Hypertrophic Pyloric Stenosis HPS

Congenital hypertrophic pyloric stenosis is characterized by hypertrophy of the circular muscle layer and represents the most common cause of gastric outlet obstruction (Hernanz-Sohulman 2003). Takahashi (2003) suggested that impaired neuronal nitric oxide synthase synthesis in the myenteric plexus is an important contributing factor in the pathogenesis of HPS as well as of achalasia, diabetic gastroparesis, Hirschsprung disease and Chagas disease.

Children usually present at the age of 3-6 weeks, but with a range from 1 week to 3 months. It is unusual in premature infants and older children. There is a definite male predominance and is also more commonly seen in firstborns in comparison with their younger siblings. The patient will typically present with increasing vomiting, leading to projectile vomiting. The vomitus is not bile stained since the obstruction is proximal to the ampulla of Vater.

The diagnosis can be made by physical examination by palpating the typical olive in the epigastrium. Peristaltic waves may also be seen on the abdominal wall.

An abdominal X-ray may be nonspecific or demonstrate a distended stomach with a small amount of air distally (Fig. 3.10). In some instances gastric pneumatosis can be seen, which resolves spontaneously after nasogastric tube placement in order to decompress the stomach. The imaging diagnosis using an upper GI study has been replaced by US in many countries worldwide, since US allows direct visualization of the hypertrophied muscle (Fig. 3.11). Typically, the patient is given water or a dextrose solution orally, and is subsequently placed in the right posterior oblique position. The left liver lobe can be used as an acoustic window to evaluate the pylorus in the supine position. The muscle thickness, as well as the muscle length, the pyloric channel length, the pyloric muscle index (calculated using pyloric length, pyloric muscle thickness and pyloric diameter) and the muscle volume have all been used as indicators of HPS (Westra et al. 1989). Overall the muscle thickness seems to be the most important criterion, with a muscle thickness equal a b c

Fig. 3.11. US reveals an elongated pyloric channel (asterisks) and a thickened longtitudinal pyloric muscle (crosses). (Courtesy of Dr. Carlo Buonomo, Boston, MA, USA)

Fig. 3.10. Plain abdominal radiograph reveals a markedly distended stomach and hyperperistalsis. (Courtesy of Dr. Carlo Buonomo, Boston, MA, USA)

or greater than 3 mm, indicating HPS, and 2 mm or less, indicating a normal pylorus muscle. The channel length should be greater than 15 mm to support the diagnosis of HPS (Blumhagen et al. 1988).

The differential diagnosis includes pylorospasm (which may cause an increased muscle thickness, but only transiently), (eosinophilic) gastroenteritis, gastric and duodenal ulcers. If the US findings are not clearly diagnostic, an upper GI examination is next.

On a barium study almost all children will show some degree of pylorospasm, which may cause a delay as long as 20-25 min in the passage of barium through the antropyloric region. Classical findings on upper GI include: the "string" sign, consistent with a narrowing of the pyloric channel, is almost always seen in conjunction with an elongated and upward curved pyloric channel. The "double track/string" sign is caused by barium which is caught between folds overlying the hypertrophied muscle. A similar sign can be seen on US, without being pathogno-monic for HPS since it can also be seen in patients with pylorospasm (Cohen et al. 2004). The "beak" sign is the result of the thickened muscle narrowing the barium column as it enters the pyloric channel.

Fig. 3.11. US reveals an elongated pyloric channel (asterisks) and a thickened longtitudinal pyloric muscle (crosses). (Courtesy of Dr. Carlo Buonomo, Boston, MA, USA)

The thickened and enlarged muscle mass resembles an 'apple core lesion' with undercutting of the distal antrum and proximal duodenum. The "pyloric tit" can be seen along the lesser curvature of the stomach, just proximal to the impression of the pyloric mass and may be consistent with a blocked peristaltic wave. The "shoulder" sign is caused by impression of the hypertrophied muscle on the antrum. All of the above mentioned findings can also be seen transiently in normal children, therefore the study should be done carefully, with documentation of the persistence of these signs. The treatment of choice is pyloromyotomy, surgically or laparoscopically. However, some countries (Sweden, Japan) also have experience with nonsurgical therapy.

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