Clinical Summary

The focused assessment with sonography for trauma (FAST) examination is a safe, portable, noninvasive diagnostic tool to investigate for hemoperitoneum, hemopericardium, and hemothorax in trauma victims. The FAST exam can help detect free fluid (ie, hemoperitoneum in the hypotensive patient); however, the FAST exam cannot exclude solid organ injury. Hemoperitoneum in the pediatric trauma patient is usually a result of hepatic or splenic injury and will appear as an anechoic (dark) collection on ultrasound (US). The primary indications for use of the FAST exam are blunt or penetrating thoracic or abdominal trauma.

Technique

Use a low-frequency (1–5 MHz) curvilinear abdominal or phased-array probe or higher-frequency (6–12 MHz) linear transducers. The latter will provide better resolution as pediatric patients have thinner abdominal walls and less subcutaneous fat. Perform the scan with the patient in the supine position. Direct probe indicator toward the patient’s head or the patient’s right side. When imaging the right upper quadrant (RUQ) and the left upper quadrant (LUQ), rotate the probe counterclockwise during scanning to allow for successful imaging between intercostal rib spaces.

Obtain the following four views:

1. 
   

   Subxiphoid view of the heart

   
   
2. 
   

   Hepatorenal space (Morison pouch) in the right upper quadrant (RUQ)

   
   
3. 
   

   Splenorenal recess, as well as the subphrenic space, in the left upper quadrant (LUQ)

   
   
4. 
   

   Suprapubic view

   
   
   
   
   1. 
      

      Rectovesicular pouch (males)

   
   
   
   
   2. 
      

      Pouch of Douglas (females)

   
   
   
   
   3. 
      

      RUQ and pelvic views are routinely performed first in the pediatric trauma patient as these are most sensitive in detecting intraperitoneal free fluid

Findings

Free fluid in RUQ appears as an anechoic collection between the liver and the right kidney. This dependent space is the most sensitive view to detect the hemoperitoneum, and it is the most important view. On the LUQ view, blood from a splenic injury appears first above the spleen in the left subphrenic space. If the volume is large enough, blood will collect in the splenorenal space and soon flow to other dependent spaces in the abdomen (ie, hepatorenal space, suprapubic space).

Use suprapubic imaging to visualize the bladder in both transverse and sagittal views. The bladder is a fluid-containing, anechoic structure on US, and serves as an acoustic window to detect free fluid in the dependent space below it. Use the pubic symphysis as an anatomic landmark for probe placement. Obtain a transverse view with the probe indicator directed toward the patient’s right side and a sagittal view with the probe indicator directed toward the patient’s head. Suprapubic imaging also helps to assess bladder volume before the placement of Foley catheters or sterile catheterizations.

Obtain a subxiphoid view to detect pericardial fluid, particularly in penetrating trauma. Direct the probe marker to the patient’s right side with the transducer below the xiphoid process and aim toward the patient’s left shoulder. Pericardial fluid appears as a dark, anechoic stripe between the heart and the liver.

Pearls

1. 
   

   Obtain a surgical consult immediately in a hypotensive patient (unresponsive to fluid boluses and blood) with a positive FAST exam for expeditious transport to the operating room.

   
   
2. 
   

   Patients with a positive FAST and stable vital signs can be managed conservatively in the pediatric intensive care unit (PICU) with serial blood counts, repeat physical exams, and vital signs.

   
   
3. 
   

   FAST exam does not rule out intra-abdominal solid organ injury; a computed tomographic (CT) scan should strongly be considered in patients with heightened suspicion for injury.

   
   
4. 
   

   A parasternal-long view of the heart can also be used to evaluate for free fluid when images of the heart cannot be obtained from the subxiphoid view.

Clinical Summary

Consider bedside US in patients with signs and symptoms suspicious for appendicitis, particularly when physical examination is unreliable. Ultrasound is a safe, nonionizing method of diagnosing appendicitis in patients with heightened suspicion. Ultrasound has poor sensitivity because it is highly operator dependent but is used to supplement the history and physical examination in patients presenting with possible appendicitis.

Technique

Use a high-frequency (6–12 MHz) linear probe. In patients with a larger body habitus, deeper visualization of the abdomen may be required, necessitating the use of the low-frequency (2–5 MHz) curvilinear [abdominal] probe. Place the patient comfortably in the supine position and direct the probe indicator toward the patient’s head or the patient’s right side. Begin scanning in the RLQ, as lateral as possible, with the probe marker aimed toward the patient’s head and gently advance the probe toward the midline, until the probe approaches the point of maximal tenderness. Use gentle, graded compression to displace gas from the bowel and move the probe closer to the appendix. Measure the diameter of the appendix in both long and short axes, from outer wall to outer wall.

Ultrasound Findings

A normal appendix has a diameter of <6 mm on US and should demonstrate peristalsis, and normally collapse with gentle compression. Ultrasound features supportive of a diagnosis of appendicitis include noncompressibility, diameter of >6 mm (in either plane), lack of peristalsis, and a bull’s-eye appearance when viewed in the transverse (short-axis) plane.

Pearls

1. 
   

   Do not delay management of suspected appendicitis for US, and obtain a surgical consult immediately.

   
   
2. 
   

   Do not use negative US to rule out appendicitis. If appendicitis is suspected and bedside US is nonconfirmatory, an official radiologist-performed US should be obtained and/or a CT scan should be considered.

   
   
3. 
   

   If an inflamed appendix has perforated, US has a much lower sensitivity in detecting an appendicitis.

   
   
4. 
   

   Finding the iliac vessels adjacent to the psoas muscle in the RLQ is another good starting location to search for the appendix.

Clinical Summary

Bedside US (noninvasive and nonradiating qualities) has become the accepted first-line diagnostic test for patients with suspected intussusception. An experienced sonographer can identify the lead point (ie, lymphoma, polyps, cysts) as well as assess blood flow to affected bowel segments.

Technique

Use a high-frequency (6–12 MHz) linear probe, or in patients with a larger body habitus, a low-frequency (2–5 MHz) curvilinear probe for deeper visualization of the abdomen. Perform the scan with the patient comfortably in the supine position. If an abdominal mass is noted on inspection or palpation, scan the mass in at least 2 planes. If no mass is immediately appreciated, scan the abdomen slowly along the path of the bowel, beginning from the ileocecal region (RLQ), and scan in a clockwise fashion around the abdomen, keeping note for any potential mass(es) below the abdominal wall.

Ultrasound Findings

The normal, unaffected bowel appears as a uniform, thin, hypoechoic rim around an echogenic centrum of variable widths and demonstrates peristaltic activity. An intussuscepted bowel appears as a “target sign,” in the transverse view representing alternating layers of mucosa, muscularis, and serosa or the “sandwich sign,” in the longitudinal view, representing alternating layers of hypoechoic bowel wall.

Pearls

1. 
   

   Contrast or air enema is required for reduction regardless of how intussusception is diagnosed.

   
   
2. 
   

   Fecal matter in the colon can imitate intussusception on US.

   
   
3. 
   

   Be aware of other pathologic causes of bowel wall thickening that can resemble an intussusception on US (ie, inflammatory bowel disease).