1. Correct Answer: A. Anechoic area between the liver and right kidney

Rationale: Intra-abdominal free fluid normally appears anechoic on ultrasound, unless clotted blood is present, in which case the image can appear hyperechoic, hypoechoic, or have mixed echogenicity. RUQ abdominal ultrasound views obtained to look for fluid include Morison’s pouch (hepatorenal recess), right paracolic gutter, and suprahepatic areas; the LUQ views evaluate the splenorenal recess, left paracolic gutter, and suprasplenic spaces in identifying free fluid. Perinephric fat is often confused for intra-abdominal fluid since both can appear as hypoechoic images; however, perinephric fat is bounded on both sides by echogenic lines, clearly distinguishing it from free fluid. The mirror image of the liver seen above the diaphragm, which is a strong reflector of ultrasound waves, is a normal artifact that essentially excludes the presence of a pleural effusion. See also Figure 63.7.

1. Kelley K, Rose JS, Bair AE. Fundamentals of ultrasound. In: Cosby KS, Kendall JL, eds. Practical Guide to Emergency Ultrasound. 2nd ed. Wolters Kluwer; 2014:10-20.

2. Laselle BT, Kendall JL. Trauma. In: Cosby KS, Kendall JL, eds. Practical Guide to Emergency Ultrasound. 2nd ed. Wolters Kluwer; 2014:21-53.

3. Mohammad A, Hefny AF, Abu-Zidan FM. Focused assessment sonography for trauma (FAST) training: a systematic review. World J Surg. 2014;38(5):1009-1018.

4. Rozycki GS, Ochsner MG, Jaffin JH, Champion HR. Prospective evaluation of surgeons’ use of ultrasound in the evaluation of trauma patients. J Trauma. 1993;34(4):516-526.

2. Correct Answer: B. FAST is able to identify free intra-abdominal and/or pericardial fluid in the trauma patient.

Rationale: FAST is a rapid ultrasonographic examination performed to determine the presence of fluid—blood in the trauma patient—within the peritoneum, pericardium, and/or thorax. It interrogates four different areas: subxiphoid, suprapubic, RUQ, and LUQ. One downside to the examination is that a significant volume of fluid is necessary to be reliably visualized sonographically (generally >100-200 mL). For this reason, serial examinations are encouraged if ongoing bleeding is suspected. Another limitation is the examination’s inability to image the retroperitoneum due to overlying abdominal gas and viscera and suboptimal patient positioning. FAST has a lower sensitivity for the detection of solid organ injuries since they may not result in detectable free fluid, and has a very low sensitivity for hollow organ injuries. Obesity can severely limit the assessment of the peritoneal cavity and make the examination less useful.

1. Abu-Zidan FM, Zayat I, Sheikh M, Mousa I, Behbehani A. Role of ultrasonography in blunt abdominal trauma: a prospective study. Eur J Surg. 1996;162:361-365.

2. Brahee D, Ogedegbe C, Hassler C, et al. Body mass index and abdominal ultrasound image quality: a pilot survey of sonographers. J Diagn Med Sonogr. 2013;29(2):66-72.

3. Richards JR, McGahan JP. Focused assessment with sonography in trauma (FAST) in 2017: what radiologists can learn. Radiology. 2017;283(1):30-48.

4. Rozycki GS, Root HD. The diagnosis of intraabdominal visceral injury. J Trauma. 2010;68(5):1019-1023.

3. Correct Answer: A. Right upper quadrant (RUQ) view

Rationale: In the supine patient, the RUQ window is the most sensitive view for identifying free peritoneal fluid. As fluid accumulates, it settles in dependent areas of the peritoneal cavity, primarily the RUQ and suprapubic regions. Changing the patient’s position can increase the sensitivity in a specific area (e.g., Trendelenburg positioning will increase sensitivity in upper abdominal views, while reverse Trendelenburg may improve sensitivity from the suprapubic view). The space between the caudal liver edge and the inferior pole of the right kidney has recently been suggested to be a more sensitive indicator for free fluid than Morison’s pouch. Although the suprapubic region is a dependent area of the peritoneal cavity, free fluid could be missed if the bladder is empty or if there is attenuation from bowel gas. The spleen’s reduced size compared to the liver makes the LUQ window more challenging to view free fluid. The subxiphoid view would be helpful in determining the presence of pericardial effusion, not intraperitoneal free fluid. See also Figure 63.8.

1. Focused Assessment with Sonography for Trauma (FAST). In: Loukas M, Burns D, eds. Essential Ultrasound Anatomy. 1st ed. Wolters Kluwer; 2020:246-258.

2. Lobo V, Hunter-Behrend M, Cullnan E, et al. Caudal edge of the liver in the right upper quadrant (RUQ) view is the most sensitive area for free fluid on the FAST Exam. West J Emerg Med. 2017;18(2):270-280.

4. Correct Answer: C. The phrenicocolic ligament restricts the flow of free fluid to the LUQ.

Rationale/Critique: Morison’s pouch and the space between the caudal liver edge and inferior kidney pole are the most dependent areas in the supine patient. On the left, the phrenicocolic ligaments restrict the flow of fluid from the left paracolic gutter to the splenorenal recess; therefore, intra-abdominal free fluid tends to cross midline and move into RUQ spaces. The phrenicocolic ligaments also explain why LUQ fluid is more likely to collect in the subphrenic/suprasplenic space before accumulating in the splenorenal recess. The LUQ view is typically found more cephalad and posterior compared to the RUQ view. Due to the more posterior location and smaller size of the spleen when compared to the liver, free fluid in the LUQ is often more difficult to visualize on ultrasound. See also Figure 63.9.

