The right upper quadrant

The right upper quadrant view uses the liver as an acoustic window to identify free fluid within the abdominal cavity. This is one of the most important views of the abdominal FAST. Free fluid often accumulates in the RUQ as the right paracolic gutter directs fluid from the pelvis to the RUQ and the phrenicocolic ligament and mesentery direct fluid from the LUQ to RUQ.

 

Technique (figure 1)

Figure 1: Scanning technique of the RUQ

1. Positioning is critical. It is important that the patient remains supine in a flat or slight Trendelenburg position to ensure any fluid collects in dependent areas.
2. Place the probe on the patient’s right mid-axillary line along the coronal plane at the level of the xyphoid with the probe indicator toward the patient’s head.
3. Center the hepatorenal interface on the screen by moving up or down an intercostal space as needed.
4. Draw your eye to the area below the diaphragm, hepatorenal interface and caudal liver tip to identify free fluid.
5. Fan slowly from anterior to posterior and back until the kidney disappears in either direction, repeat in each view, as needed, to fully evaluate the subdiaphragmatic space, hepatorenal interface and caudal liver tip.
6. Fluid will appear anechoic (black) on the screen.

 

Tips

• Fan through the area slowly so as not to miss subtle findings, drawing your eyes to the key areas of the hepatorenal interface and the caudal liver tip.
• It is common to have to fan in multiple rib spaces to ensure a view of the whole hepatorenal interface and caudal liver edge.
• If struggling to see between rib shadows, angle the probe slightly to follow the direction of the intercostal spaces to allow you to see between the ribs.

 

What am I looking at?

When placing the probe in the RUQ you are using the liver as an acoustic window to get a coronal cross section of the patient’s abdomen (figure 2).

 

Figure 2: When scanning the right upper quadrant, use the liver as an acoustic window to get a coronal view of the liver, right kidney and hepatorenal interface.

 

What is normal?

Nearest to the probe, the lateral chest wall containing muscle and ribs is easily identified. Often, the hypoechoic rib shadows can be seen projecting into the abdomen. Deep to the chest wall the liver is encountered, followed by the hepatorenal interface and right kidney. The domed diaphragm can be seen cranial to the liver and the vertebral bodies and great vessels can often be identified in the far field deep to the kidney (figure 3, video 1).

 

Figure 3: Normal RUQ sonoanatomy with the liver highlighted in blue, right kidney in green, diaphragm in red and vertebral bodies in yellow. Your areas of interest include the sub-diaphragmatic space (1), Morrison’s pouch (2) and the liver tip (3).

 

Video 1: RUQ, normal

 

What is not normal?

When intraperitoneal free fluid is encountered due to infection, ascites or hemorrhage fluid often collects in right paracolic gutter around the caudal edge of the liver and in morrison’s pouch, or the hepatorenal interface (video 2 & 3). Fluid appears as an anechoic stripe or collection in these areas only bounded by the surrounding anatomical structures. In pediatric patients the second most common area for fluid to collect is in the right paracolic gutter adjacent to the caudal liver edge [11].

Video 2: RUQ, free fluid in Morrison’s pouch

Video 3: RUQ, free fluid around the caudal liver tip

 

Pitfalls

PoCUS for abdominal free fluid is not foolproof.

False negative scans are most commonly caused by operator error. Other causes include patients who only have small amounts of fluid in their abdomen, such as trauma patients presenting early or with minimal hemorrhage. In addition, in trauma patients with delayed presentations, blood can clot which can prevent it from collecting in dependent regions or can make it harder to distinguish on ultrasound (due to the variable echogenicity of clotted blood).

False positives can occur as well, most commonly due to perinephric fat or edge artifact. In the case of perinephric fat, free fluid can often be distinguished as anechoic as opposed to hypoechoic, as fat is. In addition, free fluid is bound only by the organs themselves, while perinephric fat is lined by apparent hyperechoic fascial lines giving a “railroad track” or “marbled” appearance. Edge artifact can sometimes be seen projecting from the edge of a curved structure, usually the kidney; it often is less distinct than free fluid, gets larger as it goes deeper and crosses anatomical boundaries—similar to a rib shadow, whereas free fluid tends to be anechoic, well-defined and narrows to dissect planes and respects anatomic boundaries.

