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False positive abdominal aortic aneurysm on bedside emergency ultrasound
The Journal of Emergency Medicine, Vol. 26, No. 2, pp. 193–196, 2004 Copyright © 2004 Elsevier Inc. Printed in the USA. All rights reserved 0736-4679/04 $–see front matter
doi:10.1016/j.jemermed2003.08.012
Selected Topics: Emergency Radiology
FALSE POSITIVE ABDOMINAL AORTIC ANEURYSM ON BEDSIDE EMERGENCY ULTRASOUND Matthew Lyon,
MD,
Larry Brannam,
MD, RDMS,
Louis Ciamillo,
MD,
and Michael Blaivas,
MD, RDMS
Department of Emergency Medicine, Medical College of Georgia, Augusta, Georgia Reprint Address: Michael Blaivas, MD, RDMS, Department of Emergency Medicine, Medical College of Georgia, 1120 15th Street, AF-2056, Augusta, GA 30912-4007
e Abstract—Bedside ultrasound is the diagnostic method of choice for unstable patients with suspected abdominal aortic aneurysm. Its ability to provide rapid and accurate diagnosis is critical in an emergency setting. Previous studies have documented the ability of Emergency Physicians to accurately diagnose abdominal aortic aneurysms, thus potentially saving lives. A search of the medical literature did not reveal any reports of false positive abdominal aortic aneurysm diagnosis with ultrasound use. We report a case of a false positive abdominal aortic aneurysm diagnosed in a patient with a previously unknown large malignant paraaortic lymph node. © 2004 Elsevier Inc.
tality rate when the diagnosis of AAA is delayed, combined with the poor sensitivity of history and physical examination alone, it is not surprising that the use of ultrasound in the ED is the diagnostic method of choice (2,3). In 1998, Plummer et al. reported a study comparing patients presenting with ruptured AAA who were scanned at the bedside by Emergency Physicians (EPs) versus patients who presented to the ED when bedside ultrasound was not available (3). The time to diagnosis was markedly different, with 5.4 min for those scanned at bedside and 83 min for those diagnosed by Radiology. The groups also differed in rate of survival to discharge with 40% of those not scanned by EPs surviving to leave the hospital vs. 72% for those scanned by EPs. Because emergency ultrasound is thought to have a sensitivity and specificity of nearly 100% in the diagnosis of AAA, reports of false positive cases are quite rare (4). We report a case of a false positive AAA diagnosis made using bedside emergency ultrasound in a stable patient presenting to our ED with back pain and a pulsating, mildly tender abdominal mass.
e Keywords— emergency ultrasonography; abdominal aortic aneurysm; Emergency Medicine; abdominal pain; ultrasound
INTRODUCTION Historically, the use of ultrasound with respect to abdominal aortic aneurysm (AAA) has been primarily to screen for and monitor the progress of aneurysmal disease (1). In potentially unstable patients presenting to the Emergency Department (ED), bedside emergency ultrasound provides a fast and reliable tool for assessing for the presence of an aneurysm. The entire evaluation can take place without the patient leaving the ED. The ability to make a rapid assessment in such cases can expedite a patient’s progression to surgery (2). Given the high mor-
CASE REPORT A 56-year-old man presented with complaints of leg weakness and back pain that had worsened over the last
Selected Topics: Emergency Radiology is coordinated by Jack Keene, Rhinebeck, New York
RECEIVED: 20 November 2002; FINAL ACCEPTED: 27 August 2003
SUBMISSION RECEIVED:
25 June 2003;
193
MD,
of Emergency Treatment Associates,
194
M. Lyon et al.
Figure 1. This figure shows the aorta (A) above the vertebral body (V). Just anterior to the aorta, a large mass consistent with a saccular AAA is seen (AAA?).
