Sono Pro Tips and Tricks for Acute Appendicitis

Written by: Morgan McCarthy, MD (NUEM ‘24) Edited by: David Feiger, MD (NUEM ‘22)
Expert Commentary by: Shawn Luo, MD & John Bailitz, MD

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Welcome to the NUEM SonoPro Tips and Tricks Series where Local and National Sono Experts team up to take you scanning from good to great for a particular diagnosis or procedure.

For those new to the probe, we recommend first reviewing the basics in the incredible FOAMed Introduction to Bedside Ultrasound Book, 5 Minute Sono, and POCUS Atlas. Once you’ve got the basics beat, then read on to learn how to start scanning like a Pro!

Did you know, appendicitis is one of the most common surgical emergencies. Despite this, some data suggests that appendicitis is missed in 3.8% to 15% of children and 5.9% to 23.5% of adults in ED visits. Appendicitis is difficult to diagnose due to the early nonspecific generalized symptoms (anorexia, generalized pain, nausea, diarrhea or constipation). We can use point of care ultrasound (POCUS) to help evaluate your differential diagnosis. One study showed that after only a 20-minute training ED physicians at various levels of experience were able to scan for appendicitis with a specificity of 97.9% and a sensitivity to 42.8%.

Beyond the classic pediatric patient, who else does the SonoPro scan?

Pocus use for appendicitis is one of the leading diagnostic tools in pediatrics for acute appendicitis. In the pediatric population limiting radiation is generally thought to be of utmost importance. The lack of exposure to radiation and small habitus makes ultrasound a great alternative in the pediatric patient. These tips and tricks can be useful in other high risk adult patients, like pregnant women. It is well known that in adults there is often a higher chance of pathology and surgeons are managing the ultimate say on whether more imaging is necessary. However, the use of ultrasound for acute appendicitis may save time, expedite care, lead to quicker consultation, and potentially augment patient satisfaction and improve outcomes. 

How to scan like a Pro:

• There are a few ways to scan for the appendix. To start, we recommend simply asking for the patient to point to where the pain is worst and place the probe directly over that spot. 

•  A simple trick is to have the patient cross their right leg over their left leg; this brings the appendix closer to the abdominal wall. 

• If neither of these work, start to look for visual landmarks to orient yourself: iliac artery and vein, and the psoas muscle. The psoas muscle will be posterior, the iliac artery will be medial and the iliac crest lateral. Many times the appendix may be on top of the iliac artery. ‘Lawn mowing’ the probe up and down in this area may help it come into view.

What to Look For:

•  Try to look for a blind ending tubular structure that is not undergoing peristalsis. When you locate this, turn your probe to view the appendix in short axis and measure the anterior to posterior diameter. In a normal appendix this may be shorter than the lateral measurements as a normal appendix is compressible!

• There are two main criteria for diagnosing appendicitis on ultrasound: 

1. > 6mm*

2. non-compressible 

*Note: Make sure to consider your patient’s age; the criteria may not apply to young children as their appendix may be naturally smaller. Appendix growth typically occurs at 3 to 6 years, therefore in this population you may depend more on secondary findings.

There are many secondary findings that many experts believe may be more useful than the measurements of the appendix itself as this can be very difficult to accurately measure:

What to do next:

Ultrasound for appendicitis is very specific, however not very sensitive. If you see a dilated non-compressible blind ending loop of bowel without peristalsis, you may have identified an appendicitis - call your surgeon, follow recommendations and start antibiotics! If you are uncertain, look for secondary signs of appendicitis as above; if they are found you can increase your suspicion of appendicitis. If these findings are not present, more advanced diagnostic imaging may be required with respect to your clinical suspicion. Consider an MRI in a young patient or CT scan with contrast in an adult for further evaluation.

Where to Learn More (References)

1. Mahajan P, Basu T, Pai C, et al. Factors Associated With Potentially Missed Diagnosis of Appendicitis in the Emergency Department. JAMA Network Open. 2020;3(3):e200612. doi:10.1001/jamanetworkopen.2020.0612.

