Trauma: Right Upper Quadrant
The probe is placed in the midaxillary line between the 8th and 12th rib spaces. For this view, liver is used as an acoustic window to avoid the adjacent air-filled bowel. Sagittal oblique and a coronal scanning planes are used with the notch of the probe (also known as the probe marker) placed toward the patient’s head. This is an excellent scanning plane for visualizing the hepatorenal space located between the liver capsule and the fatty fascia of the right kidney. When fluid filled, this potential space is also known as Morison pouch (Fig. 25-2A
). Small superior probe sliding or angulations allow for evaluation of the right pleural space. With inferior probe sliding or angulations, the inferior pole of the right kidney and the right paracolic gutter can be surveyed. Both longitudinal oblique and coronal planes can be obtained to view the interface between the liver and right kidney. It is important to follow the lower edge of the liver caudally, until a sufficient view of the hepatic tip is obtained (Fig. 25-2B
) because this may be an area of early fluid accumulation in trauma24
FIGURE 25-1 Coronal placement on the probe in the right upper quadrant between the 8th and 12th intercostal spaces with the patient in supine position.
Trauma: Left Upper Quadrant
The scanning orientation for this view is the same as for the right upper quadrant with the probe placed on the left side at the midaxillary line, but now between the 7th and 10th rib space owing to the smaller-sized spleen. This can be a challenging view because of the smaller size of the spleen and often requires the probe to be placed closer to the posterior axillary line for proper visualization. This image plane will demonstrate the relationship of the spleen and left kidney (Fig. 25-3
). Both longitudinal oblique and coronal planes should be obtained to view the interface between the spleen and left kidney. With superior probe angulations, the left pleural space can be visualized. The probe should be rotated and angled to follow the renal anatomic plane to visualize fluid, if present, above the left kidney or in the left paracolic gutter.
Trauma: Pelvic Cavity
When the patient is in a supine position, the pelvis is the most dependent part of the peritoneal cavity. A fluid-filled urinary bladder typically provides a proper acoustic window to investigate for fluid anterior to the bladder, the rectouterine space in females, and behind the bladder, the rectovesical
pouch in males or rectouterine pouch in females (Fig. 25-4A
). A Trendelenburg position may be used if satisfactory images are not obtained with the patient in a supine position. Evaluation of the pelvic cavity using both longitudinal and transverse planes should be performed.
FIGURE 25-2 A: Coronal plane of right upper quadrant (RUQ). The sonogram demonstrates anechoic free fluid in the Morison pouch (Mp). The liver (L) is noted anterior to the right kidney (K). B: Longitudinal image of right upper quadrant. The full extent of the liver is displayed. The hepatic tip (t) annotates the inferior aspect of the liver. C: Coronal plane of the right upper quadrant showing evidence of free fluid in the hepatic tip.
FIGURE 25-3 Coronal image of the left upper quadrant. The sonogram demonstrates the relationship of the spleen (S) and the left kidney (K). There is no anechoic blood or fluid identified.
If free fluid is present, it is most often located superior and posterior to the urinary bladder and the uterus.22
Be aware of the possibility of a distended or overly distended urinary bladder being mistaken for free fluid in the pelvis (Fig. 25-4B
Trauma: Pericardial Effusion
Sonography of the pericardial space to evaluate for fluid collections is a well-documented practice performed in a variety of clinical settings, especially in trauma.25
For this examination, the clinician can continue with the curvilinear probe. If needed, a phased array (commonly known as cardiac probe) can be used. In the absence of fluid collections, the parietal and visceral pericardia are typically indistinguishable from each other, visualized as a combined hyperechoic line. The subxiphoid window is the most commonly used
and convenient method to sonographically visualize cardiac structures, including the pericardial sac. With the transducer oriented transversely and angled superiorly in the subxiphoid region/window, the four-chamber cardiac image can be recognized. The liver serves as an acoustic window, and often, a small segment of the liver can be visualized in the near field. The base of the heart, including both atria, should be located to the patient’s right and is slightly posterior. The apex of the heart is located more to the patient’s left and is situated more anteriorly and inferiorly. If any of the four chambers are not fully visualized within this acoustic window, an attempt should be made to adjust the transducer orientation, so that it is almost parallel to the skin of the anterior torso. In certain patients, especially those with abdominal distention or pain, the subxiphoid window may not be optimal; therefore, familiarity and mastery of all cardiac scanning planes, discussed below, will help to rule out any pericardial or cardiac pathology.29
FIGURE 25-4 A: Transverse plane, midline pelvis. There is a collection of anechoic free fluid (FF) noted lateral to the bladder (B) and superior to the uterus (Ut). B: Transverse plane, midline pelvis. The urinary bladder (B) is distended. Care should be taken not to mistake the anatomy as a large free fluid collection.
