Welcome to Probetrotters, the dedicated Ultrasound blog of the St. John's Riverside EM residency!

Table of Contents

1/2/2021, Medical Education, Ilana Rosner, MD

Approaches to the Diagnosis of Peritonsillar Abscess with Point-of-Care-Ultrasound

Ultrasound (US) is an important modality in differentiating, diagnosing and treating peritonsillar abscesses in the emergency department (ED). Peritonsillar abscesses (PTAs) are the most common deep neck infections, and 80% of cases are found in patients aged 10 to 40.8 The diagnosis is usually made clinically with a physical exam and confirmed by needle aspiration of purulent material at the time of drainage.8Incision and drainage or needle aspiration are the definitive treatment options in order to protect the patient from complications such as airway obstruction, abscess rupture, and extension to the deep tissues of the neck, carotid sheath, or posterior mediastinum.3 However, physical exam alone is unreliable in distinguishing between PTAs and peritonsillar cellulitis (PTC), with a sensitivity of 78% and specificity of 50%.7 Treatment typically consists of blind needle aspiration, aiming at the superior pole where 70% of PTAs occur.8 This is in contrast to PTC in which there is no role for drainage. This method has a false negative rate of 10 to 24% when done by experienced ENTs.1 Other drawbacks of blind aspiration include multiple insertions due to loculated abscesses or unknown locations, pain, and the close proximity of the internal carotid artery.8

Diagnostic Imaging

CT scan has a sensitivity of 100% and specificity of 75% for diagnosing PTA.2,6 MRI can also be used for diagnosis, with less radiation than CT.8 However, neither of these have a role in treatment. Ultrasound is a quick and inexpensive modality that can not only differentiate PTA from PTC, but can also guide needle drainage.7 Both intraoral ultrasound (IOU) and transcutaneous ultrasound (TCU) are good options. On ultrasound, a PTA will typically appear as enlarged tonsils with heterogeneous or cystic appearance.8 Any fluid collection adjacent to the tonsil and with tonsillar distortion is suspicious for PTA.5 Using color doppler can also aid in identification. A PTA should be hypoechoic, however it may have surrounding inflamed tonsillar tissue which can appear as a circumferential hyperechoic ring. Lack of color flow confirms it is not a vascular structure, while structures with flow are likely to be blood vessels or inflamed tonsillar tissue. There are two approaches to using US to diagnose PTAs. There is an intra- oral approach using an endo-cavitary probe or the superficial approach using a high frequency linear probe.

Fig. 6 Color doppler showing inflamed tonsillar tissue (white arrow) next to an abscess (black arrow) lacking color flow

Intraoral Approach

The intraoral approach can typically be done efficiently after practicing on 3-4 patients, and small studies have shown a sensitivity of 89 to 95%.8 One study found that compared to using landmarks, IOU diagnosed 100% of PTA vs 64% from landmarks.8It also led to a 7-fold decrease in subspecialty consults.8Importantly, given that the posterior wall of the abscess is on average 9mm from the carotid artery, it can aid in the safety of needle aspiration.8 Using an intracavitary transducer, place the probe on the tonsil, and orient it in the transverse plane.8

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  1. Anesthetize the area with topical gel, spray, or injection.

  2. A tongue blade can be used to visualize the pharynx. Alternatively, a miller blade can be used and can be held by the patient for their comfort.

  3. Use a clean endocavitary probe with a cover.

  4. Insert the endocavitary probe, starting on the contralateral side of the mouth. Begin with the probe in the transverse orientation.

  5. Identify the PTA and measure it in two planes to estimate its volume.

  6. Determine the depth from the surface.

  7. Locate the internal carotid artery, which is 5-25mm posterior to the abscess, in order to avoid puncturing it as you’re attempting aspiration. Using color flow can help in visualization.

  8. Drainage can then be done dynamically or statically with direct visualization of the needle into the abscess, or visualizing the general area of the abscess and then performing drainage statically after removal of the probe.

Fig. 3 Proximity of Internal Carotid (white arrow) to PTA (red arrow)

  • Advantages:

    • Has higher sensitivity compared to transcutaneous approach.8

  • Disadvantages:

    • This approach cannot be used if the patient has severe trismus or is uncooperative.

