Possible Pyloric Stenosis

If you work in a kids ED then you probably see babies who are tagged as “possible PS” when they present with large volume vomiting.  Pyloric stenosis is not a rare disease, yet it is much less common than the alternative diagnoses that present in small babies with vomiting… UTI, gastroenteritis, sepsis, reflux / overfeeding, mysterious metabolic diseases…. pretty much anything that upsets the little tikes tummies.  So how do we sort out the real PS from the BS PS?

PS is usually seen in weeks 2 – 12 of life, more commonly in males.  This is unhelpful information as everything bad is more common in small babies and things like intestinal malrotation, sepsis and UTI are still clearly on the radar.  There is a cabinet of catastrophes that occur in this age and PS is not the most dire… so keep your mind open to the possibilities.  Ruling out PS might be possible, however, you need to know what else is potentially going on.

Lets go through this from the start…

HISTORY:

The vomiting is likely to be getting progressively worse with time.  PS is a progressive disease and doesn’t usually “stop ‘n start”.  It is a somewhat dynamic process, especially early in the disease where the obstruction is incomplete.  As it is due to muscle hypertrophy it can get worse as the muscle gets big during active times of the day, then settle at other times of day. However, the overall trend is progressive increasing vomits over a week or two.

Most kids with PS are well.  That is they are not febrile, mottled or drowsy unless it is a really late presentation.  They usually present as hungry, angry and afebrile.  Mum may say “he just never seems to be full… wants to feed soon after a spew.“  Kids with sepsis or other serious illness tend to be sedate or anorexic. They are often drowsy, disinterested in feeding.

It is also uncommon for them to be losing weight.  They may show a failure to gain weight, but the weight doesn’t start to drop until late in PS.  Importantly, if the child is hyper-thriving… especially bottle fed babies who are putting on a lot of weight ( greater than 300 g per week) then you might want to think about overfeeding / overflow as a cause of the spewing. This is of course a diagnosis of exclusion.  However, it doesn’t hurt to ask how much the parents are feeding the child. [ FYI: about 120 mL/kg/day is the ballpark for a normal volume of formula.]

Overfed babies regurgitate, burn their oesophagus, become unsettled and “demand”another feed that calms them… until they regurgitate once more.  This can look very similar to PS – an angry, hungry little man.  However, the vomitus is really passive and smaller volume.  It never hits the opposite wall!

Ask about the vomit trajectory.  PS vomiting is truly projectile.  This feature was present in nearly 100% of true PS cases in some series.  We are not accepting a “mum badge” or a handful of spew as “projectile”.  True projectile vomiting travels distance… as much as the length of the child!  I have seen fountains of spew rising into the air!  So be really careful about the label of “projectile” as it needs careful quantification and clarification.

One last, somewhat awkward, point.  In medical school we are taught that PS produces NON-BILIOUS vomitus. True green bile is a feature of lower obstruction eg. malrotation.  It would be convenient if these were true factoids in every case…. but alas, medicine is like life: messy.

In one case series 4% of kids with a final diagnosis of pyloric stenosis has bilious vomiting. I know, it makes no anatomical sense, c’est la vie. However, the presence of bile in the spew should prompt a contrast swallow study to detect possible malrotation or other obstruction.  Our job is to find the badness, not just exclude PS.

EXAMINATION

The diagnosis of PS hinges on the triad of:

1. projectile vomiting,
2. visible peristalsis and
3. a palpable “olive” in the epigastrium.

In order to see these features you need to do a test feed in the ED.

Get Mum to feed the child and let them gulp as much as they want, a decent feed.  Then stand and watch.  Look for the stomach churning against the stenotic pylorus – waves or ripples of movement can be seen… sometimes.  It is an inconsistent finding in the trials.  Of course, looking for a forceful, projectile vomit is key. The key word here is “forceful” – vomiting is active, a strong reflex. Passive regurgitation is a gentle, effortless phenomenon.  Watch and know the difference.

