Pyloric stenosis

Hypertrophic pyloric stenosis refers to idiopathic thickening of gastric py­loric musculature which then results in progressive gastric outlet obstruction.

Epidemiology

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 4 - 8 weeks of life. There may be a positive family history. Incidence of hypertrophic pyloric stenosis is approximately two to five per 1,000 births per year in most white populations,

HPS is less common in India and among black and Asian populations

Clinical presentation

Clinical presentation is typically with non-bilious projectile vomiting in the second month of life. 

The hypertro­phied pylorus can be palpated as an olive sized mass in the right upper quadrant. It is suggested that palpation of an “olive” with the appropriate clinical symptoms is diagnostic and that such infants do not need confirma­tory imaging studies.

A succussion splash may be audible, and although common, is only relevant if heard hours after the last meal ⁶. 

Radiographic features

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 visualize the hypertrophied muscle.

Plain film (abdominal radiograph)

Non specific and may show a distended stomach with minimal distal intestinal bowel gas.

Ultrasound

Ultrasound is usually the primary imaging modality ³, and it's advantages over a barium meal are that it directly visualizes the pyloric muscle and does not use ionizing radiation. Unfortunately it is incapable of excluding other diagnoses such as midgut volvu­lus.

The hypertrophied muscle is hypoechoic, and the central mucosa is hyperechoic. There are measurement criteria that vary slightly from source to source. In a normal situation, the pyloric muscle thickness (diame­ter of a single muscular wall on a transverse image) should normally be less than 3 mm (most accurate ³) and the length (longitudinal measurement) should not exceed 15 mm.

With the patient right side down the pylorus should be watched and should not be seen to open.

Described sonographic features/signs include:

• antral nipple sign
• cervix sign
• target sign

Technique tip

The pylorus is located near the gallbladder, thus an easy technique is to find the gallbladder and turn obliquely sagittal to the body in an at­tempt to visualize the pylorus longitudinally.

Fluoroscopy (Barium meal)

Barium meals demonstrate delayed gastric emptying. When some contrast does pass into the duodenum, the pylorus appears elongated 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). Additionally the entrance to the pylorus may be beak-shaped ("beak sign") . 

Described barium signs include:

• shoulder sign
• string sign
• double-track sign
• mushroom sign
• beak sign

Treatment and prognosis

Initial medical management is essential with re-hydration 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.

Differential diagnosis

There is usually little differential when imaging findings are appropriate. Of course clinically it is important to consider other causes of vomiting in infancy, including midgut volvulus.

A degree of pylorospasm is common in infancy and is responsible for some delay in gastric emptying. The pylorus, however, appears normal.