2. Y Ravichandran, P Harrison, E Garrow, and JH Chao. Size Matters: Point of care Ultrasound in Pediatric Appendicitis. Pediatric Emergency Care. 2016; 32: 815-816.

3. Ma, John, et al. Ma and Mateer's Emergency Ultrasound. McGraw-Hill Education, 2020.

4. Macias, Micheal. TPA, The Pocus Atlas. 

5. Availa, Jacob. 5 minute Sono. 

6. US G.E.L. Podcast

7. Nelson, Chiricolo, Raio, Theodoro, Patel, Johnson. Can Emergency Physicians Positively Predict Acute Appendicitis on Focused Right Lower Quadrant Ultrasound?. Annals of Emergency Medicine, 2005; 46: 27-28

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Expert Commentary

Excellent job by Morgan and David on this engaging and informative post summarizing the latest and greatest pro-tips and tricks for POCUS for Appendicitis. POCUS again has been demonstrated to be a helpful adjunct to improve time to diagnosis and treatment when utilized by trained clinicians for appropriate patients. On your next pediatric, pregnant, or otherwise thin “Rule out Appy”, begin the exam by asking the patient to cross their leg to flex the psoas muscle to bring the appendix closer to probe. Have the patient point to the pain to identify where to start. If the appendix is not visualized, then go to McBurney’s point in the axial plane, visualizing the iliac artery & vein to find the nearby appendix. Next, start “lawn mowing” by compressing slowly but with adequate depth to displace bowel gas. Once you see what appears to be an inflamed appendix, trace the structure to verify the blind-ending and hold your probe for a few seconds to confirm the lack of peristalsis. Measure the diameter, then turn on color flow and look for other secondary signs of inflammation. Since the specificity is high, when appendicitis is visualized, call your surgeon, and consider skipping the CT. But remember, since the appendix often “hides” within the bowel the sensitivity is low, so other comprehensive imaging will be needed to reach the correct diagnosis.

John Bailitz, MD

Vice Chair for Academics, Department of Emergency Medicine

Professor of Emergency Medicine, Feinberg School of Medicine

Northwestern Memorial Hospital

Shawn Luo, MD

PGY4 Resident Physician

Northwestern University Emergency Medicine

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How To Cite This Post:

[Peer-Reviewed, Web Publication] McCarthy, M. Feiger, D. (2021, Nov 22). Sono Pro Tips and Tricks for Acute Appendicitis. [NUEM Blog. Expert Commentary by Luo, S and Bailitz, J]. Retrieved from http://www.nuemblog.com/blog/sonopro-tips-and-tricks-for-acute-appendicitis

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A Practical Approach to Abdominal Imaging

Written by: Zach Schmitz MD (PGY-3) Edited by: David Kaltman, MD (PGY-4) Expert commentary by: Samir Abboud, MD

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I often find myself in a gray zone when it comes to imaging abdominal pain. Any third year medical student worth their salt can tell you to get the RUQ ultrasound for the fat, fertile, forty year-old female with RUQ abdominal pain, fever, positive Murphy’s sign, and leukocytosis. However, my patients don’t usually fit the textbook, and I’m often thinking about what I might miss or see with test X vs test Y. Below, I’ll touch on a few common dilemmas where the optimal choice of imaging modality isn’t immediately clear by focusing on what you actually gain or lose by ordering one imaging test over another.

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Scenario 1: Stone or Appendicitis?

Case: 62 year old female with HTN and HLD presents with RLQ pain. The pain woke her this morning and has been intermittent all day, occurring exclusively when she urinates. It is sharp, non-radiating, and increasing in intensity. She never had a pain like this and can now barely sit still. She has thrown up a few times over the past few hours. Vitals are stable and she is afebrile. She appears uncomfortable with RLQ tenderness but no rebound or guarding. Labs show slight leukocytosis, and urine has no blood.

If I suspect stone over appendicitis, will a CT without contrast miss appendicitis?