The pattern of two hypoechoic ribs interrupted by a central hyperechoic pleural line is referred to as the bat sign (two ribs forming the wings superiorly and the pleural line forming the body inferiorly) (Fig. 25-5A
). A sonographic finding that is often noted, which can be seen with cardiac imaging, is the presence of up to 10 mL of normal serous physiologic fluid and sometimes a small amount of pericardial fat.30
The detection of pericardial fluid is evident by its hypoechoic presence surrounding the heart (located within the pericardial sac) (Fig. 25-5B, C
). Small effusions are smaller than 1 cm in size, moderate effusions between 1 and 2 cm in size, and large effusions are greater than 2 cm in size.31
In the acute traumatic setting, the hypoechoic echogenicity can be consistent with blood such as what is found within the cardiac chambers. When present, blood collections will most often be noted in the subxiphoid window between the liver and right side of the heart. In the parasternal window, blood will most often be noted superior to the right ventricle, or even posteriorly as it outlines the free wall of the left atria and ventricle (Fig. 25-5D
). The descending aorta may be used as a landmark for the posterior aspect of the pericardial sac and is often another site for pericardial fluid collections. Hemorrhage has the ability to quickly collect between the visceral and parietal space, which causes hypotension owing to the cascade of increasing intrapericardial pressure, which in turn causes a decrease in right heart filling, which then causes decreased LV stroke volume. Even small pericardial effusions can set this cascade in motion, causing tamponade (see the section on Cardiac Examination below). In the event of a pericardial effusion, it is imperative that patients receive immediate treatment to avoid the life-threatening clinical course with the onset of tamponade physiology.
Sonography is more sensitive than chest radiography or physical examination for the evaluation of a pneuomothorax.32
The eFAST examination is easily mastered by proper identification of the normal anatomy and its appearance during normal respiration. The curvilinear probe can be used for this examination by decreasing the depth of penetration to allow for better resolution. Alternatively, a high-frequency linear probe can be used for even better visualization of the pleura and ribs (Fig. 25-6A
). The parietal pleura can be visualized in the near field, distal to the echogenic ribs with distal shadowing, which serves as a sonographic landmark. Air has a high acoustic impedance; therefore, the air-filled lung covered by visceral pleura is a potent reflector of the ultrasound beam, blocking sound penetration deeper into the chest and producing a bright linear interface that moves with respiration.
With the transducer oriented toward the patient’s head at the intercostal space, one or two ribs will be identified, and subcutaneous tissue and muscle can be visualized between the rib shadows. Finally, the pleura itself is located within 1 cm of depth from the rib space, with the parietal pleura immediately distal to the chest muscle. The pleura is identified by its pronounced superficial echogenic line.
There are two techniques that can be used for the eFAST examination of the parietal and visceral pleura to rule out a pneumothorax. The first is to identify the normal back-and-forth movement of the pleural layers, corresponding to the patient’s respirations. This is known as the “sliding sign.” The second is to identify comet tail artifacts at the pleural interface.32,34
The sliding should be readily appreciated
once the echogenic reflectors (parietal pleura and visceral pleura) just distal to the ribs are seen in real time with the visceral pleura sliding back and forth under the parietal pleura with patient respiration (Fig. 25-6B
). The sliding sign and moving comet tail artifacts are synchronized with respiratory movement. Absence of the sliding sign indicates that there is a possible pneumothorax. Finding a sliding sign can immediately rule out a pneumothorax at this particular location; however, multiple areas should be evaluated, especially in the absence of the sliding sign. Although this imaging finding can be present along any and all acoustic windows in the upper thorax, with the patient in the supine position, the more superior location is the common site for a pneumothorax.