week. He described the pain as a deep ache, which was now associated with bilateral leg weakness and mild abdominal discomfort. The past medical history was significant only for hypertension, and the review of systems and family and social history was unremarkable. On physical examination by a senior Emergency Medicine Resident and a board certified Emergency Medicine Attending, the blood pressure was 176/98 mm Hg, heart rate was 93 beats/min, respiratory rate was 18 breaths/ min, and the patient was afebrile. The head, neck, heart, lung and neurological examinations were normal. Abdominal examination revealed a large, approximately 6 cm, pulsatile mass in the mid-abdomen that caused mild discomfort on palpation. Distal pulses were normal and equal bilaterally. The patient’s history and physical examination findings suggested the possibility of AAA to the treating EP. A bedside emergency ultrasound examination of the abdominal aorta was immediately performed using a broadband curved array transducer with a frequency range of 2 to 5 MHz and a curvature radius of 40 mm. The abdominal setting on an ATL HDI 4000 system (Philips Medical Systems, Bothell, WA) was used for the examination that was performed by an Emergency Medicine Resident and supervised by a board certified Emergency Medicine Attending with Registered Diagnostic Medical Sonographer credentialing. This study revealed a possible 4-cm fusiform AAA seen anterior to and slightly left of the distal aorta, Figure 1. The margins of the structure were indistinct and it appeared to be part of the aorta. Color Doppler evaluations revealed no obvious blood flow through the structure and it was therefore presumed
to be an abdominal aortic aneurysm containing thrombus. Because the patient’s blood pressure and heart rate continued to be within the normal range, abdominal computed tomography (CT) scan was performed revealing mild dilatation of the distal aorta to less than 3 cm, as well as a para-aortic lymph node and obvious malignant changes in the prostate. The lymph node was located immediately anterior to and left of the distal aorta, Figure 2. The patient refused admission and was discharged with referral to an outpatient clinic for further evaluation.
DISCUSSION Emergency Department ultrasound has proven to be a useful tool for the triage and diagnosis of patients with suspected ruptured or leaking AAA. Recent studies have shown that EPs with relatively limited training and experience can accurately confirm or refute the presence of an AAA (3,4). According to Kuhn et al., ultrasound examinations performed by EPs on patients in whom AAA was suspected had sensitivity and a specificity of 100% (4). In addition, Lanoix et al. demonstrated that after a 4-h ultrasound training program, EPs had a sensitivity and a specificity of 100% for detecting AAA (5). The presence of a ruptured AAA is not always recognized on presentation to the ED, with a misdiagnosis rate of approximately 30% (6). Any delay in correct diagnosis can lead to catastrophic results (3). Often the misdiagnosed ruptured AAA is not suspected until hypotension develops, which is associated with a greatly increased mortality rate (7). Bedside ED ultrasound can
False Positive AAA
195
Figure 2. An abdominal CT scan showing the aorta (A), vertebral body (V), and a large lymph node anterior to the aorta (L).
be immediately available and interpretation is performed at the time of the examination. Given the high incidence of misdiagnosis coupled with poor outcome when the diagnosis is delayed, bedside emergency ultrasonography can provide the means for improving the sensitivity of EPs in detecting AAAs. Bedside emergency ultrasound provides EPs a means of timely diagnosis with the opportunity for rapid intervention without potential delays that may be encountered when awaiting imaging from outside of the department (8). The physical examination is neither sensitive nor specific for detecting the presence of AAA, with palpation revealing only about 76% of AAA greater than 5 cm in diameter in a study by Lederle and Simel (9). Moreover, in a 4-year retrospective study of 329 patients presenting with ruptured AAA, only 18% had palpable abdominal masses (10). Furthermore, the presence of a pulsatile abdominal mass does not necessarily indicate aneurysmal disease. Kadir et al. reported that in the majority of patients, pulsatile abdominal masses represent AAA. However, tender pulsatile abdominal masses are frequently para-aortic masses transmitting the pulsation of a normal-caliber aorta (11). The diagnosis in the case presented above was confounded by a para-aortic lymph node positioned just above the aorta and in direct contact with it. This, coupled with an echogenicity consistent with thrombus, created an appearance of a fusiform AAA (Figure 1). Multiple variables could have contributed to the misinterpretation of the emergency ultrasound examination. The ultrasound transducers typically used in the examination of the abdominal aorta are of lower frequency, typically 2 to 5 mHz, to ensure adequate penetration of
the abdominal cavity and to reach the posterior location of the aorta. These lower frequency transducers have lower resolution capability as compared to higher frequency transducers and may not be able to accurately distinguish structures in close proximity to each other. In addition, each ultrasound view is two-dimensional and may not fully demonstrate the entire configuration of the area of interest. Thus, it is important to scan all structures in at least two planes to make a mental three-dimensional construct of the organ of interest. However, this may not always be possible in the midst of gas-filled small intestine that scatters the ultrasound signal. Superficial enlarged lymph nodes often show characteristic blood flow patterns on power or color Doppler. This node did not show blood flow, either due to its distance from the transducer or the transducer’s low sensitivity for slow blood flow. In comparison, hematomas or other fluid collections adjacent but not communicating with the aorta may move with aortic pulsations and hence will not show Doppler flow (12). Also, an AAA with a partial thrombosis or an entirely thrombosed saccular aneurysm may not show Doppler flow. Finally, one could argue that interpretation bias exists when the physician performing the physical also performs the ultrasound examination. However, clinical history and physical examination findings are usually available to any physician interpreting an ultrasound study. What is most critical about the possible confusion of this para-aortic node with a small AAA is the potential for error it created. In general, a patient presenting with significant hypotension without any explanation for it, other than an AAA on bedside ultrasound, is frequently taken to the operating room by vascular surgeons without
