Hypertrophic pyloric stenosis: volumetric measurement of nasogastric aspirate to determine the imaging modality

Cost-effective imaging approach to the nonbilious vomiting infant

OBJECTIVE

To develop a cost- and time-effective algorithm for differentiating hypertrophic pyloric stenosis (HPS) from other medical causes of emesis in infants referred from community-based pediatricians and family practitioners to the imaging department of a tertiary children's care facility.

METHODS

Eighty-nine vomiting infants (22 females, 67 males) between the ages of 11 and 120 days (mean, 43.5 days) had received nothing by mouth for at least 1 hour before the study. Each child was assessed for duration of vomiting, status of body weight, time and volume of last ingestion, and time of last emesis. A #8 French (Sherwood Medical, St Louis, MO) nasogastric feeding tube was placed in the child's stomach. The contents were aspirated and measured to determine likelihood of HPS. An aspirated volume >/=5 mL implicated gastric outlet obstruction, and ultrasonography (US) was performed. If this study was positive for HPS, the patient was referred for surgery. If US was negative, an upper gastrointestinal series (UGI) was performed. An aspirated stomach contents volume <5 mL suggested a medical cause for the emesis, and UGI was performed. Pediatric surgeons with no knowledge of the volume results palpated the abdomens of 73 of 89 infants (82%).

RESULTS

Twenty-three of 89 patients (25%) had HPS. The aspirate criteria for HPS had a sensitivity of 91%, a specificity of 88%, and an accuracy of 89%. Of the false-positive studies (total = 8), six were related to recent significant ingestion (within 2 hours of the study), and two were attributable to antral dysmotility. The surgeons palpated the mass in 10 of 19 patients (53%). Sensitivity and specificity were 53% and 93%, respectively. Only 6 of 89 infants (7%) required both US and UGI to determine the etiology of the nonbilious vomiting. By performing the UGI in 66 patients, it was also found that 14% had slow gastric emptying and 79% had gastroesophageal reflux. Eighty-one percent of the gastroesophageal reflux was significant.

CONCLUSION

The volumetric method of determining the proper imaging study is cost- and time-effective in the evaluation of the nonbilious vomiting infant for pyloric stenosis. If US was performed initially in all patients referred for imaging, two studies would have been performed in 68 of 89 patients (76%) to define the etiology of the emesis. Because we used the volumetric method, 62 fewer imaging studies were performed, representing a savings of $4464 and 30 hours of physician time. If children are given nothing by mouth for 3 to 4 hours before gastric aspiration, the specificity of the volumetric method improves to 94%, and the accuracy improves to 96%.

Ultrasound as a screening study for gastro-oesophageal reflux in children

A comparison of the abilities of ultrasound and scintigraphy to detect gastro-oesophageal reflux was made in 110 children (mean age 24.5 months) who were divided into groups A (n = 49) and B (n = 61). The former had scintigraphy first followed by ultrasound within about 30 min. For group B scintigraphy was also performed first, but the delay before ultrasound ranged between 1 and 30 days. In most patients (91/110) concordant results were obtained by the two modalities. The 19/110 discordant results can be explained by several plausible mechanisms. It is concluded that ultrasound should be employed much more frequently as an initial investigation when pathological reflux is suspected in children.

Controversies in abdominal imaging

Technologic improvement in ultrasound equipment, together with new clinical information, has altered the imaging of the abdomen in infants. Improvements in ultrasound equipment have allowed this to become the diagnostic test of choice for hypertrophic pyloric stenosis. Barium upper gastrointestinal radiography still remains the diagnostic test of choice for malrotation. New technologies for reduction of intussusception include air reduction and saline enemas with ultrasound monitoring. Controversies surrounding the different technologies and imaging strategies are discussed.