(Radiographics. 1999;19:1332-1339.)
© RSNA, 1999
1998 PLENARY SESSION: IMAGING SYMPOSIUM |
Role of US in the Diagnosis of Intraabdominal Catastrophes1
Kimberley L. McKenney, MD
1 From the Department of Radiology, Duke University Medical Center, Erwin Rd, Durham, NC 27710. From the Plenary Session, Friday Imaging Symposium: Acute Radiology—Where Minutes Count, at the 1998 RSNA scientific assembly. Received March 15, 1999; revision requested May 4 and received June 2; accepted June 8. Address reprint requests to the author.
Index Terms: Abdomen, hemorrhage, 791.77 • Abdomen, injuries, 70.41 • Abdomen, US, 70.12981 • Liver, injuries, 761.41 • Spleen, injuries, 775.41
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INTRODUCTION
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The use of ultrasonography (US) in the evaluation of blunt trauma has been an accepted practice in Europe and Asia for more than 20 years (1–7). This application of US was scarcely mentioned in the American medical literature until the early 1990s when use of surgically performed US for blunt abdominal trauma was reported (8). Since then, numerous studies from the United States have demonstrated the utility and advantages of US in the initial evaluation of abdominal trauma (9–14).
An optimal screening procedure for blunt abdominal trauma should be fast, accurate, portable, and easy to perform. Many believe that US meets these requirements. Like its more traditional counterpart, diagnostic peritoneal lavage, US enables the surgeon to perform rapid bedside evaluation for hemoperitoneum. Unlike peritoneal lavage, US is noninvasive, is easily repeated, and may provide additional information (eg, extent of hemoperitoneum and presence of parenchymal injury). Opponents of the use of US in this context argue that computed tomography (CT) enables more comprehensive patient evaluation that includes both intraperitoneal and retroperitoneal assessment. Abdominopelvic CT remains the standard of reference for determination of injury; even in this era of helical technology, however, such information is not available in the resuscitation area upon a patient's arrival.
US was first introduced into patient work-up for blunt abdominal trauma at our level 1 trauma center in 1992. An initial prospective investigation demonstrated screening US to have a sensitivity of 83%, a specificity of 100%, and an accuracy of 97% in the detection of intraabdominal injury (11). As a result, US was incorporated into the algorithm for the work-up of blunt trauma patients at our institution and soon became the preferred screening modality. In 1994, we reviewed our experience with routine US and found similar results, with a sensitivity, specificity, and accuracy of 86%, 99%, and 98%, respectively (12).
This article describes US technique in the evaluation of blunt abdominal trauma as well as typical imaging findings in hemoperitoneum and parenchymal injury. In addition, the article discusses the advantages and limitations of US in the trauma setting.
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US TECHNIQUE
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Emergency US is performed simultaneously with physical assessment, resuscitation, and stabilization of the trauma patient. The primary goals of this rapid examination, which can be performed in approximately 5 minutes, are to detect hemoperitoneum and determine the need for immediate laparotomy.
US is performed with a 3.5-MHZ sector transducer (a 2-MHZ transducer is used for obese patients) with the patient in the supine position. A sector transducer is used to allow intercostal scanning of the upper abdomen. To expedite patient evaluation, the pelvis may be checked initially for adequate bladder distention. If distention is inadequate, bladder filling may be achieved with an indwelling catheter as the rest of the examination is performed. Hard-copy documentation is obtained for both longitudinal and transverse US, beginning with an evaluation of the heart with a subxyphoid approach and proceeding to the right upper quadrant (including the subphrenic space and the Morison pouch), the left upper quadrant (including the subphrenic and perisplenic areas), and the pelvis. This examination differs from focused abdominal sonography for trauma (4,7,9), which is performed by surgeons, in that it includes evaluation of the liver and spleen for evidence of parenchymal injury. To facilitate examination, the trauma service routinely clamps the Foley catheter at insertion to maintain bladder distention and eliminates overhead lighting.