• CT, MR, and US are well studied in their ability to detect and accurately diagnose appendicitis.[1] 

  • CT with IV contrast is 96-100% sensitive and 91-100% specific. Per the American College of Radiology’s (ACR) appropriateness system, this is the most appropriate initial test for suspected appendicitis in adults.[2]

  • MR is 96% sensitive and 96% specific.[3]

  • Ultrasound has a wide range of data, with sensitivity ranging from 21-95.7% and specificity of 71-97%.[2]

• CT without oral or IV contrast is nearly as useful for diagnosing appendicitis

  • A meta-analysis by Xiong et al included seven original studies investigating a total of 845 patients.[4]

    • Pooled sensitivity - 0.90 (95% CI: 0.86-0.92)

    • Pooled specificity - 0.94 (95% CI: 0.92-0.97)

    • Pooled positive likelihood ratio - 12.90 (95% CI: 4.80-34.67)

    • Pooled negative likelihood ratio - 0.09 (95% CI: 0.04-0.20)

Will a contrast enhanced CT for appendicitis ruin my chance to catch a kidney stone?

• Non-contrast CT is the emergency standard in diagnosing nephrolithiasis with good reason - it is 97% sensitive and 95% specific.[5]

• Will contrast ruin the ability to detect a stone?

  • This makes theoretical sense as stones and contrast are both hyper-intense on CT.

  • Sensitivity is decreased for small stones with contrast enhanced studies.

  • However, for stones > 3mm, sensitivity remains 95%.[5]

  • Only about 5% of stones that small ultimately require intervention.

Takeaways: You sacrifice a bit with a non-contrast study looking for appendicitis and a contrast enhanced study looking for stone, but both still work well. The American Urology Association recommends consultation for stones > 10mm.[6] Urology would also need to be involved with signs of sepsis, abscess, deterioration in renal function, intractable symptoms, or a transplant/solitary kidney. It seems I am very likely to see a stone requiring something other than watchful waiting on a CT with contrast. It is worse to miss an appendicitis than a 2mm stone, so contrast might make more sense if it’s close. 

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Scenario 2: RUQ Ultrasound after Negative CT San

Case: 84 year old male with a history of prostate cancer and hypertension presents from a nursing home with 4 days of diffuse abdominal pain. He has had no vomiting or bowel movements over this time. No urinary symptoms. He is hemodynamically stable, and his abdomen is diffusely tender (maybe worse in the RUQ) and distended but overall not terribly impressive. You order a CT for possible obstruction and it just shows a large stool burden. The gallbladder was visualized and looked normal. 

If a CT is negative, should I get a RUQ US to look for cholecystitis?

• RUQ Ultrasound

  • Per ACR, this is the most appropriate initial study for RUQ pain and suspected biliary disease.[7]

  • A 2012 meta analysis showed a sensitivity of 81% (95% CI 75-87%) and specificity of 88% for acute cholecystitis.[8]

  • It has the advantage of being dynamic, with a sonographic Murphy sign independently showing an 86% sensitivity and 35% specificity, positive predictive value of 43%, and negative predictive value of 82%.[9] 

• Computed Tomography (CT) 

  • The same 2012 meta analysis only had one study with CT, but noted a sensitivity of 94% with fairly broad confidence intervals (95% CI 73-99) and a specificity of only 59%.[8]

  • ACR notes CT’s NPV for acute cholecystitis approaches 90%.[7]

  • A 2015 study looked at 101 patients who went to the OR and got both a CT and US. For acute cholecystitis, the sensitivities for CT and US were 92% and 79% respectively. For cholilithiasis, sensitivities for CT and US were 60% and 89% respectively.[10,11]

  • ACR states it is “usually appropriate” to proceed with CT for RUQ pain and suspected biliary disease with a negative or equivocal ultrasound.[7]

  • Although it lacks a sonographic murphy’s sign equivalent, its advantage is to help in operative planning and seeing complications, such as perforation or gangrene.