196
M. Lyon et al.
further testing (3). Although it is somewhat comforting that our patient was not incorrectly taken to the operating room and that no such cases could be found, it is still important for EPs to be mindful of this and other potential causes of false positive findings in just such patients. Recognition of the limitations of this imaging modality will help improve diagnostic accuracy and overcome some of the technical difficulties involved. In addition, as ED ultrasound use becomes more prevalent, this scenario may become more common. As in the case presented here, further imaging with CT scan is necessary whenever doubt exists about the diagnosis and the patient is stable enough so that transfer for performance of a CT scan is safe.
CONCLUSION Ruptured AAA is a potentially lethal entity with high rates of morbidity and mortality. The use of bedside emergency ultrasound has been shown to greatly improve the ability of the EP to make a timely diagnosis and provide expedited care for patients presenting with this disease process. Although false positive results have rarely been reported in the literature, misinterpretations do occur for various reasons. It is important to keep in mind the possibility of large para-aortic lymph nodes presenting a confusing picture and potential false positive AAAs.
REFERENCES 1. Ernst C. Abdominal aortic aneurysm. N Engl J Med 1993;328: 1167–71. 2. Miller J, Grimes P, Miller J. Case report of an intraperitoneal ruptured abdominal aortic aneurysm diagnosed with bedside ultrasonography. Acad Emerg Med 1999;6:661– 4. 3. Plummer D, Clinton J, Matthew B. Emergency department ultrasound improves time to diagnosis and survival in ruptured abdominal aortic aneurysm. Acad Emerg Med 1998;5:417. 4. 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;36:219 –23. 5. Lanoix R, Leak LV, Gaeta T, Gernsheimer JR. A preliminary evaluation of emergency ultrasound in the setting of an emergency medicine training program. Am J Emerg Med 2000;18:41–5. 6. Marston WA, Ahlquist R, Johnson G Jr, Meyer AA. Misdiagnosis of ruptured abdominal aortic aneurysms. J Vasc Surg 1992;16:17– 22. 7. Lederle FA, Parenti CM, Chute EP. Ruptured abdominal aortic aneurysm: the internist as diagnostician. Am J Med 1994;96: 163–7. 8. Aburahma AF, Woodruff BA, Stuart SP, Lucente FC, Boland JP. Early diagnosis and survival of ruptured abdominal aortic aneurysms. Am J Emerg Med 1991;9:118 –21. 9. Lederle FA, Simel DL. Does this patient have abdominal aortic aneurysm? JAMA 1999;281:77– 82. 10. Rose J, Civil I, Koelmeyer T, Haydock D, Adams D. Ruptured abdominal aortic aneurysms: clinical presentation in Auckland 1993–1997. ANZ J Surg 2001;71:341– 6. 11. Kadir S, Athanasoulis C, Brewster D, Moncure A. Tender pulsatile abdominal mass, abdominal aortic aneruysm or not? Arch Surg 1980;115:631–3. 12. Erturk H, Erden A, Yurdakul M, Calikoglu U, Olcer T, Cumhur T. Pseudoaneurysm of the abdominal aorta diagnosed by color duplex Doppler sonography. J Clin Ultrasound 1999;27:202–5.
