4-week-old (Male) with Nonbilious Projectile Vomiting

00:01 Alright guys, we have an absolutely classic USMLE question here, you will see this question on the boards to some degree. Let’s jump right in.

00:11 A fou-week-old male presents with recent onset nonbilious projectile vomiting.

00:18 His mother notes that he is eager to feed between episodes.

00:22 Other than an uncomplicated course of chlamydia conjunctivitis, the infant has been healthy.

00:29 Physical Examination is significant for a palpable mass in the right upper quadrant and visible waves of peristalsis.

00:38 What is the first line confirmatory diagnostic test and associated finding? Answer choice A: Abdominal X-ray; double bubble sign.

00:49 Answer choice B: Barium upper GI series; GE junction and portion of the stomach in the thorax.

00:58 Answer choice C: Barium upper GI series; bird beak sign and corkscrewing.

01:05 Answer choice D: Air enema; filling defect and coil spring sign.

01:11 Or answer choice E: Abdominal ultrasound; elongated pyloric channel and muscle hypertrophy.

01:19 Now take a moment to come to the answer by yourself before we go through it together.

01:26 Okay, like I was saying guys, this is classic, classic USMLE.

01:30 To some degree you are going to see this on your USMLE test day and you should also see it on your shelves.

01:37 Now let’s go into the question characteristics.

01:40 Now, this is a pediatric question.

01:42 We have a four week old patient coming in with complaints. Now this is a two step question.

01:47 The first thing we have to do is figure out based on the description of what they are telling us what is the diagnosis and then we have to figure out what is the imaging modality we use to confirm the diagnosis.

02:01 And of course the stem is required, we're gonna be taking lots of information from the stem filtering through it to come to a diagnosis.

02:09 Now going to the question stem, we see we have a male neonate patient and his chief complaint is nonbilious projectile vomiting.

02:18 Now, important to understand, nonbilious vomiting generally is a defect superior to the bile ducts.

02:27 Now this is in comparison to bilious of vomiting that involves intestinal dysfunction causing bile to flow back through the stomach and then outwards.

02:39 Now the most common cause of nonbilious vomiting in neonates is pyloric stenosis.

02:46 You just have to memorize that one, it is not high yield.

02:50 Now, pyloric stenosis is consistent with the patient’s presentation here in the question stem.

02:57 There is a palpable mass in the right upper quadrant and this is actually the hypertrophy of the pyloric sphincter.

03:05 There is characteristic projectile vomiting which is due to the pressure buildup in the stomach due to lack of an outflow through the sphincter that leads to the high pressure or projectile vomiting.

03:19 You will also have visible gastric peristalsis and of course because the patient can't consume the feeds and they vomited them out, they will have hunger between feeds. So our diagnosis is pyloric stenosis and we kind of confirm it by knowing what pyloric stenosis looks like and seeing it in the question stem.

03:41 Now, the more challenging part here is determining the associated confirmatory diagnostic test and its finding.

03:49 Now, the only diagnostic method to visualize the hypertrophy of the right pyloric sphincter is through ultrasound so that’s one way to get to the answer.

04:01 You see that you understand that ultrasound is the way to actually confirm this diagnostic finding and you could eliminate the rest.

04:10 Also, the associated finding for Answer choice E that describes the abdominal ultrasound is also consistent with pyloric stenosis.

04:19 There is an elongated pyloric channel and muscle hypertrophy, but let’s go to the other answer choices to figure out why Answer choice E is the correct answer, of abdominal ultrasound and why the other answer choices are wrong.

04:35 So let’s talk a little bit more about some of the other answer choices then we’ll go into more detail.

04:40 So going quickly for the first round, I'm gonna do two rounds for you because it’s that important of a question.

04:45 First here we see abdominal X-ray and a double bubble sign.

04:50 Well, that would not, that could show I guess I should say pyloric stenosis, you could see distention of the stomach and minimal intestinal bowel gas but that would be nonspecific so that wouldn't work so you could rule that out.

05:04 And double bubble sign, just so you are aware, is due to duodenal atresia and we’ll talk more about that in a moment.

05:12 Answer choice B, a barium upper GI study is good for excluding other causes but it can't directly visualize the pyloric hypertrophy and here, what they are describing from the associated finding is a hiatal hernia.

05:27 Answer choice C, the barium again, upper GI series is good for excluding other causes and what they're describing here in the associated finding of a bird beak sign and corkscrewing is what’s called midgut volvulus.

05:43 And Answer choice D, which is air enema, this is used for a condition called intussusception in which the small bowel goes into a large bowel and the associated finding that they're describing, the filling defect and the coil spring sign, are associated of course with intussusception.

06:03 But now let’s go through these answers a bit more detailed and make sure you really learn them because this is an outrageously high yield question.

06:11 Now, let’s start with the correct answer, Answer choice E.

06:14 Now, congenital hypertrophy of the pyloric smooth muscle produces what is called pyloric stenosis and this prevents stomach contents from entering into the small intestine.

06:25 Now, pyloric stenosis typically affects first born Caucasian males of Northern European descend that is important to know.

06:34 And associations include neonatal erythromycin treatment and also maternal smoking.

06:41 Patients are typically healthy but then presents, at three to eight weeks, with this projectile nonbilious vomiting.

