reactive lymph nodes can also be mistaken for fluid collections Lymph nodes appear oval and hypoechoic with an echogenic hilum When color flow is applied to a lymph node the vascular stalk can be identified at the hilum, helping to differentiate this hypoechoic structure from a fluid collection ( Video 131.31 ) FIGURE 131.32 Muscle FIGURE 131.33 Cobblestoning in soft tissue Foreign-Body Identification and Removal Ultrasound can be used for detection of radiolucent foreign bodies and accurate real-time two-dimensional localization of all soft tissue foreign bodies Real-time sonographic visualization can guide percutaneous removal of a soft tissue foreign body, minimizing surgical exploration Technique The technique used for subcutaneous foreign body identification is similar to evaluation for soft tissue infection A high-frequency linear transducer is preferred and the object should be identified in two planes If an object is very superficial, a water bath or a “stand-off pad” can be used to elevate the transducer off of the area of interest, improving resolution All soft tissue foreign bodies are initially hyperechoic on sonography The depth and size of the foreign body should be measured and any relationship to surrounding nerves and vessels should be noted Surrounding granulation tissue, edema, or hemorrhage can appear as a hypoechoic halo increasing visibility of the object Typically objects that are small or irregular, such as toothpicks or pencil tips, create clean shadows, while objects with large smooth surface, such as glass or metal, create reverberation artifacts such as comet tails To remove a foreign body using realtime ultrasound guidance, the transducer should be placed so that the center marker is over the foreign body and the skin should be marked to identify this optimal incision site After appropriate anesthetic injection and incision, image the foreign body in the long axis and use forceps or hemostats to grasp the object under ultrasound guidance FIGURE 131.34 Abscess Pitfalls Bone and joint surfaces appear hyperechoic with shadowing, and can be confused with foreign bodies if one is not familiar with the local anatomy Scar tissue can also appear hyperechoic and must be differentiated from foreign bodies Wooden foreign bodies may become less echogenic over time, making them more difficult to see Finally, using ultrasound dynamically to remove a foreign body is technically challenging It requires a moderate amount of ultrasound experience and dexterity The novice user may have greater success in identifying the foreign body statically in multiple planes, marking the site and attempting removal in standard fashion OTHER USES OF ULTRASOUND There are other uses of sonography that are beyond the scope of this chapter We touch upon them briefly here to introduce the concepts The interested reader should consult a textbook of ultrasonography PARACENTESIS AND PERICARDIOCENTESIS The need for these procedures is uncommon in pediatrics, but ultrasound can be helpful in identifying the location of fluid and in avoiding injury to solid organs A phased array or curvilinear probe should be used for identifying fluid and for dynamic ultrasound guidance For paracentesis, the transducer should be placed in different parts of the abdomen in order to identify the deepest pocket of fluid For pericardiocentesis, a small footprint probe will allow better visualization between the ribs Sonographic guidance allows a transthoracic approach rather than the subxyphoid approach, which reduces the risk of injury to the liver EVALUATION OF JOINTS Ultrasound can help with the detection or exclusion of joint effusion and can also be used to guide arthrocentesis The high-frequency linear probe is used Evaluation of the hip is discussed above Ultrasound has also been used for the knee, elbow, and shoulder NERVE BLOCKS Nerve blocks may obviate the need for sedation for painful procedures, and may decrease the amount of locally injected anesthetic Ultrasound guidance for nerve blocks can help prevent accidental puncture of neighboring vasculature and can direct the needle tip to within close proximity of the desired nerve structures A linear high-frequency probe should be used Ultrasound has been used to assist with nerve blocks for the femoral nerve and the nerves of the forearm ... ultrasonography PARACENTESIS AND PERICARDIOCENTESIS The need for these procedures is uncommon in pediatrics, but ultrasound can be helpful in identifying the location of fluid and in avoiding injury