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HEMOPERITONEUM
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The ability of US to rapidly and reliably demonstrate free intraperitoneal fluid as an indication of intraabdominal injury in the trauma patient explains its increasing popularity among trauma and emergency physicians. In the trauma setting, free fluid usually represents hemoperitoneum, although it may also represent bowel contents, urine, bile, or ascites. Intraperitoneal hemorrhage collects in the most dependent regions of the abdomen and is generally anechoic, conforming to the anatomic site it occupies. The subhepatic space (Morison pouch) is the most common site of fluid accumulation (Fig 1), regardless of the site of injury, followed by the pelvis. In the pelvis, blood may collect centrally in the pouch of Douglas (Fig 2) or laterally in the paravesical space. As fluid accumulates, loops of bowel that are normally poorly visualized are well seen and are separated by triangular collections of fluid. With massive hemoperitoneum, the intraperitoneal organs will float in the surrounding fluid under real-time observation.
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Figures 1, 2. (1) Intraperitoneal hemorrhage in the subhepatic space in a 20-year-old woman following a motor vehicle accident. Transverse US image demonstrates fluid in the subhepatic space (Morison pouch) (*). (2) Intraperitoneal hemorrhage in the pelvis of a 30-year-old woman following a motor vehicle accident. Longitudinal US image shows fluid in the pouch of Douglas. Bowel loops are outlined posteriorly (arrows).
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Figures 1, 2. (1) Intraperitoneal hemorrhage in the subhepatic space in a 20-year-old woman following a motor vehicle accident. Transverse US image demonstrates fluid in the subhepatic space (Morison pouch) (*). (2) Intraperitoneal hemorrhage in the pelvis of a 30-year-old woman following a motor vehicle accident. Longitudinal US image shows fluid in the pouch of Douglas. Bowel loops are outlined posteriorly (arrows).
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The ability of US to demonstrate the extent of hemoperitoneum may be an important advantage over diagnostic peritoneal lavage. It is increasingly recognized that hemoperitoneum following trauma is not necessarily an indication for immediate laparotomy. The inability of diagnostic peritoneal lavage to help quantify free intraperitoneal fluid results in a high rate of nontherapeutic surgery ranging from 19% to 39% (15,16). Although US can demonstrate the extent of hemoperitoneum, communication of this information to the surgeon has been limited to the use of words such as "trace," "moderate," or "large" to describe fluid volume. To improve information transfer and assist the surgeon in decision making, a scoring system for fluid quantification was developed at our institution in 1994 (17). On US images that demonstrated free fluid, the depth of the largest fluid collection was measured from anterior to posterior in centimeters and each additional site where fluid was present was given one point. The patient's hemoperitoneum score was calculated by adding the depth of the largest collection and the total number of points assigned to all the additional sites that demonstrated fluid (Fig 3). In our study, 90% of patients with a score of 2 or less were managed conservatively (Fig 4), whereas 75% of patients with a score higher than 2 required laparotomy. These results suggest that quantifying free fluid during the early stages of assessment may improve patient selection for laparotomy. At our surgeon's request, a hemoperitoneum score is now included for all patients with intraperitoneal hemorrhage seen on US images.
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Figure 3a. Calculation of the hemoperitoneum score in a clinically unstable 45-year-old man with a large amount of free intraperitoneal fluid. The patient had been involved in a motor vehicle accident as a pedestrian. (a) Longitudinal US image of the pelvis reveals the largest collection of fluid, whose depth (9 cm) was determined by measuring the fluid from anterior to posterior. * = partially distended bladder. (b) Longitudinal US image of the Morison pouch shows only one additional site that demonstrated fluid. One point was added for this site, resulting in a hemoperitoneum score of 10 (9 + 1). (c) Transverse US image of the spleen shows heterogeneous parenchyma with loss of normal organ contour superiorly (arrows), a finding that is consistent with splenic rupture and perisplenic clot. Emergency splenectomy was performed.
