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Acute Appendicitis


This webpage contains:

  • Appendicitis

  • Bowel Obstruction

  • Intussusception



  • Benefits of Ultrasound: Using ultrasound to diagnose acute appendicitis has many benefits.  It avoids both radiation and IV contrast and their small, but real, associated risks.  In addition, ultrasound may be faster than CT as there is no need to wait for BUN & creatinine results or for oral contrast to move distally.  If you do it yourself it is even faster!
  • Sensitivity & Specificity: Both the sensitivity & specificity of ultrasound for appendicitis are less than that of CT.  In pediatrics the values are about 88% & 94% respectively and in adults about 83% and 93%.  These values are actually not that bad when compared to CT scan whose sensitivity and specificity are around 94% and 95% respectively.  Remember however that the performance characteristics for ultrasound can be significantly worse in overweight patients or those with overlying bowel gas.  In addition if the appendix is retrocecal or is lying in a difficult anatomical plane, the study will be more challenging.  Unfortunately, you may have to still do a CT scan if your scan is non-diagnostic.
  • Patient Selection: Ultrasound is an excellent initial imaging modality for the appendix in thin individuals, especially children and young adults.  The lower amount of interfering subcutaneous fat and heightened concern over unnecessary radiation in this population makes them optimal candidates for ultrasound instead of or at least before CT.   In the pregnant patient, ultrasound is the initial study of choice to evaluate right-lower-quadrant pain and can be performed simultaneously with a pelvic scan to look for a cyst or ectopic pregnancy.
  • Probe Selection: In most patients, use a 5-7.5 mHz linear array small parts probe.  For deeper imaging, you may need to obtain images with the 3-5 mHz curvilinear probe in patients with increased subcutaneous fat, or those in whom a retrocecal appendix is suspected.
  • Technique Tips: Allow the patient to direct the ultrasound probe to the point of maximal tenderness.  Begin imaging there.  Look for a non-compressible round structure about 1cm in diameter.  Always image in at least two planes: once you find a cross-sectional view of what appears to be an inflamed appendix, adjust your probe to look for a long-axis view.  Confirm that the structure has a blind-tip at one end to avoid confusion with vascular or other structures.
  • Diagnostic Criteria: Diagnostic criteria for acute appendicitis are as follows: a non-compressible, aperistaltic blind-ended tubular structure which is greater than 7mm in diameter and connects to the cecum.  Checking for non-compressibility involves pushing down with the ultrasound probe to see if the structure you are viewing is flattened at all.  Intestines usually will demonstrate peristalsis which can be seen in real time if you look long enough.
  • Other Signs: On a transverse image of the appendix, look for the “target sign” of inflamed muscularis propria surrounded by edema and inflammatory changes.  You might see other sonographic clues, including periappendiceal fluid, prominent pericecal fat with stranding, a hyperechoic appendicolith within the tubular appendix, or presence of an abscess or phlegmon.
  • Negative Studies: You or your friendly sonographer must visualize a normal, compressible appendix on ultrasound to definitively rule-out appendicitis.  Unlike with CT scan, this is rarely the case.  If the appendix is not seen on ultrasound, you have a non-diagnostic study, so consider an 8 hour return visit for ongoing pain, a surgical consultation, or a CT scan
  • Know Thy Surgeon:  Not all surgeons are comfortable going to the OR based on an ultrasound that is positive for appendicitis.  If the pretest probability is not already very high, your surgical colleagues may still request a CT scan.  Don’t let that prevent you from doing the right thing for your patient.  If you do more ultrasounds you &/or your ultrasound techs will become more proficient and your surgeons will eventually get more comfortable when repeated ultrasounds are confirmed by either CT or operative findings.  If you impress your surgeons, they may even want to start borrowing your machine to do their own ultrasounds.
  • Disadvantages: Ultrasound is far less likely to accurately identify other causes of right lower quadrant pain such as a kidney stone, Crohn’s disease, right sided diverticulitis, mesenteric adenitis and the like.  Keep this and your differential diagnosis and relative levels of suspicion in mind when choosing your initial imaging study.

acute appendicitis – labelled


Usually it’s difficult to find a normal appendix with ultrasound.

 Sometimes you get lucky.

Click below to see a brief video.

Click & Watch: Normal Appendix Peristalsing


Appendicitis ultrasound cross section - asterixes mark the outer border, lumen is dark


