Close
New

Medscape is available in 5 Language Editions – Choose your Edition here.

 

Abdominal Bedside Ultrasonography

  • Author: Joshua J Ennis, MD; Chief Editor: Caroline R Taylor, MD  more...
 
Updated: Apr 24, 2016
 

Overview

As compared with comprehensive imaging performed in the radiology department, emergency ultrasonography is a bedside diagnostic modality that answers time-sensitive specific questions about a patient’s condition. Emergency ultrasonography is diagnostic, can be used to assess clinical response in ongoing resuscitations, and can help guide invasive procedures. It directly influences patient management decisions and interventions in multiple ways. In terms of diagnosis, emergency ultrasonography can answer time-sensitive life-saving questions such as the following: Does this 70-year-old man with low back pain have an abdominal aortic aneurysm? Does this 19-year-old assault victim have intraperitoneal bleeding?

Next

Indications

Bedside ultrasonography is indicated in the evaluation of symptoms such as the following:

  • Abdominal pain
  • Flank pain
  • Low back pain
  • Blunt abdominal trauma [1]
  • Hematuria
  • Unexplained hypotension

It is also indicated in the workup of specific abdominal disease entities such as the following:

  • Abdominal aortic aneurysm [2]
  • Acute cholecystitis
  • Biliary colic
  • Acute appendicitis
  • Nephrolithiasis
  • Urinary retention

Newer applications include the use of abdominal ultrasonography as a procedural aid (eg, in paracentesis or abscess drainage),[3] for evaluation and monitoring of central venous filling as a surrogate for central venous pressure, and for assessment of abdominal wall pathology (eg, abscess or hernia).

Previous
Next

Contraindications

When emergent treatments such as intravenous fluids or transfusion of blood are indicated, performance of abdominal sonography should not delay the initiation of these treatments.

Although ongoing resuscitation and extremis are not contraindications, abdominal sonography can be challenging to perform in such situations.

Previous
Next

Anesthesia

Anesthesia is generally not necessary for abdominal sonography; however, pain management should not be delayed, and patients may experience some discomfort due to probe pressure. For improved patient comfort, consider using warmed ultrasound-conducting gel, if available.

Previous
Next

Equipment

Equipment for abdominal bedside ultrasonography includes the following:

  • Ultrasound machine with color flow Doppler and power Doppler
  • Low-frequency (2-5 MHz) curvilinear transducer
  • Acoustic coupling gel
  • Gloves
  • Appropriate materials to drape the patient
Previous
Next

Positioning

Patients should be evaluated in the supine position but can be moved to the lateral decubitus position for improved visualization of particular structures (eg, gallbladder).

Male patients should have the entire abdomen exposed for the examination. Take care with female patients to minimize the exposure of sensitive areas.

Previous
Next

Technique

General considerations

With bedside ultrasound, a few scanning conventions merit brief discussion. Primarily by convention, the ultrasound probe marker is oriented in 1 of 2 directions. The probe indicator should be oriented towards the patient's head, or towards the patient's right side. Further, the dot on the screen, which corresponds to the ultrasound probe indicator, should be placed on screen-right to maintain consistency of images. These conventions facilitate standardization of image appearance on the ultrasound screen. However, one should be aware of differing conventions for probe marker placement, and dot screen location, which vary by specialty.

FAST examination

Clinical questions, probe selection, elements of the focused assessment with sonography in trauma (FAST) examination, patient positioning, and limitations of the FAST examination are discussed below. The discussion is organized by indication.

The American Institute of Ultrasound in Medicine (AIUM) in collaboration with the American College of Emergency Physicians published guidelines on the performance of the focused assessment with sonography for trauma (FAST) examination. They noted that FAST is a proven procedure for the evaluation of the torso for bleeding after traumatic injury, particularly blunt trauma, but that it may also be helpful in penetrating injury. FAST has evolved to include assessments of the peritoneal cavity and analysis of the pericardium and pleural spaces for hemorrhage, particularly in cases of chest trauma.[4]

The guidelines note, however, that there are certain limitations with FAST, such as the following[4] :

  • Limitations in the ability to detect free fluid in some injured children, patients with mesenteric, diaphragmatic, or hollow viscous injury, and patients with isolated penetrating injury to the peritoneum.
  • Limitation in identifying retroperitoneal hemorrhage.
  • Limitations to the pericardial assessment for hemopericardium include pericardial fat pads, cysts, and preexisting pericardial fluid.

Blunt or penetrating abdominal trauma

FAST examination is nearly 100% sensitive for detecting clinically significant hemoperitoneum[5] and, as such, has largely replaced diagnostic peritoneal lavage (DPL) in assessing for intraperitoneal free fluid. It is important to remember that the ultrasound is screening for the presence of free fluid and is not a reliable tool for visualizing the actual injury (such as liver or spleen laceration, especially in adults).

By Advanced Trauma Life Support (ATLS) protocol, the FAST examination is performed immediately after the primary survey. In hypotensive patients, it is nearly perfect for identifying intraperitoneal bleeding requiring emergent laparotomy and cardiac injury/pericardial effusion in penetrating trauma.

CT remains the diagnostic test of choice in hemodynamically stable patients with suspected intraabdominal injury, although serial abdominal examinations and serial FAST examinations have been used as an alternative means of ruling out significant injury in low-risk patients. This alternative approach has gained proliferation in some centers at a time of rising concern regarding radiation exposure from CT, responsibly embodied in the principles of ALARA (As Low As Reasonably Achievable) increasingly called for by multiple organizations.

Clinical questions

  • Is free intraperitoneal fluid present?
  • Is a pericardial effusion present?

Probe selection

  • Low frequency (2.0 - 5.0 MHz) curvilinear probe or small curved array or phased array probe (1.0-4.0 MHz) can be used for adequate tissue penetration.
  • A small curved array or phased array probe offers the benefit of a small footprint and easier imaging between rib spaces.