06:48 Parents describe an increase desire to feed after these episodes and the physical exam findings are what’s classically called an olive shaped abdominal palpable mass in the right upper quadrant of the abdomen and also visible waves of peristalsis given that you have that hypertrophy.

07:10 Important laboratory findings you have to know because they may give you a question stem with not a lot of info but based on these lab findings you have to do a lot of deduction.

07:21 So lab findings that are significant here are going to be for dehydration and they're going to have hypokalemic, hypocaloric metabolic alkalosis due to the vomiting.

07:34 Now if they were to ask you what's the first thing you need to do for this patients, the answer is stabilize them with IV fluid and make sure their electrolytes are balanced, that’s the first step because they're gonna have vomiting and they could have significant dehydration and electrolyte abnormalities and then after that, you would proceed to a confirmatory diagnosis with the ultrasound.

07:58 Now, on ultrasound, what you are going to see is an elongated pyloric channel and increase muscle thickness and this is diagnostic and as you can see here on our image the pyloric stenosis shows a very narrow opening to the pylorus and that muscle thickening.

08:16 And the definitive treatment here is what's called a pyloral myotomy, cutting the muscle to allow food to go through.

08:23 Now, let’s go through some of the other answer choices again in a little bit more detail.

08:27 So the -- using of abdominal X-ray and seeing a double bubble sign as we had mentioned before would be consistent with duodenal atresia and this results from failure of duodenal recanalization.

08:41 Now in contrast to pyloric stenosis in which patients have nonbilious vomiting after three to four weeks of normal feeding, patients with duodenal atresia present with bilious vomiting at the time of birth.

08:57 Now associations with duodenal atresia are polyhydramnios and also Down Syndrome.

09:03 And the double bubble sign is classically observed in the abdominal X-ray with no distal bowel gas.

09:11 Now looking at Answer choice B of an upper GI series with the GE junction and portion of the stomach in the thorax that’s consistent with what's called a sliding hiatal hernia and that’s actually associated with symptoms of GERD in 80% of cases.

09:28 Now, patients typically will present with simple spitting up, they don’t have projectile vomiting and they actually had a feeding aversion, they don’t want to eat, they don’t want to eat that leads to failure to thrive rather than the increase desire to feed as we’re seeing in our question stem.

09:45 Now an upper GI series will demonstrate the GE junction and a portion of the stomach in the thorax given that the sliding hiatal hernia upwards and the sequelae include unfortunately respiratory distress due to aspiration of stomach contents and also iron deficiency anemia.

10:05 Now, looking at Answer C -- Barium Upper GI series with a bird beak sign and cork screwing, now, like we said, that’s due to midgut volvulus.

10:16 When you have abnormal rotation of the midgut around, very important to know this, the superior mesenteric artery during embryologic development this results in abnormal positioning of the small bowel within the right lower quadrant and this displaces the large bowel including the cecum to the left.

10:37 Now patients with malrotation typically will have bilious vomiting and they’ll also have colicky abdominal pain in the first week of life.

10:48 Now, malrotation is associated with simply other congenital gastrointestinal anomalies.

10:55 And a Barium GI series is going to show what's called a bird beak sign and also cork screwing and these are diagnostic.

11:03 And you should not delay surgery if there is a strong suspicion for volvulus because you're going to have compromised blood flow through again the superior mesenteric artery and have a risk of bowel ischemia.

11:17 And then lastly here looking at Answer choice D, of an air enema like we had mentioned, this is for intussusception and that’s telescoping of the bowel leading to obstruction and eventual bowel necrosis due to blood vessel compression.

11:34 Now this is a very common cause of obstruction in children that are less than two months old and though patients are typically slightly older than those that present with pyloric stenosis, it can have overlapping age group.

11:48 Now patients typically here with intussusception will present with acute colicky abdominal pain, they can have lethargy and the classic USMLE buzz word of currant jelly stool due to the bowel necrosis that is a later finding.

12:04 Now ultrasound is the first test for screening just like for pyloric stenosis and you will have what is called a target sign and that’s the intussuscepted vowel showing an inner and outer circle like a target.

12:17 Now, subsequently an air enema is used that’s both diagnostic to C and therapeutic to resolve or relieve the intussusception ands when you do that you actually demonstrate a filling defect and a coil spring sign at the area of the obstruction.

12:36 Now let’s review some high yield facts for pyloric stenosis.

12:40 Now this is thickening of the gastric pyloric musculature.

12:44 The cause here really is idiopathic and associated risk factors are being a first born Caucasian male of Northern European decent, having preterm birth or having a cesarean section.

12:56 And the signs and symptoms you absolutely have to know are nonbilious projectile vomiting, abdominal mass often called that olive shaped abdominal mass in the right upper quadrant, excessive peristalsis and dehydration in advance cases.

13:13 And the confirmatory diagnostic test here is with ultrasound and the initial treatment, again remember this could be another USMLE question, the initial treatment is correction of the dehydration and electrolyte imbalance and the definitive treatment is a pyloromyotomy.

13:32 Now, you may be told that you can use atropine in these cases to relax the pyloric muscle even though it has hypertrophy, that is true but we use that much less frequently given that to do so would require a prolonged hospitalization and extensive monitoring.

13:51 And thankfully, for these neonates that have pyloric stenosis they have a good prognosis after a definitive treatment.