doi:10.1016/j.jemermed2003.08.012
Selected Topics: Emergency Radiology
FALSE POSITIVE ABDOMINAL AORTIC ANEURYSM ON BEDSIDE EMERGENCY ULTRASOUND Matthew Lyon,
MD,
Larry Brannam,
MD, RDMS,
Louis Ciamillo,
MD,
and Michael Blaivas,
MD, RDMS
Department of Emergency Medicine, Medical College of Georgia, Augusta, Georgia Reprint Address: Michael Blaivas, MD, RDMS, Department of Emergency Medicine, Medical College of Georgia, 1120 15th Street, AF-2056, Augusta, GA 30912-4007
e Abstract—Bedside ultrasound is the diagnostic method of choice for unstable patients with suspected abdominal aortic aneurysm. Its ability to provide rapid and accurate diagnosis is critical in an emergency setting. Previous studies have documented the ability of Emergency Physicians to accurately diagnose abdominal aortic aneurysms, thus potentially saving lives. A search of the medical literature did not reveal any reports of false positive abdominal aortic aneurysm diagnosis with ultrasound use. We report a case of a false positive abdominal aortic aneurysm diagnosed in a patient with a previously unknown large malignant paraaortic lymph node. © 2004 Elsevier Inc.
tality rate when the diagnosis of AAA is delayed, combined with the poor sensitivity of history and physical examination alone, it is not surprising that the use of ultrasound in the ED is the diagnostic method of choice (2,3). In 1998, Plummer et al. reported a study comparing patients presenting with ruptured AAA who were scanned at the bedside by Emergency Physicians (EPs) versus patients who presented to the ED when bedside ultrasound was not available (3). The time to diagnosis was markedly different, with 5.4 min for those scanned at bedside and 83 min for those diagnosed by Radiology. The groups also differed in rate of survival to discharge with 40% of those not scanned by EPs surviving to leave the hospital vs. 72% for those scanned by EPs. Because emergency ultrasound is thought to have a sensitivity and specificity of nearly 100% in the diagnosis of AAA, reports of false positive cases are quite rare (4). We report a case of a false positive AAA diagnosis made using bedside emergency ultrasound in a stable patient presenting to our ED with back pain and a pulsating, mildly tender abdominal mass.
e Keywords— emergency ultrasonography; abdominal aortic aneurysm; Emergency Medicine; abdominal pain; ultrasound
INTRODUCTION Historically, the use of ultrasound with respect to abdominal aortic aneurysm (AAA) has been primarily to screen for and monitor the progress of aneurysmal disease (1). In potentially unstable patients presenting to the Emergency Department (ED), bedside emergency ultrasound provides a fast and reliable tool for assessing for the presence of an aneurysm. The entire evaluation can take place without the patient leaving the ED. The ability to make a rapid assessment in such cases can expedite a patient’s progression to surgery (2). Given the high mor-
CASE REPORT A 56-year-old man presented with complaints of leg weakness and back pain that had worsened over the last
Selected Topics: Emergency Radiology is coordinated by Jack Keene, Rhinebeck, New York
RECEIVED: 20 November 2002; FINAL ACCEPTED: 27 August 2003
SUBMISSION RECEIVED:
25 June 2003;
193
MD,
of Emergency Treatment Associates,
194
M. Lyon et al.
Figure 1. This figure shows the aorta (A) above the vertebral body (V). Just anterior to the aorta, a large mass consistent with a saccular AAA is seen (AAA?).