Elements of the FAST examination

  • Four standard views are obtained, looking for free fluid (black, or anechoic, on ultrasound). See the image below.
    Image of the Morison pouch (arrows) demonstrating Image of the Morison pouch (arrows) demonstrating a small layer of dark free intraperitoneal fluid (F). Also noted is free fluid wrapping around the inferior margin of the liver.
  • Right upper quadrant view - Demonstrates fluid in Morison's pouch (hepatorenal recess), classically taught as the most sensitive area for free intraperitoneal fluid. See the images below.
    Right upper quadrant (RUQ) view of the Morison pou Right upper quadrant (RUQ) view of the Morison pouch (potential space between the liver and right kidney) where intraperitoneal fluid accumulates. This RUQ image depicts the liver and kidney (Kid). The center of the normal kidney (renal sinus) contains dense echoes.
    A marked amount of free intraperitoneal fluid in t A marked amount of free intraperitoneal fluid in the Morison pouch, visible as a broad anechoic (black) signal between the liver edge and the anterior right kidney.
  • Left upper quadrant view - Demonstrates fluid in the splenorenal recess, the subdiaphragmatic space, and along the inferior tip of the spleen and the inferior pole of the left kidney (See the image below.)
    Positive left upper quadrant view on FAST examinat Positive left upper quadrant view on FAST examination, demonstrating perisplenic free fluid in the subdiaphragmatic space.
  • Subxiphoid view - Demonstrates pericardial fluid accumulations (A parasternal view may be obtained through the chest wall at the junction of the ribs and sternum in patients with poor subxiphoid views or in patients who cannot tolerate this view because of abdominal tenderness. See the image below.)
    Subxiphoid view of the heart showing a moderate am Subxiphoid view of the heart showing a moderate amount of pericardial fluid extending almost entirely around the cardiac silhouette.
  • Suprapubic view - Demonstrates free fluid in the pelvis (Small amounts of free fluid can be physiologic in women of childbearing age.) (See the image below.)
    Sagittal view of the pelvis of a female patient. D Sagittal view of the pelvis of a female patient. Deep to the uterus, wedge-shaped intraperitoneal free fluid can be seen. Courtesy of Stanford University Ultrasound Division with editing by Joshua Ennis, MD.

Patient positioning

  • The patient should be supine to allow fluid to collect in dependent areas. Rolling the patient immediately prior to the FAST examination may decrease the sensitivity.
  • Placing the patient in the Trendelenburg position can increase the sensitivity of the right upper quadrant view for free fluid. [6]

Limitations of the FAST examination

  • Inability to distinguish between blood, urine, bile, ascites, or other fluids
  • Poor sensitivity for bowel, diaphragmatic, solid organ injury, and retroperitoneal bleeding
  • May be limited in patients with large body habitus
  • Is not reliable for the identification of bleeding from a pelvic fracture source

Abdominal aortic aneurysm (AAA)

Symptomatic AAA with hemodynamic instability is a true vascular emergency and requires prompt identification in the ED, where resuscitative efforts can be initiated.

Physical examination is insufficiently sensitive to rule out AAA in the absence of a pulsatile abdominal mass, whereas the sensitivity of bedside ED ultrasonography for detection of AAA ranges from 94-100%.[7, 8, 9]

While aneurysm rupture cannot be reliably detected on ultrasound, the presence of an AAA in the hemodynamically compromised patient requires emergent operative evaluation and should not be delayed in order obtain more definitive imaging. The presence of the aneurysm alone is sufficient to obtain emergent consultation.

Clinical questions

  • Is an AAA present?
  • Is an iliac artery aneurysm present?

Probe selection

  • A standard 2.0-5.0 MHz curvilinear abdominal probe may be used to achieve adequate tissue penetration in most patients. A larger footprint probe (large curved) is often helpful to push bowel gas aside.
  • Decreasing the probe frequency may be useful in patients with larger body habitus.

Elements of the examination

  • The entire course of the abdominal aorta should be visualized in the transverse plane, from the xiphoid process down to the iliac bifurcation (usually at or near the umbilicus). The transverse plane gives a more reliable size estimation of the aorta than the longitudinal plane (because of the potential for tangential measuring error in the longitudinal plane).
  • The common iliac arteries, which usually arise around the level of the umbilicus, should also be evaluated for aneurysm after the aorta has been evaluated.
  • Longitudinal views should also be obtained. Take care to scan laterally through the barrel of the vessel and identify its widest diameter, as a "parasagittal" view may give a false negative measurement. Further, longitudinal scanning is important to identify the much rarer saccular aneurysm.
  • AAA is typically defined as an aortic diameter >3.0 cm when measured anteriorly to posteriorly from outer wall to outer wall. Also considered an aneurysm is any increase in size with moving distally along the course of the aorta (even if < 3 cm).
  • Be sure to measure the entire aneurysm (including clot), not just the false lumen often created by the presence of echogenic thrombi adherent to the vessel walls. Measurement of this false lumen will underestimate the size of the aneurysm.
  • Iliac artery aneurysm is defined as vessel diameter >1.5 cm when measured from outer wall to outer wall at its widest point. See the images below.
    Short-axis view of an abdominal aortic aneurysm ro Short-axis view of an abdominal aortic aneurysm roughly 9 cm in transverse diameter. The hyperechoic vertebra is visible posteriorly and serves as a landmark in identifying the aorta. Though ultrasonography is an insensitive modality for evaluation of dissection and rupture, this image contains evidence of a false lumen, suggesting likely dissection.
    Color cine loop depicting abdominal aortic aneurysm (AAA). Video courtesy of Meghan Kelly Herbst, MD. Also courtesy of Yale School of Medicine, Emergency Medicine.
    Cine loop of abdominal aortic aneurysm (AAA). Video courtesy of Meghan Kelly Herbst, MD. Also courtesy of Yale School of Medicine, Emergency Medicine.

