EUS: Pyloric Stenosis, Early Pregnancy, Serratus Plane block

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Brown Ultrasound Tape Review – 11:19:15
At this week’s BUTR, we again reviewed some great ultrasound images that were scanned over the past week.
Resident reviewer: Dr. Mike Hunihan
Faculty reviewers: Drs. Erika Constantine and Otto Liebmann
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PYLORIC STENOSIS
When to suspect pyloric stenosis:
– Onset between 3-5 weeks old, but can occur up to 12 weeks old.
– More commonly affects males.
– Risk factors include family history of pyloric stenosis, maternal smoking, macrolide antibiotics administered to infant, and bottle-feeding.
– Classic presentation is “hungry vomiter”; postprandial forceful non-bilious vomiting.
How to diagnose: 
– “Olive-shaped” mass that can be palpated along the R rectus sheath is pathognomonic, but rarely found.
– Ultrasound is the gold standard test when done by an experienced ultrasonographer.
– Additional studies, when ultrasound and exam are nondiagnostic, include barium swallow and upper endoscopy.
Ultrasound diagnostic criteria: 
Pyloric Muscle Thickness = >3mm
Pyloric Muscle Length = >14mm
Helpful mnemonic to remember this: Pi =3.14 (PYloric stenosis, >3mm thick, >14mm long)
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Abnormal findings: (Upper) Channel length (Lower) Muscle wall thickness
Another component of the US exam is to watch for passage of gastric contents through the pylorus. If you visualize passage of gastric contents, this is reassuring that there is no pyloric stenosis. However, sometimes you can get passage of small volumes of liquid through a tight pylorus and still have pyloric stenosis – it’s called the string sign with barium studies.
The other pertinent signs of pyloric stenosis:
1. Antral Nipple Sign: Redundant pyloric mucosa that protrudes into gastric antrum resembling a nipple.
 image
2. Target Sign: Hypertrophied hypoechoic muscle surrounding echogenic mucosa layer, visualized in short axis.
target sign
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3. Cervix Sign: Indentation of the pylorus into the fluid filled antrum. image (1)
In 2013, there was a prospective observational trial of PEM fellows performing bedside US for diagnosis of pyloric stenosis. They had a convenience sample of patients who were suspected to have pyloric stenosis based on history and physical exam, and who were ordered to have a formal ultrasound in the radiology department. The PEM fellows also performed bedside ultrasound on those same patients and compared their results to the radiology results. They enrolled 67 patients into their study, of which, 10 patients (15%) were found to have pyloric stenosis. The results of their study showed a 100% sensitivity and 100% specificity for PEM fellows performing bedside ultrasound. They had zero false positives or false negatives. This study suggests that bedside ultrasound for evaluation of pyloric stenosis is feasible for our residents, fellows, and attendings in the ED.
Sivitz, Adam B., Cena Tejani, and Stephanie G. Cohen. “Evaluation of hypertrophic pyloric stenosis by pediatric emergency physician sonography.”Academic Emergency Medicine 20.7 (2013): 646-651.
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EARLY PREGNANCY

We also discussed the use of ultrasound in early pregnancy patients. From the ED perspective, our main question should be: IUP or no IUP?  If we cannot visualize a definitive IUP (gestational sac + yolk sac) then we need to be concerned about ectopic pregnancy.
But what about heterotopic pregnancy?
-A heterotopic pregnancy is the presence of both an IUP AND an ectopic pregnancy at the same time!
– In females who become pregnant by natural means, the chance is 1 in 10,000.
– In females who have assisted reproduction (IVF or even just hormone therapy) that chance increases to 1 in 1,000.

Moral of the story: When performing ultrasound in early pregnancy be sure to take a good history of any assisted reproduction techniques used for that pregnancy 
 
In addition to determining the location of an early pregnancy, we discussed the diagnostic criteria for non-viable IUP. A helpful review article in NEJM by Doubilet et al reviews the topic at length. 
 
Important measurements on US that are diagnostic for nonviable pregnancy: 
CRL >7mm with no heartbeat 
GS diameter >25mm with no embryo 
 
image (2)
Doubilet, Peter M., et al. “Diagnostic criteria for nonviable pregnancy early in the first trimester.” New England Journal of Medicine 369.15 (2013): 1443-1451.

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SERRATUS NERVE BLOCK
Finally, we discussed a novel serratus plane nerve block that could be useful for anesthesia for axillary abscesses, rib fractures, or even chest tube placement. The aim is to block the thoracic intercostal nerves and provide anesthesia to the lateral hemithorax. The images below show the two options for serratus nerve plane block; injecting superior or inferior to the serratus anterior.
image (3)
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Although this study gave the initial description of a serratus nerve plane block, there is still further studies to be performed. Something to keep an eye out for!
Blanco, R., et al. “Serratus plane block: a novel ultrasound‐guided thoracic wall nerve block.” Anaesthesia 68.11 (2013): 1107-1113.

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