• MRI has a sensitivity of 85% and a specificity of 81%. It is also considered “usually appropriate” by ACR if ultrasound is negative or equivocal[7]

• Cholescintigraphy is the best imaging, showing 97% sensitivity and 90% specificity for acute cholecystitis. It is also the most appropriate study if you suspect acalculous cholecystitis.[7]

Takeaways: There are a few interesting points from this set of data. First, CT seems to have at least as good of ability to pick up cholecystitis compared to ultrasound. However, it is much worse in detecting gallstones themselves, which may be very relevant to a patient with abdominal pain. Second, the sensitivity of both RUQUS or CT isn’t really that great and we are probably missing a few episodes of cholecystitis. If there is a very high index of suspicion but negative imaging, it may be worthwhile to pursue additional workup. Overall, if the CT shows a normal gallbladder, and you are not worried about intractable biliary colic, the ultrasound probably won’t add much. 

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Scenario 3: Female Pelvic Pain

Case: 33 year old female with a history of chlamydia infection presenting with right sided abdominal pain. The pain has gradually been getting worse for 1 day. She has had a few episodes of vomiting. There is some white vaginal discharge she always has. On exam, she is tachycardic, normotensive, and febrile to 101.5. She has RLQ tenderness with voluntary guarding. On pelvic exam, there is some white vaginal discharge, CMT, R adnexal tenderness that seems less intense than her RLQ tenderness, and no masses noted.

If this patient had a normal appendix and ovaries after a contrast enhanced CT for appendicitis, how useful is an additional transvaginal ultrasound to rule out gynecologic pathologies?

For ovarian torsion:

• A retrospective study of 834 patients showed the NPV of a contrast enhanced CT of the pelvis for ovarian torsion is 100%.[12]

• A prospective study of 199 patients showed doppler ultrasound has a sensitivity and specificity for torsion of 100 and 97%.[13]

For Tubo-Ovarian Abscess (TOA):

• CT is thought to be between 78 and 100% sensitive.[14]

• 2011 literature review gives a broad range of sensitivity and specificity for US in TOA with a sensitivity of 56-93% and specificity from 89-98%.[15]

Takeaways: ACR appropriates rates ultrasound as the most appropriate test for female pelvic pain.[14] However, it also rates CT with contrast as more appropriate for suspected appendicitis.[2] This patient raises concerns for both, and a CT was done first. CT is good for finding intra abdominal and pelvic abscess. It is more difficult to assess how useful ultrasound is for TOA, as many studies in the literature review were either before year 2000 or used a transabdominal approach. Overall, if someone has a CT scan for appendicitis that shows normal ovaries, the transvaginal ultrasound seems to add little for either torsion or TOA.

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One potential dangerous conclusion from this set of data is that we should just CT everyone up front. While CT shows good sensitivities for many of the pathologies in question, simply ordering a CT first ignores the many good reasons - such as cost, radiation dose, speed, improved specificity and comparable sensitivity, resource utilization, sonographic murphy sign - RUQUS and pelvic ultrasound are the most appropriate initial tests for suspect biliary and pelvic pathology. That said, it a patient has an entirely normal CT that was already performed for other indicated reasons, the use of additional imaging may be unnecessary and should be considered carefully. Overall, the question of exactly what imaging test to order when ruling out common, emergent, abdominal pathologies is often a difficult one with shades of gray. By having a better understanding of exactly what type of information we are getting and missing from each test we order, emergency physicians can more quickly, safely, and accurately diagnose and treat our patients.

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Expert Commentary

This is a thoughtful, well-reasoned approach to optimizing the imaging strategy in challenging, atypical clinical scenarios. To add a few nuances to some of the points raised:

When considering a contrast-enhanced versus non-contrast CT (both IV and PO) in the clinically ambiguous scenario, it is important to consider your patient’s body habitus. Figure 1 includes representative images from a non-contrast enhanced CT of a patient with a BMI above 25. You can clearly see the inflammatory stranding in the right lower quadrant mesenteric fat (Figure 1a) and portions of an appendicolith (Figure 1 b), in this patient who ultimately proved to have appendicitis. The natural contrast provided by the patient’s mesenteric fat in this scenario helps us work around the absence of IV contrast.