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Figure 3b. Calculation of the hemoperitoneum score in a clinically unstable 45-year-old man with a large amount of free intraperitoneal fluid. The patient had been involved in a motor vehicle accident as a pedestrian. (a) Longitudinal US image of the pelvis reveals the largest collection of fluid, whose depth (9 cm) was determined by measuring the fluid from anterior to posterior. * = partially distended bladder. (b) Longitudinal US image of the Morison pouch shows only one additional site that demonstrated fluid. One point was added for this site, resulting in a hemoperitoneum score of 10 (9 + 1). (c) Transverse US image of the spleen shows heterogeneous parenchyma with loss of normal organ contour superiorly (arrows), a finding that is consistent with splenic rupture and perisplenic clot. Emergency splenectomy was performed.
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Figure 3c. Calculation of the hemoperitoneum score in a clinically unstable 45-year-old man with a large amount of free intraperitoneal fluid. The patient had been involved in a motor vehicle accident as a pedestrian. (a) Longitudinal US image of the pelvis reveals the largest collection of fluid, whose depth (9 cm) was determined by measuring the fluid from anterior to posterior. * = partially distended bladder. (b) Longitudinal US image of the Morison pouch shows only one additional site that demonstrated fluid. One point was added for this site, resulting in a hemoperitoneum score of 10 (9 + 1). (c) Transverse US image of the spleen shows heterogeneous parenchyma with loss of normal organ contour superiorly (arrows), a finding that is consistent with splenic rupture and perisplenic clot. Emergency splenectomy was performed.
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Figure 4a. Small fluid collection in an 18-year-old man who was clinically stable following a motor vehicle accident. (a) Longitudinal US image shows 1 cm of fluid adjacent to the spleen (the width of fluid is determined in small, curvilinear collections). No additional areas demonstrated fluid, resulting in a hemoperitoneum score of 1. (b) Longitudinal US image of the spleen obtained lateral to a shows a hyperechoic region (arrow), a finding that is consistent with parenchymal injury. (c) Helical CT scan helps confirm the splenic injury (arrows). The patient was successfully treated nonsurgically.
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Figure 4b. Small fluid collection in an 18-year-old man who was clinically stable following a motor vehicle accident. (a) Longitudinal US image shows 1 cm of fluid adjacent to the spleen (the width of fluid is determined in small, curvilinear collections). No additional areas demonstrated fluid, resulting in a hemoperitoneum score of 1. (b) Longitudinal US image of the spleen obtained lateral to a shows a hyperechoic region (arrow), a finding that is consistent with parenchymal injury. (c) Helical CT scan helps confirm the splenic injury (arrows). The patient was successfully treated nonsurgically.
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Figure 4c. Small fluid collection in an 18-year-old man who was clinically stable following a motor vehicle accident. (a) Longitudinal US image shows 1 cm of fluid adjacent to the spleen (the width of fluid is determined in small, curvilinear collections). No additional areas demonstrated fluid, resulting in a hemoperitoneum score of 1. (b) Longitudinal US image of the spleen obtained lateral to a shows a hyperechoic region (arrow), a finding that is consistent with parenchymal injury. (c) Helical CT scan helps confirm the splenic injury (arrows). The patient was successfully treated nonsurgically.
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PARENCHYMAL INJURY
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Although CT remains the standard of reference for evaluating organ parenchyma, valuable information regarding the presence of parenchymal injury may be obtained at US evaluation of the acutely injured patient. The US appearance of hepatic and splenic injury will vary with both the type (hematoma vs laceration) and time of injury. Hematomas and localized lacerations will manifest as regions of increased echogenicity (Fig 5) that over time will become anechoic with the onset of hemolysis (18,19). Brisk intraparenchymal hemorrhage may be identified as an anechoic region within the abnormal parenchyma (Fig 6). Global parenchymal injury manifests in the liver as widespread architectural disruption with absence of the normal vascular pattern, whereas extensive splenic injury frequently manifests as a diffusely heterogeneous parenchymal pattern with both hyper- and hypoechoic regions (Fig 7).
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Figure 5. Laceration of the liver in a 25-year-old man who had suffered a fall. Longitudinal US image of the right upper quadrant reveals a localized area of increased echogenicity in the liver (arrows), a finding that is compatible with a liver laceration.
