Brown Sound: Point-Of-Care Ultrasound Diagnosis of Pyloric Stenosis

Case Presentation

An ex-full term six-week old male presented to the pediatric emergency department with three weeks of forceful, non-bloody, non-bilious emesis.  He was having two to four episodes of vomiting that occurred after feeding.  Three weeks prior, the patient had been transitioned from breast milk to formula, and attempts to thicken the formula by adding rice had not improved his vomiting.  More recently, he had poor PO intake and his parents were concerned about his weight.  He had no fevers, no change in number of wet diapers or stooling, and no other acute complaints.

Vital signs showed a blood pressure of 110/59, heart rate of 136, respiratory rate of 40. He was afebrile with a normal oxygen saturation.

On exam, the patient was resting in his mother’s arms in no apparent distress.  His abdomen was soft and non-tender.  There were no palpable masses or organomegaly.

D I A G N O S I S

Pyloric Stenosis

Discussion

Pyloric stenosis typically presents between three to six weeks of age and is associated with male sex, prematurity, being a first-born child, smoking during pregnancy, bottle feeding, and erythromycin use during the first two weeks of life.[1] It is characterized by hypertrophy of the pylorus, leading to gastric outlet obstruction and the classic presentation of an infant with forceful, non-bloody, non-bilious vomiting after eating.[2] In the past, the physical exam finding of a palpable olive-like mass in the right upper quadrant and lab abnormalities such as a hypochloremic metabolic alkalosis were more relied upon for diagnosis, but an increasing awareness of the disease process and the availability of ultrasound can often lead to a diagnosis before these findings develop.[3]

Ultrasound is the study of choice to diagnose pyloric stenosis as sensitivity and specificity can reach greater than 95% when performed by experienced operators.[1] Though this is typically done by radiologists, there is also some limited evidence to suggest that with training, emergency physicians can utilize point of care ultrasound with similar sensitivity and specificity.[4,5]

To visualize the pylorus, use a high frequency linear transducer.  With the infant supine or in the right lateral decubitus position and the transducer held transversely, the operator first identifies landmarks such as the liver and gallbladder to the right and stomach to the left.  Often the pylorus can be found medially and posteriorly to the gallbladder.  Alternatively, one can follow the stomach as it transitions to the antrum and subsequently to the pylorus.[1,2]

When seen in a transverse view, the pylorus may exhibit a “target sign” with the hypoechoic muscular layer surrounding the hyperechoic pyloric channel (Figure 1).[1] By rotating the transducer, one can visualize the pylorus in its long axis as well, again noting the hypoechoic muscular layer above and below the hyperechoic pyloric channel.

Figure 1. Transverse view showing the target sign and measurement of pyloric muscle thickness.[2]

The key to diagnosing pyloric stenosis with ultrasound are a combination of measurements that fall within or above the upper limits of normal.  Because the pylorus is often not visualized in a pure transverse or longitudinal view, these can be difficult to obtain.  Though many measurements have been used, the most common are[1]:

• Pyloric muscle thickness (upper limit of normal: 3-4mm).  Obtain measurements in both transverse and longitudinal views of the hypoechoic anterior muscle layer (Figure 1 and 2). 

• Pyloric muscle length (upper limit of normal: 15-19mm).  Obtain measurement in the longitudinal view (Figure 2).

Figure 2. Longitudinal view of the pylorus. PM = pyloric muscle thickness; the longer line shows the pyloric muscle length.[2]

While not diagnostic on their own, other findings that may be seen in pyloric stenosis include the “shoulder sign,” in which the pyloric muscle extends into the antrum and the “antral nipple,” in which the pyloric channel mucosa similarly protrudes into the antrum (Figure 3).[3] Additionally, one may use the “hamburger sign,” or the subjective appearance of a hamburger when evaluating the pylorus in the longitudinal view.

Figure 3. Visualization of the antral nipple.[6]

Case Conclusion

The patient was taken to the operating room the following day and underwent a laparoscopic pyloromyotomy without complications.  The patient did well post-operatively and was discharged the day following his surgery after tolerating multiple feeds.

Take-Aways

• Do not rely solely on classic exam findings and lab abnormalities when diagnosing pyloric stenosis.

• Ultrasound is the study of choice for diagnosing this condition.

• Increased pyloric thickness and length are the key measurements to obtain through ultrasound.

 Faculty Reviewer

Dr. Zachary Binder

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References

1. Olive AP, Erin EE. Infantile Hypertrophic Pyloric Stenosis. UpToDate, 22 Jan. 2020, www.uptodate.com/contents/infantile-hypertrophic-pyloric-stenosis. Accessed January 25, 2020.

2. Dorinzi N, et al. Immediate Emergency Department Diagnosis of Pyloric Stenosis with Point-of-Care Ultrasound. Clin Pract Cases Emerg Med. 2017; 1(4): 395–398.

3. Pyloric Stenosis. Harwood-Nuss' Clinical Practice of Emergency Medicine, by Wolfson AB, et al. Wolters Kluwer, 2015: 1245–1247.

4. Malcom GE, et al. Feasibility of Emergency Physician Diagnosis of Hypertrophic Pyloric Stenosis Using Point-of-Care Ultrasound: A Multi-Center Case Series. J Emerg Med. 2009; 37(3): 283–286.

5. Sivitz AB., et al. Evaluation of Hypertrophic Pyloric Stenosis by Pediatric Emergency Physician Sonography. Acad Emerg Med. 2013; 20(7): 646–651.

6. Carpenter G, Behrang A. Pyloric Stenosis: Radiology Reference Article. Radiopaedia Blog RSS. www.radiopaedia.org/articles/pyloric-stenosis. Accessed January 25, 2020.