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Abdominal Ultrasound

Gallbladder disease is well suited for emergency ultrasound investigations. Use of diagnostic ultrasound frequently leads to either confirmation of a presumptive diagnostic or rapid narrowing of the differential diagnoses. However, if biliary ultrasound findings are equivocal or conflict with initial clinical impressions, the emergency physician should be reminded that formal studies or other imaging modalities may be complementary.
Manual of Emergency and Critical Care Ultrasound

Vicki E. Noble

All renal masses are malignant until proven otherwise. Detection of a renal mass by point-of-care ultrasound requires further workup with additional radiographic imaging.
Point of Care Ultrasound E-book

Soni et al. 2020

Objectives 

To reach the objectives for this module read the following text, watch the videos and finish the QUIZ.

Objectives Acute Abdominal Pain

  • Understanding the indication for focused exams when looking for hydronefrosis, gallstones/cholecystitis, and small bowel obstruction
  • Performing the examination and obtaining the following views: RUQ & LUQ & suprapubic (urinary bladder) for hydronefrosis, and long- and short-axis subcostal views of the gallbladder
  • Reviewing clinical cases with pathological findings
  • Understanding the limitations and pitfalls of the mentioned abdominal examinations

1. Introduction 

For abdominal ultrasound we have included three areas of focus: gallbladder, kidneys and hydronephrosis, and small bowel obstruction (SBO). The reason behind these specific areas are: they are relatively easy to learn, patients with pathology concerning one of the three areas present at emergency departments relatively frequently, and the exams are supported by the literature for yielding a relatively high sensitivity and specificity when used by proficient examiners (which can be gained without extensive training).

2. Gallbladder 

Video gallblader part 1 -anatomy – (9min)

[Credit: Phillips Perera & SonoSite]

Video gallblader part 2 – gallstones – (8min)

[Credit: Phillips Perera & SonoSite]

Video gallblader part 3 – kolcystitis – (5min)

[Credit: Phillips Perera & SonoSite]

To evaluate the gallbladder we can use the RUQ view, with either the curvilinear prove or the phased array probe (for smaller footprint) using the abdominal protocol, with the marker on the left side of the screen and the probe marker towards the patients head (in RUQ). When starting in the RUQ position, visualize the liver and fan the probe to the anterior part of the abdomen (the tail of the probe moving towards the stretcher). It helps if the patient has been fasting for the last hours as the gallbladder fills and extends in between meals.

The second view needed to evaluate the gallbladder is obtained by putting the prove subcostal on the ribcage of the patient with the marker aimed towards the head (long-axis orientation) and towards the patients right (short-axis orientation).

The primary focused questions for a gallbladder exam are:

  1. Is there gallstones and/or sludge?
  2. Is there wall thickening >3mm?
  3. Is there edema surrounding the gallbladder or liver (pericholecystic fluid)?
  4. Is there a sonographic Murphy’s sign present (maximum point of tenderness with the probe directed over the gallbladder)?

The gallbladder will appear as a hypoechogenic cystic structure with well defined borders (similar to the urinary bladder, albeit different in shape as it can be more elongated). Any gallstones will appear as hyperechoic structures casting shadows below them on the image.

For this course and for the novice POCUS practitioner identifying and evaluating the gallbladder is our primary learning focus. The other structures named in the videos above can take time to learn to visualize and identify and should be seen as secondary learning objectives gained over time (beyond the timeframe of this course).

Gallstones

In a retrospective study from 2008, bedside ultrasound gallbladder exams, the identification of gallstones by physicians in the ED had a 88% sensitivity and 87% specificity, with a positive predictive value of 91% and negative predictive value of 83% compared to radiology ultrasound (n=575)*.