Figure 1a

Figure 1b

Figure 2 includes representative images from a contrast enhanced CT of a very thin patient, with a relative paucity of intra-abdominal fat. In this patient, the relative absence of natural contrast would greatly reduce our chances to diagnose appendicitis (or even identify the appendix) in the absence of IV contrast. PO contrast is additionally likely to be most helpful in very thin patients [Alabousi 2015].

Figure 2

The author asks (and answers) a very insightful question with regards to identifying kidney stones on contrast enhanced CT. A few points to add:

Assuming the contrast enhanced study is obtained prior to the excretory phase of imaging (and most routine studies are) ureteral stones should still be largely visible - the stones that will generally be more difficult to identify will be the non-obstructing stones still within the collecting system. Additionally, while there is indeed a small sacrifice in sensitivity for small stones with contrast enhanced studies, the identification of secondary complications is much improved.

Consider Figure 3, which demonstrates a 2 mm stone in the proximal left ureter identified on a contrast enhanced study. Notice the slightly delayed nephrogram on the left relative to the right, which could indicate a component of obstructive uropathy. Similarly, identification of such complications as pyonephrosis, pyelonephritis, and perinephric abscess is much improved with contrast enhanced images. For this reason, I would suggest that in the clinically ambiguous scenario, erring on the side of the contrast enhanced study would be wise.

Figure 3

It is important to note that the CT scanner installed in our emergency department is a dual-energy machine. Many of our other departmental scanners are dual-energy as well. With these scanners, we are able to apply algorithms to deconstruct the elemental composition of stones and provide more information than simply size and location - i.e. uric acid or non-uric acid stone - if requested. We can additionally generate virtual non-contrast images from the contrast-enhanced images, without exposing our patients to additional radiation. While it is tempting to think that we could recapture some of the sensitivity for renal stones using these virtual non-contrast images, this has unfortunately not been borne out in the literature at this time [Vrtiska 2010], though remains an area of continued investigation as imaging technology is further improved.

The advantages of dual-energy imaging are not only limited to the kidneys. With regards to the evaluation of biliary colic, virtual monochromatic images can be generated with resulting increased conspicuity of gallstones, even those that appear isodense to bile on the conventional images [Ratanaprasatporn 2018].

In general, if you find yourself with a high degree of suspicion for any disease process and discordant imaging findings, I would encourage you to call your radiologist. The additional clinical information exchanged during such a call may direct what additional data sets should be generated and what additional imaging studies may be of most benefit. Last, but certainly not least, that “second look” armed with additional clinical information can pick up on subtle findings that are, in isolation, entirely non-specific, but in a certain clinical scenario could clinch the diagnosis you are seeking.

References:

Alabousi A et al. Is Oral Contrast Necessary for Multidetector Computed Tomography Imaging of Patients With Acute Abdominal Pain? Canadian Association of Radiologists Journal. 2015;66(4): 318 - 322

Ratanaprasatporn L et al. Multimodality Imaging, including Dual-Energy CT, in the Evaluation of Gallbladder Disease. Radiographics 2018;38(1): 75-89

Vrtiska TJ et al. Genitourinary Applications of Dual-Energy CT. American Journal of Roentgenology. 2010;194: 1434-1442.

Samir Abboud, MD

Assistant Professor of Radiology

Northwestern University

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How To Cite This Post:

[Peer-Reviewed, Web Publication] Schmitz, Z. Kaltman, D. (2020, Feb 10). An Approach to Abdominal Imaging. [NUEM Blog. Expert Commentary by Abboud, S]. Retrieved from http://www.nuemblog.com/blog/abdominal-imaging.

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References

1. Dahabreh IJ, Adam GP, Halladay CW, Steele DW, Daiello LA, Weiland LS, Zgodic A, Smith BT, Herliczek TW, Shah N, Trikalinos TA. Diagnosis of Right Lower Quadrant Pain and Suspected Acute Appendicitis. Comparative Effectiveness Review No. 157. (Prepared by the Brown Evidence-based Practice Center under Contract No. 290-2012-00012-I.) AHRQ Publication No. 15(16)-EHC025-EF. Rockville, MD: Agency for Healthcare Research and Quality; December 2015. www.effectivehealthcare.ahrq.gov/reports/final.cfm.

