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We describe a systematic approach to the ultrasound US examination of the antropyloric region in children. US is the modality of choice for the diagnosis of hypertrophic pyloric stenosis HPS.
The imaging features of the normal pylorus and the diagnostic findings in HPS are reviewed and illustrated in this pictorial essay. Common difficulties in performing the examination and tips to help overcome them will also be discussed. Hypertrophic pyloric stenosis HPS is the most frequent surgical condition in infants in the first few months of life [ 1 ]. The condition is characterised by thickening of the muscular layer and failure of the pyloric canal to relax resulting in gastric outlet obstruction.
Elongation of the canal and thickened mucosa are also seen. Ultrasound US is the preferred diagnostic modality [ 2 ] as it is a non-invasive technique, allowing direct observation of the pyloric canal morphology and behaviour. It is important to carry out a systematic and dynamic study and to be aware of the common technical difficulties and how to overcome them. HPS is the most common surgical cause of vomiting in infants. It has an incidence of 3 per 1, live births per year, although wide variations have been documented with geographic location, season and ethnic origin [ 3 ].
This disease usually presents between the second and sixth weeks of life, more commonly in the white population, in males male:female ratio and typically in first-born children [ 4 ]. A history of an affected first-degree relative increases the risk more than five-fold [ 5 ]. The US examination allows the radiologist to perform a brief clinical history, which can reveal essential clues to the diagnosis. A recent history of projectile and nonbilious vomiting, which may be intermittent or with every feeding is the classical complaint.
Typically the infant has a voracious appetite. When the vomiting persists, other clinical and biochemical findings may occur such as dehydration, hypochloraemic alkalosis and unconjugated jaundice. Prompt US diagnosis is important as these late findings make the infants sub-optimal candidates for surgery.
US is the first modality of choice when there is clinical suspicion of HPS, as it is non-invasive and does not use radiation, which is a crucial advantage in children. It is also a commonly available with relatively low cost. US also allows a dynamic study with direct observation of the pyloric canal morphology and behaviour. The US should be performed by an experienced radiologist.
Having a systematic approach will improve the sensitivity of the technique. Before performing the US, some general conditions for examining infants should be addressed, as these can affect the quality of the examination. The key is to keep the baby comfortable, for example with US gel warmed to a suitable ambient temperature. If possible the examination should be performed after a feeding and accompanied by a parent. A high-frequency transducer adjusted to the size of the patient and the depth of the pylorus should be used.
First step: In the supine position with the transducer in a transverse position and sometimes with slight anti-clockwise rotation, identify the gallbladder. The pylorus is usually located slightly medial and posterior in relation to the gallbladder Fig. Second step: Assess the appearance and measurements of the pylorus Fig. It is important to be aware that tangential views and contractions can produce pseudo-thickening.
Third step: Visualize the passage of the gastric content through the pylorus, distending the antropyloric region. This dynamic evaluation is vital, as a wide open pylorus with normal passage of the gastric contents excludes HPS Fig.
Passage of the gastric content through the pylorus, distending the antropyloric region arrow. One common difficulty is a stomach filled with gas Fig. The easiest way to avoid this is by placing the infant in an oblique position with the right side down, as this will allow fluid to fill the antrum, acting as an acoustic window. A stomach completely filled with milk can also cause artefacts, other possibilities are to give the infant water or even to place a nasogastric tube, empty the stomach and then fill it with water.
Another frequent problem is that a markedly distended stomach can displace the pylorus dorsally making it very difficult to access Fig.
In this situation, moving the infant into an oblique position with the left side down will help to move the pylorus to a more anterior position. The identification of the pylorus can be difficult, but a systematic approach will improve chances of success. Remember that a normal pylorus is much harder to visualise than a hypertrophied one. The main diagnostic criterion is measurement of the thickness of the muscular layer.
The other principal sonographic size criterion is the length of the pyloric canal. In HPS the thickened muscle and elongated pylorus are fixed over time, which helps the operator to identify this condition. The appearance of the hypertrophied pylorus has previously been described as the cervix sign [ 11 ], as it resembles the appearance of the uterine cervix Fig. Additional US findings in HPS are hypertrophy of the mucosa and a markedly distended and actively peristalsing stomach. A double internal layer of crowded and redundant mucosa may be identified Fig.
