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Student Corner: Ultrasound Approach to DVT

January 28, 2016

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Deep venous thromboses are thought to occur in as many as 1 in 1000 people annually1, although many instances never present to urgent care or emergency room settings. When a patient does make it to the ER, the most common presentation is a swollen, tender lower extremity. Although there are many things on the differential, the emergency room physician must rule out DVT because of the potential risk of subsequent pulmonary embolism.

Ultrasound has become the go-to method for evaluation of DVT. In the ER setting, the limited compression ultrasound technique is most widely used due to the ease and speed at which it can be performed. A duplex scan with color Doppler can be useful in other scenarios, but these evaluations can take up to an hour, require a skilled technician, and have not been shown to be any more accurate in detection of proximal DVTs compared to limited compression ultrasound2.

Limited compression ultrasound frequently targets two main locations for DVTs: the common femoral vein and the popliteal vein. The ultrasound is typically done using the linear or vascular probe (6-10 MHz), which was designed for imaging vessels, but has the added benefit of being flat, which helps with uniform compression when assessing for DVTs.

During the ultrasound exam, is important for the leg to be in a dependent position, which will allow for ideal assessment during compression. This can be achieved by putting the patient in reverse Trendelenburg, or by having them partially seated with 30 degrees of hip flexion.

Start by palpating for the femoral artery in the groin crease, which will allow you to easily locate the common femoral vein, which lies just medially. Hold the probe in transverse orientation, so that you can see the cross-sections of both the artery and vein. Follow the vessels distally, looking for the common femoral vein to bifurcate into the superficial and deep femoral veins approximately 6 cm from the inguinal ligament. Look closely at the branch points, as these are common areas for thrombi to form.

Lower_Ext_Vasc

(Image courtesy of David Darling)

*A note about the nomenclature: the superficial femoral vein is actually a deep vein, and thrombi are much more common in the superficial femoral compared to the deep femoral vein. The superficial femoral vein is sometimes referred to as simply the femoral vein.

Follow the superficial femoral vein as it becomes the popliteal vein, and then passes behind the knee. Scan about 5-7 cm distal to the popliteal crease – thrombi distal to this are very unlikely to generate threatening emboli. The vein should be just superficial to the artery as you follow the popliteal vein and artery near the knee.

As you are conducting the ultrasound you will apply pressure approximately every centimeter with the probe. As pressure is applied, the vein should start to compress, with the anterior and posterior walls eventually coming into contact. The pressure needed to completely collapse the vein should not disrupt the architecture of the femoral artery. If the vein does not completely collapse, or if the pressure necessary becomes so great that the artery becomes distorted as well, there is likely a thrombus in that segment of the vein. Scan proximally and distally from that point to examine the extent of the thrombus.

Below are two ultrasound images of the superficial femoral vein (blue) and femoral artery (red). The image on the left is without compression. The artery is superficial to the vein, and the lumen of the femoral vein is slightly larger than the artery. These characteristics help with identification. The image on the right shows the same vessels during compression with the ultrasound probe. The artery is now very ovoid and almost flat, while the vein is still round, and the lumen shows some, which represents a thrombus.

DVT Baseline vs Compress

Before (left) and after compression (right)


Illustration courtesy of David Darling

Ultrasound images courtesy of Dr. Kenneth Kelley


References:

  1. Silverstein MD, Heit JA, Mohr DN, Petterson TM, O’Fallon WM, Melton LJ 3rd.
    Trends in the incidence of deep vein thrombosis and pulmonary embolism: a 25-year population-based study. Arch Intern Med.1998;158:585-593.
  2. Lensing AW, Prandoni P, Brandjes D, Huisman PM, Vigo M, Tomasella G, Krekt J, Wouter Ten Cate J, Huisman MV, Büller HR. Detection of deep-vein thrombosis by real-time b-mode ultrasonography. N Engl J Med.1989;320:342-345.
  3. Dean, AJ, Ku, BS(2008). Deep Venous Thrombosis. Retrieved from http://www.sonoguide.com/dvt.html
  4. Theodoro D, Blaivas M, Duggal S, Snyder G, Lucas M. Real-time B-mode ultrasound in the ED saves time in the diagnosis of deep vein thrombosis (DVT). Am J Emerg Med.2004;22:197-200.

Author: Mitchell Datlow

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Student Corner: Peritonsillar Abscess

July 7, 2015

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Peritonsillar abscess (PTA) is one of the most common head and neck infections that is diagnosed in the emergency department. The common presenting symptoms are a muffled/altered voice, throat pain, fever and odynophagia. A non-contrast CT image of a  particularly severe example of a PTA is shown below.

PTA2

 

The next horizontal cut image is below, with red arrows to highlight the abscess.

 

PTA1 with arrows

One of the more striking aspects of the image is the large degree of airway compression, with the maximum measured diameter of the airway being 2cm. Also, the first image shows that the abscess has two distinct “pockets” that eventually coalesce.

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To backtrack, this particular patient initially presented with symptoms of fever, chills, dysphagia, dysphonia and trismus. On examination, there were thin tonsillar exudates, erythema and deviation of the uvula. A diagnosis of peritonsillar abscess was made without imaging and the patient underwent incision and drainage, given antibiotics and discharge. The above images were taken after the patient returned to the ED several days later with continued, worsening symptoms.

The options for imaging of a soft tissue infection of the head and neck include CT and ultrasound. In the ED setting, ultrasound is becoming more and more utilized as the preferred imaging modality. However, this patient received a CT because they failed therapy. CT is superior to ultrasound in differentiation between peritonsillar abscess and other infections of the oral cavity and pharynx. It also allows clinicians to determine the degree of airway compromise. Other indications for CT imaging in suspected peritonsillar abscess include: uncertain diagnosis, obstructed view through physical exam or suspicion of an associated infection such as peritonsillar cellulitis.

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Overall, peritonsillar abscess is one of the most common soft tissue infection of the head and neck that is encountered in the emergency department. Most of the time, the diagnosis is clinical. Ultrasound is the preferred imaging modality, but CT is useful in a variety of situations as well.

References:

Powell, J. and Wilson, J.A. (2012), An evidence-based review of peritonsillar abscess. Clinical Otolaryngology, 37: 136–145.
Author:  Jaymin Patel
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Interesting ultrasound of the RUQ…

February 24, 2013

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This is a right upper quadrant (RUQ) ultrasound in a middle-aged female presenting with upper abdominal pain:

West Sign GB

What the heck is going on here?

In this image there is an example of a “Wes” sign.  Wes sign is when you see two echogenic lines separated by a hypoechoic space at the expected wall of the gallbladder (1).  This sign is often found with a large calculi occupying the entire lumen of the gallbladder (or when the gallbladder is contracted around a large calculi).  This case, however, is somewhat interesting in that there isn’t an acoustic shadow beyond the majority of the hyperechoic mass inside the gallbladder.  You can the typical expected acoustic shadow near the neck of the gallbladder in this image.  Our thoughts as well as radiology’s thoughts were that this image represents a large calculus at the neck with dense sludge or a bunch of very small calculi filling the rest of the gallbladder (thus allowing sound waves to penetrate beyond).  Fortunately for the patient her pain got much better, she was discharged and is expected to get an elective cholecystectomy in the near future.  Here is a link to an article discussing the “Wes” sign from the Radiology Society of North America:

Wes Sign

Author:  Russell Jones, MD

References:

1.  Rybicki F.  The Wes Sign.  Radiology 2000; 214: 881-882.

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