The impact of high-frequency transducers on the sonographic measurements of the pyloric muscle thickness in infants

The impact of high-frequency transducers on the sonographic measurements of the pyloric muscle thickness in infants

REVIEWED BY Ilona Lavender, FASA |ASA SIG: Paediatric

REFERENCE | Authors: Yousef A, Daneman A, Amirabadi A, Faingold R

WHY THE STUDY WAS PUBLISHED

Ultrasound is often performed when hypertrophic pyloric stenosis (HSP) is suspected. With increasing resolution and better ultrasound machines over the years, this article aimed to standardise the measurements and evaluate the appearance of the normal and HSP with high frequency transducers.

HOW THE STUDY WAS PERFORMED

With ethics approval, the PACS system was used to search for patients who had an ultrasound for a differential diagnosis of HSP. Data was collected over a two-year period (Jan 2019 – Dec 2020). Studies with a longitudinal image using a linear transducer of 12–18 MHz were included in the analysis. Any poor quality studies were excluded. Measurements were taken off the longitudinal views as they found this plane to be the most reliable.

• Two paediatric radiologists independently measured the transverse muscle thickness of the pylorus.

• Measurement (a) includes the outer layer of muscularis propria until the inner layer of muscularis mucosa, including the hyperechoic stripe (submucosa).

• Measurement (b) includes only the muscularis propria without the submucosa and muscularis mucosa.

(Fig. 1) Cases were divided into positive and negative, where positive cases were confirmed surgically and negative cases were presumed when the patient didn’t have surgery and was discharged.

Fig. 1 Normal sonographic appearance of the wall of the pylorus using a linear-array transducer, 18 MHz, in a 6-week-old female who presented with vomiting. In these transverse images of the upper abdomen, the normal pylorus is shown in longitudinal view. A Image shows the normal layers of the pylorus. (a) Hypoechoic muscularis propria; (b) Hyperechoic stripe of submucosa; (c) Hypoechoic muscularis mucosa; (d) Hyperechoic stripe of interface between mucosa and intraluminal echogenic contents.

B Image shows two different methods of measurement of the thickness of the pylorus. (a) Measurement from the outer surface of the hypoechoic muscularis propria down to the hyperechoic interface between the mucosa and intraluminal content; (b) Measurement from the outer surface of the hypoechoic muscularis propria down to the level of the outer surface of the hyperechoic stripe of the submucosa.

WHAT THE STUDY FOUND

There were 554 patients with a differential diagnosis of HPS. After the exclusion criteria, 300 patients were used in this study of which 114 were female and 186 were male. HPS was confirmed in 59 cases (19.7%).

In the first 100 cases, both radiologists performed the measurements – the intraclass correlation coefficient was high at 0.99.

• Measurement (a) had a mean of 2.4 mm in normal cases and 4.8 mm in abnormal cases.

• Measurement (b) had a mean of 4.8 mm in confirmed cases of HPS.

• The muscularis propria was more hyperechoic in all HPS in contrast to all normal cases, where the muscularis propria was hypoechoic showing similar echogenicity to the muscularis mucosa.

• Measurement of the thickness was demonstrated to be the most useful to confirm or exclude HPS.

• There was no statistical difference in method (a) or (b) when measuring the thickness in the longitudinal view; however, method (b) demonstrated a 100% specificity.

• New cut-off values were established with high accuracy

• 3.6 mm for measurement (a)

• 2.8 mm for measurement (b)

Measuring only the muscularis propria improves diagnostic accuracy by reducing overlap between negative and positive cases. The absence of pyloric wall stratification and echogenic muscularis propria is specific to HPS.

RELEVANCE TO CLINICAL PRACTICE

It is important to use a high frequency transducer when performing a scan for a suspected hypertrophied pyloric stenosis. Sonographers should suspect a positive HPS when there is increased echogenicity of the muscularis propria and a loss of mural stratification. Furthermore, it appears that assessment and measurement of the muscularis propria solely in the longitudinal view is highly specific for the diagnosis of HPS. The function assessment should be used in conjunction with the measurements and borderline cases can be rescanned.