    • Accessing the tonsil for drainage may be limited due to the size and positioning of the probe.

Transcutaneous Approach

There are limited studies suggesting that TCU diagnosed PTAs 100% of the time IOU could not be used, and led to an increased quantity of aspirate.2If the patient is unable to open their mouth due to trismus or there is not an available endocavitary probe then a linear or curvilinear transducer can be used transcutaneous.4 Place the probe under and medially to the angle of the mandible, with the probe marker facing the patient's ear.6 Find the internal jugular and carotid artery and fan the transducer cephalad.6Identify the submandibular gland, and the tonsil will be deep to this structure.8

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  1. Using a high frequency linear transducer, place it under mandible with the probe marker facing the right of the patient. First evaluate the unaffected side.

  2. Locate the internal jugular vein and carotid artery using color doppler. Then fan cephalad until the pharyngeal tonsil is located.

  3. Once the tonsil is identified, move the probe laterally.

  4. If you come across a hypoechoic structure, this may be an abscess. These can be surrounded by a hyperemic rim from inflamed tonsillar tissue. If there is no flow, it confirms that it is not a vascular structure.

  5. Drainage can then be done dynamically with direct visualization of the needle into the abscess.

Fig. 6 Transcutaneous approach showing tonsil (black arrow) and Internal Carotid (white arrow)


  • When intraoral cannot be used such as when the patient has significant trismus, or when it is a pediatric patient who is uncooperative and won’t tolerate the probe in their mouth.4

  • Higher specificity than IOU.2


  • There is more subcutaneous tissue that needs to be penetrated in order to see the abscess and there may be interference from bone.


Ultrasound is an ideal modality for diagnosis and management of peritonsillar abscesses in the emergency department. It is quick, inexpensive, limits the amount of radiation exposure, and is the only modality that guides needle drainage.


[1] Blaivas M, Theodoro D, Duggal S. Ultrasound-guided drainage of peritonsillar abscess by emergency physician. Am J Emerg Med 2003;21(2):155–8.

[2] Filho, B et al. Intraoral and transcutaneous cervical ultrasound in the differential diagnosis of peritonsillar cellulitis and abscesses,Brazilian Journal of Otorhinolaryngology,Volume 72, Issue 3, 2006, 377-381, doi:10.1016/S1808-8694(15)30972-1.

[3] Froehlich MH, Huang Z, Reilly BK. Utilization of ultrasound for diagnostic evaluation and management of peritonsillar abscesses. Curr Opin Otolaryngol Head Neck Surg. 2017;25(2):163-168. doi:10.1097/MOO.0000000000000338

[4] Halm, Brunhild, Ng, Carrie, Larrabee, Yuna. Diagnosis of a Peritonsillar Abscess by Transcutaneous Point-of-Care Ultrasound in the Pediatric Emergency Department. Pediatr Emerg Care. 2016;32(7):489-492. doi:10.1097/PEC.0000000000000843.

[5] Kew J, Ahuja A, Loftus WK, Metreweli C. Peritonsillar abscess appearance on intraoral ultrasound. Clin Radiol 1998;53:143–6.

[6] Rehrer, Matthew et al. Identification of peritonsillar abscess by transcutaneous cervical ultrasound. The American Journal of Emergency Medicine , Volume 31 , Issue 1 , 267.e1 – 267.e3

[7] Scott PM, Loftus WK, Kew J, Yue V, van Hasselt CA. Diagnosis of peritonsillar infections: a prospective study of ultrasound, computerized tomography and clinical diagnosis. J Laryngol Otol 1999;13:229–32.

[8] Secko M, Sivitz A, Think ultrasound first for peritonsillar swelling, Am J Emerg Med (2015), j.ajem.2015.01.031

11/23/2020, Journal Article Review, Nathan Denicoff, MD

Comparison of the Accuracy of Emergency Department-Performed Point-of-Care-Ultrasound (POCUS) in the Diagnosis of Lower-Extremity Deep Vein Thrombosis

García, Jorge Pedraza, et al. The Journal of Emergency Medicine, vol. 54, no. 5, 2018, pp. 656–664., https://doi:10.1016/j.jemermed.2017.12.020

Objective and Study Design

This was a prospective cross-sectional study and diagnostic test assessment with the goal of determining the accuracy of emergency physician-performed three-point compression ultrasound to diagnose DVT in comparison to the standard radiology-performed Doppler ultrasound.