Indications

• Blunt or penetrating thoraco-abdominal trauma
• Multi-system trauma
• The undifferentiated, unstable patient
• Suspected ruptured ectopic pregnancy
• Suspicion of ascites or intraperitoneal free fluid

 

Equipment

• Ultrasound machine
• Curvilinear or phased array probe
• Gel

 

To fully evaluate the peritoneal cavity for free fluid, the abdomen must be scanned systematically in three areas. Studies have shown that while the pelvic view is generally the most sensitive, there are several scenarios such as isolated organ trauma in which fluid can be found in one view but not another. We will discuss each view separately.

 

Introduction

Point of Care Ultrasound (PoCUS) is the use of portable ultrasonography to answer specific, focused clinical questions at the bedside. It is an extension of both our clinical acumen and physical exam. PoCUS is commonly used in adult trauma cases as part of the focused assessment with sonography in trauma (FAST) examination. In undifferentiated and hemodynamically unstable patients, PoCUS can rapidly identify intra-abdominal free fluid which can expedite management and disposition decisions. When ascites is suspected, PoCUS may be used to confirm the diagnosis and guide further management. In recent years, the use of PoCUS has expanded to include pediatric patients as well.

 

Why Ultrasound?

PoCUS is superior to physical exam in detecting intra-abdominal free fluid. In addition, PoCUS can be performed quickly at the bedside without exposure to ionizing radiation. Physical exam alone is a poor test for the detection of peritoneal free fluid, with an overall accuracy of 58% [1]. Studies have shown that as little as 10-50cc of peritoneal free fluid can now be detected with ultrasound. In the hands of emergency doctors, volumes of 100-200 mL of fluid can be routinely detected at the bedside [2,3]. These numbers hold true for trauma patients as well. In 2007, Soyuncu et al. showed emergency physician performed ultrasound detected intraperitoneal hemorrhage with a sensitivity of 86% and specificity of 99% while physical examination reported a sensitivity of 39% and specificity of 90%, respectively [4].

The use of ultrasound in the child who has sustained trauma requires special mention. In the setting of the unstable trauma patient it is critical to identify the cause of decompensation as early as possible as it helps guide and prioritize management decisions, including further diagnostic workup and early disposition from the ER.  The focused abdominal sonography in trauma (FAST) exam is both sensitive and specific in critically ill, hypotensive pediatric trauma patients [5]. It is best used to screen for significant intra-abdominal injuries requiring emergent transfer to the operating room in the unstable patient. In the stable patient, the utility of the FAST is debated and the sensitivities range from 25-80% for the detection of all intra abdominal injuries, though it performs better in those injuries with hemoperitoneum [6]. Performing serial FAST as well as the combining findings with clinical exam and laboratory investigations can increase the sensitivity of the FAST examination [7, 8, 9]. While CT remains the gold standard screening tool for intra-abdominal injuries, the use of the FAST exam may have the ability to decrease CT use in pediatric patients.

The FAST scan can be a challenging scan to master as adequate sonographic windows may be difficult to obtain and multiple areas must be investigated under challenging conditions. Studies show the false negative rate of scans decreases with increasing physician experience. Deliberate practice is key to attaining proficiency [10].

 