1. Bahner D, Blaivas M, Cohen HL, et al. AIUM practice guideline for the performance of the focused assessment with sonography for trauma (FAST) examination. J Ultrasound Med. 2008;27(2):313-318.

2. Laselle BT, Kendall JL. Trauma. In: Cosby KS, Kendall JL, eds. Practical Guide to Emergency Ultrasound. 2nd ed. Wolters Kluwer; 2014:21-53.

3. Rose JS. Ultrasound in abdominal trauma. Emerg Med Clin North Am. 2004;22:581-599.

5. Correct Answer: A. The intersection of the horizontal subxiphoid line with the midaxillary line

Rationale/Critique: RUQ structures are viewed by placing the ultrasound probe at the intersection of the horizontal subxiphoid line with the midaxillary line, between the 8th and 11th rib spaces. After identifying the hepatorenal recess, one should scan cephalad to look at the right subphrenic space, as well as caudally to assess the space between the caudal liver edge and inferior kidney pole. In the LUQ view, the spleen can often be technically more difficult to image due to its posterior location and smaller size. To obtain a window, place the probe at the intersection of the horizontal subxiphoid line with the posterior axillary line at the level of the 8th rib (generally about two rib spaces superior to the RUQ view, and more posterior). A probe is placed inferior to the xiphoid process to evaluate for pericardial fluid. Positioning the probe midline and just superior to the pubic symphysis is the approach taken to image the pelvis. See Figure 63.10.

1. Rozycki GS, Ochsner MG, Feliciano DV, et al. Early detection of hemoperitoneum by ultrasound examination of the right upper quadrant: a multicenter study. J Trauma. 1998;45(5):878-883.

6. Correct Answer: D. A normal appearance of perinephric fat

Rationale/Critique: Perinephric fat can be confused for clotted blood or free fluid in Morison’s pouch. It is usually of even thickness, hypoechoic with sharp borders, and does not shift with movement. In contrast, free fluid tends to appear anechoic and can accumulate more in the RUQ with changes in positioning. In this case, her presentation immediately after injury makes clotted blood less likely, and a hypoechoic region of liquid blood is not described in the stem. A subcapsular renal hematoma would be expected to have a hypoechoic appearance initially, like free fluid, although after a clot develops, it may appear hyperechoic.

1. Salen PN, Melanson SW, Heller MB. The focused abdominal sonography for trauma (FAST) examination: considerations and recommendations for training physicians in the use of a new clinical tool. Acad Emerg Med. 2000;7(2):162-168.

2. Sierzenski PR, Schofer JM, Bauman MJ. The double-line sign: a false positive finding on the focused assessment with sonography for trauma (FAST) examination. J Emerg Med. 2011;40(2):188-189.

7. Correct Answer: A. Free fluid in Morison’s pouch

Rationale: This RUQ image (Figure 63.1) demonstrates free fluid in Morison’s pouch: an anechoic stripe in the potential space between the liver and right kidney. An ultrasonographic fluid collection in the pelvis would appear in the rectovesical pouch (space between the bladder and prostate) in males and in the pouch of Douglas (posterior to the uterus) in females. A pleural effusion is found above the diaphragm in the RUQ or LUQ view, and a pericardial effusion is seen best on a subxiphoid view.

1. Branney SW, Wolfe RE, Moore EE, et al. Quantitative sensitivity of ultrasound in detecting free intraperitoneal fluid. J Trauma Acute Care Surg. 1995;39(2):375-380.

2. Pearl WS, Todd KH. Ultrasonography for the initial evaluation of blunt abdominal trauma: a review of prospective trials. Ann Emerg Med. 1996;27(3):353-361.

8. Correct Answer: D. Double line sign

Rationale: Figure 63.2 demonstrates the double line sign, which is often mistaken for intra-abdominal clotted blood or free fluid in Morison’s pouch on the RUQ examination. The red arrow highlights two hyperechoic fascial edges (the double line sign) outlining the perinephric fat that surrounds the kidney. Clotted blood in Morison’s pouch would not have these two hyperechoic lines surrounding it. A mirror image of the liver parenchyma above the diaphragm is a normal artifact and excludes the presence of a significant pleural effusion. The spine sign is abnormal visualization of thoracic vertebral bodies above the diaphragm, which signals the presence of a pleural effusion.

1. Auckland AK. Unexplained hematocrit drop. In: Sanders RC, ed. Clinical Sonography: A Practical Guide. 5th ed. Wolters Kluwer; 2016:588-595.

2. Patwa AS, Cipot S, Lomibao A. Prevalence of the “double-line” sign when performing focused assessment with sonography in trauma (FAST) examinations. Intern Emerg Med. 2015;10(6):721-724.

9. Correct Answer: D. Full bladder

Rationale/Critique: Inexperienced ultrasonographers may misinterpret normal abdominal structures for free fluid. On abdominal ultrasound, free fluid has sharp edges, dives between structures, and shifts with movement or respiration, features that help distinguish it from normal fluid-filled structures. Gastric contents typically present as a mix of hypoechoic and hyperechoic densities, and again commonly have rounded edges. Perinephric fat located near Morison’s pouch is identified by the double line sign and has a higher echodensity than fresh blood. In the suprapubic region, acoustic enhancement produced by urine in the bladder can obscure posteriorly positioned free fluid, generating a false-negative examination. Therefore, it is important to scan in both transverse and sagittal planes to completely assess for free fluid in the pelvis. See also Figure 63.11.

1. Jang T, Kryder G, Sineff S, Naunheim R, Aubin C, Kaji AH. The technical errors of physicians learning to perform focused assessment with sonography in trauma. Acad Emerg Med. 2012;19(1):98-101.