Patient positioning and imaging tips

  • If bowel gas prevents adequate visualization using a midline approach, left lateral decubitus positioning and imaging through the liver may provide better visualization of the aorta.
  • Asking the patient to inspire deeply may assist in visualizing the proximal abdominal aorta, as diaphragmatic excursion pushes the liver inferiorly.
  • Holding firm pressure with a large footprint probe may help to displace bowel gas and improve visualization of the aorta. Often times, displacing bowel can be further assisted by applying firm pressure with a second hand immediately adjacent to the probe.
  • In older patients, the aorta may take a tortuous path. Once the aorta is identified, follow it even if it goes off of midline.
  • At times, the aorta can be seen from the coronal plane (midaxillary view), using the liver or spleen as the sonographic window. Increasing the depth is necessary compared to the FAST views. This is more useful as a "rule in" tool rather than a "rule out" tool, as the aorta may not be visible in its full entirety; additional imaging modalities will be needed.
  • Saccular aneurysms (small aneurysm pouches) are easier to miss compared to fusiform aneurysms. It is critical that the entire aorta be visualized in two planes in the assessment of AAA.
  • Tricks for identifying the aorta include the following:
    • Increase the image depth and identify the vertebral bodies by their characteristic hyperechoic appearance with posterior acoustic shadowing; the aorta should be immediately anterior and slightly to the patient's left of the echogenic vertebrae.
    • Do not mistake the spinal canal and the brightly walled superior mesenteric artery for the aorta.
    • Ask the patient to sniff; the inferior vena cava (IVC) often collapses during this maneuver, while the aorta typically does not.
    • You may also use color to help differentiate between the IVC and aorta. When aiming the transversely oriented probe up toward the head from the umbilicus, aortic blood is flowing toward the feet and, therefore, toward the probe. In this orientation, aortic flow will be red and IVC flow will be blue. These colors will reverse if the probe is pointed down toward the feet, so take care in using this technique. Also, the aorta will have pulsatile flow whereas the IVC will have a more continuous hum of blood flow.

Limitations of ultrasonography in AAA evaluation

  • Ultrasonography has poor sensitivity for detecting aneurysmal leak or rupture.
  • If the aneurysm ruptures, bleeding is often retroperitoneal (rather than intraperitoneal) and thus cannot be well evaluated with ultrasonography; do not look for a positive FAST examination result in these patients. The presence of the aneurysm alone is sufficient to mobilize resources in the appropriate clinical setting.
  • Visualization of the aorta may be limited because of bowel gas and in patients with large body habitus.

Inferior vena cava

IVC ultrasound has been widely adopted as a measure of intravascular volume status in the spontaneously breathing patient.[10, 11] It has been shown to grossly correlate with central venous pressure and may be considered a noninvasive surrogate for assessing volume status. Although IVC ultrasound may not predict fluid responsiveness, it is a decent marker for fluid tolerance of crystalloid resuscitation.

The most widely adopted measures include absolute IVC size and respirophasic variation known as the collapsibility index. These measurements allow one to estimate central venous pressure to help guide diagnostic workup and fluid resuscitation (both upon initial evaluation as well as over time).

Clinical questions

  • What is absolute IVC diameter?
  • How much respiratory variation is seen in the IVC diameter?

Probe selection

  • A standard 2- to 5-MHz curvilinear abdominal probe may be used to achieve adequate tissue penetration in most patients. A larger footprint probe (large curved) is often helpful to push bowel gas aside.
  • Decreasing the probe frequency may be useful in patients with larger body habitus.

Elements of the examination

  • Visualization of the IVC is usually accomplished by using the liver as an acoustic window in the right upper quadrant, following the IVC as it courses through the liver and into the right atrium. If unable, an alternative is an axillary transhepatic approach.
  • The IVC is usually identified in the longitudinal axis, with slow fanning side-to-side, to identify its maximal dimension. It may also be identified in the transverse plane.
  • Measurements are taken 1-2cm distal to the junction of the hepatic veins and IVC.
  • M-mode can be used to assist in measuring maximal dimension and respiratory variation.
  • Ask the patient to sniff; the inferior vena cava (IVC) often collapses during this maneuver, while the aorta typically does not.
  • Correlations can be made between IVC size and central venous pressure.
  • IVC size less than 1.5 cm, with respiratory change at total collapse, central venous pressure is 0-5 cm water.
  • IVC size 1.5 cm, with respiratory change at greater than 50%, central venous pressure is 6-10 cm water.
  • IVC size 1.5-2.5 cm, with respiratory change at less than 50%, central venous pressure is 11-15 cm water.
  • IVC size greater than 2.5 cm, with respiratory change at less than 50%, central venous pressure is 16-20 cm water.
  • IVC size greater than 2.5 cm, with no respiratory change, central venous pressure is greater than 20 cm water.
  • See the image below.
    M-mode of an inferior vena cave (IVC) measured 2 c M-mode of an inferior vena cave (IVC) measured 2 cm distal to the confluence of hepatic veins with the IVC. In this image, the nadir measures 2.19 cm and minimally varies with respirations, consistent with an elevated central venous pressure. Courtesy of Stanford University Ultrasound Division with editing by Joshua Ennis, MD.

Patient positioning and imaging tips

  • If bowel gas prevents adequate visualization using a midline approach, a transhepatic axillary view is an alternative.
  • Holding firm pressure with a large footprint probe may help to displace bowel gas and improve visualization of the IVC.
  • Tricks for identifying the IVC include (1) asking the patient to sniff, as the IVC often collapses during this maneuver, while the aorta typically does not; (2) using color to help differentiate between the IVC and aorta, because when aiming the transversely oriented probe up toward the head from the umbilicus, aortic blood is flowing toward the feet and, therefore, toward the probe, and, in this orientation, aortic flow is red and IVC flow is blue; these colors reverse if the probe is pointed down toward the feet, so take care in using this technique; and (3) noting that the aorta has pulsatile flow, whereas the IVC has a more continuous hum of blood flow.