This study was conducted between March 2012 and May 2014 in an emergency department in Spain. Patients with suspected above-knee lower extremity DVT were enrolled and risk-stratified using a Wells score and D-dimer algorithm, as shown in the article’s Figure 1 below.

* note the DD- and DD+ under “3 point ultrasound in the ED” should be US- and US+

Those with a low Wells score of <2, indicating DVT unlikely, were tested with a D-dimer. If the D-dimer was negative, no further testing was pursued. If positive, patients underwent three-point compression ultrasound, with the sites of compression highlighted the figure below. If US positive, patients were anticoagulated and followed up with a Doppler US within 48 hours. If US negative, they were not anticoagulated, but were still followed up with Doppler within 48 hours. For patients with a moderate/high risk of DVT on the modified Wells score, all were tested with D-dimer, ED ultrasound, and follow up Doppler. All patients who underwent compression ultrasound were followed up in a DVT clinic for one year to monitor for complications and resolution of the DVT.

Figure 2: Three-point compression ultrasound anatomy[1]


As per the above algorithm, 109 patients underwent an EM-performed compression ultrasound. The results are summarized in the article’s Figure 2 below.

These results demonstrate that POCUS DVT is an effective diagnostic method, as summarized in Table 1 below:

Table 1: Diagnostic accuracy of POCUS DVT

Discussion and Limitations

  • Extensive training and practice in POCUS DVT prior to data collection may skew the results towards increased accuracy and limit generalizability to physicians less experienced in this diagnostic method.

  • The study was conducted in Spain, which may limit generalizability to other populations.

  • The study identifies the following pitfalls in accurate diagnosis of DVT by compression ultrasound: not placing the probe perpendicular to the skin when compressing, patient obesity or edema, and mistaking a lymph node or Baker’s cyst for a DVT.

  • Both the POCUS and Doppler ultrasounds did not examine the calf veins, which may not in fact be problematic, as these distal DVTs may not have clinical significance, with lower risk of embolization.

  • Incorporation bias: the gold standard test, the Doppler ultrasound, incorporates or relies on the studied test, the three-point compression ultrasound. The up to 48 hour delay in Doppler may allow for proximal DVTs identified on POCUS to resolve prior to Doppler, or for unidentified distal DVTs to extend proximally, thus changing the result. This limitation could have been mitigated by performing a Doppler ultrasound minutes after the POCUS, but this was likely not feasible.

  • Convenience sampling rather than consecutive sampling was used, as there were times when no POCUS-trained attendings were in the department, such as from midnight to 8am.


  • With sufficient training, emergency physicians can effectively use three-point compression ultrasound to diagnose proximal lower extremity DVTs.

  • POCUS DVT is less time consuming than comprehensive ultrasound, and it was performed in an average of five minutes in this study. This speed can reduce ED length of stay.

  • POCUS DVT can be especially helpful at times when radiology technicians are not in the hospital to perform a Doppler ultrasound, which is often the case at night.

  • While not touched upon in this study, POCUS DVT is also part of the expanded RUSH exam (Rapid Ultrasound for Shock and Hypotension) when PE is suspected.[2] This significantly broadens the potential applications of POCUS DVT in my clinical practice to patients with undifferentiated shock with concern for PE.

  • This study was initiated in 2008 at a time when the attending physicians may not have had much experience with ultrasound, and they benefited from dedicated training prior to this study. Today, EM residency programs have much more robust ultrasound teaching and higher expectations of residents’ ultrasound skills. This study is convincing evidence that I should make POCUS DVT part of my practice as a resident, and that I should perform this study consistently in order to become proficient.


  1. Ahn J and Dinh V et al. DVT Ultrasound Made Easy: Step-By-Step Guide. POCUS 101.

  2. Seif D, Perera P, Mailhot T, et al. Bedside ultrasound in resuscitation and the rapid ultrasound in shock protocol. Crit Care Res Practice. 2012;2012:503254.

11/2/2020, Medical Education, Mary McLean, MD

Transesophageal Echocardiography (TEE) for Cardiopulmonary Resuscitation

Hi Team! This Ultrasound Teaching Post is about something I’ve never seen performed in-person and have been wanting to look into: Transesophageal Echocardiography (TEE) for Cardiopulmonary Resuscitation.