Cholecystitis

A prospective study from Summer et al in 2010 bedside ultrasound gallbladder exams by physicians in the ED had a 87% sensitivity and 82% specificity, with a positive predictive value of 44% and a negative predictive value of 97% as it related to diagnosing cholecystitis *. The authors of that study defined the criteria for cholecystitis as positive if the patient had cholelithiasis plus one the following secondary findings:

  1. wall thickening greater than 3 mm
  2. pericholecystic fluid, or;
  3. a sonographic Murphy’s sign

In the prospective study above by Summers et al they did not use radiology as the criterion standard and instead compared both ED physicians and radiologists ultrasound with pathology reports and a 2 week clinical follow-up. The radiologists performing ultrasound of the gallbladder in the study had similar results to the ED physicians with 83% sensitivity and 86% specificity, positive predictive value of 59%, and a negative predictive value of 95%. Leading the authors to conclude that: that the detection of acute cholecystitis are similar between the two groups, and that negative bedside ultrasonography results are “unlikely to require cholecystectomy or admission for cholecystitis within 2 weeks of their initial presentation” *.

The use of bedside ultrasound in the EDs of hospitals in Sweden for evaluating gallbladder pathology is to our knowledge still very limited, user-dependent, and not yet standardised or evaluated systematically (except for, perhaps, in one of the five emergency hospitals in Stockholms). In contrast, the study above that was conducted in an urban hospital (with an annual patient consensus of 36 000) in California, mentions that their emergency medicine residents must complete 150 proctored gallbladder examinations before graduation, a stark contrast to the absence of systematic bedside ultrasound trainee programs in most Swedish urban hospitals.

Gallbladder Polyps

Gallbladder polyps is a clinical problem since they are present in about 5% of all gallbladder ultrasound exams.* A polyp can be difficult to differentiate from a gallstones, however they should be stationary and lack an acoustic shadow. When uncertain try changing the position of the patient to evaluate if the structure inside the gallbladder moves or not. According to local guidelines [in Swedish] from “västra sjukvårdsregionen” 2007, all gallbladder polyps need follow up:*

polyps

[Image credit: ‘Primär cancer i lever, gallblåsa och gallvägar’ Regionala vårdprogram/riktlinjer västra sjukvårdsregionen 2007.]

However, according to guidelines from [in Swedish] Gallblåse- och gallvägscancer: Nationellt vårdprogram 2019 polyps above >5mm should be followed up. Our recommendation is to check your local guidelines and be generous with follow up with official ultrasound exams by radiologists of all suspected polyps you might find in the beginning of your POCUS learning period.

3. Hydronephrosis

Video hydronephrosis (8min)

[Credit: Phillips Perera & SonoSite]

For the evaluation of hydronephrosis we can use the RUQ & LUQ views we have practiced during the FAST-exam. While the instructor in the videos above recommends using a probe with smaller footprint like the phased array probe, the curvilinear probe can also work for this purpose. If you find yourself having a difficult time visualizing the kidneys due to ribs obstructing the view (the left kidney especially often being more difficult to visualize) switch to the phased array probe but remember to run an abdominal exam protocol on the ultrasound machine to optimize the image. With an abdominal protocol the screen marker will be on the left side of the screen and our probe should therefore be aimed towards the patients head just like the RUQ/LUQ views in the FAST protocol.

grading hydronephrosis

Grading hydronephrosis (see image above) ranges from mild with dilatation of the renal pelvis and no parenchymal atrophy, then moderate including blunting of fornices and flattening of papillae, to severe with gross dilatation of the renal pelvis and loss of borders between the renal pelvis and calyces and renal atrophy seen as cortical thinning (source: radiopaedia). As radiopaedia points out ‘all hydronephrosis grading systems are controversial in terms of their intra- and interobserver reliability’ * and should be taken as an approximate judgment helping you in clinical assessment of the patient and not as a definitive classification.

As mentioned in the video above urinary stones can sometimes been seen in the calyx, ureteropelvic junction (UPJ), or in the bladder (vesicoureteric junction (VUJ)), and evaluation of the bladder should be included in the exam to help determine the source of the obstruction (bilateral hydronephrosis with an extended bladder indicating urinary retention). It can be difficult for the novice bedside ultrasound physician to identify kidney stones, and similar to most of POCUS this exam should not be considered as guaranteed to rule out kidney stones (also considering as the ureters on each side are not included in the examination, any stones that might exist there will not be assessed).

Measuring the urinary bladder volume with bedside ultrasound.

Using the above formula for measuring the bladder, with width x depth in the short-axis view and height in the long axis view times a correction coefficient of 0,7 (0,72 was used in the paper), the authors were able to estimate bladder volume with mean percentage error of 16.9% ± 11.9% and got a coefficient of correlation (r) that was 0,913 compared with volume that was emptied by either void or catheter (n = 24)*.