FIGURE 25-5 A: Parasternal long axis. The sonogram demonstrates the close proximity of the parietal and visceral pericardia (arrow). B, C: Subxiphoid four chambers. The sonograms demonstrate a pericardial effusion (arrow). D: Parasternal long axis (PLAX) showing pericardial effusion (PE). Ao, aortic root; LA, left atrium; LV, left ventricle; PE, pericardial effusion; RA, right atrium; RV, right ventricle. (A: Courtesy of Zonare Medical Systems, Mountain View, CA.)
A second sonographic technique used to identify a pneumothorax is with the application of M-mode (motion mode), which is used to detect motion along a select line of interrogation (line of site). In this technique, motion creates waves or curves, and stillness creates straight horizontal lines. A tracing is displayed by placing the M-mode cursor on the pleura between the ribs. The M-mode will reveal parallel lines above the pleural line corresponding to the motionless parietal tissue of the chest wall. In the presence of sliding, a homogeneous granular (sandy) pattern is seen below the pleural line because of the corresponding constant motion of the underlying lung. This normal lung sliding motion has the appearance of a sandy beach intersecting with rolling waves and is known as the “seashore sign” (Fig. 25-6C, D
In the case of pneumothorax with absent normal sliding, the M-mode reveals a series of parallel horizontal lines, suggesting complete lack of movement both over and under the pleural line. This pattern is known as the “barcode sign” or “stratosphere sign.”33
Although absent lung sliding suggests pneumothorax, it can occur in the presence of many other conditions, such as main stem intubation, acute respiratory distress syndrome, or pleural adhesions.37
If a pneumothorax is suspected, one should attempt to document the size or extent of the pneumothorax by localizing the point on the chest wall, where the normal lung pattern can be seen. The “lung point” sign determines where the visceral pleura begins to separate from the chest wall at the margin of the pneumothorax. At this point, both absent
and normal lung sliding can be demonstrated between the pneumothorax and the normal lung.27
At the lung point position during expiration, no sliding is seen; but, with inspiration, the lung inflates and the visceral pleura moves up in apposition with the parietal pleura beneath the probe and sliding is again seen.35
The ability to demonstrate the alternating lung sliding and absence of lung sliding within the same field is diagnostic of pneumothorax with a sensitivity of 66% and specificity of 100%.26
FIGURE 25-6 A: Transverse plane of the upper thorax. The echogenic ribs (R) can be seen with normal distal shadowing. The intercostal muscles (M) are seen between the ribs. Distal to the ribs, the parietal pleura (P) lining the chest wall is seen, and distal to this is the visceral pleura (V). The parietal pleura and visceral pleura should be visualized sliding over each other with respiration (arrowheads). B: Longitudinal plane of the upper thorax. The echogenic rib (RIB) can be seen with its normal distal shadowing. The parietal and visceral pleura are noted in close proximity (red arrows). On normal individuals, a sliding motion caused by the movement of the mobile visceral pleural during respiration along the static parietal pleura to slide over one another with patient respirations can be observed in real time. C and D: M-mode (motion mode) tracing of the upper thorax. The grayscale image corresponds anatomically with the M-mode tracing. The nonmobile superficial structures of the chest, ribs, and muscle above the pleural line correspond to the “ocean waves” on the M-mode display. The moving parietal and visceral pleura are noted in the “ocean seashore” area, with normal air in the lungs corresponding to the inhomogeneous M-mode tracing below. E: Coronal plane. The sonogram shows a hemothorax in the costophrenic angle and within the pleural cavity as the diaphragm is located inferiorly. (B-D: Courtesy of Zonare Medical Systems, Mountain View, CA. D: Courtesy of Mathew Ahern, Salt Lake City, UT.)
The incidence of a hemothorax after blunt or penetrating chest injury can be noted sonographically as an anechoic or hypoechoic fluid collection localized to the costophrenic angle.36,37
Visualizing an intact diaphragm inferiorly will allow for the certainty that the fluid collection rests within the pleural cavity (Fig. 25-6E
). If there is a pleural cavity fluid collection, the lung may sometimes be identified as a triangular structure superior to the diaphragm and should display rhythmic movement corresponding to the patient’s respirations.