TEE is increasingly used in emergency departments to guide cardiopulmonary resuscitation, as an alternative to the more common Trans Thoracic Echo (TTE). TEE provides a visual stimulus during pulse checks, allowing the resuscitation team to check the effectiveness of ongoing chest compressions, and can provide additional diagnostic information (see below). It has been shown by Andersen et al, found that TEE used to visualize chest compressions directly over the left ventricle (LV)versus traditional placement and compression of the aortic root improve hemodynamics and increased Return of Spontaneous Circulation (ROSC) rates.1

Additional resources: There is a great 8-minute intro to the procedure here from the Resuscitative TEE Project,2 and a 19 minute podcast here from EMCrit.3 Check them out!

Advantages and Disadvantages of TEE use in the ED for CPR:

It sounds like TEE may be better management than TTE for a) certain patients, b) certain clinical scenarios, and c) certain physicians/teams/hospitals.

  1. Certain patients. What patient is potentially the right patient for TEE? Who should be excluded?

They need to be in cardiac arrest, sedated, intubated or with a tracheostomy tube. There should be a reason why TEE is preferable to TTE for acquisition of hemodynamic information, e.g. unable to get adequate TTE windows 2/2 super-morbid obesity or other reasons. TEE-appropriate patients should not have active upper GI Bleed (UGIB); history of esophagectomy, esophageal varices or perforation, or tracheoesophagal fistula.

  1. Certain clinical situations. What is the appropriate scenario for TEE over TTE during resuscitation?

TTE should be adequate for a patient who coded over an hour ago but never regained pulses and is expected to have a very short resuscitation with only a few rounds of chest compressions under the ACLS algorithm. In this case, TTE is sufficient once they arrive to the ED to assess for a pericardial effusion and confirm or assess cardiac activity. Even in the most advanced ED with TEE trained staff this doesn’t seem like the appropriate clinical scenario. However, in a patient who codes in front of our eyes, and is requiring or already intubated or has obesity, COPD, and/or a prior sternotomy,4 or expected to require prolonged resuscitation per ACLS, TEE is probably a better option.

  1. Certain physicians/teams/hospitals. What is the right clinical setting?

It’s generally not advisable to perform a new advanced procedure if the provider, medical team, or hospital is not used to it, including TEE.

So how does an emergency physician become qualified to perform TEE for cardiopulmonary resuscitation?

Physicians should complete training and meet competency standards for basic TTE, and additionally should complete4:

    1. 4 hours of TEE didactic

    2. 10 proctored TEE examinations on either high-fidelity sim models or live patients

    3. A standardized assessment by a credentialed TEE provider.

TEE Protocols

That brings us to protocols for the actual procedure. The Resuscitative TEE Project® has a website with tons of information, including algorithms like the one below.

Image courtesy of the Resuscitative TEE Project.4

TEE Sonographic Anatomy:

There are actually 12 different possible TEE views for the more advanced TEE sonographer, but only four of these are essential for TEE for cardiopulmonary resuscitation. These four are mentioned above in the algorithm and are depicted in the table below along with their TTE equivalents.

4 essential TEE views: (1) mid-esophageal 4 chamber, (2) mid-esophageal long axis, (3) transgastric short axis, and (4) mid-esophageal bicaval:

Image courtesy of the Resuscitative TEE Project.4

These four views are more easily seen in the top four images from the following series (labeled ME 4C, ME LAX, TG SAX PAP, and ME Bicaval):

In Conclusion:

TEE for cardiopulmonary resuscitation might be something that becomes mainstream over the next decade but is still not ubiquitous in all ED’s due to training and cost. I hope this helps demystify it a little bit for those of us who have not seen or done it in the ED!

