blood in stool; Dx? –> intussusception.
18-month-old + intermittent squatting + crying + FOBT positive; Dx? –> intussusception.
18-month-old + occasionally brings legs to chest + vomits + FOBT positive; Dx? –> intussusception.
18-month-old + occasionally brings legs to chest + vomits + FOBT negative; Dx? –> volvulus –> this is congenital midgut volvulus.
Presentation sounds like intussusception but no blood per rectum –> answer = congenital midgut volvulus.
Cause of intussusception? –> >99% are in kids under age 2; caused by lymphoid hyperplasia due to viral infection (e.g., rotavirus) or recent vaccination; if in adult (usually elderly), it is caused by colorectal cancer.
Dx and Tx of intussusception? –> USMLE wants enema as the answer. Even though ultrasound can be done which shows a target sign, the USMLE always wants enema. And it can be any type. I’ve seen “air contrast enema”, “air enema,” “contrast enema,” all as answers. I also had a student simply get “water-soluble contrast enema” on the exam, which means gastrografin. Barium would refer to regular contrast.