Author: Melanie Willimann, MD FRCPC

Secondary Author: Mark Bromley , MD FRCPC

Reviewer(s): Nicholas Packer, MD FRCPC

References

1. Valley, V & Stahmer, S. Targeted Musculoarticular Sonography in the Detection of Joint Effusions. Academic Emergency Medicine. 2001. 8:361-367
2. Cruz, C et al. Point-of-care hip ultrasound in a pediatric emergency department. American Journal of Emergency Medicine. 2018. 36:1174-1177. https://doi.org/10.1016/j.ajem.2017.11.059
3. Kane, Balint, & Sturrock. Ultrasonography is superior to clinical examination in the detection and localization of knee joint effusion in rheumatoid arthritis. J Rheumatology. 2001; 30(5):966-971.
4. Zieger, M et al. Ultrasonography of hip joint effusions. Skeletal Radiology. 1987. 16:607-611
5. Tsung, J & Blaivas, M. Emergency Department Diagnosis of Pediatric Hip Effusion and Guided Arthrocentesis Using Point-of-Care Ultrasound. The Journal of Emergency Medicine. 2008. 35:393–399. doi:10.1016/j.jemermed.2007.10.054
6. Shavit, I et al. Sonography of the Hip Joint by the Emergency Physician: Its role in the evaluation of children presenting with acute limp. Pediatric Emergency Care. 2006. 22:570-573.
7. Vieira, R & Levy, J. Bedside Ultrasonography to Identify Hip Effusions in Pediatric Patients. Annals of Emergency Medicine. 2010. 55:284-289. doi:10.1016/j.annemergmed.2009.06.527
8. Adhikari & Blavais. Utility of bedside sonography to distinguish soft tissue abnormalities from joint effusions in the emergency department. J Ultrasound Med. 2010; 29(4):519-526.
9. Deanehan, J et al. Bedside Hip Ultrasonography in the Pediatric Emergency Department: A Tool to Guide Management in Patients Presenting with Limp. Pediatric Emergency Care. 2014. 30:285-287.
10. Alves, T et al. US of the Knee: Scanning Techniques, Pitfalls, and Pathologic Conditions. RadioGraphics. 2016. 36:1759-1775. https://doi.org/10.1148/rg.2016160019
11. Wiler, J et al. Comparison of Ultrasound-Guided and Standard Landmark Techniques for Knee Arthrocentesis. The Journal of Emergency Medicine. Vol 39. No 1. 2010. https://doi.org/10.1016/j.jemermed.2008.05.012
12. Wu, T et al. Ultrasound-guided versus landmark in knee arthrocentesis: A systematic review. Seminars in Arthritis and Rheumatism. 2016. http://dx.doi.org/10.1016/j.semarthrit.2015.10.011
13. Lueders, D, Smith, J, & Sellon, J. Ultrasound-Guided Knee Procedures. Physical Medicine Rehabilitation Clinics of North America. 2016. 27:631-648. http://dx.doi.org/10.1016/j.pmr.2016.04.010]
14. Daniels, J & Williams, D. Basics of musculoskeletal ultrasound. Springer. 2013.
15. Edsonoshare.com

Indications

• Refusal to weight bear
• Limp
• Painful joint
• Swollen joint

 

Equipment

• Ultrasound machine
• Linear array probe (the curvilinear may be required for deep joins such as the hip in larger patients)
• Ultrasound gel

 

 

Sonoanatomy Review

Normal skin and soft tissue have many layers (Figure 1). The most superficial structures are the epidermis and dermis, which appear as if one hyperechoic structure. Deep to this, you will find subcutaneous fat, which is hypoechoic and globular. Blood vessels, nerves and lymph nodes are found within the hypodermis, and are varying in their echogenicity. Deep to these structures, the muscle is found beneath a hyperechoic layer of fascia. Muscle is seen as highly organized hypoechoic and striated fibers.

Figure 1: Anatomy of normal skin

 

 

Tendons are visualized as hypoechoic fibrillar organized structures, whereas fat pads are also hypoechoic, but are more homogenous in their appearance (Figure 2). Finally, smooth hyperechoic bone cortex may be seen as the deepest layer.

Figure 2: Anatomy of a normal joint

 

Tip:

Scan with dual screen functionality

In order to facilitate comparing an affected joint with the contralateral side, it can be useful to use the dual screen function on the ultrasound machine.

1. Choose “More Controls” from the main screen, found at the bottom right corner (Figure 3a).Figure 3a: Choose “more controls”
2. Select “Dual” from the options screen (Figure 3b)Figure 3b: Choose “dual”
3. Touch the screen on either side to start scanning. When ready to switch, freeze the area of interest on the screen and then touch the opposite screen to begin scanning the opposite side (Figure 3c).Figure 3c: Toggle between screens by touching the desired side
4. Below is an example of a split screen view (Figure 3d).Figure 3d: Dual screen example

Knee Anatomy Review

The knee is made up of the articulating surfaces of the femur and the tibia, with the patella lying anteriorly. The quadriceps tendon inserts on the patella, and the patellar tendon extends distally to the tibial tuberosity. The fluid within the synovial capsule is continuous with the suprapatellar bursa. The fat pads found within the knee joint include the quadriceps fat pad and the pre-femoral fat pad (Figure 10).

Figure 10: Anatomy of the knee joint. 

 

Technique

• Position the patient supine.
• Use a towel roll to place the affected knee in 20-30 degrees of flexion [1] (Figure 11).

Figure 11: Probe position for knee ultrasound

• Place the linear array probe longitudinally in the sagittal plane on the patella [10].
• Identify the patella and scan proximally to assess for effusion within the suprapatellar recess [10].
• Assess for presence of joint effusion.
• Repeat on the contralateral joint.

 

What am I looking at?

Figure 12: Labelled normal knee ultrasound.