If you want more info, ACEP released a clear and concise policy statement in April 2017 entitled Guidelines for the Use of Transesophageal Echocardiography (TEE) in the ED for Cardiac Arrest.7


  1. Andersen et al. “Left ventricular compressions improve return of spontaneous circulation and hemodynamics in a swine model of traumatic cardiopulmonary arrest.” J Trauma Acute Care Surg. 2018 Aug;85(2):303-310. doi: 10.1097/TA.0000000000001901

  2. Teran F, Zeidan A. “Brief Intro to Resuscitative Transesophageal Echocardiography (TEE).” 2018.

  3. Weingart S, Teran F. “EMCrit Podcast 208 - You are Doing CPR All Wrong” EMCrit. 2017.

  4. Andrus P, Teran F. Protocols — Resuscitative TEE Project. Resuscitative TEE Project. Published 2020. Accessed October 24, 2020.

  5. Moore G. On the Proper Care of a Transesophageal (TEE) Probe. Published 2014. Accessed October 24, 2020.

  6. Fair J 3rd, Mallin MP, Adler A, et al. Transesophageal Echocardiography During Cardiopulmonary Resuscitation Is Associated With Shorter Compression Pauses Compared With Transthoracic Echocardiography. Ann Emerg Med. 2019;73(6):610-616. doi:10.1016/j.annemergmed.2019.01.018

  7. Guidelines for the Use of Transesophageal Echocardiography (TEE) in the ED for Cardiac Arrest. Ann Emerg Med. 2017;70(3):442-445. doi:10.1016/j.annemergmed.2017.06.033

10/22/2020, Journal Article Review, Nishad Rahman, MD

Utility of Point-of-Care Lung Ultrasonography for Evaluating Acute Chest Syndrome in Young Patients With Sickle Cell Disease

Cohen, S. G., et al. (2020, September 1). Utility of Point-of-Care Lung Ultrasonography for Evaluating Acute Chest Syndrome in Young Patients With Sickle Cell Disease. Annals of Emergency Medicine, 76(3), S46-S55.

What type of study is this?

Prospective observational study

What was the objective of this study?

The objective of this study was to determine the accuracy of point-of-care lung ultrasound compared to the gold standard of chest X-ray in identifying an infiltrate suggestive of acute chest syndrome in patients with sickle cell disease.

Acute chest syndrome is the leading cause of mortality in patients with sickle cell disease, and therefore this is a question with significant clinical relevance. As a result, these patients experience multiple radiological exposures starting at very young ages. If ultrasound is comparable to the current gold standard of chest radiography, patients with sickle cell disease may experience significantly less radiation exposure over their lifetimes.

Briefly summarize the methods used in this study

This prospective observational study was conducted at 2 freestanding urban pediatric centers between November 2015 and July 2017. The study population was a convenience sample based on the availability of ultrasonographers. Exclusion factors included hemodynamic instability, chest radiography at an outside institution, and unavailability of a study ultrasonographer. Inclusion factors included documented sickle cell disease, aged 0-21 years old, and chest radiography within the current admission. Symptoms concerning for acute chest syndrome included chest pain, fever, vomiting, and respiratory symptoms such as cough. Ultrasonography was performed by sonographers who were blinded to physical examination and chest radiographic findings, ideally before chest radiography was performed.

Study sonographers included one expert blinded reviewer with 6 years of experience and specialized training in point-of-care lung ultrasonography, as well as five novice ultrasound trainees. The 5 novice sonographers underwent a 1-hour lecture on lung ultrasonography, a 1-hour practical hands-on imaging session, and 5 point-of-care lung ultrasonographic examinations before enrolling patients in the study. Consolidated lung findings by ultrasound were characterized by a hypoechoic region with irregular borders containing hyperechoic air bronchograms, requiring measurement greater than 1 cm to be determined positive. This is because consolidations less than 1 cm are often not identified on chest radiography. The expert sonographer was blinded to any previous interpretation and reviewed all studies that were performed.

Secondary outcomes included patient or guardian satisfaction, tolerability of the examination, and inter-operator reliability between trainees and the expert blinded reviewer. Satisfaction was assessed through a 10-question survey, using a Likert scale of 1 to 5 (1 being the least satisfied and 5 being the most satisfied). Satisfaction questions included queries about the entire ED visit as well as specific questions concerning the experience with point-of-care lung ultrasonography, including measures such as “pain and comfort during the scan, efficiency of the scan, whether the patient and family would like a point-of-care lung ultrasonographic examination at subsequent visits, how the scan affected interactions with healthcare providers, and the total patient experience in the ED.” The gold standard was the pediatric radiologist’s interpretation of the chest radiography.