Appendicitis ultrasound long axis - asterixes mark the outer border



  • Know your limitations: Ultrasound may help clarify findings elicited by a thorough history and physical exam.  When used correctly, it can greatly improve diagnostic accuracy, and help guide patient management, especially for time-critical diagnosis and treatment of unstable patients.  If you use ultrasound in your ED, your department should have a quality improvement program set up that is approved by both ED administration and radiology.
  • Scan the sausage: The intussusception usually sits in the right upper quadrant.  If you feel something that is shaped like a sausage, that’s the best place to start your scan.  You are looking for a “target sign” or “donut sign” of one concentric cross section of bowel within another.
  • Know the pros and cons: Ultrasound has a reported sensitivity of 85% and specificity of 98% for intussusception and is radiation-free.  However, it is not therapeutic.  Consider it’s use when you are not worried that it will cause a significant delay or when attempts at radiographic reduction are contraindicated.  Since it is a rare condition, the skill level and experience of the sonographer may play a large role.
  • Know your other studies: X-ray is not sensitive, but may show obstruction or decreased stool or air in the right lower quadrant.  A CT scan can diagnose intussusception, but is not a first line study; consider its use when other conditions, such as appendicitis, are also high on your list of differential diagnoses.   The study of choice is an air or gastrografin enema, which is diagnostic as well as therapeutic in most cases.
  • Heed Pregerson’s Rule: This rule boils down to not trusting the consultant when your gut tells you they are wrong.  It states “When the consultants says there is no way that a patient has disease-X the risk for disease-X doubles.”  Corollary:  “If the consultant is an orthopedist or a radiologist the risk quadruples.”
  • Practice Makes Perfect: With bedside ultrasound there is no substitute for experienceThe more ultrasounds you do, the better you will be able to differentiate abnormal from normal, even when you may not be sure exactly what the abnormality is. Take a look at the abdomen of the next pediatric patient you see with abdominal pain.  Most of us probably wouldn’t recognize an inflamed appendix, intussusceptum or hypertrophied pylorus if it was staring us in the face in the middle of our screen, but you might!  Either way, it’s a good idea to practice on kids just like adults.  You don’t want a sick trauma case to be your first time sounding your way through the pediatric abdomen.


Intussusception with “Target” sign


Diagnosis of intussusception by physician novice sonographers in the emergency department.

Ann Emerg Med.  2012; 60(3):264-8 (ISSN: 1097-6760)

Riera A; Hsiao AL; Langhan ML; Goodman TR; Chen L Department of Pediatrics, Section of Emergency Medicine, Yale University School of Medicine, New Haven, CT. STUDY OBJECTIVE: We investigate the performance characteristics of bedside emergency department (ED) ultrasonography by nonradiologist physician sonographers in the diagnosis of ileocolic intussusception in children. METHODS: This was a prospective, observational study conducted in a pediatric ED of an urban tertiary care children’s hospital. Pediatric emergency physicians with no experience in bowel ultrasonography underwent a focused 1-hour training session conducted by a pediatric radiologist. The session included a didactic component on sonographic appearances of ileocolic intussusception, review of images with positive and negative results for intussusceptions, and a hands-on component with a live child model. On completion of the training, a prospective convenience sample study was performed. Children were enrolled if they were to undergo diagnostic radiology ultrasonography for suspected intussusception. Bedside ultrasonography by trained pediatric emergency physicians was performed and interpreted as either positive or negative for ileocolic intussusception. Ultrasonographic studies were then performed by diagnostic radiologists, and their results were used as the reference standard. Test characteristics (sensitivity, specificity, positive and negative predictive values) and likelihood ratios were calculated. RESULTS: Six pediatric emergency physicians completed the training and performed the bedside studies. Eighty-two patients were enrolled. The median age was 25 months (range 3 to 127 months). Thirteen patients (16%) received a diagnosis of ileocolic intussusception by diagnostic radiology. Bedside ultrasonography had a sensitivity of 85% (95% confidence interval [CI] 54% to 97%), specificity of 97% (95% CI 89% to 99%), positive predictive value of 85% (95% CI 54% to 97%), and negative predictive value of 97% (95% CI 89% to 99%). A positive bedside ultrasonographic result had a likelihood ratio of 29 (95% CI 7.3 to 117), and a negative bedside ultrasonographic result had a likelihood ratio of 0.16 (95% CI 0.04 to 0.57). CONCLUSION: With limited and focused training, pediatric emergency physicians can accurately diagnose ileocolic intussusception in children by using bedside ultrasonography.



  • Know your limitations: Ultrasound may help clarify findings elicited by history and physical exam.  When used correctly, it can greatly improve diagnostic accuracy, and help guide patient management, especially for time-critical diagnosis and treatment in unstable patients.  There is no substitute for hands-on practice to improve your skills, but if you use ultrasound in your ED, your department should also have a quality improvement program set up that is approved by both ED administration and radiology.
  • Hollow Viscus Imaging: Imaging the bowel is not part of the core-curriculum in Emergency Medicine Bedside Ultrasound Applications.  However, if you do come across abnormal bowel images during your scan of the other areas of the abdomen, it is useful to understand what those findings may imply.
  • Bowel Obstruction: Dilated loops of bowel will measure >3cm in diameter and contain anechoic (black) fluid within their lumen.  Gas-filled bowel may be difficult to visualize and will cause scatter over far-field structures.
  • Pseudo-mass: A loop of bowel may occasionally look like a mass.  This is especially common when imaging the gallbladder.  The duodenum may look like a solid mass just behind and below the gallbladder.  If the duodenum is filled with solid matter, it may also produce acoustic shadowing and confuse you to think you are looking at a gallbladder filled with gallstones.  When in doubt, scan through the structure in question and see if it connects to the common bile duct.
  • Peristalsis: If you keep your probe steady, you may be able to see the bowel peristalsing.  This may help you to identify certain structures as bowel.  It is also interesting to watch or show your patients.
  • Other Applications: Ultrasound evaluation of the bowel is a time-intensive process and requires additional training and credentialing.  Although you may not have the requisite skill to detect appendicitis or intussusception by ultrasound, your ultrasound tech may.  Always keep in mind the potential advantages of ultrasound when ordering imaging tests on patients in whom you may want to minimize exposure to ionizing radiation, such as pregnant patients and young children. An added benefit of imaging the appendix with ultrasound is that there is no delay for the passage of oral contrast.


Small Bowel Obstruction (bowel lumen is black).  If bowel if fille


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