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Figure 6a. Intraparenchymal hemorrhage in a 40-year-old man who sustained injuries in a motor vehicle accident. (a) Transverse US image of the liver reveals heterogeneous parenchyma with a central anechoic area (arrow). (b) Helical CT scan helps confirm the hepatic laceration and demonstrates an area of active contrast material extravasation (arrow). The diagnosis was confirmed at angiography, and the patient underwent successful embolization.
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Figure 6b. Intraparenchymal hemorrhage in a 40-year-old man who sustained injuries in a motor vehicle accident. (a) Transverse US image of the liver reveals heterogeneous parenchyma with a central anechoic area (arrow). (b) Helical CT scan helps confirm the hepatic laceration and demonstrates an area of active contrast material extravasation (arrow). The diagnosis was confirmed at angiography, and the patient underwent successful embolization.
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Figure 7a. Global parenchymal injury. (a) Transverse US image of the liver obtained in a 60-year-old woman following a motor vehicle accident reveals heterogeneous hepatic parenchyma involving the entire right lobe. Normal vascular structures cannot be identified. (b) Longitudinal US image of the spleen obtained in a 45-year-old man following a motor vehicle accident shows diffuse involvement with areas of both increased and decreased echogenicity. The contour of the spleen is irregular and poorly demarcated.
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Figure 7b. Global parenchymal injury. (a) Transverse US image of the liver obtained in a 60-year-old woman following a motor vehicle accident reveals heterogeneous hepatic parenchyma involving the entire right lobe. Normal vascular structures cannot be identified. (b) Longitudinal US image of the spleen obtained in a 45-year-old man following a motor vehicle accident shows diffuse involvement with areas of both increased and decreased echogenicity. The contour of the spleen is irregular and poorly demarcated.
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Although the primary goal of trauma US is the rapid detection of intraperitoneal hemorrhage, early diagnosis of parenchymal injury can affect patient treatment. The clinically unstable or marginally stable patient with hemoperitoneum and an obvious splenic injury at US can be taken directly to surgery, thereby eliminating the risk of transporting the patient to the CT suite. Conversely, when US reveals extensive hepatic disruption, which results from injuries that are notoriously difficult to manage surgically, the surgeon may consider CT and possibly angiographic intervention as preferred options over laparotomy.
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LIMITATIONS OF US
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Patient obesity may make it difficult to obtain satisfactory results at US. In the obese patient, use of a 2-MHZ transducer may be adequate for the exclusion of intraperitoneal fluid but does not usually permit adequate assessment of the organ parenchyma. In the clinically stable patient, CT is the preferred modality for complete evaluation.
Rarely, the presence of subcutaneous emphysema precludes adequate US examination. Subcutaneous air from a pneumothorax that dissects inferiorly may collect over the liver or spleen and prevent adequate imaging of the affected portion of the abdomen. This may be particularly evident in the left upper quadrant, where the spleen provides only a small acoustic window that can easily be obscured by air (Fig 8). Fluid or parenchymal injury can be missed if an area is not completely imaged; in such cases, the US examination should be considered incomplete and CT or diagnostic peritoneal lavage should be performed.
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Figure 8a. Subcutaneous emphysema in a 40-year-old man with a left pneumothorax sustained in an altercation. (a) On a suboptimal longitudinal US image of the left upper quadrant, the spleen is not visualized. Open arrow indicates the diaphragm, solid arrows indicate the region of the spleen. (b) CT scan through the upper abdomen reveals a small splenic laceration with perisplenic fluid (solid arrow). Subcutaneous emphysema overlying the splenic region (open arrows) precluded adequate US evaluation.
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Figure 8b. Subcutaneous emphysema in a 40-year-old man with a left pneumothorax sustained in an altercation. (a) On a suboptimal longitudinal US image of the left upper quadrant, the spleen is not visualized. Open arrow indicates the diaphragm, solid arrows indicate the region of the spleen. (b) CT scan through the upper abdomen reveals a small splenic laceration with perisplenic fluid (solid arrow). Subcutaneous emphysema overlying the splenic region (open arrows) precluded adequate US evaluation.