Limitations of ultrasonography in IVC evaluation

  • IVC measurements referenced above do not apply to patients receiving positive-pressure ventilation.
  • Findings must be interpreted within their respective clinical context/scenario. For example, a large/plethoric IVC may not necessarily be indicative of intravascular volume overload, but rather cardiac tamponade or mitral stenosis, among others.
  • Visualization of the IVC may be limited because of bowel gas and in patients with large body habitus.

Biliary tract

Right upper quadrant or epigastric discomfort or pain or tenderness are the primary indications for bedside biliary ultrasonography.

Patients with jaundice may benefit from bedside biliary ultrasonography, however, the ability of novice or untrained sonographers to interpret findings is more limited. Further studies may be indicated.

Clinical questions

  • Are gallstones present?
  • Is evidence of cholecystitis present?
  • Is the common bile duct (CBD) dilated?

Probe selection

  • A small or large curved array probe of low or intermediate frequency (2.0-5.0 MHz) will suffice.
  • Probes with smaller footprints allow for easier imaging through rib spaces. Probes with larger footprints offer better abdominal views. Either type is acceptable.

Elements of the examination

  • The normal gallbladder appears as a pear-shaped, hypoechoic structure on ultrasound.
  • Find the gallbladder in the right upper quadrant and scan through it in both the transverse and longitudinal axes. This may require an intercostal approach between the ribs using the liver as an acoustic window, or a subcostal approach.
  • Interrogate the gallbladder looking for gallstones, which are hyperechoic with associated posterior acoustic shadowing (darkened area deep to the stone). Be sure to visualize the neck of the gallbladder, as symptomatic gallstones can be found impacted in the neck. See the images below.
    Longitudinal view of the gallbladder (gb) revealin Longitudinal view of the gallbladder (gb) revealing a large gallstone (st) with associated acoustic shadowing (sh). This gallstone is located near the neck of the gallbladder. If impacted, it would need to be surgically removed.
    Longitudinal view of the gallbladder with 2 large Longitudinal view of the gallbladder with 2 large stones visible in the fundus, with associated posterior acoustic shadowing. Notably, the anterior wall does not appear to be thickened and no evidence of pericholecystic fluid is present.
  • Measure the anterior wall of the gallbladder (often easiest on a longitudinal view). A wall thickness greater than 3 mm is considered abnormal and is called thickened. Avoid measuring the posterior wall of the gallbladder, as posterior acoustic enhancement makes this challenging and can lead to incorrect values.
    Right upper quadrant view of the gallbladder in lo Right upper quadrant view of the gallbladder in longitudinal section reveals hyperechoic material in the fundus. Note the posterior shadowing consistent with cholelithiasis. In addition, the anterior gallbladder wall appears thickened, and the presence of a narrow stripe of hypoechoic fluid along the anterior wall suggests inflammation consistent with cholecystitis.
  • Assess for a sonographic Murphy sign. Reproduction of the patient’s abdominal pain by pressing with the ultrasound probe over the gallbladder constitutes a positive finding.
  • Look for a hypoechoic rim of pericholecystic fluid (PCF) adjacent to the gallbladder. Pericholecystic fluid can be evidence of inflammation due to gallbladder disease but can also be secondary to hepatitis or congestive heart failure.
  • While individual findings on biliary ultrasound have insufficient sensitivity and specificity, the combination of multiple findings offers improved predictive value. A normal emergency physician–performed bedside ultrasound has a negative predictive value (NPV) of 90% for acute cholecystitis. [12] The combination of gallstones and anterior gallbladder wall thickening has a positive predictive value (PPV) >95% for acute cholecystitis. [13] The combination of gallstones and sonographic Murphy sign has a PPV of 92% for acute cholecystitis. [13]
  • Identify the common bile duct (CBD). A hypoechoic, tubular structure anterior to the portal vein, it can be visualized near the neck of the gallbladder in a longitudinal view or in a transverse view from the epigastrium. Following the main lobar fissure away from the gallbladder sometimes proves useful. See the image below.
    Here can be seen the gallbladder (GB) with the mai Here can be seen the gallbladder (GB) with the main lobar fissure (MLF) coursing down towards the portal triad. Lack of flow with color Doppler applied over the portal triad would confirm the common bile duct (CBD). Courtesy of Stanford University Ultrasound Division with editing by Joshua Ennis, MD.
  • Measure the CBD from inner wall to inner wall. CBD diameter greater than 5 mm is considered abnormal, though this cutoff increases with advancing age (a good rule of thumb is for every decade over 50 y, an additional 1 mm is allowed; eg, 6 mm at 60 y, 7 mm at 70 y). Patients often have a nonpathological dilated CBD (up to 1 cm) after cholecystectomy. CBD dilatation is evidence of extrahepatic biliary obstruction, either intraductal (eg, stones) or secondary to extrinsic compression (eg, tumor), and may warrant additional imaging (CT or magnetic resonance cholangiopancreatography [MRCP]) or GI evaluation and management via endoscopic retrograde cholangiopancreatography (ERCP).
  • Novice ultrasonographers often struggle in finding and identifying the CBD. In a patient with otherwise normal laboratory studies and an otherwise normal bedside biliary ultrasound, finding the CBD by bedside ultrasound in an emergency setting may not actually be necessary for low-risk scenarios according to a recent retrospective chart review, although this approach likely requires prospective validation prior to widespread adoption. [14]