The advantage of measuring the bladder by bedside ultrasound instead of a bladder scan, are many and depend on the clinical context. In patients with abdominal tumours or large volumes of ascites bladder scans can return false high volumes. There is also additional information that can be gained such as if stones, tumours, or blood clots are present (however, further radiology and adjunct testing might be necessary if a difficult to assess object is identified in the bladder). Ultrasound of the bladder can help determine whether the catheter placement is correct (and/or cuffed) when it comes to trouble shooting catheterization. And, finally, in the ER when doing initial assessments on acutely ill patients, a quick look on the bladder will also give you a sense of bladder volume instead of having to wait for a bladder scan, an important metric for judging the clinical context and helping the physician with clinical planning when it comes to geriatric patients in particular.

4. Small Bowel Obstruction (SBO)

Video small bowel obstruction (12 min)

For small bowel obstruction (SBO) the RUQ and LUQ views can be used for looking for extended bowels. The probe used is usually the curvilinear but the phased array probe can be used as well, and with thin patients (or with kids) even a linear probe can be used too. As you will notice when practicing ultrasound on each other (healthy adults), and as dr. Heather Hames mentions in the video above, bowels are usually not seen at all in healthy patients, just small pockets of air. So the first rule of thumb for abdominal ultrasound, when the focused question is SBO/ileus, is: if bowels are extended and easy to visualize = possible SBO/ileus present.

Notice that the video makes a differentiation between SBO and ileus, where the former is an actual blockage (like adhesions, cancer, etc) on the intestine while the latter is the bowels not moving without the presence of blockage. In Sweden we don’t (usually) differentiate between the two: calling both ileus but instead subgrouping them into mechanical ileus (blockage) and paralytic ileus (increased peristalsis).

I personally find the RUQ and LUQ views to (often) yield the best image in the hand full of cases of SBO/ileus I have seen with ultrasound and that later were confirmed with CT scans. But, as the video mentions, when the focused question is SBO you should also try to scan the anterior abdomen (with the patient lying on their back), in a criss-cross pattern. Dr. Hames calls it “mowing the lawn” movement. Sometimes you’ll get some good images of extended bowels from this view too, depending on the degree and placement of the obstruction.

To help you diagnose a SBO the following criteria can be applied, as mentioned in the video above:

  • Dilated small bowel >25mm
  • Peristalsis (To/Fro)
  • Tanga sign (free fluid between the bowel loops)
  • Wall thickening (>3mm)

In a study from 2011 where emergency medicine physicians completed a 10 min training module and had only five prior ultrasound exams of SBO, identifying dilated bowels (defined as ≥25 mm) demonstrated a sensitivity of 91% and specificity of 84% for SBO (n = 76) compared to CT *. The same study also looked at increased bowel peristalsis (defined as back and forth movements of spot echoes inside the fluid-filled bowel), and while they found a lower sensitivity of just 27%, the specificity was 98%.

Another study from 2010 found similar results when using POCUS for the diagnosis of SBO when looking at dilated bowels with a sensitivity of 91% and a specificity of 84% (n = 174) *. The study used the following criteria over all to diagnose SBO, if two of the following three signs were present:

  • Small bowel loops greater than 25 mm in jejunum or greater than 15 mm in ileum over a length of mare than three loops
  • Increased peristalsis
  • Collapsed colonic lumenWhen using the criteria above the study showed a sensitivity of 97,7%, specificity of 92,7%, positive predictive value of 93,3%, and negative predictive value of 97,4%, for diagnosing SBO by bedside ultrasound when performed by emergency physicians who had been through a 6 hour training program. They also compared these number to ultrasound performed by third year radiology residents and found no significant statistical difference between the two groups (outcome in the study was determined by surgical findings if they were operated on or self-reports at 1-month follow-up).

5. Summary

In this part of module two we looked at evaluating the gallbladder, hydronephrosis, and SBO – three relatively easy to evaluate exams that can be assed by the RUQ/LUQ views and with some additional probe orientations when you are doing a focused assessment.

Abdominal ultrasound can provide you with valuable information and help with clinical management even if an abdominal CT exam is scheduled for the patient.