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Intraperitoneal clot is usually hyperechoic relative to adjacent structures (Fig 9); occasionally, however, it is isoechoic, and intraperitoneal bleeding or parenchymal injury may go unrecognized. Familiarity with the typical appearance of the peritoneal reflections and of the normal configuration of the solid organs should improve recognition of intraperitoneal clot.
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Figure 9a. Intraperitoneal clot in a 29-year-old woman who was involved in a motor vehicle accident. (a) Longitudinal US image reveals an isoechoic clot filling the cul de sac (arrows). (b) CT scan of the pelvis helps confirm the presence of a high-density clot posterior to the uterus (arrows). (c) Longitudinal US image of the left upper quadrant reveals a hyperechoic clot between the spleen and kidney (arrows). The splenic contour is poorly defined due to parenchymal injury.
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Figure 9b. Intraperitoneal clot in a 29-year-old woman who was involved in a motor vehicle accident. (a) Longitudinal US image reveals an isoechoic clot filling the cul de sac (arrows). (b) CT scan of the pelvis helps confirm the presence of a high-density clot posterior to the uterus (arrows). (c) Longitudinal US image of the left upper quadrant reveals a hyperechoic clot between the spleen and kidney (arrows). The splenic contour is poorly defined due to parenchymal injury.
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Figure 9c. Intraperitoneal clot in a 29-year-old woman who was involved in a motor vehicle accident. (a) Longitudinal US image reveals an isoechoic clot filling the cul de sac (arrows). (b) CT scan of the pelvis helps confirm the presence of a high-density clot posterior to the uterus (arrows). (c) Longitudinal US image of the left upper quadrant reveals a hyperechoic clot between the spleen and kidney (arrows). The splenic contour is poorly defined due to parenchymal injury.
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Contained parenchymal injuries of the liver and spleen as well as bowel injuries may not be accompanied by hemoperitoneum and may therefore be missed if screening US alone is used to evaluate blunt trauma victims. Chiu et al (20) addressed this concern in a prospective investigation of the use of US at surgery. In their study, 29% of patients who presented with intraabdominal injury had no hemoperitoneum at focused abdominal sonography for trauma or nonhelical CT. Although these results are cause for concern, their validity is limited by the investigators' reliance on surgically obtained US images that were negative for fluid and the use of nonhelical CT with 10-mm section intervals as the standard of reference for fluid identification. Determination of the true prevalence of missed injuries due to lack of free fluid will require further investigation.
The significance of parenchymal injury that is missed due to absence of detectable hemorrhage is difficult to determine. For many years, these injuries went undetected at peritoneal lavage. Significant parenchymal injuries can be detected by an experienced ultrasonographer even in the absence of hemoperitoneum. For this reason, evaluation of the organ parenchyma has become part of screening US for trauma at our institution. For the trained ultrasonographer, parenchymal evaluation is automatic and requires no additional time. Inability to help detect small, contained parenchymal injuries and occasional bowel injuries will continue to represent a limitation of US. To avoid missing significant injuries, all patients with negative findings at US should be observed for several hours after imaging (this observation continues for at least 4–6 hours at our institution). In addition, liberal use of serial US or CT should be considered in patients in whom such injuries are strongly suspected at clinical examination.
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CONCLUSIONS
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In many trauma centers, US is becoming the screening modality of choice in blunt abdominal trauma. US can help determine the need for surgical intervention within minutes of a patient's arrival. The rapidity, noninvasiveness, and portability of US are responsible for its increasing popularity. At our institution, US has replaced diagnostic peritoneal lavage and has redefined the role of CT in the immediate evaluation of the trauma patient. Successful use of US in the trauma setting requires real-time interpretation with a targeted approach for the detection of intraabdominal injury. Inclusion of assessment of the organ parenchyma, awareness of the limitations and potential pitfalls of US, and close interaction with the surgical team will reduce the risk of missed injury.
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Footnotes
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LEARNING OBJECTIVE • Identify and describe the US appearance of free intraperitoneal fluid and parenchymal injury in patients with blunt abdominal trauma.
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References
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INTRODUCTION
US TECHNIQUE