Patient positioning and imaging tips

  • Supine positioning is the typical starting point, but the gallbladder is quite variable in its position and may be difficult to visualize in this position. Improved views of the gallbladder may be obtained with the patient in either a sitting position or in a left lateral decubitus position. Both of these positions bring the gallbladder out from beneath the costal margin. Asking the patient to take and hold a deep breath may bring the gallbladder farther down and into view.
  • To find the gallbladder, use the following 2 landmarks: (1) the portal triad (portal vein, common bile duct, and hepatic artery) and (2) the main lobar fissure. The gallbladder lies within the main lobar fissure (hyperechoic line), is the functional division between the right half and the left half of the liver, and is present and seen in most patients.
  • Imaging through the liver from the midanterior axillary line to locate the gallbladder and then moving the probe over it can also be helpful.
  • If the gallbladder proves difficult to visualize despite patient positioning and inspiration, consider repeating the exam after keeping the patient NPO for a period of time.
  • If uncertain whether gallbladder contents represent stones (eg, posterior acoustic shadowing is not seen), try repositioning the patient; stones generally shift to dependent areas, whereas polyps or masses remain stationary. Gallbladder sludge appears hyperechoic but does not result in acoustic shadowing and does layer or move dependently with patient positioning.
  • A gallbladder full of stones may result in the wall-echo-shadow (WES) sign, where the anterior gallbladder wall is seen with a hyperechoic stripe just behind and broad, dark shadowing posteriorly. The WES sign can easily be confused with the acoustic scatter caused by adjacent small bowel.

Limitations of bedside biliary ultrasonography

  • Biliary ultrasonography can be challenging (in particular, assessment of the CBD) and, thus, can be operator-dependent.
  • The gallbladder can be difficult to visualize in nonfasting patients.
  • The finding of gallstones does not by itself explain the patient's symptoms. While gallstones place patients at increased risk for biliary disease, they can be and are often asymptomatic.

Renal

Indications for renal ultrasonography include assessment for obstructive uropathy, as evidenced by hydronephrosis or bladder distension in the following settings:

  • Unilateral flank pain, low back pain, or lower abdominal pain
  • Hematuria
  • Anuria or decreased urinary output

An important cautionary note is that AAAs frequently present in a manner similar to renal colic, so bedside ultrasonography to assess for and rule out an AAA is indicated in at-risk populations. Hydronephrosis and even hematuria from an AAA adjacent to the ureter can occur, making it even more important to screen for both in at-risk groups.

Clinical questions

  • Is hydronephrosis present?
  • If hydronephrosis is present, is it unilateral or bilateral?
  • Is the bladder distended? Is urinary retention present?

Probe selection

  • A standard curvilinear abdominal probe (2.0-5.0 MHz) is typically the best choice.

Elements of the examination

  • Both kidneys should be interrogated in the transverse and longitudinal planes. The asymptomatic side should be scanned first to establish a baseline for comparison.
  • Normal ultrasound appearance of renal parenchyma, from exterior to interior (as follows):
    • Hyperechoic renal capsule
    • Hypoechoic renal cortex
    • Hypoechoic medullary pyramids
    • Hyperechoic renal pelvis
  • Assess for hydronephrosis.
    • In hydronephrosis, the renal pelvis is dilated and filled with dark anechoic fluid, seen coalescing centrally within the hyperechoic renal pelvis. Hydronephrosis is generally classified as mild, moderate, and severe. With increasing severity of hydronephrosis, the standard architecture of the kidneys becomes more abnormal, with compression of the cortex. See the images below.
      Image demonstrating moderate hydronephrosis (Hy) a Image demonstrating moderate hydronephrosis (Hy) and the bear claw sign. Dilatation of the renal collecting system with extension into and splaying of the renal calyces is seen. Renal parenchyma (p).
      Moderate hydronephrosis, with dilatation of the co Moderate hydronephrosis, with dilatation of the collecting system and blunting of calyceal fornices. The thickness of renal parenchyma remains relatively intact.
      Cine loop depicting renal hydronephrosis. Video courtesy of Meghan Kelly Herbst, MD. Also courtesy of Yale School of Medicine, Emergency Medicine.
    • Be sure to look for hydronephrosis in both kidneys, as bilateral hydronephrosis is indicative of more distal obstruction or dysfunction.
    • Mild hydronephrosis may be present in the absence of obstruction in patients who are pregnant or overhydrated. In these instances, the finding should be present bilaterally. A very full bladder would also suggest this.
  • Visualize the bladder in both the transverse and sagittal planes.
    • Bladder volume can be estimated by measuring its diameter in 3 perpendicular planes and applying the formula 3/4 x (L x W x H).
    • Controversy exists over the utility of assessing for ureteral jets in obstructive uropathy.[15] Assessing for ureteral jets can be somewhat time-consuming in a busy ED setting.

Patient positioning and imaging tips

  • Supine positioning is the typical starting point.
  • Asking the patient to take and hold a breath may be helpful, especially when trying to visualize the left kidney, which is more superior and posterior in the abdomen than the right kidney.
  • Right lateral decubitus positioning may further assist in visualizing the left kidney.

Limitations of renal and urinary ultrasonography

  • Renal stones are rarely directly seen (unless large and positioned in the proximal or distal ureter). Hydronephrosis is the surrogate marker for obstructing stones.
  • Hydroureter can be challenging to visualize on ultrasound unless significant hydroureter is present.
  • Hydronephrosis is a nonspecific finding that can be secondary to many causes both intrinsic (eg, nephrolithiasis) or extrinsic (eg, pelvic mass).

Appendicitis

Indications include the presence of any of the typical signs and symptoms of acute appendicitis (periumbilical or right lower quadrant abdominal pain or tenderness, abdominal rebound or guarding, fever, nausea and vomiting, or anorexia). See the images below.