We have not included gynaecological/obestric ultrasound in the first iteration of this course. Neither have we included exam/diagnosis of appendicitis. The reasons for this is due to our own lack of practice and knowledge in these areas, and also because of time restraints.

We have not included the aorta exam in this module but will cover it in the M5 module: vascular.

 

6. Pitfalls

Gallbladder

  • If you’re having difficulties visualizing the gallbladder: have the patient sit up and roll onto their left side to improve visualization.
  • If rib shadows are obstructing the view: try rotating the probe obliquely to mirror the angle of the intercostal space.
  • Asking the patient to take and hold a deep breath can help bring the gallbladder into better viewing position.
  • Indistinct “dirty” shadows can be caused by bowel gas, differentiate these from shadows that originate from discrete hyperechoic foci (stones) within the gallbladder lumen.
  • Edge artifact can cause shadows from the sides of the gallbladder due to refraction and should not be mistaken for gallstones.
  • Polyps within the gallbladder should stay stationary and gallstones should move with gravity, and they can therefor often be differentiated from gallstones by changing the patient’s position. Polyps should, as a rule, not create posterior shadowing either.
  • Polyps in the gallbladder need to be followed up with an official ultrasound examination by a radiologist (see this document and this one [Swedish] for guidance)

Hydronephrosis

  • Hydronephrosis can be missed in patient who are hypovolemic, reevaluate patients with suspected hydronephrosis after fluid resuscitation.
  • Color doppler can be used do differentiate between renal blood vessels that sometimes can be misinterpreted as mild hydronephrosis.
  • The left kidney can sometimes be more difficult to visualize due to its more cranial and posterior position compared to the right kidney, using a probe with smaller footprint and, when possible, tilting the patient to his/her side can help.
  • Varying degrees of hydronephrosis, often on the right side, is common in pregnancy and may not be pathologic.
  • If you detect a renal mass that you can’t identify you need to get further workup. All renal masses are malignant until proven otherwise.
  • A scan of the bladder should be included in all bedside ultrasound exams when evaluating hydronephrosis.

SBO

  • It can be difficult to know what part of the bowl you’re looking at in the beginning. Large bowels will have visible haustra, jejunum will have “valvulae connivents” on the interior aspect of the wall, and ileum will not have haustra or valvulae connivents.

7. QUIZ 

Question 1


Correct!
D: Hydronephrosis is the correct answer!

Incorrect!
Try again.

 


Question 2

<img class="alignnone size-full wp-image-32590" src="https://colligoacademy.se/wp-content/uploads/2022/09/sbo-gif-21.gif" alt=""

Correct!
A is FALSE!
A small bowel lumen over >25mm in jejunum and >15mm in ileum are considered pathological and indicative for SBO. For this course however we conclude that differentiating between small bowel loops can be difficult, and instead put the threshold at >25mm for any small bowel section that you can visualize with ultrasound. According to one study (see link below) identifying a small bowel section >25mm had a sensitivity of 91% and specificity of 84% for SBO compared to CT scan. The Tanga sing is free fluid deep to the dilated loop of bowel and is not always present or detectable by ultrasound.

Incorrect!
Try again.

8. Further Reading

Books

Noble. ‘Manual of Emergency and Critical Care Ultrasound’. 2nd Edition. 2011. Ch. 6 Renal and Bladder Ultrasound Ch. 7 Gallbladder Ultrasound Ch. 12 Gastrointestinal Ultrasound Dawson & Mallin. ‘Introduction to Bedside Ultrasound – Vol 1’. 2013. Ch. 6 Renal Dawson & Mallin. ‘Introduction to Bedside Ultrasound – Vol 2’. 2013. Ch. 14 Small Bowel Obstruction Ch. 15 Right Upper Quadrant (Gallbladder Exam) Soni et al. ‘Point-of-Care-Ultrasound’. 2nd Edition. 2020 Ch. 25 Kidneys Ch. 26 Bladder Ch. 27 Gallbladder Ch. 32 Abdominal Pain

[Version 2.0 — Last updated 2022-06-28 — Status: Active]
[Version 2.0: separated the abdominal module from the E-FAST module, added the subsection “Gallbladder Polyps” under section 2. Gallbladder. Changed QUIZ from google documents to in-page. ]