Feeling for the “tumour” or Olive involves slowly feeling in the epigastrium as the belly muscles relax. My friend, Dr. Ross Fisher (Paeds Surgeon) recommends examining from the ‘wrong’ side to allow you to feel the right epigastrium without going through the rectus sheath.  Others advocate holding the infant in the prone position and allowing the belly to relax as the child is suspended over your palm.

This is an art, not easy to do if you have never done it before.  Having an empty stomach makes it easier to feel the lump, so an NGT may help.  Paradoxically you may need to place an NG tube, then feed the kid to settle and then…  sneakily aspirate the stomach to make the exam possible!

A positive exam – actually feeling the lump is great, and can clinch the diagnosis.  Unfortunately, it is often not palpable…about half of kids with PS will not have a positive olive sign… so where to from here?

ULTRASOUND

Using point-of-care US on small infants sounds tricky. It is certainly not a simple thing to do for your first few scans, but it is doable.  The scan should be done immediately after a decent volume feed to fill the stomach.

The antrum and pyloris are identified usually just to he right of the midline in the epigastrium.  You are looking for something that looks a lot like a cervix on a sagittal pelvic scan.  Now if you find the pyloris it should have a thick hypoechoic wall (there are 5 layers to the gastric wall) with a hyperechoic lumen.  Sometimes gas shadows are seen.  Measurement is key.  This is where it gets really nerdy.  You will need to measure the muscle thickness (of a single wall side), the total diameter of the pylorus and then the lengthof the pyloric canal. Here are the key numbers:

1. Muscle thickness  =  > 3 mm
2. Pyloric total diameter >14 mm
3. Pyloric canal length > 15 mm

Nerds will recognize 3.1415 as… pi!  So the numbers for PS are as easy as pi to remember.

The other thing to watch for as you scan dynamically is the passage of milk from the antrum through the pyloric canal. This does not rule out PS, but is reassuring if there are no hard signs of PS on the scan.

Now, I accept that I am a die-hard POCUS proponent and my enthusiasm may outstrip the technical possibilities for many ED docs… but it is really a lot easier than looking for the CBD in the average chubby, colicky character.

BIOCHEMISTRY

Kids with PS vomit gastric acid aka HCl.  Over time they develop a hypochloremic metabolic alkalosis.

So we need a gas to diagnose this, a heel prick sample will suffice- nobody wants to cannulate babies unnecessarily. ( however, if you think it is PS and the child is dry, an IV is inevitable. So crack on !)

In the presence of a reasonable length of symptoms (days) one should get at least some degree of alkalosis.  So if you are thinking PS and the gas is normal, then you may need to rethink.

Although as diagnosis is getting earlier and earlier we are seeing more kids with normal biochemistry.  So interpret the gases in context of the duration and severity of symptoms.

The other number that is useful on a blood gas is the pCO2. In response to the metabolic acid losses the CO2 levels rise in compensation… this can cause apnoeas to occur, especially in smaller and preterm infants. So beware if the CO2 is up, monitoring is advised and careful fluid resuscitation.

Kids with later stage PS get dry and may develop hypoperfusion, shock and metabolic acidosis.. so be aware of that trick too.

OBSERVATION

My friend and esteemed Paeds ED fellow, Damian Roland, wisely says that a period of observation is the most useful “INVESTIGATION “ in the arsenal of the Paediatric ED team.

This is certainly the case when faced with a vomiting infant. An hour or two allows us to get a clean urine specimen, looks for new changes in temperature or heart rate etc. Test feed and reweigh our thoughts along with the child. It is also immensely reassuring for parents.

ASK: A SURGEON

If you are lucky enough to work in a hospital where there is a surgeon with experience in this problem, then use their expertise.  This can be a tricky diagnosis, feeling that olive is not so easy. This is a great time to swallow one’s pride ( hopefully past the pyloric valve ) and phone a friend to get help.

Thanks to Dr Ross Fisher (@ffoliet)  and Dr Justin Morgenstern (@First10EM) for their feedback and expertise in crafting this post.