Transverse view of appendix. This image demonstrat Transverse view of appendix. This image demonstrates an enlarged appendix, noncompressible in real time, consistent acute appendicitis. Courtesy of Stanford University Ultrasound Division with editing by Joshua Ennis, MD.
Appendix in longitudinal axis. This dilated blind- Appendix in longitudinal axis. This dilated blind-ending tubular structure measuring larger than 6 mm was not compressible in real time, consistent with acute appendicitis. Courtesy of Stanford University Ultrasound Division with editing by Joshua Ennis, MD.

Clinical questions

  • Is the appendix dilated?
  • Is the appendix compressible?
  • Is there a lack of peristalsis in the appendix?
  • Is there a fecalith in the appendix?

Probe selection

  • A linear array probe of intermediate to high frequency (5.0-10.0 MHz), depending on the body habitus of the patient.

Elements of the examination

  • Begin scanning over the point of maximal pain, as indicated by the patient. This improves the accuracy of the examination. [16]
  • Search for the appendix by slowly and firmly compressing the abdomen with the linear probe at the point of maximal tenderness; slowly applied firm pressure may help displace overlying loops of bowel.
  • Move progressively through all quadrants until the appendix is located or until a thorough abdominal survey has been completed.
  • It is often helpful to use the psoas muscle and iliac vessels as a guide to locating the appendix.
  • Once the appendix is found, complete the following steps:
    • Visualize the appendix along its entire length in both the short and long axes.
    • Measure the diameter of the appendix from external wall to external wall; a diameter >6 mm is considered abnormal.
    • Assess the compressibility of the appendix. An inflamed and swollen appendix does not compress under gradual compression.
    • Look for evidence of continued peristalsis. Normal peristalsis is impaired in the inflamed appendix. This may be better assessed with a long-axis view.
    • Examine the cross-sectional appearance of the appendix, as it takes on a multilaminar targetoid appearance in the setting of acute inflammation.

Patient positioning and imaging tips

  • Supine positioning is standard.

Limitations of the examination

  • The limited sensitivity of the examination renders it insufficient for ruling out acute appendicitis.
  • This is a technically challenging and time-consuming examination with significant inter-operator variability.
  • The appendix is extremely difficult to visualize in the setting of perforation and in patients with large body habitus.
  • Of all the techniques discussed in this article, this is the most difficult. If suspicion for acute appendicitis remains high, further imaging, surgical consultation or both are indicated.

Paracentesis

Indications for bedside ultrasonography in paracentesis include the following:

  • Bedside ultrasonography can give immediate information regarding the presence or absence of ascites because of its high sensitivity for free fluid. It is much more reliable than assessing for a fluid wave or shifting dullness on examination.
  • Bedside ultrasonography has high utility in patients with suspected spontaneous bacterial peritonitis (SBP). It is also helpful in patients who need a tap for therapeutic indications (eg, to decrease abdominal pain from distention or to help reduce compressive dyspnea due to abdominal distension).
  • Ultrasound-guided paracentesis increases patient safety, especially as many of these patients also have a coagulopathy.

Clinical questions

  • Is ascites present?
  • Where are the largest pockets of fluid located?
  • Where is the safest location to place the needle that also clears vital organs (such as liver, spleen, bladder, and bowel)?

Probe selection

  • Use a 2.5-5.0 MHz probe similar to those used in the FAST and aorta applications above.

Elements of the examination

  • Run the probe over the abdomen, evaluating for the most accessible large fluid pocket that also clears vital organs. See the image below.
    Abdominal ultrasound showing ascites fluid (dark) Abdominal ultrasound showing ascites fluid (dark) surrounding loops of bowel, with a significant fluid pocket extending to a depth of around 9 cm.
  • There are 2 approaches to ultrasound-guided paracentesis: static and dynamic.
    • The static approach: The site is marked and then the paracentesis procedure is performed in standard fashion.
    • If this approach is used, the patient must not move in between the marking and the procedure. Special note should also be made of the depth of the fluid collection to estimate the depth of needle placement. In addition, the angle of the probe at the time of marking should be mirrored by the angle of the needle to recreate the conditions appropriately.
    • The dynamic approach: This approach includes real-time ultrasonographic guidance.
    • The site may be marked, but after prepping and draping the patient in the usual fashion, the probe is also placed in a sterile sheath (with gel between the probe and the sheath and sterile gel on the outside of the sheath).
    • The fluid pocket is re-evaluated in real time as the needle is placed under direct ultrasonographic visualization. Care should be taken to visualize the tip of the needle.
Previous
Next

Pearls

Repositioning the patient or the probe is often the key to capturing otherwise difficult-to-obtain images. Some examples are as follows:

  • Seated or left lateral decubitus positioning for biliary ultrasound
  • Breath-holding in inspiration for visualizing the left kidney or gallbladder
  • Imaging through the liver to visualize the gallbladder from the coronal approach when it is not easily seen anteriorly
  • Mild Trendelenburg positioning for improving the sensitivity of the right upper quadrant view in the FAST examination

Be familiar with relevant anatomy and know how to distinguish sonographically similar structures (eg, have the patient sniff to distinguish the inferior vena cava (IVC) from the aorta, or use vertebral bodies to locate the abdominal aorta).

Bedside emergency department ultrasonography is preferable to radiology department imaging in an unstable patient. However, in a stable patient, more definitive imaging (eg, CT) may be indicated.

Previous
Next

Complications

Ultrasound imaging does not use ionizing radiation and has not been shown to be associated with genetic damage or oncogenesis.

Tissue damage secondary to heat production when using Doppler imaging is a theoretical risk, so high-energy modes are typically avoided with fetal ultrasonography.

Previous
Next

Future Directions

As ultrasound technology and the training to use such technology both improve, new clinical applications and indications for use in the ED will continue to grow. New and investigational applications of abdominal ultrasound include the following:

  • Identification of abdominal wall pathology, including hernias, abscesses, solid masses, and wound evaluation [17, 18]
  • Use of sonographic contrast agents to improve assessment for solid organ injuries in trauma patients [19]
Previous
 
Contributor Information and Disclosures
Author

Joshua J Ennis, MD Emergency Physician, San Francisco Emergency Medical Associates; Co-Director, Emergency Ultrasound, Sutter Hospital Lakeside

Joshua J Ennis, MD is a member of the following medical societies: American College of Emergency Physicians, American Institute of Ultrasound in Medicine, Society for Academic Emergency Medicine

Disclosure: Nothing to disclose.