Based on the afore-mentioned inclusion and exclusion criteria, 220 patients were eligible for participation. Of these, 21 patients declined enrollment, ultrasonography was incomplete for 7 patients, and 1 patient withdrew in the middle of examination due to discomfort. Ultimately, 191 patients were included in the data analysis.

What are some possible flaws in the methods used?

  1. This is a prospective observational study, which is not randomized or double-blinded. This study design is intrinsically at risk for confounding factors and potential selection bias. Furthermore, observational studies are only able to support correlation, never causation.

  2. Included only six study ultrasonographers

  3. Only 191 patients were enrolled out of possible 220. The small study size can skew the results and subsequent conclusions by encapsulating only a limited group, which is not generalizable to the general population.

  4. Included only two centers

  5. Convenience sample based on availability of ultrasonographers

  6. Included only pediatric patients, so not generalizable to adults

Briefly summarize the results of this study

Enrolled patients had a median age of 8 years (interquartile range 3 to 13 years), with 41% being female. Chest radiography identified an infiltrate in 32 patients (17%). 31 of 32 patients (97%) who had positive chest radiographic results and 67 of 159 (42%) who had negative chest radiographic results were admitted, making up ninety-eight admitted patients in total (51% of the study population). Two required critical care.

Forty of the total 191 patients in the study (21%) were found to have lung consolidation greater than 1 cm. Novice sonographers were able to detect acute chest syndrome with an accuracy of 89%, while the expert sonographer had higher accuracy at 92%. Interobserver agreement between novice and reviewing sonographer was moderate (κ=0.67 [95% CI 0.54 to 0.80]). Notably, ultrasound had a negative predictive value of 92-100% among trainees and 93-99% for the expert. Positive predictive value was also found to be greater than that of clinical symptoms such as cough, abnormal respiratory rate, shortness of breath, and chest pain.

In terms of secondary outcomes, questionnaires were at least partially completed by a total of 141 families (73%). Ninety percent of individuals (124/138) responded that they had little or no pain; however, 1 patient withdrew from the study because of discomfort. 93% of patients reported being satisfied with their ED care, with only 4% of enrolled patients stating that they would not like an ultrasonographic examination during subsequent visits.

Briefly summarize the discussion of this study?

The results of this study suggest that ultrasonography may be useful as a screening tool with relatively good accuracy for the presence of consolidation in young patients with sickle cell disease and concern for acute chest syndrome, thereby potentially limiting radiation exposure. This is supported by the high negative predictive value shown by both trainees and an advanced clinician.

What are the main take-away points of this study?

  • POCUS lung ultrasonography has high negative predictive value for acute chest syndrome in young patients with sickle cell disease

  • Screening with POCUS lung ultrasonography could potentially reduce the necessity for radiation exposure

  • Lung ultrasonography can be learned by novice sonographers, suggesting that expanded education may have clinical utility

What are the main limitations in this study?

  • Recruitment of patients based on convenience sample

  • Imperfect gold standard (chest radiography itself has shown poor inter-operator reliability and lower sensitivity compared to ultrasound. CT chest would be more accurate, but has ethical issues with significantly more radiation exposure)

  • No assessment of improved trainee sonography with more examinations

  • Difficulty differentiating acute versus chronic lung changes by ultrasonography. In previous lung ultrasonography studies, patients with chronic cardiorespiratory changes have been excluded, as pulmonary scarring looks similar to consolidation under ultrasound. This is not a feasible exclusion criteria when studying patients with sickle cell disease, who by definition have chronic lung changes. This was demonstrated by four false positives within this study due to chronic pulmonary scarring being incorrectly identified as new consolidations.

  • Potential loss of blinding (unable to blind from visible tachypnea or respiratory distress)

Does this study influence your practice? If so, in what way?

This study makes me more likely to perform a screening point-of-care lung ultrasound searching for a consolidation of greater than 1 cm prior to ordering a chest X ray in young patients concerning acute chest syndrome, a life threatening complication in sickle cell disease.

Expert Content Reviewers

Angela Cirilli, MD, RDMS, FACEP

Ultrasound Director, Department of Emergency Medicine

Ellen Kurkowski, DO

Associate Ultrasound Director

Connie Yu, MD

Director of Resident Education in Ultrasound