Patella

• Hyperechoic line in caudal field of view.

Femur

• Hyperechoic line in cephalad field of view.

Quadriceps tendon

• Hyperechoic fibrillar structure in near field.

Fat Pads

• Pre-femoral fat pad – hyperechoic soft tissue collection just anterior to femur.

Quadriceps fat pad – hyperechoic soft tissue collection just inferior to quadriceps tendon.

Suprapatellar bursa

• Hypoechoic potential space.

Prepatellar bursa

• Hypoechoic area superficial to patella.

 

What is normal?

Visualization of the knee joint in this view will show you the patella caudally and the femur extended cranially (Video 2). The quadriceps tendon will be a fibrous structure running in the near field (Figure 13).  The suprapatellar bursa should be less than 2mm thick [1].

Video 2: Normal knee ultrasound.

Figure 13: Normal right and left knee ultrasound. 

 

What is NOT normal?

Fluid will collect in the suprapatellar bursa, found in between the prefemoral and quadriceps fat pads (Video 3). The ultrasound is positive for a knee effusion by a collection of hypoechoic fluid which is >2mm thick [1] (Figure 14). If you are not seeing any fluid collection, flexion of the knee can increase the fluid in the suprapatellar recess [13]. In addition, fluid can collect on both the medial and lateral side of the suprapatellar region, therefore scanning these areas can help identify fluid collections. To do this, slide the probe laterally and medially within the sagittal plane to identify hypoechoic fluid collections.  This can help with performing ultrasound guided arthroscopy of the knee, although that is outside the scope of this module.

Video 3: Knee joint effusion. Note the fluid collection between the quadriceps fat pad and quadriceps tendon superiorly and the prefemoral fat pad inferiorly.   

Figure 14: Positive knee effusion.  

Ankle Anatomy Review

The area where an effusion in the ankle collects is at the intersection of the tibia and the talus (Figure 15). There is a fat pad (the anterior fat pad) at the junction of these two bones. Superficial to the boney surfaces, the tibialis anterior tendon is found.

Figure 15: Anatomy of the ankle joint.

 

Technique

• Position the patient supine.
• Have the patient flex their knee and place their foot on the bed to place their ankle in dorsiflexion [1].
• Place the linear array probe along the longitudinal axis of the tibia at the joint line between the tibia and talus [1] (Figure 16).

Figure 16: Probe position for ankle ultrasound.

• Identify synovial space at the junction of the talus and the tibia.
• Assess for presence of joint effusion.
• Repeat on the contralateral joint.

 

What am I looking at?

Figure 17: Labelled normal ankle ultrasound. Note that physiologic fluid and cartilage can appear similarly, so differentiate them with compression of the structures. Fluid will compress, cartilage will not.

 

Tibia

• Hyperechoic line cephalad.

Talus

• Hyperechoic line caudal.

Tibialis anterior tendon

• Fibrillar hyperechoic structure in near field.

Anterior fat pad

• Immediately superficial to the synovial space.

Anterior talotibial recess or synovial space

• Superficial to the bony surfaces of the joint.

 

What is normal?

On ultrasound of the ankle, you will see the tibia extending cephalad and the joint line between the tibia and the talus (Video 4). Within the joint space, near field to the bony structures, there may be a small amount of physiologic fluid, and an anterior fat pad. As in the other joints, physiologic fluid will follow the contours of the bone, and have a more concave appearance (Figure 18).

Video 4: Normal ankle ultrasound.

Figure 18: Normal ankle ultrasound.

 

What is NOT normal?

An ankle effusion is characterized by a convex shaped hypoechoic fluid collection anterior to the tibial and talar joint (Figure 19). In the ankle, unlike in the hip, there is no specific measurement for a positive effusion – the important feature to look for is the convexity of the collection (Video 5).

Figure 19: Positive ankle effusion.

Video 5: Ankle joint effusion. Again, note the convex appearance of the fluid.

Pitfalls

In all joints, it is important to assess both the affected joint, and the contralateral side, as a small amount of fluid within the spaces can be normal. In addition, cartilage can appear hypoechoic within these spaces, but will be non-compressible [1]. Finally, fluid within an effusion can be simple (anechoic) or complex (heterogenous in echogenicity) depending on what caused the effusion. Examples of potential complex effusions include hemarthrosis with clots or loculated septic arthritis [1, 3]. Synovitis can mimic a complex effusion, but can be differentiated with the addition of color to look for low grade venous flow.