Coauthor(s)

Sarah R Williams, MD, FACEP, FAAEM Clinical Associate Professor of Surgery (Emergency Medicine), Associate Residency Director, Stanford/Kaiser Emergency Medicine Residency Program, Co-Director, Stanford Emergency Medicine Ultrasound Fellowship, Stanford University School of Medicine

Sarah R Williams, MD, FACEP, FAAEM is a member of the following medical societies: American Academy of Emergency Medicine, American College of Emergency Physicians, American Institute of Ultrasound in Medicine, Council of Emergency Medicine Residency Directors

Disclosure: Nothing to disclose.

Chief Editor

Caroline R Taylor, MD Associate Professor, Department of Diagnostic Radiology, Yale University School of Medicine; Chief, Diagnostic Imaging Service, Veterans Affairs Connecticut Health Care System

Caroline R Taylor, MD is a member of the following medical societies: Radiological Society of North America

Disclosure: Nothing to disclose.

Additional Contributors

James Quan-Yu Hwang, MD RDMS, RDCS, FACEP, Staff Physician, Emergency Department, Kaiser Permanente

James Quan-Yu Hwang, MD is a member of the following medical societies: American Academy of Emergency Medicine, American College of Emergency Physicians, American Institute of Ultrasound in Medicine, Society for Academic Emergency Medicine

Disclosure: Received salary from 3rd Rock Ultrasound, LLC for speaking and teaching; Received consulting fee from Schlesinger Associates for consulting; Received consulting fee from Philips Ultrasound for consulting.

Acknowledgements

Acknowledgments

Medscape Reference thanks Meghan Kelly Herbst, MD, Emergency Ultrasound Director, Department of Emergency Medicine, Hartford Hospital, for assistance with the video contribution to this article. Medscape Reference also thanks Yale School of Medicine, Emergency Medicine for assistance with the video contribution to this article.

References
  1. Nishijima DK, Simel DL, Wisner DH, Holmes JF. Does this adult patient have a blunt intra-abdominal injury?. JAMA. 2012 Apr. 307(14):1517-27. [Medline].

  2. Rubano E, Mehta N, Caputo W, Paladino L, Sinert R. Systematic review: emergency department bedside ultrasonography for diagnosing suspected abdominal aortic aneurysm. Acad Emerg Med. 2013 Feb. 20(2):128-38. [Medline].

  3. Sekiguchi H, Suzuki J, Daniels CE. Making paracentesis safer: a proposal for the use of bedside abdominal and vascular ultrasonography to prevent a fatal complication. Chest. 2013 Apr. 143(4):1136-9. [Medline].

  4. American Institute of Ultrasound in Medicine, American College of Emergency Physicians. AIUM practice guideline for the performance of the focused assessment with sonography for trauma (FAST) examination. J Ultrasound Med. 2014 Nov. 33 (11):2047-56. [Medline].

  5. Wherrett LJ, Boulanger BR, McLellan BA, Brenneman FD, Rizoli SB, Culhane J, et al. Hypotension after blunt abdominal trauma: the role of emergent abdominal sonography in surgical triage. J Trauma. 1996 Nov. 41(5):815-20. [Medline].

  6. Abrams BJ, Sukumvanich P, Seibel R, Moscati R, Jehle D. Ultrasound for the detection of intraperitoneal fluid: the role of Trendelenburg positioning. Am J Emerg Med. 1999 Mar. 17(2):117-20. [Medline].

  7. Kuhn M, Bonnin RL, Davey MJ, Rowland JL, Langlois SL. Emergency department ultrasound scanning for abdominal aortic aneurysm: accessible, accurate, and advantageous. Ann Emerg Med. 2000 Sep. 36(3):219-23. [Medline].

  8. Tayal VS, Graf CD, Gibbs MA. Prospective study of accuracy and outcome of emergency ultrasound for abdominal aortic aneurysm over two years. Acad Emerg Med. 2003 Aug. 10(8):867-71. [Medline].

  9. Costantino TG, Bruno EC, Handly N, Dean AJ. Accuracy of emergency medicine ultrasound in the evaluation of abdominal aortic aneurysm. J Emerg Med. 2005 Nov. 29(4):455-60. [Medline].

  10. Nagdev AD, Merchant RC, Tirado-Gonzalez A, Sisson CA, Murphy MC. Emergency Department Bedside Ultrasonographic Measurement of the Caval Index for Noninvasive Determination of Low Central Venous Pressure. Ann Emerg Med. 2009 Jun 25. [Medline].

  11. Blehar DJ, Dickman E, Gaspari R. Identification of congestive heart failure via respiratory variation of inferior vena cava diameter. Am J Emerg Med. 2009 Jan. 27(1):71-5. [Medline].

  12. Rosen CL, Brown DF, Chang Y, Moore C, Averill NJ, Arkoff LJ, et al. Ultrasonography by emergency physicians in patients with suspected cholecystitis. Am J Emerg Med. 2001 Jan. 19(1):32-6. [Medline].

  13. Ralls PW, Colletti PM, Lapin SA, Chandrasoma P, Boswell WD Jr, Ngo C, et al. Real-time sonography in suspected acute cholecystitis. Prospective evaluation of primary and secondary signs. Radiology. 1985 Jun. 155(3):767-71. [Medline].

  14. Becker BA, Chin E, Mervis E, Anderson CL, Oshita MH, Fox JC. Emergency biliary sonography: utility of common bile duct measurement in the diagnosis of cholecystitis and choledocholithiasis. J Emerg Med. 2014 Jan. 46(1):54-60. [Medline].

