Pyloric Stenosis or Infantile Hypertrophic Pyloric Stenosis (IHPS)
Pyloric stenosis or Infantile Hypertrophic Pyloric Stenosis (IHPS) is gastric outflow obstruction caused by hypertrophy of the muscular layers in the pyloris.
Hypertrophy and hyperplasia of the 2 muscular layers of the pylorus leads to lengthening and thickening of the pyloric canal. Both of these are readily seen on ultrasound.
Whilst no specific inherited gene has been identified, there is a strong familial tendancy.
Some environmental factors such as nitric oxide and gastric hyperacidity have been suggested as contributing factors also.
Treatment is generally surgical.The Ramstedt pyloromyotomy (named after the original surgeon who described the technique in 1912) has a high success rate with very few complications.
The typical presentation is a neonate with projectile vomiting, failure to thrive and unsettled.
There may be suggestion of constipation but a baby with IHPS will produce very little faeces due to the gastric obstruction.
On examination the hypertrophied pylorus has been described as a firm epigastric lump similar to an olive, or the tip of your nose.
Measure the length of the pyloric canal (Black arrow).
The muscle thickness also must be measured (Blue arrow)
Rotate the probe 90degrees to view the Pylorus in transverse.
Measure the transverse muscle diameter.
Normal Ultrasound Appearances
A longitudinal view of the normal Pylorus
Ultrasound view in Transverse, the thin rim of Muscle is typical of a normal Pylorus.
A 2nd helpful finding, is that the hypertrophied pylorus is generally displaced to lie subjacent to the gallbladder. This is an indicator only and care must be taken that a full stomach is not the cause for the displaced pylorus. (REF: “Pylorus subjacent to the gallbladder: An additional finding in hypertrophic pyloric stenosis”. Authors:Deborah Levine MD1, David C. Wilkes MD2, Roy A. Filly. MD32 DEC 2005 DOI: 10.1002/jcu.1870230706)
Ultrasound of the normal Pylorus, distant to the Gall Bladder.
Ultrasound image of water in the pyloric canal.
Ultrasound of a Complex material (milk) passing through the pyloric canal.
Treatment is generally surgical. The Ramstedt pyloromyotomy (named after the original surgeon who first performed the technique in 1912).
The technique has a high success rate with very few complications.
Role of Ultrasound
To identify the cause for projectile vomiting and failure to thrive in the neonate.
If the baby has been crying alot, there will often be gas in the stomach making visualisation difficult.
It is important to explain the procedure to the parents so they will assist in entertaining and keeping the baby calm. Some parents are very emotional and become distressed themselves because the baby is crying. This increases tension in the examination room which the baby will further react to.
The baby needs to be fasted. Ideally for 4 hours. This avoids gastric gas obscuring the view of the pylorus. Also, if there is a substantial amount of stomach contents still present after a 4hour fast, then suspicion is high for a gastric outflow obstruction or transit problem.
Parents/carers need to bring a feed for the baby. Pre-boiled, tepid water is the best. The water creates a good acoustic window. Milk creates echogenic heterogeneous material in the stomach.
If the baby is breast fed and the parents do-not want to deviate from that, then allow the baby to feed for 5 minutes then rescan.
Warm gel and warm room are essential.
2 Probes will usually be utilised, depending on the amount of bowel gas and what pathology is encountered.
A linear array mid – high frequency (6-10MHz) – usually ideal to view the Pylorus.
A small foot-print, high frequency annular array or curvilinear probe (6-8MHz)
Position the baby supine initially and perform a survey scan of the abdomen to ensure there are no gross pathologies.
Scan the epigastrium for the Pylorus. Possibly incline the baby on a pillow, and rolled slightly left side elevated. (this will promote fluid towards the Pylorus an gas away towards the stomach antrum.
If the pylorus appears normal, assess the Coeliac axis and mesenteric vessels for any anatomical variants because malrotation is a differential diagnosis for IHPS.
Position the baby in the inclined, left side elevated position and watch for material to run through the pylorus.
Criteria for IHPS
Hypertrophy of the pyloris leads to it’s lengthening and widening.
The criteria for IHPS:
Length: > 16mm Transverse Muscle diameter: > 3.5mm (ref: Ultrasound in the diagnosis of idiopathic hypertrophic pyloric stenosis. N Engl J Med 1977; 296: 1149-1150 Author:Teele RL, Smith EH)
Basic Hardcopy Imaging
Longitudinal pylorus with canal length measurement.
Transverse pylorus with muscle thickness measurement.
Relationship of pylorus to the gallbladder
Right kidney/adrenal region
Left kidney/adrenal region
If negative for IHPS, images of the coeliac axis and mesenteric arteries should be taken to confirm normal alignment and no malrotation.