2. American College of Radiology. ACR Appropriateness Criteria®: RLQ pain. Available at https://acsearch.acr.org/docs/69357/Narrative/ Accessed 5/10/19.

3. Duke E, Kalb B, Arif-Tiwari H, et al. A Systematic Review and Meta-Analysis of Diagnostic Performance of MRI for Evaluation of Acute Appendicitis. AJR Am J Roentgenol 2016;206:508-17.

4. Xiong B, Zhong B, Li Z, Zhou F, Hu R, Feng Z, Xu S, Chen F. Diagnostic Accuracy of Noncontrast CT in Detecting Acute Appendicitis: A Meta-analysis of Prospective Studies. Am Surg. 2015 Jun;81(6):626-9.

5. Curhan G, Aronson M, Preminger G. Diagnosis and acute management of suspected nephrolithiasis in adults. UpToDate.com. April 30 2019. 

6. Assimos D, Krambek A, Miller N et al. Surgical Management of Stones: AUA/Endourology Society Guideline (2016). https://www.auanet.org/guidelines/kidney-stones-surgical-management-guideline. Accessed 5/10/19.

7. American College of Radiology. ACR Appropriateness Criteria®: RUQ pain. Available at https://acsearch.acr.org/docs/69474/Narrative/ .

8. Kiewiet J.J., Leeuwenburgh M.M., Bipat S., et al: A systematic review and meta-analysis of diagnostic performance of imaging in acute cholecystitis. Radiology 2012; 264: pp. 708-720.

9. Bree, Robert L. Further observations on the usefulness of the sonographic Murphy sign in the evaluation of suspected acute cholecystitis. Journal of Clinical Ultrasound. March/April 1995.

10. Wertz JR1,2, Lopez JM3, Olson D4, Thompson WM1,2. Comparing the Diagnostic Accuracy of Ultrasound and CT in Evaluating Acute Cholecystitis. AJR Am J Roentgenol. 2018 Aug;211(2):W92-W97. doi: 10.2214/AJR.17.18884. Epub 2018 Apr 27.

11. Fagenholz, P et al. Computed Tomography Is More Sensitive than Ultrasound for the Diagnosis of Acute Cholecystitis. Surg Infect (Larchmt). 2015 Oct;16(5):509-12. doi: 10.1089/sur.2015.102. Epub 2015 Sep 16. 

12. Lam A1, Nayyar M2, Helmy M2, Houshyar R2, Marfori W2, Lall C2.Assessing the clinical utility of color Doppler ultrasound for ovarian torsion in the setting of a negative contrast-enhanced CT scan of the abdomen and pelvis. Abdom Imaging. 2015 Oct;40(8):3206-13. Doi: 10.1007/s00261-015-0535-4.

13. Laufer, M. Ovarian and fallopian tube torsion. UpToDate. April 30 2019. https://www.uptodate.com/contents/ovarian-and-fallopian-tube-torsion?search=ovarian%20torsion&source=search_result&selectedTitle=1~70&usage_type=default&display_rank=1 .

14. Beigi, R. Epidemiology, clinical manifestations, and diagnosis of tubo-ovarian abscess. UpToDate. April 30 2019. https://www.uptodate.com/contents/epidemiology-clinical-manifestations-and-diagnosis-of-tubo-ovarian-abscess?search=tuboovarian%20abscess&source=search_result&selectedTitle=2~24&usage_type=default&display_rank=2 .

15. Lee DC1, Swaminathan AK. Sensitivity of ultrasound for the diagnosis of tubo-ovarian abscess: a case report and literature review. J Emerg Med. 2011 Feb;40(2):170-5. doi: 10.1016/j.jemermed.2010.02.033. Epub 2010 May 13.

16. American College of Radiology. ACR Appropriateness Criteria®: Female Pelvic Pain. Available at https://acsearch.acr.org/docs/69503/Narrative/ .