This was classically described as the nipple sign in conventional contrast studies. The double layer of thickened mucosa is hyperechogenic and can be confused with echogenic contents passing through the pylorus.
Thickening of the pyloric canal may be transient due to peristalsis or pylorospasm. In the majority of cases of pylorospasm, the muscle is not hypertrophied. With prolonged observation, pyloric opening may be visualised. Particular attention should be paid to pre-term infants and those in the younger age range. In premature infants, HPS develops at the same age as in term infants, but their smaller size should be taken into consideration.
Argyropoulou et al. Haider et al. However these authors also highlight the importance of the morphological appearance of the pylorus in premature infants. The treatment of HPS is surgical pyloromyotomy. A further US examination may be requested if vomiting persists following surgery.
In the first week after surgery, the muscle can be the same thickness or even thicker than before surgery and then the dimensions gradually return to normal.
This order of changes is related to the anterior surgical approach to the muscle [ 15 ]. An upper GI examination may also be performed if emesis continues post-operatively, in order to exclude a duodenal leak or to assess an incomplete pyloromyotomy or gastro-oesophageal reflux [ 16 ].
Pyloric US examination is a dynamic investigation, which should be performed in a systematic way. The radiologist should be aware of the pitfalls of the examination and how to overcome them. It is important to be familiar with the normal and hypertrophied pyloric appearances, as this will provide a greater diagnostic confidence, assisting in early diagnosis and improving the management of infants with HPS.
National Center for Biotechnology Information , U. Journal List Insights Imaging v. Insights Imaging. Published online May 1. Author information Article notes Copyright and License information Disclaimer. Corresponding author. This article has been cited by other articles in PMC. Abstract We describe a systematic approach to the ultrasound US examination of the antropyloric region in children. Keywords: Hypertrophic pyloric stenosis, Ultrasound.
Introduction Hypertrophic pyloric stenosis HPS is the most frequent surgical condition in infants in the first few months of life [ 1 ]. Clinical features HPS is the most common surgical cause of vomiting in infants. Imaging technique US is the first modality of choice when there is clinical suspicion of HPS, as it is non-invasive and does not use radiation, which is a crucial advantage in children. US examination of the antropyloric region Before performing the US, some general conditions for examining infants should be addressed, as these can affect the quality of the examination.
Identification of the pylorus First step: In the supine position with the transducer in a transverse position and sometimes with slight anti-clockwise rotation, identify the gallbladder. Open in a separate window. Observe the pyloric morphology Second step: Assess the appearance and measurements of the pylorus Fig. Observe the pyloric behaviour Third step: Visualize the passage of the gastric content through the pylorus, distending the antropyloric region.
Tips and tricks One common difficulty is a stomach filled with gas Fig. US diagnostic criteria of HPS The main diagnostic criterion is measurement of the thickness of the muscular layer. Borderline measures Thickening of the pyloric canal may be transient due to peristalsis or pylorospasm. Conclusion Pyloric US examination is a dynamic investigation, which should be performed in a systematic way.
References 1. Ohshiro K, Puri P. Pathogenesis of infantile hypertrophic pyloric stenosis: recent progress. Pediatr Surg Int. Hiorns MP. Gastrointestinal tract imaging in children: current techniques. Pediatr Radiol. Panteli C. New insights into the pathogenesis of infantile pyloric stenosis. Chandran L, Chitkara M. Vomiting in children: reassurance, red flag, or referral? Pediatr Rev. Hernanz-Schulman M.
Congenital hypertrophic pyloric stenosis
Case Presentation A one month old male child presents with projectile vomitting after feeds. An abdominal ultrasound was performed. Infantile or congenital hypertrophic pyloric stenosis is one of the most common surgical causes of vomiting in infancy. The infant may present with failure to retain feeds, persistent non-bilious vomiting after feeds, a palpable epigastric mass [which is the thickened pylorus] and dehydration [hypochloremic metabolic alkalosis due to loss of acid in the vomitus]. The circular muscle hypertrophies and the thickened muscle reduces the lumen of the pyloric channel and also elongates it.
Pyloric stenosis is a narrowing of the opening from the stomach to the first part of the small intestine the pylorus. The cause of pyloric stenosis is unclear. Treatment initially begins by correcting dehydration and electrolyte problems. About one to two per 1, babies are affected.