  15. Delair SM, Kurzrock EA. Clinical utility of ureteral jets: disparate opinions. J Endourol. 2006 Feb. 20(2):111-4. [Medline].

  16. Chesbrough RM, Burkhard TK, Balsara ZN, Goff WB 2nd, Davis DJ. Self-localization in US of appendicitis: an addition to graded compression. Radiology. 1993 May. 187(2):349-51. [Medline].

  17. Young J, Gilbert AI, Graham MF. The use of ultrasound in the diagnosis of abdominal wall hernias. Hernia. 2007 Aug. 11(4):347-51. [Medline].

  18. Gokhale S. Sonography in identification of abdominal wall lesions presenting as palpable masses. J Ultrasound Med. 2006 Sep. 25(9):1199-209. [Medline].

  19. Manetta R, Pistoia ML, Bultrini C, Stavroulis E, Di Cesare E, Masciocchi C. Ultrasound enhanced with sulphur-hexafluoride-filled microbubbles agent (SonoVue) in the follow-up of mild liver and spleen trauma. Radiol Med. 2009 Aug. 114(5):771-9. [Medline].

  20. Ma OJ, Mateer JR, Blaivas M. Emergency Ultrasound. 2nd ed. New York: McGraw Hill; 2008. 435.

  21. Noble VE, Nelson B, Sutingco AN. Manual of Emergency and Critical Care Ultrasound. New York: Cambridge University Press; 2007. 249.

 
Previous
Next
 
Right upper quadrant (RUQ) view of the Morison pouch (potential space between the liver and right kidney) where intraperitoneal fluid accumulates. This RUQ image depicts the liver and kidney (Kid). The center of the normal kidney (renal sinus) contains dense echoes.
Image of the Morison pouch (arrows) demonstrating a small layer of dark free intraperitoneal fluid (F). Also noted is free fluid wrapping around the inferior margin of the liver.
Longitudinal view of the gallbladder (gb) revealing a large gallstone (st) with associated acoustic shadowing (sh). This gallstone is located near the neck of the gallbladder. If impacted, it would need to be surgically removed.
Image demonstrating moderate hydronephrosis (Hy) and the bear claw sign. Dilatation of the renal collecting system with extension into and splaying of the renal calyces is seen. Renal parenchyma (p).
Short-axis view of an abdominal aortic aneurysm roughly 9 cm in transverse diameter. The hyperechoic vertebra is visible posteriorly and serves as a landmark in identifying the aorta. Though ultrasonography is an insensitive modality for evaluation of dissection and rupture, this image contains evidence of a false lumen, suggesting likely dissection.
Abdominal ultrasound showing ascites fluid (dark) surrounding loops of bowel, with a significant fluid pocket extending to a depth of around 9 cm.
Subxiphoid view of the heart showing a moderate amount of pericardial fluid extending almost entirely around the cardiac silhouette.
Positive left upper quadrant view on FAST examination, demonstrating perisplenic free fluid in the subdiaphragmatic space.
A marked amount of free intraperitoneal fluid in the Morison pouch, visible as a broad anechoic (black) signal between the liver edge and the anterior right kidney.
Right upper quadrant view of the gallbladder in longitudinal section reveals hyperechoic material in the fundus. Note the posterior shadowing consistent with cholelithiasis. In addition, the anterior gallbladder wall appears thickened, and the presence of a narrow stripe of hypoechoic fluid along the anterior wall suggests inflammation consistent with cholecystitis.
Longitudinal view of the gallbladder with 2 large stones visible in the fundus, with associated posterior acoustic shadowing. Notably, the anterior wall does not appear to be thickened and no evidence of pericholecystic fluid is present.
Moderate hydronephrosis, with dilatation of the collecting system and blunting of calyceal fornices. The thickness of renal parenchyma remains relatively intact.
Sagittal view of the pelvis of a female patient. Deep to the uterus, wedge-shaped intraperitoneal free fluid can be seen. Courtesy of Stanford University Ultrasound Division with editing by Joshua Ennis, MD.
Appendix in longitudinal axis. This dilated blind-ending tubular structure measuring larger than 6 mm was not compressible in real time, consistent with acute appendicitis. Courtesy of Stanford University Ultrasound Division with editing by Joshua Ennis, MD.
Transverse view of appendix. This image demonstrates an enlarged appendix, noncompressible in real time, consistent acute appendicitis. Courtesy of Stanford University Ultrasound Division with editing by Joshua Ennis, MD.
Here can be seen the gallbladder (GB) with the main lobar fissure (MLF) coursing down towards the portal triad. Lack of flow with color Doppler applied over the portal triad would confirm the common bile duct (CBD). Courtesy of Stanford University Ultrasound Division with editing by Joshua Ennis, MD.
M-mode of an inferior vena cave (IVC) measured 2 cm distal to the confluence of hepatic veins with the IVC. In this image, the nadir measures 2.19 cm and minimally varies with respirations, consistent with an elevated central venous pressure. Courtesy of Stanford University Ultrasound Division with editing by Joshua Ennis, MD.
Color cine loop depicting abdominal aortic aneurysm (AAA). Video courtesy of Meghan Kelly Herbst, MD. Also courtesy of Yale School of Medicine, Emergency Medicine.
Cine loop of abdominal aortic aneurysm (AAA). Video courtesy of Meghan Kelly Herbst, MD. Also courtesy of Yale School of Medicine, Emergency Medicine.
Cine loop depicting renal hydronephrosis. Video courtesy of Meghan Kelly Herbst, MD. Also courtesy of Yale School of Medicine, Emergency Medicine.
 
 
 
All material on this website is protected by copyright, Copyright © 1994-2016 by WebMD LLC. This website also contains material copyrighted by 3rd parties.