Hypertrophic pyloric stenosis (HPS) refers to idiopathic thickening of gastric pyloric musculature which then results in progressive gastric outlet obstruction.
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Pyloric stenosis is relatively common and has a male predilection (M:F ~4:1), and is more commonly seen in Caucasians 4. It typically occurs between first week to 3 months of age. There may be a positive family history.
Incidence of hypertrophic pyloric stenosis is approximately 2-5 per 1,000 births per year in most white populations. HPS is less common in India and among black and other Asian populations.
Clinical presentation is typically with non-bilious projectile vomiting. The hypertrophied pylorus can be palpated as an olive sized mass in the right upper quadrant. A succussion splash may be audible, and although common, is only relevant if heard hours after the last meal 6.
- maternal history of pyloric stenosis 10
HPS is the result of both hyerplasia and hypertrophy of the pyloric circular muscles fibres. The pathogenesis of this is not understood. There are four main theories 9:
- immunohistochemical abnormalities
- genetic abnormalities
- infectious cause
- hyperacidity theory
Children with hypertrophic pyloric stenosis may show gastric distension, prominent peristaltic waves (caterpillar sign), and mottled retained gastric content.
A upper gastrointestinal series (barium meal) excludes other, more serious causes of pathology, but the findings of a UGI series infer rather than directly visualise the hypertrophied muscle.
Abdominal x-ray findings are non-specific but may show a distended stomach with minimal distal intestinal bowel gas.
Ultrasound is the modality of choice in right clinical setting because of its advantages over a barium meal are that it directly visualises the pyloric muscle and does not use ionising radiation. Unfortunately it is incapable of excluding other diagnoses such as midgut volvulus. Easy ultrasound technique is to find gallbladder then turn the probe obliquely sagittal to the body in an attempt to find pylorus longitudinally.7
The hypertrophied muscle is hypoechoic, and the central mucosa is hyperechoic. Normal measurements include:
- pyloric muscle thickness, i.e. diameter of a single muscular wall on a transverse image: <3 mm (most accurate 3)
- length, i.e. longitudinal measurement: <15-17 mm
- pyloric volume: <1.5 cc
- pyloric transverse diameter: < 13 mm
With the patient right side down the pylorus should be watched and should not be seen to open.
Described sonographic signs include:
On upper gastrointestinal fluoroscopy:
- delayed gastric emptying
- elongated pylorus with a narrow lumen (string sign) which may appear duplicated due to puckering of the mucosa (double-track sign)
- the pylorus indents the contrast-filled antrum (shoulder sign) or base of the duodenal bulb (mushroom sign)
- the entrance to the pylorus may be beak-shaped ("beak sign")
Described barium signs include:
Treatment and prognosis
Initial medical management is essential with rehydration and correction of electrolyte imbalances. This should be completed prior to surgical intervention.
Treatment is surgical with a pyloromyotomy in which the pyloric muscle is divided down to the submucosa. This can be performed both open and laparoscopically. The operation is curative and has very low morbidity 4-5.
There is usually little differential when imaging findings are appropriate. Of course clinically it is important to consider other causes of vomiting in infancy.
A degree of pylorospasm is common in infancy and is responsible for some delay in gastric emptying. The pylorus, however, appears normal.
Gastro-oesophageal reflux which represents the cause of vomiting in two-thirds of infants referred to radiology 8.
Other causes of proximal gastrointestinal obstruction can be considered 8:
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