week. He described the pain as a deep ache, which was now associated with bilateral leg weakness and mild abdominal discomfort. The past medical history was significant only for hypertension, and the review of systems and family and social history was unremarkable. On physical examination by a senior Emergency Medicine Resident and a board certified Emergency Medicine Attending, the blood pressure was 176/98 mm Hg, heart rate was 93 beats/min, respiratory rate was 18 breaths/ min, and the patient was afebrile. The head, neck, heart, lung and neurological examinations were normal. Abdominal examination revealed a large, approximately 6 cm, pulsatile mass in the mid-abdomen that caused mild discomfort on palpation. Distal pulses were normal and equal bilaterally. The patient’s history and physical examination findings suggested the possibility of AAA to the treating EP. A bedside emergency ultrasound examination of the abdominal aorta was immediately performed using a broadband curved array transducer with a frequency range of 2 to 5 MHz and a curvature radius of 40 mm. The abdominal setting on an ATL HDI 4000 system (Philips Medical Systems, Bothell, WA) was used for the examination that was performed by an Emergency Medicine Resident and supervised by a board certified Emergency Medicine Attending with Registered Diagnostic Medical Sonographer credentialing. This study revealed a possible 4-cm fusiform AAA seen anterior to and slightly left of the distal aorta, Figure 1. The margins of the structure were indistinct and it appeared to be part of the aorta. Color Doppler evaluations revealed no obvious blood flow through the structure and it was therefore presumed
to be an abdominal aortic aneurysm containing thrombus. Because the patient’s blood pressure and heart rate continued to be within the normal range, abdominal computed tomography (CT) scan was performed revealing mild dilatation of the distal aorta to less than 3 cm, as well as a para-aortic lymph node and obvious malignant changes in the prostate. The lymph node was located immediately anterior to and left of the distal aorta, Figure 2. The patient refused admission and was discharged with referral to an outpatient clinic for further evaluation.
DISCUSSION Emergency Department ultrasound has proven to be a useful tool for the triage and diagnosis of patients with suspected ruptured or leaking AAA. Recent studies have shown that EPs with relatively limited training and experience can accurately confirm or refute the presence of an AAA (3,4). According to Kuhn et al., ultrasound examinations performed by EPs on patients in whom AAA was suspected had sensitivity and a specificity of 100% (4). In addition, Lanoix et al. demonstrated that after a 4-h ultrasound training program, EPs had a sensitivity and a specificity of 100% for detecting AAA (5). The presence of a ruptured AAA is not always recognized on presentation to the ED, with a misdiagnosis rate of approximately 30% (6). Any delay in correct diagnosis can lead to catastrophic results (3). Often the misdiagnosed ruptured AAA is not suspected until hypotension develops, which is associated with a greatly increased mortality rate (7). Bedside ED ultrasound can
False Positive AAA
195
Figure 2. An abdominal CT scan showing the aorta (A), vertebral body (V), and a large lymph node anterior to the aorta (L).
be immediately available and interpretation is performed at the time of the examination. Given the high incidence of misdiagnosis coupled with poor outcome when the diagnosis is delayed, bedside emergency ultrasonography can provide the means for improving the sensitivity of EPs in detecting AAAs. Bedside emergency ultrasound provides EPs a means of timely diagnosis with the opportunity for rapid intervention without potential delays that may be encountered when awaiting imaging from outside of the department (8). The physical examination is neither sensitive nor specific for detecting the presence of AAA, with palpation revealing only about 76% of AAA greater than 5 cm in diameter in a study by Lederle and Simel (9). Moreover, in a 4-year retrospective study of 329 patients presenting with ruptured AAA, only 18% had palpable abdominal masses (10). Furthermore, the presence of a pulsatile abdominal mass does not necessarily indicate aneurysmal disease. Kadir et al. reported that in the majority of patients, pulsatile abdominal masses represent AAA. However, tender pulsatile abdominal masses are frequently para-aortic masses transmitting the pulsation of a normal-caliber aorta (11). The diagnosis in the case presented above was confounded by a para-aortic lymph node positioned just above the aorta and in direct contact with it. This, coupled with an echogenicity consistent with thrombus, created an appearance of a fusiform AAA (Figure 1). Multiple variables could have contributed to the misinterpretation of the emergency ultrasound examination. The ultrasound transducers typically used in the examination of the abdominal aorta are of lower frequency, typically 2 to 5 mHz, to ensure adequate penetration of
the abdominal cavity and to reach the posterior location of the aorta. These lower frequency transducers have lower resolution capability as compared to higher frequency transducers and may not be able to accurately distinguish structures in close proximity to each other. In addition, each ultrasound view is two-dimensional and may not fully demonstrate the entire configuration of the area of interest. Thus, it is important to scan all structures in at least two planes to make a mental three-dimensional construct of the organ of interest. However, this may not always be possible in the midst of gas-filled small intestine that scatters the ultrasound signal. Superficial enlarged lymph nodes often show characteristic blood flow patterns on power or color Doppler. This node did not show blood flow, either due to its distance from the transducer or the transducer’s low sensitivity for slow blood flow. In comparison, hematomas or other fluid collections adjacent but not communicating with the aorta may move with aortic pulsations and hence will not show Doppler flow (12). Also, an AAA with a partial thrombosis or an entirely thrombosed saccular aneurysm may not show Doppler flow. Finally, one could argue that interpretation bias exists when the physician performing the physical also performs the ultrasound examination. However, clinical history and physical examination findings are usually available to any physician interpreting an ultrasound study. What is most critical about the possible confusion of this para-aortic node with a small AAA is the potential for error it created. In general, a patient presenting with significant hypotension without any explanation for it, other than an AAA on bedside ultrasound, is frequently taken to the operating room by vascular surgeons without
196
M. Lyon et al.
further testing (3). Although it is somewhat comforting that our patient was not incorrectly taken to the operating room and that no such cases could be found, it is still important for EPs to be mindful of this and other potential causes of false positive findings in just such patients. Recognition of the limitations of this imaging modality will help improve diagnostic accuracy and overcome some of the technical difficulties involved. In addition, as ED ultrasound use becomes more prevalent, this scenario may become more common. As in the case presented here, further imaging with CT scan is necessary whenever doubt exists about the diagnosis and the patient is stable enough so that transfer for performance of a CT scan is safe.
CONCLUSION Ruptured AAA is a potentially lethal entity with high rates of morbidity and mortality. The use of bedside emergency ultrasound has been shown to greatly improve the ability of the EP to make a timely diagnosis and provide expedited care for patients presenting with this disease process. Although false positive results have rarely been reported in the literature, misinterpretations do occur for various reasons. It is important to keep in mind the possibility of large para-aortic lymph nodes presenting a confusing picture and potential false positive AAAs.
REFERENCES 1. Ernst C. Abdominal aortic aneurysm. N Engl J Med 1993;328: 1167–71. 2. Miller J, Grimes P, Miller J. Case report of an intraperitoneal ruptured abdominal aortic aneurysm diagnosed with bedside ultrasonography. Acad Emerg Med 1999;6:661– 4. 3. Plummer D, Clinton J, Matthew B. Emergency department ultrasound improves time to diagnosis and survival in ruptured abdominal aortic aneurysm. Acad Emerg Med 1998;5:417. 4. 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;36:219 –23. 5. Lanoix R, Leak LV, Gaeta T, Gernsheimer JR. A preliminary evaluation of emergency ultrasound in the setting of an emergency medicine training program. Am J Emerg Med 2000;18:41–5. 6. Marston WA, Ahlquist R, Johnson G Jr, Meyer AA. Misdiagnosis of ruptured abdominal aortic aneurysms. J Vasc Surg 1992;16:17– 22. 7. Lederle FA, Parenti CM, Chute EP. Ruptured abdominal aortic aneurysm: the internist as diagnostician. Am J Med 1994;96: 163–7. 8. Aburahma AF, Woodruff BA, Stuart SP, Lucente FC, Boland JP. Early diagnosis and survival of ruptured abdominal aortic aneurysms. Am J Emerg Med 1991;9:118 –21. 9. Lederle FA, Simel DL. Does this patient have abdominal aortic aneurysm? JAMA 1999;281:77– 82. 10. Rose J, Civil I, Koelmeyer T, Haydock D, Adams D. Ruptured abdominal aortic aneurysms: clinical presentation in Auckland 1993–1997. ANZ J Surg 2001;71:341– 6. 11. Kadir S, Athanasoulis C, Brewster D, Moncure A. Tender pulsatile abdominal mass, abdominal aortic aneruysm or not? Arch Surg 1980;115:631–3. 12. Erturk H, Erden A, Yurdakul M, Calikoglu U, Olcer T, Cumhur T. Pseudoaneurysm of the abdominal aorta diagnosed by color duplex Doppler sonography. J Clin Ultrasound 1999;27:202–5.